Light-driven increase in C yield is linked to maintenance in the proteorhodopsin-containing photobacterium angustum S14
2015
Courties, Alicia | Riedel, Thomas | Rapaport, Alain | Niesldottir, Maria | Caparros, Jocelyne | Catala, Philippe | Salmeron, Christophe | Batailler, Nicole | Lebaron, Philippe | Suzuki, Marcellino | Niesldottir, Maria
Proteorhodopsin-containing prokaryotes (PCPs) are photoheterotrophic microorganisms containing transmembrane light-driven proton pumps called proteorhodopsins (PRs). Due to the prevalence of these organisms in the upper water column of the World’s Ocean, and their potential for ATP generation, PCPs have been suggested to significantly influence energy and matter flows in the biosphere. So far, evidence for the significance of PCP light-driven metabolism has been obtained by comparing growth in batch culture, under light versus dark conditions, and it appears that responses to light are in the majority of the cases linked to unfavorable conditions. We studied light responses to carbon yields of the PCP Photobacterium angustum S14 using chemostat conditions and light-dark cycles. We observed significant effects of light-dark cycles as well as significant differences between samples after 12 h illumination versus 12 h darkness only under higher substrate levels leading to higher cell counts (c.a. 5-10 • 108 cells • ml-1) and lower pH. Responses of yield to changes in growth rate were used to estimate Pirt’s maintenance coefficient and to assign for the first time a metric for these so-called unfavorable conditions that might be useful to evaluate energetic budgets and the potential for light-driven metabolism by PCPs. It appears that light responses by Photobacterium angustum S14 are linked to energetic balance rather than to substrate concentrations
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