Deep-sea in situ and laboratory multi-omics provide insights into the sulfur assimilation of a deep-sea Chloroflexotabacterium

Abstract

Chloroflexotabacteria are abundant and globally distributed in various deep-sea ecosystems. It has been reported based on metagenomics data that two deep-sea Chloroflexotalineages (the SAR202 group and Dehalococcoidia class) have the potential to drive sulfur cycling. However*the absence of cultured Chloroflexotarepresentatives is a significantbottleneck toward understanding their contribution to the deep-sea sulfur cycling. In this study*we findthat Phototrophicus methaneseepsis ZRK33 isolated from deep-sea sediment has a heterotrophic lifestyle and can assimilate sulfate and thiosulfate. Using combined physiological*genomic*proteomic*and in situ transcriptomic methods*we findthat strain ZRK33 can perform assimilatory sulfate reduction in both laboratory and deep-sea conditions. Metabolism of sulfate or thiosulfate by strain ZRK33 significantlypromotes the transport and degradation of various macromolecules and thereby stimulates the energy production. In addition*metagenomic results show that genes associated with assimilatory and dissimilatory sulfate reduction are ubiquitously distributed in the metagenome-assembled genomes of Chloroflexotamembers derived from deep-sea sediments. Metatranscriptomic results also show that the expression levels of related genes are upregulated*strongly suggesting that Chloroflexotabacteria may play undocumented roles in deep-sea sulfur cycling.