Photosynthetic Apparatus in Roseateles depolymerans 61A Is Transcriptionally Induced by Carbon Limitation

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Abstract
Production of a photosynthetic apparatus in Roseateles depolymerans 61A, a recently discovered freshwater β- Proteobacterium showing characteristics of aerobic phototrophic bacteria, was observed when the cells were subjected to a sudden decrease in carbon sources (e.g., when cells grown with 0.1 to 0.4% Casamino Acids were diluted or transferred into medium containing ≤0.04% Casamino Acids). Accumulation of bacteriochlorophyll (BChl) a was observed in the presence of oxygen and was enhanced under semiaerobic conditions (2% oxygen) but was reduced in the presence of light. Similarly to what has been reported regarding some aerobic phototrophic bacteria belonging to the α subclass of the Proteobacteria , viability of the cells in the carbon source-free medium was prolonged under aerobic-light (10 W m −2 ) conditions, possibly due to photosynthetic energy conversion, but was not prolonged under aerobic-dark conditions. The puf operon, which encodes most of the apoproteins of light-harvesting and reaction center complexes, was sequenced, and the effect of changes in Casamino Acids concentrations, oxygen, and light on its expression was estimated by the accumulation of its mRNA. The expression of the puf operon was induced by the decrease in carbon sources, similarly to what was observed for the accumulation of BChl a under aerobic and semiaerobic conditions (≥0.2% O 2 ), and was reduced in the presence of light. Transcription of the R. depolymerans puf operon is considered to be controlled by changes in carbon nutrients in addition to oxygen tension and light intensity.

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