Degradation of organically synthesized herbicides by the symbiosis of plants and endophytes.

西马津[2-氯-4，6-二(乙氨基)-S-三嗪]被广泛用于杂草防除，在日本已被检测出是地下水和地表水中的一种污染物。已有多种微生物对S-三嗪类除草剂进行降解。然而，这些微生物在受污染的土壤上的大多数应用都没有促进除草剂的矿化。这似乎是因为接种物难以在土壤中持续存在，并难以从贫营养环境中获得能源。本文报道了从玉米和大豆中分离到的一些内生细菌对西马津的有效降解作用。茶树和大豆在前一年以2.6g m^-2的速度供应西马津的土壤上种植。从玉米和大豆表面灭菌的根中分别分离到4株放射型农杆菌和6株慢生根瘤菌。这些菌株在含有0.2 mM西马津作为唯一氮源的基本液体培养基中生长。这些分离株在培养7天后消耗了50%以上的西马津。将西马津降解菌株接种到COMS土壤中，导致土壤中西马津的快速消耗。大豆对西马津的敏感性远高于玉米。然而，降解西马津的B.Japan onicum形成的根瘤增加了大豆对西马津的抗性。这些结果表明，利用内生菌修复受除草剂污染的土壤或生产抗西马津的作物系统是可能的。

Simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] is extensively used for the control of weeds, and has been detected as a pollutant in ground and surface water in Japan. Many kinds of microorganisms have been shown to degrade s-triazine herbicides. A majority of applications of these microorganisms to the contaminated soils, however, failed to promote the mineralization of the herbicides. It seems to be because of the difficulty for the inocula in persisting in soils and obtaining energy sources from the oligotrophic environments. This report presents that some of the endophytic bacteria isolated from com and soybean effectively degrade simazine in association with the host plants.Tea may and Glycine max were grown on the soils which had been supplied with simazine at the rate of 2.6 g m^<-2> in the previous year. Four strains of Agrobacterium radiobacter and six strains of Bradyrhizobium japonicum were isolated from the surface-sterilized roots of com and soybean, respectively. These isolates grew in a basal liquid medium containing 0.2 mM simazine as a sole nitrogen source. More than 50% of simazine were consumed after 7 days of culture of these isolates. Inoculation of the simazine-degrading A. radiobacte strains to coms resulted in the rapid consumption of simazine in the soils. Soybean is much more sensitive to simazine than com. Formation of nodules by the simazine-degrading B. japonicum, however, increased resistance of soybeans against simazine. These results suggest a possibility of utilization of endophytes for remediation of herbicide-contaminated soils or production of simazine resistant cropping systems.