Bacterial carbon cycling in the sea: exploring the use of proteorhodopsin light-harvesting for managing nutrient limitation

Two decades of research into the biogeochemical implications of phototrophy through proteorhodopsin (PR) - a light-driven proton pump - has established its importance for bacterial carbon cycling in sun-lit waters.

However, the influence of nitrogen (N) or phosphorus (P) limitation, key factors determining ocean productivity, on bacterial PR phototrophy remains entirely unexplored.

The research strategy proposed here includes experimental work with PR-containing model bacteria, natural bacterial assemblages, and field studies, with the aims:To quantify the influence of PR phototrophy on biomass production yields and respiration when challenged with N- versus P-limitation.To determine the effect of PR phototrophy on the uptake and assimilation of inorganic and organic N and P sources in natural seawater.To examine the adaptations in metabolic strategies under N- and P-limitation in the light compared to darkness, using gene expression analyses.Given the ubiquity of nutrient limitation in the sea, the working hypothesis of this research is that substantial portions of the energetic benefits of PR phototrophy are effectuated by increasing the ability of bacteria to assimilate the nutrients that limit bacterial growth.

The proposed analyses will yield novel understanding of how PR-phototrophy affects bacterial carbon cycling in the face of nutrient limitation.