Abstract
The dissolution of minerals plays an important role in the formation of soils and sediments. In nutrient 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 bacteria 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 community 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 granite as the sole source of bio-essential elements. Sixty six percent of the isolates significantly enhanced 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 limiting soils can enhance the rate of granite dissolution, which is an important part of the biogeochemical cycle.
Highlights
The silicates account for over 90% of the Earth’s crust
X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis confirmed the composition of the bedrock was granite
Taxonomical assignment of the sequences demonstrated that over 85% of the microbial community was dominated by three bacterial classes (Figure 2)
Summary
The silicates account for over 90% of the Earth’s crust. The dissolution of silicate minerals results in the formation of soil and sediment, and is an important process in long-term carbon cycling. In nutrient limiting soils, such as acidic soils, silicate minerals constitute a major reservoir of bio-essential cations, for example, calcium, potassium and magnesium [1]. Microorganisms, such as bacteria and fungi are known to enhance the dissolution rates of silicates (for reviews on the role of fungi and bacteria see [2] and [3], respectively). Laboratory-based experiments, with granite-forming minerals, have suggested that microorganisms produce organic acids, siderophores and extracellular polysaccharides that enhance granite dissolution [13] [14] These studies have predominately focused on single minerals rather than the whole rock scale, where the rate of dissolution and reaction pathways would be different [13]-[17]. Previous experiments have mainly focused on commercial bacteria rather than bacteria isolated from a granitic environment
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