Persistence of microbial extracellular enzymes in soils under different temperatures and water availabilities

Microbial extracellular enzyme activity (EEA) is critical for the decomposition of organic matter in soils. Generally, EEA represents the limiting step governing soil organic matter mineralization. The high complexity of soil microbial communities and the heterogeneity of soils suggest potentially complex interactions between microorganisms (and their extracellular enzymes), organic matter, and physicochemical factors. Previous studies have reported the existence of maximum soil EEA at high temperatures although microorganisms thriving at high temperature represent a minority of soil microbial communities. To solve this paradox, we attempt to evaluate if soil extracellular enzymes from thermophiles could accumulate in soils. Methodology at this respect is scarce and an adapted protocol is proposed. Herein, the approach is to analyze the persistence of soil microbial extracellular enzymes at different temperatures and under a broad range of water availability. Results suggest that soil high-temperature EEA presented longer persistence than enzymes with optimum activity at moderate temperature. Water availability influenced enzyme persistence, generally preserving for longer time the extracellular enzymes. These results suggest that high-temperature extracellular enzymes could be naturally accumulated in soils. Thus, soils could contain a reservoir of enzymes allowing a quick response by soil microorganisms to changing conditions. This study suggests the existence of novel mechanisms of interaction among microorganisms, their enzymes and the soil environment with relevance at local and global levels.