Isolation and Characterization of Methanethiol-Producing Bacteria from Agricultural Soils

Methanethiol (MT) produced from terrestrial soils can have important effects on atmospheric chemistry and ecosystem-level processes, and it originates mainly from the metabolism of sulfur-containing amino acids by microorganisms. Methanethiol producing bacteria (MPB) were enriched and isolated from agricultural soils in a modified basal medium containing methionine (Met) as the sole carbon source. The isolates were identified as Bacillus sp. WH-R1, WH-R2, and WH-R3; Arthrobacter sp. SZLB-W3; and Delftia sp. CHZG-R4 based on cell morphology, physiological and biochemical characteristics, and 16S rRNA sequence analysis. Delftia sp. CHZG-R4 was identified as a novel strain producing MT using Met as a precursor, and it had the most active MT-producing potential, with the production of MT being 21.8 μg at 30 °C and pH 7.0. Optimal MT production was observed at 35 ° C and pH 6.0, with 51.3% of sulfur content in Met being converted into MT. Under these conditions, MT production changed according to the supply of both carbon and nitrogen sources. The addition of 2 g L−1 each of starch, sucrose, urea, and potassium nitrate promoted MT production by more than 10%, whereas addition of 2 g L−1 each of ammonia sulfate and peptone decreased MT production by 16% and 87%, respectively. This is the first study to report MT production by Delftia sp. CHZG-R4, providing useful information for the microbial mechanism of MT production from agricultural soils. Our findings also contribute to improving our knowledge of the function of Delftia sp. CHZG-R4.