Hosni Hassan
North Carolina State University, Microbiology, Faculty Member
Oxygen-intolerant mutants of Escherichia coli K12 were selected by a replica plating technique after treatment with the mutagen, N-methyl-N'-nitro-N-nitrosoguanidine, to a lethality of 99.5%. One group of mutants had lost the... more
Oxygen-intolerant mutants of Escherichia coli K12 were selected by a replica plating technique after treatment with the mutagen, N-methyl-N'-nitro-N-nitrosoguanidine, to a lethality of 99.5%. One group of mutants had lost the ability to induce both peroxidase and catalase when exposed to oxygen but retained the ability to induce the manganese-superoxide dismutase. The second group of mutants had lost the ability to induce the activity of all these enzymes. Failure to induce peroxidase and catalase was associated with enhanced susceptibility of the bacteria to the lethal effect of oxygen. When a member of the first group of mutants was prevented from producing the manganese-superoxide dismutase by the presence of puromycin, its susceptibility to the lethal effects of oxygen was greatly increased. Two types of revertants were seen. In one group the ability to induce enzyme activity was recovered and was accompanied by the return of oxygen tolerance. Members of the other group lost the ability to respire and, therefore, no longer produced O2- AND H2O2. These results indicated that enzymic scavenging of both H2O2 and O2- provides an important defense against oxygen toxicity. The parallel loss of peroxidase and catalase, which was seen in all mutants, suggests that these enzymes constitute a precursor-product pair in E. coli. The parallel loss in two of these mutants of peroxidase, catalase, and the manganese-superoxide dismutase suggests a control linkage for these enzymes, the basis of which remains to be explored.
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Paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride) was used as an intracellular generator of oxygen free radicals and was found to be highly mutagenic for Salmonella typhimurium. It caused both base-pair substitution and... more
Paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride) was used as an intracellular generator of oxygen free radicals and was found to be highly mutagenic for Salmonella typhimurium. It caused both base-pair substitution and frameshift mutations. Paraquat was much more toxic and mutagenic in a simple nutritionally restricted medium than in a rich complex medium. The mutagenicity of paraquat was dependent upon the presence of a supply of both electrons and oxygen. Cells containing high levels of superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1) were more resistant to the toxicity and the mutagenicity of paraquat than were cells containing normal levels of this enzyme. The mutagenicity of paraquat thus appears to be due to its ability to exacerbate the intracellular production of superoxide radicals.
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Exposure of Escherichia coli growing in a rich medium to pyocyanine resulted in increased intracellular levels of superoxide dismutase and of catalase. When these adaptive enzyme syntheses were prevented by nutritional paucity, the toxic... more
Exposure of Escherichia coli growing in a rich medium to pyocyanine resulted in increased intracellular levels of superoxide dismutase and of catalase. When these adaptive enzyme syntheses were prevented by nutritional paucity, the toxic action of pyocyanine was augmented. The antibiotic action of pyocyanine was dependent upon oxygen and was diminished by superoxide dismutase and by catalase, added to the suspending medium. Pyocyanine slightly augmented the respiration of E. coli suspended in a rich medium, but greatly increased the cyanide-resistant respiration. Pyocyanine was able to cause the oxidation of reduced nicotinamide adenine dinucleotide, with O2- production, in the absence of enzymatic catalysis. It is concluded that pyocyanine diverts electron flow and thus increases the production of O2- and H2O2 and that the antibiotic action of this pigment is largely a reflection of the toxicity of these products of oxygen reduction.
Research Interests: Biochemistry, Bacteriology, Biology, Medicine, Biological Sciences, and 14 moreEscherichia coli, Catalase, Phenazines, Superoxide Dismutase, Pseudomonas aeruginosa, Hydrogen Peroxide, Oxygen, Isoenzymes, Pseudomonas Aeruginosa, Oxygen Consumption, Superoxides, Enzyme Induction, Nicotinamide adenine dinucleotide, and Medical and Health Sciences
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Studies on the induction of the manganese-containing superoxide dismutase in several strains of Escherichia coli with different mutations in recA and lexA revealed that the inductions of the Mn-isozyme and of the SOS system by oxygen free... more
Studies on the induction of the manganese-containing superoxide dismutase in several strains of Escherichia coli with different mutations in recA and lexA revealed that the inductions of the Mn-isozyme and of the SOS system by oxygen free radicals are not coregulated. We also studied the synthesis of the manganese-superoxide dismutase in the temperature-dependent, protease-constitutive strain recA441(tif-1) that also contained a lac fusion in an SOS gene. A shift to the temperature at which recA441 has constitutive protease activity did not induce Mn-superoxide dismutase but did induce beta-galactosidase. The data clearly demonstrate that induction of the Mn-superoxide dismutase is independent of the SOS system.
Research Interests: Chemistry, Free Radicals, Molecular Biology, Biology, Biological Chemistry, and 15 moreDNA repair, Medicine, Manganese, Biological Sciences, Protease, Mutation, Escherichia coli, Nitrates, Iron, Paraquat, Superoxide Dismutase, CHEMICAL SCIENCES, Isoenzymes, Enzyme Induction, and Medical and Health Sciences
UK PubMed Central (UKPMC) is an archive of life sciences journal literature.
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Anaerobically grown Escherichia coli K-12 contain only one superoxide dismutase and that is the iron-containing isozyme found in the periplasmic space. Exposure to oxygen caused the induction of a manganese-containing superoxide dismutase... more
Anaerobically grown Escherichia coli K-12 contain only one superoxide dismutase and that is the iron-containing isozyme found in the periplasmic space. Exposure to oxygen caused the induction of a manganese-containing superoxide dismutase and of another, previously undescribed, superoxide dismutase, as well as of catalase and peroxidase. These inductions differed in their responsiveness towards oxygen. Thus the very low levels of oxygen present in deep, static, aerobic cultures were enough for nearly maximal induction of the manganese-superoxide dismutase. In contrast, induction of the new superoxide dismutase, catalase, and peroxidase required the much higher levels of oxygen achieved in vigorously agitated aerobic cultures. Anaerobically grown cells showed a much greater oxygen enhancement of the lethality of streptonigrin than did aerobically grown cells, in accord with the proposal that streptonigrin can serve as an intracellular source of superoxide. Anaerobically grown cells i...
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Escherichia coli produces two distinct species of catalase, hydroperoxidases I and II, which differ in kinetic properties and regulation. To further examine catalase regulation, a lacZ fusion was placed into one of the genes that is... more
Escherichia coli produces two distinct species of catalase, hydroperoxidases I and II, which differ in kinetic properties and regulation. To further examine catalase regulation, a lacZ fusion was placed into one of the genes that is involved in catalase synthesis. Transductional mapping revealed the fusion to be either allelic with or very close to katE, a locus which together with katF controls the synthesis of the aerobically inducible hydroperoxidase (hydroperoxidase II). katE was expressed under anaerobic conditions at levels that were approximately one-fourth of those found in aerobically grown cells and was found to be induced to higher levels in early-stationary-phase cells relative to levels of exponentially growing cells under both anaerobic and aerobic conditions. katE was fully expressed in air and was not further induced when the growth medium was sparged with 100% oxygen. Expression of katE was unaffected by the addition of hydrogen peroxide or by the presence of additi...
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Publisher Summary Increased oxygen tension has been known, for more than two decades, to cause chromosomal breaks and mutations both in eukaryotes and in prokaryotes. Recently, it has been shown that the physiological concentrations of... more
Publisher Summary Increased oxygen tension has been known, for more than two decades, to cause chromosomal breaks and mutations both in eukaryotes and in prokaryotes. Recently, it has been shown that the physiological concentrations of oxygen (-5% O 2 ) are mutagenic in certain oxygen-sensitive histidine auxotrophs of Salmonella typhimurium strain TA100. A basic understanding of these deleterious effects of oxygen came with the advent of the theory of oxygen toxicity. This theory states that the partially reduced intermediates of oxygen––the superoxide anion (O 2 - ), hydrogen peroxide (H 2 O 2 ), and the hydroxyl radical (OH·)––are the damaging agents. In accordance with this theory, it has been shown that ionizing radiation generates oxygen free radicals, that superoxide radicals can indirectly cause DNA strand scission in vitro , and that oxygen free radicals generated by paraquat (PQ) are mutagenic. This chapter presents methods for assessing the mutagenicity of oxygen free radicals in microbial systems. These methods are usually rapid, simple, and inexpensive.
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Manganese-containing superoxide dismutase (MnSOD-sodA) in Escherichia coli (E. coli) is regulated at the transcriptional level as observed in studies using both operon and gene fusions. In this paper we examine the regulation of sodA gene... more
Manganese-containing superoxide dismutase (MnSOD-sodA) in Escherichia coli (E. coli) is regulated at the transcriptional level as observed in studies using both operon and gene fusions. In this paper we examine the regulation of sodA gene at the level of mRNA. We examine the effects of several aerobic inducing conditions (i.e., nalidixic acid, paraquat, or 2,2'-dipyridyl) on mRNA stability, transcription initiation, and translation. The half-life of sodA mRNA was found to be approximately 3-4 min, showing no differences in mRNA stability between induced and uninduced cells. We also found, by reverse transcriptase, that the second putative promoter is not functional under normal or stress conditions, and the amount of mRNA was found to be proportional to active MnSOD. Thus, these results indicate that under oxidative stress/inducing conditions, the increase in aerobic transcription of sodA occurs from only one transcription start site without affecting the stability of sodA mRNA. In addition, the 1:1 ratio found between increases in sodA mRNA and active MnSOD suggests that no translational regulation occurs aerobically.
Research Interests: Free Radicals, Biology, Oxidative Stress, Medicine, Manganese, and 15 moreTranslation, Transcription, Reactive Oxygen Species, Escherichia coli, Paraquat, Superoxide Dismutase, Oxidative stress and free radical biology and medicine, Shell Half-Life, Base Sequence, Drug Stability, Transcription Start Site, Oxidation-Reduction, Biochemistry and cell biology, Nalidixic acid, and Molecular Sequence Data(Translation, Transcription, Reactive Oxygen Species, Escherichia coli, Paraquat, Superoxide Dismutase, Oxidative stress and free radical biology and medicine, Shell Half-Life, Base Sequence, Drug Stability, Transcription Start Site, Oxidation-Reduction, Biochemistry and cell biology, Nalidixic acid, and Molecular Sequence Data)
(Translation, Transcription, Reactive Oxygen Species, Escherichia coli, Paraquat, Superoxide Dismutase, Oxidative stress and free radical biology and medicine, Shell Half-Life, Base Sequence, Drug Stability, Transcription Start Site, Oxidation-Reduction, Biochemistry and cell biology, Nalidixic acid, and Molecular Sequence Data)
Growth in aerobic environments has been shown to generate reactive oxygen species (ROS) and to cause oxidative stress in most organisms. Antioxidant enzymes (i.e., superoxide dismutases and hydroperoxidases) and DNA repair mechanisms... more
Growth in aerobic environments has been shown to generate reactive oxygen species (ROS) and to cause oxidative stress in most organisms. Antioxidant enzymes (i.e., superoxide dismutases and hydroperoxidases) and DNA repair mechanisms provide protection against ROS. Acid stress has been shown to be associated with the induction of Mn superoxide dismutase (MnSOD) in Lactococcus lactis and Staphylococcus aureus . However, the relationship between acid stress and oxidative stress is not well understood. In the present study, we showed that mutations in the gene coding for MnSOD ( sodA ) increased the toxicity of lactic acid at pH 3.5 in Streptococcus thermophilus . The inclusion of the iron chelators 2,2′-dipyridyl (DIP), diethienetriamine-pentaacetic acid (DTPA), and O -phenanthroline (O-Phe) provided partial protection against 330 mM lactic acid at pH 3.5. The results suggested that acid stress triggers an iron-mediated oxidative stress that can be ameliorated by MnSOD and iron chelat...
Research Interests: Biochemistry, Physiology, Biology, Oxidative Stress, Medicine, and 15 moreMultidisciplinary, Antioxidants, Bacterial resistance, Reactive Oxygen Species, Escherichia coli, Applied, Antioxidant, Applied Environmental Microbiology, Bacteria, Staphylococcus aureus, Iron, Antioxidant enzyme, Physiological Stress Markers, Lactic Acid, and Organic Acid
The univalent reduction of oxygen to the superoxide radical is a commonplace event in biological systems, and the superoxide dismutases, which catalytically scavenge this radical, are the primary defence against its potential... more
The univalent reduction of oxygen to the superoxide radical is a commonplace event in biological systems, and the superoxide dismutases, which catalytically scavenge this radical, are the primary defence against its potential cytotoxicity. The superoxide radical and hydrogen peroxide, can interact to generate the hydroxyl radical. Superoxide dismutases are metalloenzymes that can prevent the generation of hydroxyl radical by keeping the level of superoxide radical vanishingly low. Superoxide dismutases are essential for the survival of all oxygen metabolizing organisms. There are three types of superoxide dismutases: the manganese-containing, the iron-containing, and the copper-zinc-containing superoxide dismutases. The copper-zinc containing superoxide dismutases have generally been isolated from eukaryotic cells except for the enzyme from the symbiotic marine bacterium Photobacterium leiogenthi. The copper-zinc containing superoxide dismutases, from different sources, have a molec...
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Conditions for continuous culture of Escherichia coli K-12 His- Thi- under glucose limitation were established. Both the capacity for respiration, at D greater than 0.2/h, and specific activity of superoxide dismutase increased as a... more
Conditions for continuous culture of Escherichia coli K-12 His- Thi- under glucose limitation were established. Both the capacity for respiration, at D greater than 0.2/h, and specific activity of superoxide dismutase increased as a function of specific growth rate, whereas peroxidase and catalase were either invariant with or inversely related to this growth rate. The abrupt increase in the availability of glucose, as a means of elevating the growth rate, was followed by an increase in superoxide dismutase, which reached a plateau before there was a significant increase in the growth rate. Thus, an increase in superoxide dismutase appeared to be a prerequisite for an increase in the rate of growth. Cells that had higher levels of superoxide dismutase, because of varying specific growth rates, were more resistant to the toxicity of hyperbaric oxygen. Superoxide dismutase thus behaved like an essential defense against the toxicity of oxygen. Sensitivity towards streptonigrin increase...
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In this study, we determined the internal cellular pH response of Leuconostoc mesenteroides and Lactobacillus plantarum to the external pH created by the microorganisms themselves or by lactic or acetic acids and their salts added to the... more
In this study, we determined the internal cellular pH response of Leuconostoc mesenteroides and Lactobacillus plantarum to the external pH created by the microorganisms themselves or by lactic or acetic acids and their salts added to the growth medium. Growth of Leuconostoc mesenteroides stopped when its internal pH reached 5.4 to 5.7, and growth of L. plantarum stopped when its internal pH reached 4.6 to 4.8. Variation in growth medium composition or pH did not alter the growth-limiting internal pH reached by these microorganisms. L. plantarum maintained its pH gradient in the presence of either 160 mM sodium acetate or sodium lactate down to an external pH of 3.0 with either acid. In contrast, the ΔpH of Leuconostoc mesenteroides was zero at pH 4.0 with acetate and 5.0 with lactate. No differences were found between d -(−)- and l -(+)-lactic acid for the limiting internal pH for growth of either microorganism. The comparatively low growth-limiting internal pH and ability to mainta...
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Publisher Summary The importance of superoxide dismutase (SOD) as a defense against the cellular damage caused by oxygen free radicals has been extensively demonstrated in microbial systems. Most of the studies have been carried out with... more
Publisher Summary The importance of superoxide dismutase (SOD) as a defense against the cellular damage caused by oxygen free radicals has been extensively demonstrated in microbial systems. Most of the studies have been carried out with gram-negative enteric organisms, but a few studies have been done using gram-positive staphylococci. In this type of study, a generator of oxygen free radicals and a test organism are required. Cellular damage may be assessed by the enumeration of viable cells, loss of some vital cellular function, such as transport of nutrients, structural changes as observed by electron microscopy or by the release of some intracellular marker enzymes. This chapter presents methods for generating oxygen free radicals, for manipulating the cellular concentration of SOD, and for assessing the damage caused by oxygen free radicals. Loss of viability is normally caused by irreparable damage to one or more of the vital cellular components. Therefore, the use of specific repair deficient mutants may further amplify the damage and loss of viability.
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Publisher Summary Paraquat, also known as methyl viologen, is the active ingredient of many commercially available broad-spectrum herbicides. Paraquat seems to be universally toxic both in prokaryotes and eukaryotes, and incidents of... more
Publisher Summary Paraquat, also known as methyl viologen, is the active ingredient of many commercially available broad-spectrum herbicides. Paraquat seems to be universally toxic both in prokaryotes and eukaryotes, and incidents of fatal paraquat poisonings have been reported in man and animals. Crude cell-free extracts from plants, animals, and bacterial origins have been shown to reduce PQ 2+ to PQ· + in the presence of nicotinamide adenine dinucleotide phosphate (NADPH) or an NADPH-generating system (i.e., glucose-6-phosphate, glucose-6-phosphate dehydrogenase, and NADP + ). The enzyme that reduces PQ 2+ is a diaphorase-like enzyme usually present in the cytoplasm and specific for NADPH. Paraquat is readily reduced by a single electron to a stable but dioxygen-sensitive monocation radical (PQ· + ). The reaction between the paraquat radical and dioxygen (O 2 ) generates the true toxic species, the superoxide radical (O 2 - ), and subsequently hydrogen peroxide (H 2 O 2 ). Hydroxyl radicals (OH·) may also be generated because of secondary interactions between O 2 - and H 2 O 2 . This chapter presents methods for measuring and identifying the partially reduced oxygen species generated during the reaction of PQ· + and O 2 .
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A strain of Pseudomonas aeruginosa, which was resistant to 400 μg/ml of chloramphenicol (CM), was isolated. The generation time of the resistant strain was the same in the presence or absence of CM and similar to that of the parent strain... more
A strain of Pseudomonas aeruginosa, which was resistant to 400 μg/ml of chloramphenicol (CM), was isolated. The generation time of the resistant strain was the same in the presence or absence of CM and similar to that of the parent strain growing in the absence of chloramphenicol. Resistance is eliminated by treatment with acridine dyes, mitomycin C, and sodium dodecyl sulfate, suggesting that resistance may be expressed by a plasmid. The resistant strain does not produce the pigment pyocyanine and the addition of pyocyanine to this strain eliminates the resistance factor. A strain sensitive to CM was isolated. This strain does not produce the enzyme acetyl CoA: chloramphenicol transacetylase whereas the resistant strain does. The sensitive strain accumulates 14C-CM at a greater rate and to a greater extent than the resistant strain grown in the presence of CM. The results suggest that the resistant strain inactivates CM by acetylation and, in addition, develops a "permeability...
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Axenically grown Bdellovibrio stolpii (i.e., grown independently of the host) was examined for superoxide dismutase, catalase, and peroxidase activities. Kinetics of enzyme synthesis were determined for aerobically grown cultures and for... more
Axenically grown Bdellovibrio stolpii (i.e., grown independently of the host) was examined for superoxide dismutase, catalase, and peroxidase activities. Kinetics of enzyme synthesis were determined for aerobically grown cultures and for cultures exposed to 100% oxygen. Enzymatic activities varied with the age of the culture. Normally grown cultures exhibited maximum activity during the first 10 h of growth and again as the stationary phase was approached, beginning at about 48 h. Polyacrylamide gel electropherograms of cell-free extracts revealed that B. stolpii contained one major band (1) and two minor bands (II, III) of superoxide dismutase activity. Each of these enzymes was inactivated by H2O2, indicating that they were iron-containing enzymes. Manganese-containing superoxide dismutase was not detected in B. stolpii. Increased oxygenation did not appreciably stimulate enzyme synthesis, for only superoxide dismutase was induced, reaching maximum activity at 10 h and then rapidl...
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Salmonella is estimated to cause one million food-borne illnesses in the United States every year. Salmonella-contaminated poultry products are one of the major sources of Salmonellosis. Given the critical role of the gut microbiota in... more
Salmonella is estimated to cause one million food-borne illnesses in the United States every year. Salmonella-contaminated poultry products are one of the major sources of Salmonellosis. Given the critical role of the gut microbiota in Salmonella transmission, manipulation of the chicken intestinal microenvironment could prevent animal colonization by the pathogen. In Salmonella, the global regulator gene fnr (Fumarate Nitrate Reduction) regulates anaerobic metabolism, and is essential for adapting to the gut environment. This study tested the hypothesis that an attenuated Fnr-mutant of Salmonella Typhimurium (attST), or the prebiotic galacto-oligosaccharides (GOS) could improve resistance to wild-type Salmonella via modifications to the structure of the chicken gut microbiome. Intestinal samples from a total of 273 animals were collected weekly for 9 weeks to evaluate the impact of attST or prebiotic supplementation on microbial species of cecum, duodenum, jejunum, and ileum. We ne...
Research Interests: Genetics, Immune response, Helicobacter pylori, Biological Sciences, Humans, and 15 moreDeveloping Country, Female, Animals, Applied Environmental Microbiology, Bacteria, Immunization, Genetic transformation, Feces, DNA vaccine, Child mortality, Base Sequence, Immunoglobulin, H Pylori, Antibody Response, and Immunization Schedule
The manganese-containing superoxide dismutase in Escherichia coli is an inducible enzyme that protects cells against oxygen toxicity. The manganese-enzyme is induced by oxygen, nitrate, redox active compounds that react with oxygen to... more
The manganese-containing superoxide dismutase in Escherichia coli is an inducible enzyme that protects cells against oxygen toxicity. The manganese-enzyme is induced by oxygen, nitrate, redox active compounds that react with oxygen to generate ...
Research Interests: Regulation, Biological Chemistry, Manganese, Cell Culture, Biological Sciences, and 13 moreEscherichia coli, Bacteria, Nitrates, Superoxide Dismutase, CHEMICAL SCIENCES, Hydrogen Peroxide, Oxygen, Densitometry, Oxidation-Reduction, Ammonium Sulfate, Enzyme Induction, Redox Potential, and Medical and Health Sciences
An analysis of arc discharges in which changes normal to the electrode are more important than those along electrodes is presented. In this case, the current is different from zero and the diffusion is not ambipolar. Both planar and... more
An analysis of arc discharges in which changes normal to the electrode are more important than those along electrodes is presented. In this case, the current is different from zero and the diffusion is not ambipolar. Both planar and axisymmetric discharges in the presence of a magnetic field are considered. This analysis is based on the complete conservation of mass and momentum equations for the ions and electrons. Using the complete equations leads, in the plasma approximation, to plasma boundaries which correspond to the anode and cathode sheaths.
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ABSTRACT Abstract This study showed that encapsulation of ampicillin (Amp) in liposomes prepared with synthetic lecithins enhanced its antibiotic activity against both Amp-sensitive and Amp-resistant Escherichia coli. This was... more
ABSTRACT Abstract This study showed that encapsulation of ampicillin (Amp) in liposomes prepared with synthetic lecithins enhanced its antibiotic activity against both Amp-sensitive and Amp-resistant Escherichia coli. This was demonstrated by growth inhibition of E. coli in the presence of the liposomal preparations containing Amp. Growth inhibition was also seen in the presence of exogenous β-lactamase. Adsorption of Amp onto the surface of the liposomes did not result in enhanced activity of the drug against E. coli. The encapsulation efficiency of Amp in liposomes prepared by the Bangham method (BM) was greatly affected by the phospholipids used. The efficiency increased with a rise in the phase transition temperature (Tc) of the phospholipid, the maximum encapsulation of Amp being obtained with distearoylphosphatidylcholine (DSPC). The entrapment efficiency of Amp with the reverse phase evaporation method (REV) was largely superior to that with the BM method. Kinetic studies using DSPC liposomes prepared by the REV and BM protocols demonstrated that Amp-loaded liposomes contained 60 and 72% of drug, respectively, after 24 h at 37°C.
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Summary Specific growth rate models of product-inhibited cell growth exist but are rarely applied to fermentations beyond ethanol and large-scale antibiotic production. The present paper summarizes experimental data and the development of... more
Summary Specific growth rate models of product-inhibited cell growth exist but are rarely applied to fermentations beyond ethanol and large-scale antibiotic production. The present paper summarizes experimental data and the development of a model for growth of the commercially important bacterium,Lactobacillus plantarum, in cucumber juice. The model provides an excellent correlation of data for the influence on bacterial growth rate
Research Interests: Industrial Biotechnology, Cucumber, Lactic Acid Bacteria, Industrial microbiology, Bacterial growth, and 11 moreLactobacillus Plantarum, Food Sciences, Acetic Acid, Large Scale, INDUSTRIAL MICROBIOLOGY AND BIOTECHNOLOGY, Lactic Acid, Experimental Data, Sodium Chloride, Functional Form, Specific Growth Rate, and Cell Growth
Two pioneering achievements by Ilya Ilyich Metchnikoff were recorded in 1908. Most notable was his Nobel Prize in Medicine for discovering the innate cellular immune response to an infectious challenge. Of lesser note was his... more
Two pioneering achievements by Ilya Ilyich Metchnikoff were recorded in 1908. Most notable was his Nobel Prize in Medicine for discovering the innate cellular immune response to an infectious challenge. Of lesser note was his recommendation, "...to absorb large quantities of microbes, as a general belief is that microbes are harmful. This belief is erroneous. There are many useful microbes, amongst which the lactic bacilli have an honorable place." While his discovery of the inflammatory response was rapidly incorporated into our understanding of cellular immunity, his recommendation "to absorb large quantities of microbes," on the other hand, languished for decades in limbos of indifference, skepticism, and disbelief. The present chapter is a synopsis of salient discoveries made during the past 100 years, which gradually displaced these skepticisms, validated his concept of "useful microbes," and propelled his "lactic bacilli" into the mainstream of modern medical science, practice, and therapy.
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ABSTRACT Recent calculations of turbulent supersonic reacting shear flows using an assumed multivariate beta PDF (probability density function) resulted in reduced production rates and a delay in the onset of combustion. This result is... more
ABSTRACT Recent calculations of turbulent supersonic reacting shear flows using an assumed multivariate beta PDF (probability density function) resulted in reduced production rates and a delay in the onset of combustion. This result is not consistent with available measurements. The present research explores two possible reasons for this behavior: use of PDF's that do not yield Favre averaged quantities, and the gradient diffusion assumption. A new multivariate beta PDF involving species densities is introduced which makes it possible to compute Favre averaged mass fractions. However, using this PDF did not improve comparisons with experiment. A countergradient diffusion model is then introduced. Preliminary calculations suggest this to be the cause of the discrepancy.
Two pioneering achievements by Ilya Ilyich Metchnikoff were recorded in 1908. Most notable was his Nobel Prize in Medicine for discovering the innate cellular immune response to an infectious challenge. Of lesser note was his... more
Two pioneering achievements by Ilya Ilyich Metchnikoff were recorded in 1908. Most notable was his Nobel Prize in Medicine for discovering the innate cellular immune response to an infectious challenge. Of lesser note was his recommendation, "...to absorb large quantities of microbes, as a general belief is that microbes are harmful. This belief is erroneous. There are many useful microbes, amongst which the lactic bacilli have an honorable place." While his discovery of the inflammatory response was rapidly incorporated into our understanding of cellular immunity, his recommendation "to absorb large quantities of microbes," on the other hand, languished for decades in limbos of indifference, skepticism, and disbelief. The present chapter is a synopsis of salient discoveries made during the past 100 years, which gradually displaced these skepticisms, validated his concept of "useful microbes," and propelled his "lactic bacilli" into the mainstream of modern medical science, practice, and therapy.
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Research Interests: Industrial Biotechnology, Multidisciplinary, Saccharomyces cerevisiae, Industrial microbiology, Copper, and 12 moreCytochrome C, Ethanol Production, Oxygen Uptake, Catalase, Superoxide Dismutase, Steady state, Applied Microbiology and Biotechnology, Antioxidant enzyme, Specific Activity, Food Sciences, INDUSTRIAL MICROBIOLOGY AND BIOTECHNOLOGY, and Specific Growth Rate
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Milkfat globule membranes (MFGMs) were prepared from bovine cream according to standard procedures. These membranes and peptide hydrolysates, which were generated by proteolysis with immobilized digestive enzymes, were screened for... more
Milkfat globule membranes (MFGMs) were prepared from bovine cream according to standard procedures. These membranes and peptide hydrolysates, which were generated by proteolysis with immobilized digestive enzymes, were screened for antibacterial activity against Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica Typhimurium, Pseudomonas fluorescens, Bacillus cereus, Lactobacillus acidophilus, and Lactobacillus gasseri. Assays were first performed on beef heart infusion (BHI) plates spotted with test protein-peptide fractions and then seeded with lawns of indicator cells to monitor the zone of growth inhibition. Under these experimental conditions, MFGMs were most active against Salmonella Typhimurium and P. fluorescens. However, antibacterial activity was not seen after plating on Luria-Bertani (LB) medium. We determined that the antimicrobial effects observed on BHI plates were due to the generation of H2O2 by xanthine oxidase, a major protein constituent of the ...
Research Interests: Food, Membrane Proteins, Multidisciplinary, Food Microbiology, Food Preservation, and 15 moreProperties, Animals, Lactobacillus, Pseudomonas Fluorescens, Milk, Membrane, Cattle, Hydrogen Peroxide, Microbial Sensitivity Tests, Bacillus Cereus, Food Contamination, Food Preservatives, Culture Media, Protein hydrolysates, and Antimicrobial agent
Superoxide dismutases (EC 1.15.1.1) are metalloenzymes that catalytically scavenge the superoxide radical. They are essential for the aerobic survival of all forms of life. There are three types of superoxide dismutase, containing... more
Superoxide dismutases (EC 1.15.1.1) are metalloenzymes that catalytically scavenge the superoxide radical. They are essential for the aerobic survival of all forms of life. There are three types of superoxide dismutase, containing manganese, iron, or copper and zinc. The copper--zinc type has generally been isolated from eukaryotic cells except for the enzyme for the symbiotic marine bacterium Photobacterium leiognathi. The copper--zinc type, from different sources, has a molecular weight of about 32 000, and is composed of two identical subunits, each containing one atom of copper and one atom of zinc. The copper participates in the catalytic activity of the enzyme, while the zinc plays only a structural role. The enzyme has been resolved reversibly. Superoxide dismutases provide protection against oxygen toxicity, against compounds that cause exacerbation of oxygen toxicity, against ionizing radiation, and also against the damaging sequelae of prolonged inflammation.
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The effect of external Na plus concentration on the transport of K plus was studied using K plus-depleted cells of a marine pseudomonad. K plus transport was found to be a saturable process and requires Na plus. The initial rates for K... more
The effect of external Na plus concentration on the transport of K plus was studied using K plus-depleted cells of a marine pseudomonad. K plus transport was found to be a saturable process and requires Na plus. The initial rates for K plus transport over a range of external K plus concentrations were measured in suspensions containing various fixed concentrations of Na plus. Reciprocals of the initial rates for K plus transport were plotted against reciprocals of the external concentration of K plus or Na plus to yield two primary Lineweaver-Burk plots. The experimental data were found to fit bisubstrate enzyme kinetics, with a sequential type mechanism. However, the initial rate data did not allow distinction between ordered or random mechanisms. The results suggest that Na plus and K plus form a ternary complex with a specific K plus carrier molecule on the outer surface of the membrane prior to translocation and the release of K plus inside the cell.
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The presence of oxygen in the environment presents both advantages and a threat to all forms of life. The use of oxygen as a final electron acceptor provides more energy than that afforded by anaerobic fermentation. Oxygen is also useful... more
The presence of oxygen in the environment presents both advantages and a threat to all forms of life. The use of oxygen as a final electron acceptor provides more energy than that afforded by anaerobic fermentation. Oxygen is also useful in many biosynthetic reactions. ...
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... of the hide powder azure assay for quan-titating the protease of Pseudomonasfluorescens** Brian H. Himelbloom and Hosni M. Hassan* Department of ... experiments growth was at 25 and 150 rpm, in a Psychrotberm G-26 shaker (New... more
... of the hide powder azure assay for quan-titating the protease of Pseudomonasfluorescens** Brian H. Himelbloom and Hosni M. Hassan* Department of ... experiments growth was at 25 and 150 rpm, in a Psychrotberm G-26 shaker (New Brunswick Scientific Co., Inc., Edison, NJ). ...
Research Interests:
Research Interests: Animal Science, Diet, Immunology of the Gut, Energy Metabolism, Biological Sciences, and 14 moreSheep, Animal Feed, Animals, Male, Dietary Supplements, Gram Positive Bacteria, Chickens, Time Factors, Erythrocytes, Oxygen Consumption, Enzyme Linked Immunosorbent Assay, immunoglobulin G, Gene Expression Regulation, and Immunoglobulin A
Research Interests: Metabolism, Regulation, Manganese, Cell Division, Free Radical, and 12 moreMutagenesis, Toxicity, Glucose, Escherichia coli, Iron, Superoxide Dismutase, Oxidative stress and free radical biology and medicine, Hydrogen Peroxide, Oxygen, Eukaryotic Cells, Superoxides, and Biochemistry and cell biology
The antioxidant enzymes, catalase and superoxide dismutase, are inactivated upon exposure to ozone. In this study, the mechanism of this inactivation was examined using catalase as a model system. The data show that the inactivation of... more
The antioxidant enzymes, catalase and superoxide dismutase, are inactivated upon exposure to ozone. In this study, the mechanism of this inactivation was examined using catalase as a model system. The data show that the inactivation of catalase is dependent on ozone concentration, time of exposure, and pH. Loss of catalase activity is accompanied with loss of the heme spectra. Tiron, desferal-Mn, trolox-c, and pyruvate protect the enzyme against ozone inactivation. SOD is less effective due to its inactivation by ozone. On the other hand, alcohols do not provide significant protection. The data suggest the possible involvement of superoxide radicals in the inactivation of catalase by ozone.
Research Interests: Water, Free Radicals, Free Radical, Antioxidants, Peroxidase, and 13 moreIn Vitro, Animals, Catalase, Spectrophotometry, Oxidative stress and free radical biology and medicine, Cattle, Digestive System, Buffers, Ozone, Enzyme activity, Gel electrophoresis, Hydrogen-Ion Concentration, and Biochemistry and cell biology
Paraquat is univalently reduced to the relatively stable, but oxygen-sensitive, paraquat radical (PQ∙+). This PQ∙+ can react with dioxygen to generate the superoxide radical, which can further generate other more deleterious species of... more
Paraquat is univalently reduced to the relatively stable, but oxygen-sensitive, paraquat radical (PQ∙+). This PQ∙+ can react with dioxygen to generate the superoxide radical, which can further generate other more deleterious species of oxygen free radicals (i.e., hydroxyl radical, OH∙). These oxygen free radicals are known to cause chromosomal breaks; therefore, it was logical to postulate that paraquat is a mutagen. This proved to be the case when tested in a modified Ames test using a liquid incubation assay. Salmonella typhimurium strains TA98 and TA100 were grown in the presence of various concentrations of PQ, as well as in the presence of known mutagenic compounds: mitomycin C, azide, and proflavine. Paraquat was much more toxic and mutagenic in a simple nutritionally restricted medium than in a rich complex medium and these toxic and mutagenic effects were oxygen dependent. Furthermore, cells containing high levels of superoxide dismutase were more resistant to the toxic and ...