Abstract
Methylophaga sulfidovorans is an obligately methylotrophic, DMS-oxidizing organism, isolated from microbial mat sediment. DMS and H2S, both present in marine microbial mats, can be used as energy sources by this organism. In batch cultures of M. sulfidovorans, sequential H2S and DMS utilization occurred. In energy-limited continuous cultures, with DMS, methanol and H2S as substrates, mixotrophic growth of M. sulfidovorans was observed, showing that at low concentrations these substrates can be used simultaneously. Oxygen and H2S uptake experiments showed that the critical concentration at which sulfide inhibition of DMS oxidation occurred was between 15 and 40 μmol l−1. Also in crude enrichments of DMS oxidizers a decrease of 50% in DMS-oxidizing capacity for about 200 μmol l−1 H2S was observed. The new physiological data obtained with the pure cultures of M. sulfidovorans were incorporated in a compartment model of a microbial mat and gave improved predictions of DMS profiles and DMS emissions from the mat, both when phototrophic activity is present (day) and when it is absent (night).
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