Bacterial communities' response to microcystins exposure and nutrient availability : linking degradation capacity to community structure

Eutrophication of freshwater bodies followed by cyanobacterial bloom and toxin production is an important issue in freshwater supply in both developed and developing countries. The primary mechanism for microcystins (MCs) (the main class of cyanobacterial toxins) dissipation is microbial degradation. Repeated exposure of freshwater bodies to cyanobacterial toxins MCs may affect indigenous microbial communities and may also enhance biodegradation of MCs, but the factors driving this relationship remain unclear. Six Scottish freshwater bodies with different histories of natural exposure to MCs and ability to degrade MC-LR (the most common microcystin) were chosen as case study. Terminal Restriction Fragment Length Polymorphism (T-RFLP) and Biolog EcoPlate™ were used to study the structure and physiology of the bacterial communities. Previous exposure to MCs significantly contributed to the bacterial communities shape and microbial physiology of the water bodies under study. Other factors that significantly affected the bacterial communities were dissolved organic carbon and concentration of nitrogen compounds as well as temperature. Moreover a significant relationship was found between bacterial communities' structure and MC-LR half-life. These data suggest that exposure to MCs drives changes in structure and physiology of bacterial communities and in turn those communities differentially perform degradation of MC-LR.