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Abstract:
The marine sulfate-reducing bacterium Desulfobacterium autotrophicum HRM2 belongs to the deltaproteobacterial family Desulfobacteraceae and stands out for its capacity of facultative chemolithoautotrophic growth (next to heterotrophy). Here, proteomics-driven metabolic reconstruction was based on a combination of 2D-DIGE, shotgun proteomics, and analysis of the membrane protein enriched fraction applied to eight different substrate adaptation conditions (seven aliphatic compounds plus H-2/CO2). In total, 1344 different proteins were identified (similar to 27% of the 4947 genome-predicted), from which a complex metabolic network was reconstructed consisting of 136 proteins (124 detected; similar to 91%). Peripheral degradation routes for organic substrates feed directly or via the methylmalonyl-CoA pathway into the Wood-Ljungdahl pathway (WLP) for terminal oxidation to CO2. Chemolithoautotrophic growth apparently involves the periplasmic [Ni/Fe/Se]-containing hydrogenase HysAB (H-2 oxidation), the reductively operating WLP (CO2 fixation), and classical gluconeogenesis. Diverse soluble proteins (e.g., Hdr, Etf) probably establish a fine balanced cytoplasmic electron transfer network connecting individual catabolic reactions with the membrane menaquinone pool. In addition, multiple membrane protein complexes (Nqr, Qmo, Qrc, Rnf1, Rnf2, and Tmc) provide ample routes for interacting with the reducing equivalent pool and delivering electrons to dissimilatory sulfate reduction (both localized in the cytoplasm). Overall, this study contributes to the molecular understanding of the habitat-relevant Desulfobacteraceae.
