Abstract
Toxin production in algal blooms presents a significant problem for the water industry. Of particular concern is microcystin, a potent hepatotoxin produced by the unicellular freshwater species Microcystis aeruginosa. In this study, the proteomes of six toxic and nontoxic strains of M. aeruginosa were analyzed to gain further knowledge in elucidating the role of microcystin production in this microorganism. This represents the first comparative proteomic study in a cyanobacterial species. A large diversity in the protein expression profiles of each strain was observed, with a significant proportion of the identified proteins appearing to be strain-specific. In total, 475 proteins were identified reproducibly and of these, 82 comprised the core proteome of M. aeruginosa. The expression of several hypothetical and unknown proteins, including four possible operons was confirmed. Surprisingly, no proteins were found to be produced only by toxic or nontoxic strains. Quantitative proteome analysis using the label-free normalized spectrum abundance factor approach revealed nine proteins that were differentially expressed between toxic and nontoxic strains. These proteins participate in carbon-nitrogen metabolism and redox balance maintenance and point to an involvement of the global nitrogen regulator NtcA in toxicity. In addition, the switching of a previously inactive toxin-producing strain to microcystin synthesis is reported.
Highlights
Blooms of cyanobacteria occur worldwide in nutrient-rich waters and can pose a public health threat when toxin-producing species are involved
The Core Proteome of M. aeruginosa Strains—Proteome analysis of the six strains in this study identified 475 proteins reproducible in biological triplicates, which were considered for further statistical analysis
Ten functional categories were represented in the core proteome, the highest fraction being comprised of proteins involved in photosynthesis and respiration
Summary
Blooms of cyanobacteria occur worldwide in nutrient-rich waters and can pose a public health threat when toxin-producing species are involved. From the ‡School of Biotechnology and Biomolecular Sciences, University of New South Wales, NSW 2052, Australia; §Department of Chemistry and Biomolecular Sciences, Macquarie University, NSW 2109 Australia Microcystins exert their hepatotoxicity in mammals by inhibiting protein phosphatases in the liver (PP1 and PP2a) [7, 8]. The currently available nontoxic strains generated by insertional inactivation of mcyS genes show altered morphology, compared with the wild-type toxic strain Microcystis aeruginosa PCC 7806. Some of these changes are readily observable, such as the presence of gas vesicles, changes in pigmentation and thylakoid organization, reduced cell size, as well as the tendency of mutant cells to form aggregates [18, 19]. Such changes have been suggested to Molecular & Cellular Proteomics 10.9
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