Characterization of growing bacterial populations in McMurdo Dry Valley soils through stable isotope probing with (18) O-water.

Soil microbial communities of the McMurdo Dry Valleys, Antarctica (MDV) contain representatives from at least fourteen bacterial phyla. However, given low rates of microbial activity, it is unclear whether this richness represents functioning rather than dormant members of the community. We used stable isotope probing (SIP) with O-18-water to determine if microbial populations grow in MDV soils. Changes in the microbial community were characterized in soils amended with (H2O)-O-18 and (H2O)-O-18-organic matter. Sequencing the 16S rRNA genes of the heavy and light fractions of the bacterial community DNA shows that DNA of microbial populations was labeled with O-18-water, indicating these micro-organisms grew in the MDV soils. Significant differences existed in the community composition of the heavy and light fractions of the (H2O)-O-18 and (H2O)-O-18-organic matter amended samples (Anosim P < 0.05 of weighted Unifrac distance). Control samples and the light DNA fraction of the (H2O)-O-18 amended samples were dominated by representatives of the phyla Deinococcus-Thermus, Proteobacteria, Planctomyces, Gemmatimonadetes, Actinobacteria and Acidobacteria, whereas Proteobacteria were more prevalent in the heavy DNA fractions from the (H2O)-O-18-water and the (H2O)-O-18-waterorganic matter treatments. Our results indicate that SIP with (H2O)-O-18 can be used to distinguish active bacterial populations even in this low organic matter environment.