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Abstract The origin(s) of dissimilatory sulfate and/or (bi)sulfite reducing organisms (SRO) remains enigmatic despite their importance in global carbon and sulfur cycling since at least 3.4 Ga. Here, we describe novel, deep-branching archaeal SRO populations distantly related to other Diaforarchaea from two moderately acidic thermal springs. Dissimilatory (bi)sulfite reductase homologs, DsrABC, encoded in metagenome assembled genomes (MAGs) from spring sediments comprise one of the earliest evolving Dsr lineages. DsrA homologs were expressed in situ under moderately acidic conditions. MAGs lacked genes encoding proteins that activate sulfate prior to (bi)sulfite reduction. This is consistent with sulfide production in enrichment cultures provided sulfite but not sulfate. We suggest input of volcanic sulfur dioxide to anoxic spring-water yields (bi)sulfite and moderately acidic conditions that favor its stability and bioavailability. The presence of similar volcanic springs at the time SRO are thought to have originated (>3.4 Ga) may have supplied (bi)sulfite that supported ancestral SRO. These observations coincide with the lack of inferred SO42− reduction capacity in nearly all organisms with early-branching DsrAB and which are near universally found in hydrothermal environments.
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Distribution and abundance of tetraether lipid cyclization genes in terrestrial hot springs reflect pH
Abstract Many Archaea produce membrane‐spanning lipids that enable life in extreme environments. These isoprenoid glycerol dibiphytanyl glycerol tetraethers (GDGTs) may contain up to eight cyclopentyl and one cyclohexyl ring, where higher degrees of cyclization are associated with more acidic, hotter or energy‐limited conditions. Recently, the genes encoding GDGT ring synthases,grsAB, were identified in two Sulfolobaceae; however, the distribution and abundance ofgrshomologs across environments inhabited by these and related organisms remain a mystery. To address this, we examined the distribution ofgrshomologs in relation to environmental temperature and pH, from thermal springs across Earth, where sequences derive from metagenomes, metatranscriptomes, single‐cell and cultivar genomes. The abundance ofgrshomologs shows a strong negative correlation to pH, but a weak positive correlation to temperature. Archaeal genomes and metagenome‐assembled genomes (MAGs) that carry two or moregrscopies are more abundant in low pH springs. We also findgrsin 12 archaeal classes, with the most representatives in Thermoproteia, followed by MAGs of the uncultured Korarchaeia, Bathyarchaeia and Hadarchaeia, while several Nitrososphaeria encodes >3 copies. Our findings highlight the key role ofgrs‐catalysed lipid cyclization in archaeal diversification across hot and acidic environments.
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- Award ID(s):
- 1928309
- PAR ID:
- 10406199
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Environmental Microbiology
- Volume:
- 25
- Issue:
- 9
- ISSN:
- 1462-2912
- Format(s):
- Medium: X Size: p. 1644-1658
- Size(s):
- p. 1644-1658
- Sponsoring Org:
- National Science Foundation
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