# Identifying the active microbes driving organosulfur cycling from taurine and methionine in marine sediment

## TL;DR

This study identifies bacteria and archaea in marine sediment that use organosulfur compounds like taurine and methionine, revealing new insights into sulfur cycling in the ocean.

## Contribution

First quantitative assessment of organosulfur cycling by uncultivated microbes in marine sediment using 13C-DOS qSIP.

## Key findings

- Taurine utilization is mainly by bacteria, while methionine is used by bacteria and archaea like Methanococcoides.
- Gammaproteobacteria and Deltaproteobacteria are key in DOS cycling and prefer taurine/methionine over glucose.
- Only one OTU (Neptuniibacter) assimilates both DOS substrates, suggesting such microbes are rare.

## Abstract

Studies on microbial sulfur cycling in marine sediment have primarily centered on the cycling of inorganic sulfur. The microbial diversity underlying the cycling of organosulfur compounds is largely unexplored. In this study, we present the first quantification of dissolved organic sulfur (DOS) microbial assimilation in marine surface sediments using 13C-DOS quantitative DNA stable isotope probing (qSIP). We sampled marine sediment from 493 m water depth on the Puerto Rico continental slope, measured 13C-assimilation from two DOS substrates (13C-taurine and 13C-methionine), and compared the 13C-DOS assimilation to 13C-glucose uptake. Taurine utilization was confined to bacteria, whereas methionine was degraded by bacteria and archaea, including methanogenic Methanococcoides. Globally widespread uncultivated clades of Gammaproteobacteria and Deltaproteobacteria were the main drivers of DOS cycling and exhibited increased assimilation of carbon from taurine and methionine, compared to glucose. Only one operational taxonomic unit (OTU) affiliated with Neptuniibacter was found to assimilate taurine and methionine, but not glucose, implying that microbes exclusively utilizing both DOS substrates as a carbon source in marine sediments are rare. Still, a substantial number of bacterial taxa exhibited a higher assimilation of 13C from taurine or methionine, compared to glucose, indicating their preference for both DOS substrates over glucose as a carbon source in the sediment. These results represent the first quantitative assessment of organosulfur cycling from taurine and methionine by uncultivated microbes in a marine benthic environment.