Living in the cold. Thermophiles in temperate soils

Abstract

Soils are highly heterogeneous environments and hold a huge microbial diversity. Microorganisms play a major role in the cycling of nutrients and the maintenance of soil ecosystems. Nevertheless, scarce information is available on the living conditions of microorganisms and in most cases their actual contribution to soil functioning. In this study, we use some soil thermophiles as a model to evaluate the potential living strategy of ubiquitous soil bacteria. Thermophilic Firmicutes (e.g. Parageobacillus related bacteria) are present in soils mainly as viable cells and live in temperate soils taking advantage of periodic heat events. Results showed that the thermophiles actively participate in the cycling of C, N, S and P in soils processing organic matter and making inorganic nutrients available to either plants or other microorganisms. Besides, their extracellular enzymes, which represent the limiting step of organic matter mineralization in soils, are apparently well fitted to function under high temperature and low water availability usually encountered during extreme heat events at upper soil layers. Global warming trends are expected to induce more frequent extreme heat events and so the role of soil thermophiles is expected to be enhanced in a near future. Soil thermophiles represent a model type of microorganisms that can help us to understand the living strategies of microorganisms thriving in soils. The role of soil thermophiles is of interest to understand the functioning of soils, and specially arid-like environments, with important consequences at local soil ecosystems and global scales.