| Summary: | <p>Abstract</p> <p>Background</p> <p>In the present work the central carbon metabolism of <it>Dinoroseobacter shibae </it>and <it>Phaeobacter gallaeciensis </it>was studied at the level of metabolic fluxes. These two strains belong to the marine <it>Roseobacter </it>clade, a dominant bacterial group in various marine habitats, and represent surface-associated, biofilm-forming growth (<it>P. gallaeciensis</it>) and symbiotic growth with eukaryotic algae (<it>D. shibae</it>). Based on information from recently sequenced genomes, a rich repertoire of pathways has been identified in the carbon core metabolism of these organisms, but little is known about the actual contribution of the various reactions <it>in vivo</it>.</p> <p>Results</p> <p>Using <sup>13</sup>C labelling techniques in specifically designed experiments, it could be shown that glucose-grown cells of <it>D. shibae </it>catabolise the carbon source exclusively via the Entner-Doudoroff pathway, whereas alternative routes of glycolysis and the pentose phosphate pathway are obviously utilised for anabolic purposes only. Enzyme assays confirmed this flux pattern and link the lack of glycolytic flux to the absence of phosphofructokinase activity. The previously suggested formation of phosphoenolpyruvate from pyruvate during mixotrophic CO<sub>2 </sub>assimilation was found to be inactive under the conditions studied. Moreover, it could be shown that pyruvate carboxylase is involved in CO<sub>2 </sub>assimilation and that the <it>cyclic </it>respiratory mode of the TCA cycle is utilised. Interestingly, the use of intracellular pathways was highly similar for <it>P. gallaeciensis</it>.</p> <p>Conclusion</p> <p>The present study reveals the first insight into pathway utilisation within the <it>Roseobacter </it>group. Fluxes through major intracellular pathways of the central carbon metabolism, which are closely linked to the various important traits found for the <it>Roseobacter </it>clade, could be determined. The close similarity of fluxes between the two physiologically rather different species might provide the first indication of more general key properties among members of the <it>Roseobacter </it>clade which may explain their enormous success in the marine realm.</p>
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