PNNL

Abstract

Thisstudyemployed16SrRNAgeneampliconpyrosequencingtoexaminethehypothesisthatchemolithotrophicFe(II)-oxidizing bacteria(FeOB)would preferentially colonizetheFe(II)-bearing mineral biotite compared to quartz sand whenthe minerals were incubated in situ within a subsurface redox transition zone(RTZ) at the Hanford 300 Area site in Richland, WA, USA.The work was motivated by the recently documented presence of neutral-pH chemolithotrophic FeOB capable of oxidizing structural Fe(II) in primary silicate and secondary phyllosilicate minerals in 300 Area sediment sand groundwater (Benzineetal.,2013). Sterilized portions of sand+biotite or sand alone were incubated in situ for 5 months within a multilevel sampling(MLS) apparatus thats pannedaca. 2-minterval across the RTZ in two separate groundwater wells.Parallel MLS measurements of aqueous geochemical species were performed prior to deployment of the minerals. Contrary to expectations, the 16S rRNA gene libraries showed no significant difference in microbial communities that colonized the sand+biotite vs. sand-only deployments.Both mineral-associated and groundwater communities were dominated by heterotrophictaxa, with organisms from the Pseudomonadaceae accountingforupto70% of all reads from the colonized minerals. These results are consistent with previous results indicating the capacity for heterotrophic metabolism(including anaerobic metabolism below the RTZ) as well as the predominance of heterotrophictaxa within 300 Area sediments and ground water.Although heterotrophic organisms clearly dominated the colonized minerals,several putativelithotrophic (NH4+,H2,Fe(II),andHS-oxidizing) taxa were detected in significant abundance above and within the RTZ. Such organisms may play a role in the coupling of anaerobic microbial metabolism to oxidative pathways with attendant impacts on elemental cycling and redox-sensitive contaminant behavior in the vicinity of the RTZ.