SCycDB: A curated functional gene database for metagenomic profiling of sulphur cycling pathways

Microorganisms play important roles in the biogeochemical cycling of sulphur (S), an essential element in the Earth's biosphere. Shotgun metagenome sequencing has opened a new avenue to advance our understanding of S cycling microbial communities. However, accurate metagenomic profiling of S cycling microbial communities remains technically challenging, mainly due to low coverage and inaccurate definition of S cycling gene families in public orthology databases. Here we developed a manually curated S cycling database (SCycDB) to profile S cycling functional genes and taxonomic groups for shotgun metagenomes. The developed SCycDB contains 207 gene families and 585,055 representative sequences affiliated with 52 phyla and 2684 genera of bacteria/archaea, and 20,761 homologous orthology groups were also included to reduce false positive sequence assignments. SCycDB was applied for functional and taxonomic analysis of S cycling microbial communities from four habitats (freshwater, hot spring, marine sediment and soil). Gene families and microorganisms involved in S reduction were abundant in the marine sediment, while those of S oxidation and dimethylsulphoniopropionate transformation were abundant in the soil. SCycDB is expected to be a useful tool for fast and accurate metagenomic analysis of S cycling microbial communities in the environment.