A detection method of soil microorganisms which is related to soil protease production was developed as follows. In paddy fields and several upland fields the major proteolytic soil microorganisms were Bacillus spp., which produced extracellular serine protease with similar properties to those of soil protease of these fields. In upland fields amended with a large amount of slurry, however, the major proteolytic soil microorganisms were gram-negative bacteria such as Serratia marcescens. This microorganism produced extracellular metalloprotease with similar properties to those of soil protease in these fields. The results obtained suggested that difference in the soil conditions might cause differences in proteolytic bacterial flora which resulted in characteristic difference in the major soil proteases. DNA primers, which were obtained from the N-terminal amino acid sequence of the protease of S.marcescens amplified not only the serratial metalloprotease gene but also that of the other gram-negative bacteria isolated from the slurried fields.
However they did not amplify protease genes of proteolytic Bacillus spp. By use of the DNA primers and DNA probes which were synthesized by PCR, the homologous metalloprotease gene was detected in DNA directly extracted from soils.