Photoheterotrophy in marine prokaryotes

Despite considerable advances in the understanding of the various microbial photoheterotrophic mechanisms, the role of solar radiation in the metabolism of bacterioplankton in the ocean is difficult to assess. It is already apparent that rates of CO2 fixation by prokaryotic cells may be only a part of the picture. Photophosphorylation is difficult to differentiate from respiratory phosphorylation and other types of ATP synthesis. Solar energy could by-pass ATP synthesis, instead being used to generate a proton-motive force, which in turn could be directly used for cell motility or even for importing molecules into cells. In addition, photoheterotrophic prokaryotes could actively regulate intake and use of solar energy for different metabolic functions depending on the energetic demands of the cell. The factors listed above hence require consideration when solar energy input into metabolism of oceanic photoheterotrophic prokaryotes is experimentally quantified and numerically modelled.