Colonization and S(0) mineralization of sulfur oxidizing biofilms in the Frasassi Cave System
Date
2018
Authors
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Publisher
University of Delaware
Abstract
Elemental sulfur (S(0)) is an important geologic resource, yet we are still understanding the mechanisms by which sulfur oxidizing microbial communities facilitate its formation. The Pozzo dei Cristalli stream in the Frasassi Cave System is inhabited by Sulfurovum streamers rich in S(0), implying a microbial role in mineral formation. Using metagenomics and metatranscriptomics, we examined how the community functions to make S(0), and more specifically, to explore genetic diversity within the Sulfurovum. We sequenced metagenomes and 16S rRNA from colonization net samples, over seventeen days, that were placed in the air water interface of the Pozzo dei Cristalli steam. The community structure was simple with two taxa making up 75% to 95% of the community abundance: a Gammaproteobacteria Halothiobacillaceae (PC16-C1) and a Campylobacterota Sulfurovum (PC16-C2). After dereplication, we recovered thirty high-quality representative metagenome assembled genomes (MAGs), of which included seven Sulfurovum. From the metatranscriptomes, transcripts mapping to these MAGs show that the Sulfurovum conduct sulfur oxidation by multiple (differing by MAG), aerobic respiration, denitrification, and carbon fixation. Sulfurovum PC16-C2 was by far the most abundant and active in the streamer community, suggesting this population are the streamer architects and primary producers. This population, Sulfurovum PC16-C2, highly expressed sqr, which would lead to S(0) formation, likely making PC16-C2 the primary contributor of S(0). To understand the role of the flanking Sulfurovum (seven in total), we performed a pangenomic to detect core (shared) and strain-specific genes in the Sulfurovum MAGs. This revealed that 21% to 35% of genes found in the Sulfurovum MAGs are core, while 12% to 44% of genes were strain specific. All but one Sulfurovum MAG has sqr, but diversity was apparent in the gene content of the sox pathway. Remarkably, the seven Frasassi Sulfurovum MAGs span the phylogenetic diversity of Sulfurovum. Future work should focus on understanding if the Frasassi Sulfurovum are representative of their phylogenetic group; perhaps by performing a more comprehensive pangenomic analysis. In the case that the Frasassi Sulfurovum are characteristic, these MAGs could be used to understand what genes drive diversity and success of the cosmopolitan Sulfurovum, and fundamentally the geochemical niches that could support biogenic S(0) formation.