The regulation and ecological importance of novel metabolic pathways in freshwater bacterial communities

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Bacteria play a major role in the functioning of all aquatic systems. Research over the past decades has also revealed a remarkable metabolic flexibility of aquatic microbes, and in particular, it has now become clear that many aquatic prokaryotes are capable of both harvesting light energy and consuming organic materials (referred to as photoheterotrophs hereafter). These alternative phototrophic pathways have not been captured by conventional approaches, but there is increasing evidence that they may play a significant role in the overall movement of energy and C in aquatic ecosystems. I propose here to explicitly address the magnitude and ecological role of bacterial photoheterotrophy in freshwaters, initially focusing on aerobic anoxygenic phototrophic bacteria, and subsequently extending the work to other forms of bacterial mixotrophy. The main objectives of the research program are: 1) to quantify the spatial and temporal variability of phototrophic bacterial abundance and activity in freshwaters; 2) to assess the phylogenetic composition, diversity and biogeographical patterns of phototrophic bacteria; 3) to explore the environmental and biological factors that regulate the distribution and activity of phototrophic bacteria; and 4) to explore the ecological and biogeochemical role that these pathways may play in freshwaters. The program will involve large-scale comparative studies across a wide range of freshwaters and also small-scale experimental manipulations to assess the role that light and other environmental factors play on the distribution and functioning of phototrophic bacterioplankton. The proposed work will establish the foundation for understanding the environmental controls and ecological significance of these microbes in freshwaters, and will provide the tools to effectively incorporate these organisms and their associated metabolic pathways into our current models of energy pathways in freshwaters. This research has the potential to fundamentally shift the current paradigms concerning the movement of energy and carbon in lakes, and the functioning of freshwater food webs.