Diversity and activity of group 5/1h high-affinity H2 oxidizing bacteria is non-responsive to pH

Abstract

Biological high-affinity H₂ uptake in soil is the largest global sink for atmospheric H₂. Soil pH often influences soil biological activity but the impact of pH on high-affinity H₂ oxidizing bacteria (HOB) was not confirmed. We compared the activity and diversity of group 5/1h HOB in agricultural and forest soils across a gradient from pH 4 to pH 8. The potential H₂ uptake activity was approximately 2 times higher in agricultural soil than in forest soil across the pH gradient. Both H₂ oxidizing activity and HOB community structure were non-responsive to pH adjustment in these soils, and no pH optima was observed. Greater H₂ oxidizing activity was associated with higher iron content and lower carbon and nitrogen concentrations in soil. Catabolic repression of HOB was likely triggered when more organic carbon was present, due to the mixotrophic metabolism in the HOB community. A few hhyL genotypes (5%) responded to pH manipulation, but preference for acidic or alkaline pH was not consistent at the HOB taxonomic level. We conclude that pH preference is not an ecological trait that predicts group 5/1h HOB distribution in soil.