Microcystis

AbstrAct: In the past 30 years, Lake Dojran (Macedonia) has experienced extreme periods of droughts and water removal for irrigation purposes that have resulted in an accelerated process of eutrophication leading to hypertrophy. In the present paper, we document successive changes of the microflora in plankton communities as a result of the prolonged eutrophication impact over this period. The original well established phytoplankton community in the lake, which was rich in species (especially coccoid green forms belonging to the genera Pediastrum, Scenedesmus, Staurastrum and Tetraedon) and which followed the natural annual succession in the form of diatoms > green algae > cyanobacteria, has been greatly modified over the years. Two episodes of intensive 'water blooms' have been recorded, one involving Gloeotrichia natans (in 1993/94) and the other the dinoflagellates Ceratium hirudinella and C. monoceros (1996/97), events that indicated drastic changes of the ecological conditions. Dominance of Dolichospermum aff. flosaquae was recorded in 2008. Finally, the phytoplankton in Lake Dojran completed a turnover towards the overall dominance of Microcystis spp., with a total of nine co-existing species. The first documented record of Microcystis protocystis outside pan-and neotropical regions is here presented. The described successions in phytoplankton species composition and dominance are attributed to gradual and constant changes in the nutrient status of the lake in the direction of hypertrophy, the basic nutritive parameters, total P and N content, having increased more than 40-and eight-fold, respectively, over the years. Measurements of cyanobacterial toxicity have been few, and they were sporadically performed. Nonetheless, the presence of microcystins in the water has been documented, with indications of significant concentration peaks. The paper is intended to be a tribute to all scientific workers who, like Professors Jelena and Živojin Blaženčić, have devoted their expertise and time to the task of revealing forced changes in the lake's biota in the hope of creating a favourable atmosphere for immediate human intervention to save this once very rich and diverse ecosystem.

Reliable cyanotoxin monitoring in water reservoirs is difficult because of, among other reasons, unpredictable changes in cyanobacteria biomass, toxin production, and inadequate sampling frequency. Therefore, it would be useful to identify potentially microcystin-producing strains of cyanobacterial populations in field samples. With this aim, we developed a methodology to distinguish microcystin-producing from non-producing Microcystis strains by amplifying six characteristic segments of the microcystin synthetase mcy cluster, three corresponding to the nonribosomal peptide synthetase, genes mcyA, mcyB, and mcyC, and three to the polyketide synthase, genes mcyD, mcyE, and mcyG. For this purpose five new primer sets were designed and tested using purified DNA, cultured cells, and field colonies as DNA sources. Simultaneous amplification of several genes in multipex PCR reactions was performed in this study. The results obtained showed that: (i) the expected specific amplicons were obtained with all microcystin-producing strains but not with nonproducing strains; (ii) cells could be directly used as DNA templates, 2000 cells being a sufficient number in most cases; (iii) simultaneous amplification of several gene regions is feasible both with cultured cells and with field colonies. Our data support the idea that the presence of various mcy genes in Microcystis could be used as a criterion for ascribing potential toxigenicity to field strains, and the possibility of applying whole-cell assays for the simultaneous amplification of various genes may contribute significantly to simplifying toxigenicity testing. © 2005 Wiley Periodicals, Inc. Environ Toxicol 20: 235–242, 2005.

Cyanobacteria and particularly Microcystis sp. (Chroococcales) are known to produce a multitude of peptide metabolites. Here we report on the mass spectral analysis of cyanobacterial peptides in individual colonies of Microcystis sp. collected in a drinking water reservoir. A total number of more than 90 cyanopeptides could be detected, 61 of which could be identified either as known peptides or new structural variants of known peptide classes. For 18 new peptides flat structures are proposed. New congeners differed from known ones mainly in chlorination (aeruginosins), methylation (microginins), or amino acid sequences (cyanopeptolins). The high number of peptides and especially the new peptides underline the capability of Microcystis strains as producers of a high diversity of potentially bioactive compounds.

Eutrophication of surface waters caused by toxic cyanobacteria such as Microcystis aeruginosa leads to the release of secondary metabolites called Microcystins (MCs), which are heptapeptides with adverse effects on soil microbiota, plants, animals, and human health. Therefore, to avoid succumbing to the negative effects of these cyanotoxins, various remediation approaches have been considered. These techniques involve expensive physico-chemical processes because of the specialized equipment and facilities required. Thus, implementing eco-technologies capable of handling this problem has become necessary. Indeed, multi-soil-layering (MSL) technology can essentially meet this requirement. This system requires little space, needs simple maintenance, and has energy-free operation and high durability (20 years). The performance of the system is such that it can remove 1.16 to 4.47 log10 units of fecal contamination from the water, 98% of suspended solids (SS), 92% of biological oxygen de...

The aim of this study was to test the effects of cyanobacteria toxicity on feeding behavior of the golden mussel Limnoperna fortunei. First, it was tested the hypothesis that L. fortunei preferentially graze on non-toxic phytoplankton and reject toxic cyanobacteria. Second, it was tested the hypothesis that toxic cyanobacteria negatively affect feeding and survival of L. fortunei. The present study is the first to evaluate the effects of toxic cyanobacteria on L. fortunei feeding and survival. In the short-term grazing, golden mussel filtration rates were evaluated in the presence of toxic and non-toxic strains of cyanobacteria Microcystis aeruginosa, and non-toxic phytoplankton Nitzschia palea. Highest filtration rates were registered when mussels fed on Nitzschia. Despite that, golden mussel expelled Nitzschia cells in large quantities and preferentially ingested Microcystis cells, both toxic and non-toxic strains. In the long-term grazing, mussels were exposed to toxic and non-to...