Abstract
Methanol (MOH) and monomethylamine (MMA) are two typical one-carbon (C1) compounds found in natural environments. They play an important role in marine and atmospheric chemistry, cloud formation, and global climate. The main biological sink of MOH and MMA is rapid consumption by marine microbes. Here, field-based time-series incubations with supplemental 13C-labelled MOH and MMA and isotope ratio analyses were performed. A substantial difference in the MOH and MMA incorporation rates and bacterial taxa were observed between the South China Sea (SCS) and the Pearl River estuary. C1 substrates were assimilated more quickly in the estuary than the SCS shelf where MOH and MMA had similar bio-availability. However, microbial responses to MMA may be faster than to MOH in the coastal and basin surface water of the SCS despite similar active bacterial populations. Three ecological types of bacteria, in terms of response to supplemented MOH and MMA, were identified: rapid incorporation (I, dominant C1-incorporating group), slow incorporation (II, minor C1-incorporating group), and no incorporation (III, C1-non-incorporating group). Members of the families Methylophilaceae (β-Proteobacteria) and Piscirickettsiaceae (γ-Proteobacteria) belonged to type I and actively incorporated substrates in the estuary and SCS, respectively. Diverse MOH and MMA-incorporating type II bacteria were identified by stable isotope probing in the SCS, and could play a more important role in the transformation of C1 compounds in marine environments than hitherto assumed.
Highlights
One-carbon (C1) compounds consist of a single carbon atom such as methane, methanol (MOH), monomethylamine (MMA), halogenated methanes and methylated sulphur[1]
It decreased with increasing incubation time of samples at site P1, indicating that some microbially assimilated 13C-MOH was degraded to carbon dioxide
The substrate assimilation rates were not measured at sites C3 and B4 as all culture volumes were collected for ultracentrifugation and molecular analysis
Summary
One-carbon (C1) compounds consist of a single carbon atom (lacking carbon-carbon bonds) such as methane, methanol (MOH), monomethylamine (MMA), halogenated methanes and methylated sulphur[1]. C1 compounds exert influence on marine and atmospheric chemistry, cloud formation, and global climate. The amount of stored MOH in the global ocean is about 228 Tg, 67 times higher than the atmosphere[8]. MOH is a ubiquitous source of C1 substrate, which aids the widespread distribution of methylotrophic organisms throughout the surface ocean. This, combined with its high solubility, suggests that consumption by microorganisms prevents MOH from escaping into the atmosphere in significant quantities. MMA, another important C1 compound in atmospheric and marine environments, is a derivative of ammonia, with one hydrogen atom replaced by a methyl group. The concentration of MMA generally ranges from 0 to 66 nM, with higher values in shoals, off shore, and high productivity areas, and lower values in oligotrophic areas, the deep sea (
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