Properties of soil proteases and proteases from Bacillus spp. obtained from water-logged paddy fields treated with organic manure or chemical fertilizer or not treated with fertilizer were compared to elucidate the sources of soil proteases. The major extractable soil proteases were metal chelator sensitive neutral proteases that were active in hydrolyzing benzyloxycarbonyl-L-phenylalanyl-L-leucine and benzyloxycarbonyl-L-phenylalanyl-L-tyrosyl-L-leucine. In this respect they resembled extracellular proteases from Bacillus subtilis (six isolates), Bacillus cereus (four isolates), and Bacillus mycoides (three isolates) isolated from the same fields. The major extractable soil protease from the manured field was a serine neutral protease that was active in hydrolyzing casein. It resembled an extracellular protease from B. subtilis (eight isolates) isolated from the same field. Extractable soil proteases accounted for 18–96% of the total soil protease in the aforementioned soil. We concluded that a major source of soil protease in water-logged paddy fields is proteolytic Bacillus spp.Key words: soil protease, metal chelator sensitive neutral protease, serine neutral protease, proteolytic Bacillus spp.
Effect of soil organic matter chemical compositions on soil protease and urease activity in alpine grassland soils in Northern Xizang, China
