title: Light-driven increase in carbon yield is linked to maintenance in the proteorhodopsin-containing Photobacterium angustum S14.
abstract: 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.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire d'Océanographie Microbienne (LOMIC), Observatoire Océanologique , Banyuls-sur-Mer, France.
authors.forename: Alicia
authors.initials: A
authors.lastname: Courties
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire d'Océanographie Microbienne (LOMIC), Observatoire Océanologique , Banyuls-sur-Mer, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Riedel
authors.affiliation: INRA-Supagro, UMR MISTEA , Montpellier, France ; INRA-INRIA, MODEMIC Team , Sophia Antipolis, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Rapaport
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire de Biodiversité et Biotechnologies Microbiennes (LBBM), Observatoire Océanologique , Banyuls-sur-Mer, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Lebaron
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire de Biodiversité et Biotechnologies Microbiennes (LBBM), Observatoire Océanologique , Banyuls-sur-Mer, France.
authors.forename: Marcelino T
authors.initials: MT
authors.lastname: Suzuki
keywords: Photobacterium angustum; Pirt model; carbon yield; photoheterotrophy; proteorhodopsin