Bacterial extracellular protease activities in field soils under different fertilizer managements

The major extracellular endopeptidase from Bacillus subtilis PF212 (isolated from paddy field soil) and B. subtilis CF80 (isolated from upland field soil) belongs to the group of serine proteases produced by Bacillus spp. known as subtilisins (optimum pH 7.0, optimum temperature 60 degrees C, and molecular mass 28 kDa). The NH2-terminal amino acid sequence (20 amino acids) of the endopeptidase from (i) strain CF80 was identical with that of subtilisin BPN' and (ii) strain PF212 was identical with that of subtilisin Amylosacchariticus. The properties (i.e., effect of inhibitors) of these endopeptidases were similar to those of the overall soil endopeptidase and soil endopeptidases extracted from paddy field soil. From the numbers of B. subtilis we isolated from paddy fields and found to produce a subtilisin-like serine protease, it seemed possible to consider that subtilisin was one of the soil endopeptidases in paddy field soils. The major extracellular endopeptidase from Serratia marcescens (strains 4-12-132, 4-12-131, and 4-60-110) isolated from upland field soils applied with animal slurry is a serratial metalloprotease (optimum pH 9.5, optimum temperature 40 degrees C, and molecular mass 50 kDa). The NH2-terminal amino acid sequence (20 amino acids) of the endopeptidase from strain 4-12-132 was identical with that of serratial metalloprotease, and partial DNA sequence of the endopeptidase gene of S. marcescens 4-12-132 had high homology with that of the serratial metalloprotease gene. The properties (i.e., effect of inhibitors) of this endopeptidase were similar to those of the overall soil endopeptidase in upland fields applied with animal slurry. Thus, it was possible to consider that serratial metalloprotease was one of the soil endopeptidases in upland fields applied with animal slurry.