Freshwaters dominated by cyanobacteria

with Charles Greer, NRC

Cyanobacterial blooms occur in lakes worldwide, and almost yearly in many Quebec lakes. The dominant member of the bloom's microbial community is typically the cyanobacterium Microcystis aeruginosa, some strains of which produce toxic compounds such as microcystin. Blooms can therefore pose a public health threat, and much research has gone into understanding the biology of bloom dynamics and microcystin production. Yet the adaptive value of microcystin production (encoded by the mcy gene cluster) is still controversial, and it is unknown how the other ~6000 genes encoded in the Microcystis genome contribute to fitness of the population in the wild. In addition to its importance in freshwater ecosystem function and public heath, Microcystis is numerically abundant (at least during the bloom), making it possible to obtain a deep sample of genetic diversity in the population through metagenomic shotgun sequencing of lakewater. Microcystis is also culturable in the lab, facilitating isolation of individual strains for whole genome sequencing and population genomic analysis. Time-course sequencing of a few marker genes suggests substantial genetic variation within the Microcystis population, but it remains unknown if this microdiversity is maintained by natural selection, providing the genetic basis for adaptation to different niches.