Willms, Inka M.

Abstract Members of the verrucomicrobial clade ‘ Candidatus Udaeobacter’ rank among the most dominant bacterial phylotypes in soil. Nevertheless, despite this global prevalence, in‐depth analyses with respect to pH preferences of ‘ Ca . Udaeobacter’ representatives are still lacking. Here, we utilized a recently designed primer pair, specifically targeting ‘ Ca . Udaeobacter’, to investigate links between soil pH and the abundance as well as phylotype composition of this largely unexplored verrucomicrobial clade. Based on 150 forest and 150 grassland soils, comprising a broad pH range, we determined the highest total abundance of ‘ Ca . Udaeobacter’ in strongly acidic soil (pH, ~5.1) and, noteworthy, in ultra‐acidic soil (pH < 3.5) and at a pH ≥ 7, its abundance drastically declined. When we analysed the six most dominant amplicon sequence variants affiliated with ‘ Ca . Udaeobacter’ separately, their abundances peaked within a pH range of approximately 4.7–5.2, and only in one case at slightly acidic soil pH (pH, 6.1). Our study benefits from a combination of quantitative real‐time PCR and high‐throughput amplicon sequencing, enabling for the first time a highly specific abundance analysis of representatives affiliated with ‘ Ca . Udaeobacter’, which revealed that this globally abundant verrucomicrobial clade shows preferences for acidic soil.

Soil bacteria have been investigated for more than a century, but one of the most dominant terrestrial groups on Earth, “ Candidatus Udaeobacter,” remains elusive and largely unexplored. Its natural habitat is considered a major reservoir of antibiotics, which directly or indirectly impact phylogenetically diverse microorganisms. Here, we found that “ Ca. Udaeobacter” representatives exhibit multidrug resistance and not only evade harmful effects of antimicrobials but even benefit from antibiotic pressure in soil. Therefore, “ Ca. Udaeobacter” evidently affects the composition of soil resistomes worldwide and might represent a winner of rising environmental pollution with antimicrobials. In addition, our study indicates that “ Ca. Udaeobacter” representatives utilize H 2 and thereby contribute to global hydrogen cycling. The here-reported findings provide insights into elementary lifestyle features of “ Ca. Udaeobacter,” potentially contributing to its successful global dissemination.