pH is a good predictor of the distribution of anoxygenic purple phototrophic bacteria in Arctic soils

• Arctic soils contain diverse and abundant anoxygenic purple phototrophic bacteria (AnPPB).
• About one third of the AnPPB detected in this study appear to be novel phylotypes.
• Soil pH and moisture content were key factors driving the diversity and abundance of AnPPB in the Arctic.

Anoxygenic purple phototrophic bacteria (AnPPB) are ecologically important microorganisms that are sensitive to shifts in environmental variables. However, there is little information about the composition and distribution of AnPPB in the Arctic. Here we present the first study of the spatial distribution of soil AnPPB in Arctic soils using pyrosequencing and quantitative real-time PCR. We show that the AnPPB community in Arctic soils is as diverse and abundant as that in lower latitudes. The phylum Alphaproteobacteria accounted for 54.1% of the total sequences; about one third of total sequences were identified as novel phylotypes. Consistent with their anaerobic niche, AnPPB abundances were positively correlated with soil moisture content. Furthermore, the relative and absolute abundances of several dominant AnPPB taxa were significantly correlated with soil pH. AnPPB phylogenetic community structure was correlated with soil pH, as was alpha diversity, with a minimum around pH 6.0. Previous research has shown that pH is a good predictor of the structure of soil bacterial communities. Our results here suggest that pH could be a key factor driving phylogenetic diversity of not just overall bacterial communities but also of discrete functional guilds of bacteria in terrestrial ecosystems.