# Two Novel S‐methyltransferases Confer Dimethylsulfide Production in Actinomycetota

## TL;DR

Scientists discovered two new enzymes in bacteria from the Mariana Trench that convert toxic sulfur gases into dimethylsulfide, a key player in global sulfur cycles and climate regulation.

## Contribution

Identification of two novel S-methyltransferases, MddM1 and MddM2, in Actinomycetota that detoxify H2S and MeSH into DMS.

## Key findings

- MddM1 and MddM2 convert H2S and MeSH into DMS in Mycolicibacterium poriferae from the Mariana Trench.
- mddM1 is more abundant than mddM2 and widespread in Actinomycetota and diverse environments.
- Expression of mddM1 and mddM2 in E. coli enhances tolerance to H2S, MeSH, and oxidative stress.

## Abstract

Hydrogen sulfide (H2S), methanethiol (MeSH), and dimethylsulfide (DMS) are abundant sulfur gases with crucial roles in global sulfur cycling, chemotaxis, and climate regulation. Microorganisms can S‐methylate H2S and MeSH, which can be cytotoxic, to yield non‐toxic DMS via MddA or MddH enzymes in largely terrestrial or marine environments, respectively. However, the potential of many important and abundant bacteria like Actinomycetota is underestimated due to unknown Mdd enzymes. Here, two novel S‐adenosine‐methionine‐dependent H2S and MeSH S‐methyltransferases, MddM1 and MddM2 are identified, in the DMS‐producing actinomycete Mycolicibacterium poriferae (M. poriferae) ZYF656, isolated from the Mariana Trench. M. poriferae ZYF656 MddM1 and MddM2 likely detoxify H2S and MeSH and alleviate oxidative stress, since mddM1 and mddM2 transcription is induced by H2S, MeSH, and oxidative stress, and their expression in E. coli enhances H2S, MeSH, and oxidative stress tolerance. MddM1 and/or MddM2 are in >50% of actinomycetota, including the model Streptomyces species, S. venezuelae, but are also seen in some Chloroflexota, Acidobacteriota, and Proteobacteria. mddM1 is always more abundant than mddM2 in diverse environments and is prevalent in soils and marsh sediments. This study highlights the significance of H2S‐ and MeSH‐dependent DMS production and, principally, of Actinomycetota in global DMS production and sulfur cycling.

This study identifies two novel S‐adenosine‐methionine‐dependent methyltransferases, MddM1 and MddM2, in actinomycetes from the Mariana Trench. These enzymes can convert toxic hydrogen sulfide (H2S) and methanethiol (MeSH) into dimethylsulfide (DMS), serving as a cellular detoxification and oxidative stress response. mddM1 gene is widespread in Actinomycetota and diverse environments, revealing their underestimated, crucial roles in global sulfur cycling and DMS production.