Diversity of aromatic compound-degrading genes in relation to soil capacity to protect from pollution

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It is indispensable to develop the sustainable agriculture on the earth. To realize the sustainable agriculture, it is essential to develop the technology to protect the soil fertility from various stresses such as pesticides and mono-cropping, and keep the soil microbial diversity. In this study, we investigate the structure and diversity of soil microorganisms and ita relation wity the capacity of soil to protect from the chemical stresses.The extraction method of soil DNA was optimized. The PCR amplifications of16SrDNA using universal primet sets and endonuclease digestion showed specific patterns of restriction fragment length polymorphism in the soils recieving different fertilizing practices. Melitng point measurement revealed the increase in high G+C DNA in the soil receiving farmyard manure. This results were compared with other methods to anaiyze the microbial community structure in soil : phospholipid fatty acids composition, respiratory quinone profile, Biolog^<<encircledR>> plate substrate assimilation test. The increase in the high G+C DNA was comfirmed. The soil capacity to protect from chemical stresses was examined by measuring the degradation rate of pentachlorophenol (PCP) and 2,4,5,6-tetrachl oroisophthalonitrile (TPN) in soil. The soil receiving farmyard manure degraded them faster. The major degrading microorganisms were a Gram-negative rod for PCP and various fungi (especialy Fusarium spp.) for TPN.The active microhial gropus for the degradation capacity did not admit with the tendency of total microbial community structure in soil. The detestion of oxgenase genes such as bphc was also tried by PCR amplification method.