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Open Access Research article

Mixotrophic growth of bacteriochlorophyll a-containing members of the OM60/NOR5 clade of marine gammaproteobacteria is carbon-starvation independent and correlates with the type of carbon source and oxygen availability

Stefan Spring1* and Thomas Riedel23

Author Affiliations

1 Leibniz Institute DSMZ – German Collection of Microorganisms and Cell Cultures, Inhoffenstr. 7B, Braunschweig 38124, Germany

2 Helmholtz-Centre for Infection Research (HZI), Research Group Microbial Communication, Inhoffenstr. 7, Braunschweig 38124, Germany

3 Present address: Observatoire Océanologique de Banyuls, Université P. et M. Curie, UMR-CNRS 7621, Laboratoire Arago, 66650 Banyuls-sur-Mer, France

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BMC Microbiology 2013, 13:117  doi:10.1186/1471-2180-13-117

Published: 24 May 2013

Abstract

Background

Populations of aerobic anoxygenic photoheterotrophic bacteria in marine environments are dominated by members of the Roseobacter lineage within the Alphaproteobacteria and the OM60/NOR5 clade of gammaproteobacteria. A wealth of information exists about the regulation of pigment production and mixotrophic growth in various members of the Roseobacter clade, but a detailed knowledge about aerobic bacteriochlorophyll a-containing gammaproteobacteria is still limited to one strain of the species Congregibacter litoralis.

Results

The production of photosynthetic pigments and light-dependent mixotrophic growth was analysed in Luminiphilus syltensis DSM 22749T, Chromatocurvus halotolerans DSM 23344T and Pseudohaliea rubra DSM 19751T, representing three taxonomically diverse strains of bacteriochlorophyll a-containing gammaproteobacteria affiliated to the OM60/NOR5 clade. In these strains the expression of a photosynthetic apparatus depended mainly on the type of carbon source and availability of oxygen. The effect of illumination on pigment expression varied significantly between strains. In contrast to Chromatocurvus halotolerans, pigment production in Luminiphilus syltensis and Pseudohaliea rubra was repressed by light of moderate intensities, probably indicating a higher sensitivity to light-induced oxidative stress. The efficiency of using light for mixotrophic growth did not correlate with the cellular level of photosynthetic pigments, but depended mainly on the type of metabolized substrate with malate being the optimal carbon source in most cases.

Conclusions

Oligotrophic growth conditions or carbon limitation were not required for light-dependent mixotrophic growth in members of the OM60/NOR5 clade. The ability of using light as energy source and the fine tuning of photosynthesis gene expression depended mainly on the type of carbon source and oxygen availability, which indicates that the regulation of pigment production is controlled by the cellular redox state. While light has the main impact on the regulation of photosynthetic pigments in photoheterotrophic representatives of the Roseobacter lineage this was not the case in strains of the OM60/NOR5 clade.

Keywords:
Photoheterotrophy; Photophosphorylation; Roseobacter clade; Carbon starvation; Coastal marine environment