Metagenomic identification of active methanogens and methanotrophs in serpentinite springs of the Voltri Massif, Italy

Abstract

The production of hydrogen and methane by geochemical reactions associated with the serpentinization of ultramafic rocks can potentially support subsurface microbial ecosystems independent of the photosynthetic biosphere. Methanogenic and methanotrophic microorganisms are abundant in marine hydrothermal systems heavily influenced by serpentinization, but evidence for methane-cycling archaea and bacteria in continental serpentinite springs has been limited. This report provides metagenomic and experimental evidence for active methanogenesis and methanotrophy by microbial communities in serpentinite springs of the Voltri Massif, Italy. Methanogens belonging to family Methanobacteriaceae and methanotrophic bacteria belonging to family Methylococcaceae were heavily enriched in three ultrabasic springs (pH 12). Metagenomic data also suggest the potential for hydrogen oxidation, hydrogen production, carbon fixation, fermentation, and organic acid metabolism in the ultrabasic springs. The predicted metabolic capabilities are consistent with an active subsurface ecosystem supported by energy and carbon liberated by geochemical reactions within the serpentinite rocks of the Voltri Massif.

Magmatism, serpentinization and life: Insights through drilling the Atlantis Massif (IODP Expedition 357)

“…The cell densities in the IODP Expedition 357 drill cores are distinctly lower than in the actively venting Lost City carbonate towers (10 7 to 10 8 per gram of wet weight; Kelley et al, 2005). They are also low in comparison to cell densities in fluids sampled in actively serpentinizing environments on land, which are typically less than 10 5 cells ml -1 , and as low as 10 2 cells mL -1 , although continental sites of serpentinization represent different niches within the subsurface ecosystem (e.g., Schrenk et al, 2013;Brazelton et al, 2017). These cell densities are also lower than in mafic subseafloor cores, which have been estimated at ~10 4 cells per gram of rock (Jørgensen and Zhao, 2016).…”

Unusual metabolic diversity of hyperalkaliphilic microbial communities associated with subterranean serpentinization at The Cedars

“…Geochemical features and microbial taxonomic diversities of various serpentinization sites have been described previously (Brazelton et al, 2010(Brazelton et al, , 2013Tiago and Verissimo, 2013;Quéméneur et al, 2014Quéméneur et al, , 2015Sanchez-Murillo et al, 2014;Postec et al, 2015;Miller et al, 2016). In addition, several metagenomic studies of serpentinization sites have further described the presence of genes related to the methane and hydrogen cycling in the serpentinizing systems (Brazelton and Baross, 2009;Brazelton et al, 2012Brazelton et al, , 2016. However, life strategies used by the majority of microbial community members living in the serpentinization systems remain elusive, especially for the members associated with the deep subsurface serpentinization.…”

Carbon Assimilation Strategies in Ultrabasic Groundwater: Clues from the Integrated Study of a Serpentinization-Influenced Aquifer

“…In situ microbial communities may utilize the products of serpentinization-including methane, carbon monoxide, formate, and acetate-as sources of carbon (14,(20)(21)(22)(23)(24)(25). Microbial communities in serpentinite springs in the Voltri Massif, Italy, appear to perform both aerobic methanotrophy and methanogenesis using CO 2 liberated from acetate (26). Methanogens in The Cedars, CA, are capable of producing methane from both inorganic carbon and a variety of organic carbon substrates.…”