Effect of subtilisin, a protease from Bacillus sp., on soil biochemical parameters and microbial biodiversity

Proteinaceous material constitute the main source of nitrogen in soil organic matter. Use of this nitrogen is limited by the breakdown of proteins into peptides and free amino acids. Proteases, therefore, are important in the use of protein N. The aim of this study is to assess the effect of subtilisin, which is a soil extracellular endopeptidase from Bacillus sp., both on soil microbial biostimulation and biodiversity. In addition to the protease, keratins, an insoluble-protein and low-bioavailable substrate, was added to enhance the effect of protease in soil. Protease, both on its own and in combination with keratins, has a biostimulant effect on soil microbial activity that was reflected in the protease, dehydrogenase and phosphatase activities. DNA metabarcoding analysis further revealed specific changes in soil biodiversity, mainly defined by the enrichment of plant-growth promoting microorganisms, specifically those producing hydrolase enzymes such as phosphatase and ammonifiers. Surprisingly, the addition of keratins specifically showed a rapid stimulation of soil proteolytic bacteria. Thus, the present work supports the use of subtilisin as biofertiliser and values the recycling of keratinous industrial waste in the field of biofertilisation. [Display omitted] •The effect of protease and keratin supplementation was evaluated on soil with a biochemical and microbiological approach.•Both protease and keratin, individually or in combination, favoured soil biostimulation.•Possible PGPR bacteria were specifically favoured by protease and keratin.