Microbial metabolism of methanol and methylamine in the Gulf of Mexico: insight into marine carbon and nitrogen cycling.

One carbon (C1) metabolism plays an important role in marine carbon cycling but the dynamics and modes of C1 transformations are not fully understood. We made contemporaneous measurements of methylamine and methanol metabolism to elucidate the role of C1 compounds as sources of carbon, energy and nitrogen. Methanol and methylamine were predominantly used as an energy source in offshore waters (oxidation rate constant: kmethanol : 0.02-0.10 day-1 ; kmethylamine : 0.01-0.18 day-1 ), but were also important sources of biomass carbon in coastal waters (assimilation rate constant: kmethanol : 0.04-0.10 day-1 ; kmethylamine : 0.01-0.05 day-1 ). The relative extent of assimilation versus oxidation for these substrates correlated positively with chlorophyll, nutrients and heterotrophic bacterial production. Methanol oxidation and assimilation were stimulated significantly by nutrient addition. In contrast, methylamine metabolism was inhibited by ammonium or nitrate, suggesting that methylamine served as a nitrogen source. A preliminary metagenomic survey revealed a diverse population of putative C1-utilizing microorganisms. These results show that the remineralization of methylamine could provide both C and N sources for microbes. Both methanol and methylamine contribute to microbial energetic and carbon substrate demands with a distinctly different signature in nearshore versus offshore environments.