Sulfur Comproportionation and Sulfur Disproportionation in the Karst of Frasassi, Italy?
Abstract
Based on geochemical analyses and thermodynamic calculations, sulfur disproportionation and sulfur comproportionation may serve as microbial energy metabolisms in different parts of the sulfidic karst at Frasassi, Italy. These caves host a thriving lithoautotrophic biota and have emerged as a valuable model system for sulfur biogeochemistry. A coupled thermodynamic and geochemical analysis was used to predict exergonic sulfur redox reactions at Frasassi. Sulfur comproportionation (3H2S(aq) + SO42- + 2H+ = 4S0 + 4H2O) is an as-of-yet undetected microbial catabolism that could plausibly exist within the caves. This reaction can be thought of either as the anaerobic oxidation of sulfide to elemental sulfur using sulfate as an electron acceptor, or as the lithotrophic reduction of sulfate to elemental sulfur using sulfide as an electron donor. Extremely acidic (pH 0-2) microbial biofilms called "snottites," are ideal geochemical niches in which to search for microbes capable of catalyzing sulfur comproportionation. If these putative organisms are present, targeted enrichments and deep metagenomic sequencing of snottites may allow for their isolation and detailed characterization. Elemental sulfur disproportionation, the reverse of sulfur comproportionation, is thermodynamically favorable under different geochemical conditions (presence of elemental sulfur and neutral to alkaline pH). Such conditions are found within Frasassi stream sediments, and 16S rRNA surveys of these sediments have revealed high abundances of Desulfocapsa thiozymogenes, a known S0 disproportionator. Cultivation experiments and transcriptomics will provide insight into the genes and pathways involved in elemental sulfur disproportionation, which remain undetermined. Investigating both sulfur disproportionation and comproportionation at Frasassi will clarify the sulfur cycle within the caves and will uncover new ways in which life can obtain energy and thrive in subsurface environments.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B11L2253A
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0460 Marine systems;
- BIOGEOSCIENCES;
- 0463 Microbe/mineral interactions;
- BIOGEOSCIENCES;
- 0488 Sulfur cycling;
- BIOGEOSCIENCES