Bacterial Chloromethane degradation in forest soil samples
Chloromethane (CH3Cl) is the most abundant halogenated organic compound in the atmosphere and substantially responsible for destruction of the stratospheric ozone layer. Its global budget is imbalanced due to unrecognized sinks. With the application of the Montreal Protocol (1987), anthropogenic CH3Cl sources became negligible whereas natural sources, such as vegetation and soils, became substantial for its global budget. CH3Cl-degrading methylotrophs occur both in soils and in aerial parts of plants (phyllosphere), and might be an important and overlooked sink. The objective of our project was to link information on CH3Cl degradation and the identity of microorganisms and their biochemical pathways for CH3Cl degradation in forest soil and phyllosphere. Biological CH3Cl consumption occurred in organic and mineral soil horizons, and in leaf litter and senescent leaves as determined in labo microcosms. Highest consumption rates occurred in organic soil and senescent leaves and ranged from 0.59 to 1.96 and from 0.32 to 2.05 mmol CH3Cl gDW-1 h-1, respectively. Our results provide evidence that topsoil layers are important compartments of forest ecosystems with regard to (micro-)biological CH3Cl degradation. In addition, the phyllosphere of the fern Cythea australis also exhibited CH3Cl-degradation. The CH3Cl-degrading microbial community and its metabolic potentials were assessed by stable isotope probing (SIP) combined with 16S rRNA gene high-throughput sequencing and metagenomics. SIP of forest soil suggested strains closely related to Methylovirgula and Actinobacteria to be involved in CH3Cl degradation. Analysis of metagenome data will lead to knowledge on pathways of one-carbon metabolism of methylotrophs actively involved in the chloromethane sink.