A type of photoheterotrophic bacteria contain a transmembrane light-driven proton pump called proteorhodopsins (PRs). Due to the prevalence of these organisms in the upper water column of the World’s Ocean, and their potential for light-driven ATP generation, they have been suggested to significantly influence energy and matter flows in the biosphere. To date, evidence for the significance of the light-driven metabolism of PR-containing prokaryotes has been obtained by comparing growth in batch culture, under light versus dark conditions, and it appears that responses to light are linked to unfavorable conditions, which so far have not been well parameterized. We studied light responses to carbon yields of the PR-containing Photobacterium angustum S14 using continuous culture conditions and light–dark cycles. We observed significant effects of light–dark cycles compared to dark controls, as well as significant differences between samples after 12 h illumination versus 12 h darkness. However, these effects were only observed under higher cell counts and lower pH associated with higher substrate concentrations. Under these substrate levels Pirt’s maintenance coefficient was higher when compared to lower substrate dark controls, and decreased under light–dark cycles. It appears that light responses by P. angustum S14 are induced by the energetic status of the cells rather than by low substrate concentrations.
Strain MOLA814 is a marine betaproteobacterium that was isolated from seawater in the Beaufort Sea. Here, we present its genome sequence and annotation. Genome analysis revealed the presence of a proteorhodopsin-encoding sequence together with its retinal-producing pathway, indicating that this strain might generate energy by using light.
Strain MOLA455 is a marine gammaproteobacterium isolated from the bay of Banyuls-sur-Mer, France. Here, we present its genome sequence and annotation. Genome analysis revealed the presence of genes associated with a possibly photoheterotrophic lifestyle that uses a proteorhodopsin protein.
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