title: Insights into environmental controls on microbial communities in a continental serpentinite aquifer using a microcosm-based approach.
abstract: Geochemical reactions associated with serpentinization alter the composition of dissolved organic compounds in circulating fluids and potentially liberate mantle-derived carbon and reducing power to support subsurface microbial communities. Previous studies have identified Betaproteobacteria from the order Burkholderiales and bacteria from the order Clostridiales as key components of the serpentinite-hosted microbiome, however there is limited knowledge of their metabolic capabilities or growth characteristics. In an effort to better characterize microbial communities, their metabolism, and factors limiting their activities, microcosm experiments were designed with fluids collected from several monitoring wells at the Coast Range Ophiolite Microbial Observatory (CROMO) in northern California during expeditions in March and August 2013. The incubations were initiated with a hydrogen atmosphere and a variety of carbon sources (carbon dioxide, methane, acetate, and formate), with and without the addition of nutrients and electron acceptors. Growth was monitored by direct microscopic counts; DNA yield and community composition was assessed at the end of the 3 month incubation. For the most part, results indicate that bacterial growth was favored by the addition of acetate and methane, and that the addition of nutrients and electron acceptors had no significant effect on microbial growth, suggesting no nutrient- or oxidant-limitation. However, the addition of sulfur amendments led to different community compositions. The dominant organisms at the end of the incubations were closely related to Dethiobacter sp. and to the family Comamonadaceae, which are also prominent in culture-independent gene sequencing surveys. These experiments provide one of first insights into the biogeochemical dynamics of the serpentinite subsurface environment and will facilitate experiments to trace microbial activities in serpentinizing ecosystems.
authors.affiliation: Department of Geological Sciences, Michigan State University East Lansing, MI, USA ; Center for Environmental Education, Conservation and Research, Inter American University of Puerto Rico San Juan, PR, USA.
authors.forename: Melitza
authors.initials: M
authors.lastname: Crespo-Medina
authors.affiliation: Department of Geological Sciences, Michigan State University East Lansing, MI, USA.
authors.forename: Katrina I
authors.initials: KI
authors.lastname: Twing
authors.affiliation: SETI Institute Mountain View, CA, USA.
authors.forename: Michael D Y
authors.initials: MD
authors.lastname: Kubo
authors.affiliation: Exobiology Branch, Ames Research Center, NASA Moffett Field, CA, USA.
authors.forename: Tori M
authors.initials: TM
authors.lastname: Hoehler
authors.affiliation: Department of Geosciences, University of Rhode Island Kingston, RI, USA.
authors.forename: Dawn
authors.initials: D
authors.lastname: Cardace
authors.affiliation: Center for Astrobiology and Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, CO, USA.
authors.forename: Tom
authors.initials: T
authors.lastname: McCollom
authors.affiliation: Department of Geological Sciences, Michigan State University East Lansing, MI, USA.
authors.forename: Matthew O
authors.initials: MO
authors.lastname: Schrenk
keywords: carbon; metabolism; nutrients; serpentinization; subsurface