AUTHOR=Kutvonen Heini , Rajala Pauliina , Carpén Leena , Bomberg Malin 

TITLE=Nitrate and ammonia as nitrogen sources for deep subsurface microorganisms

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.01079

DOI=10.3389/fmicb.2015.01079

ISSN=1664-302X

ABSTRACT=<p>We investigated the N-utilizing bacterial community in anoxic brackish groundwater of the low and intermediate level nuclear waste repository cave in Olkiluoto, Finland, at 100 m depth using <sup>15</sup>N-based stable isotope probing (SIP) and enrichment with <sup>14∕15</sup>N-ammonium or <sup>14∕15</sup>N-nitrate complemented with methane. Twenty-eight days of incubation at 12°C increased the concentration of bacterial 16S rRNA and nitrate reductase (<italic>nar</italic>G) gene copies in the substrate amended microcosms simultaneously with a radical drop in the overall bacterial diversity and OTU richness. <italic>Hydrogenophaga/Malikia</italic> were enriched in all substrate amended microcosms and <italic>Methylobacter</italic> in the ammonium and ammonium+methane supplemented microcosms. <italic>Sulfuricurvum</italic> was especially abundant in the nitrate+methane treatment and the unamended incubation control. Membrane-bound nitrate reductase genes (<italic>nar</italic>G) from <italic>Polarimonas</italic> sp. were detected in the original groundwater, while <italic>Burkholderia, Methylibium</italic>, and <italic>Pseudomonas nar</italic>G genes were enriched due to substrate supplements. Identified <italic>amo</italic>A genes belonged to <italic>Nitrosomonas</italic> sp. <sup>15</sup>N-SIP revealed that Burkholderiales and Rhizobiales clades belonging to the minority groups in the original groundwater used <sup>15</sup>N from ammonium and nitrate as N source indicating an important ecological function of these bacteria, despite their low number, in the groundwater N cycle in Olkiluoto bedrock system.</p>