Occurrence and potential activity of denitrifiers and methanogens in groundwater at 140 m depth in Pliocene diatomaceous mudstone of northern Japan

Abstract

Anaerobic microbial activity has a major influence on the subsurface environment. We investigated the denitrification and methanogenesis in anoxic groundwater at a depth of 140 m in two boreholes drilled in a sedimentary geological setting, where the redox potential fluctuated. The average maximum potential denitrification rates, measured under anaerobic conditions in the two boreholes using an (15) N tracer, were 0.060 and 0.085 nmol (30) N2 mL(-1) h(-1) . The deduced NirS amino acid sequences obtained from in situ samples were similar to those of isolates belonging to the α-, β-, and γ-Proteobacteria, and the Firmicutes (72-100% similarity). Based on the nirS gene, the same operational taxonomic unit dominated incubated samples from each borehole. Methanogenesis candidates were detected by 16S rRNA gene analysis, but no sequence was detected using primers for the functional methanogenesis gene mcrA. Although the stable isotope signatures suggested that some of the dissolved methane was of biogenic origin, no potential for methane production was evident during the incubations. The groundwater at 140 m depth did not contain oxygen, had an Eh ranging from -144 to 6.8 mV, and was found to be a potential field for denitrification.

Incongruous variation of denitrifying bacterial communities as soil N level rises in Canadian canola fields

“…The occurrence of the nirS gene in g-proteobacteria has been reported recently (Katsuyama et al, 2013), but such large proportion of the nirS gene-carrying denitrifier from g-proteobacteria, as we found in this study, has never been reported before. We also detected nirS gene-carrying denitrifiers belonging to the Actinobacteria; this has only been reported in an aquatic environment (Li et al, 2012).…”

Depth and Dissolved Organic Carbon Shape Microbial Communities in Surface Influenced but Not Ancient Saline Terrestrial Aquifers

“…phylum Zixibacteria, formerly RBG-1 (one-way ANOVA post hoc test, p < 0.05, n = 48 for MM, n = 3 for TM, and n = 12 for OS; Supplementary Table S4) that has been identified as the dominant microorganisms in aquifer sediments and has the ability to assimilate ammonium (Castelle et al, 2013). Previously, the deep continental biosphere was suggested to be mainly supported by sulfate reduction (Nielsen et al, 2006; Hallbeck and Pedersen, 2008; Katsuyama et al, 2013). However, although nitrate, nitrite, and ammonium concentrations were very low in this oligotrophic subsurface environment and regardless of their ultimate source (Swanner and Templeton, 2011), this study also supports that nitrogen cycling may be important for the microorganisms inhabiting the deep biosphere (Kutvonen et al, 2015).…”

Spatial Distribution of Microbial Communities in the Alluvial Aquifer along the Oyodo River, Miyakonojo Basin, Japan

“…Others variables such as NO 3 -concentration, nutrients, pH, and microbial acclimation only exert secondary influences on denitrification rate in aquifers [29]. In the case of aquifer in Miyakonojo Basin, although denitrifiers were found in the oxic sample Md-5, the denitrification process could not proceed due to 5.9 mg/L oxygen [29,30]. Conversely, as for sample K-3, the presence of denitrifiers and the anoxic environment could support the occurrence of the denitrification process.…”