A Study of the Microbial Community at the Interface between Granite Bedrock and Soil Using a Culture-Independent and Culture-Dependent Approach

Abstract

The dissolution of minerals plays an important role in the formation of soils and sediments. In nu- trient limiting soils, minerals constitute a major reservoir of bio-essential cations. Of particular interest is granite as it is the major rock type of the continental land mass. Although certain bacte- ria have been shown to enhance weathering of granite-forming minerals, little is known about the dissolution of granite, at the whole rock scale, and the microbial community involved. In this study, both culture-independent and culture-dependent approaches were used to study the bacterial com- munity at the interface between granite bedrock and nutrient limiting soil in Dartmoor National Park, United Kingdom. High throughput sequencing demonstrated that over 70% of the bacterial population consisted of the bacterial classes Bacilli, Beta-proteobacteria and Gamma-proteo- bacteria. Bacteria belonging to the genera Serratia, Pseudomonas, Bacillus, Paenibacillus, Chromo- bacterium and Burkholderia were isolated from the sample site. All of the isolates were able to grow in a minimal growth medium, which contained glucose and ammonium chloride, with gran- ite as the sole source of bio-essential elements. Sixty six percent of the isolates significantly en- hanced basalt dissolution (p < 0.05). Dissolution of Si, K, Ca and Mg correlated with production of oxalic acid and acidification. The results of this study suggest that microorganisms in nutrient lim- iting soils can enhance the rate of granite dissolution, which is an important part of the biogeochemical cycle. Keywords