Abstract
Dissolved organic matter (DOM) release by anoxygenic phototrophic bacteria belonging to diverse taxonomic groups is a ubiquitous process, resulting in 5–20% of the CO2 fixed by photosynthesis leaving the cell. The green photosynthetic bacterium Chlorobaculum limnaeum releases ~10% of the carbon assimilated during autotrophic СО2 fixation. Extracellular DOM release by Cba. limnaeum is a normal function of living cells, since it does not occur in the dark and is inhibited by fluoroacetate, an inhibitor of СО2 fixation via the reducing TCA acids cycle, which is used for CO2 assimilation in this bacterium. In the presence of acetate or pyruvate in the medium, DOM release increases to 30 and 60%, respectively. Nitrogen limitation stimulates DOM release by Cba. limnaeum up to 60% of assimilated СО2. Under these conditions, addition of acetate results in DOM release increasing up to 100%. Therefore, the extracellular release of DOC by anoxygenic phototrophic bacteria can be considered as an important source of substrates for the growth of heterotrophic bacteria in oxygen-free aquatic ecosystems.
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