Over the last several decades changes in climate, population and
land use have caused an increase in toxic or harmful cyanobacterial blooms
(cyanoHABs), which now form a major global threat to water quality and
security. As a first step towards a predictive, geographic model of cyanoHAB
emergence, we searched for evidence of genes encoding the production of
Microcystins, potent hepatotoxins produced by Microcystis spp, in ~60
freshwater bodies in Israel which are situated across gradients of geography, climate
and land use. We detected the mcyD gene
in about 70% of the samples,
suggesting that the distribution of potentially harmful species is much wider
than previously
thought. Local conditions within the
water body and the intended use of the water, rather than regional conditions
such as land use, altitude or average temperature, were better predictors of
the presence of toxinogenic populations. Phylogenetic analysis of the mcyA gene
revealed that specific clades of toxin biosynthesis genes are associated with,
and potentially selected for, in different types of water bodies. Our results demonstrate the ubiquity of “seed
populations” of toxinogenic strains, which are a prerequisite for bloom
formation, suggest a strong connection between these populations and agriculture
or aquaculture, and highlight the need to identify how microbial populations
affect, and are affected by, water quality. This latter point is currently
being studied in freshwater bodies across Israel as part of a collaborative,
infrastructure project termed “the freshwater microbiome”.
