Summary: Trimethylamine--oxide (TMAO) supported anoxic growth in the non-fermentative marine bacterium sp. NCMB 400 and was reduced quantitatively to trimethylamine. The properties of TMAO reductase were those expected of a terminal reductase in anaerobic respiration. The enzyme was induced in the presence of trimethylamine oxide, repressed at high oxygen tensions and derepressed under anaerobic conditions. The cellular location of TMAO reductase was investigated by determining its distribution with respect to enzymes in cellular fractions prepared after lysozyme/EDTA treatment. A spheroplasting technique was developed, based on the method of Birdsell & Cota-Robles, that gave a high yield of intact spheroplasts from cells of marine alteromonads, and marker enzyme distribution indicated a clean fractionation. TMAO reductase was located in the periplasmic fraction, but it was released less readily than alkaline phosphatase; full release required EDTA treatment. The results are consistent with the role of TMAO as a terminal electron acceptor for anoxic growth, and the location of TMAO reductase does not preclude the possibility that TMAO reduction is linked to enerav conservation.


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