Soil and Water Management Research Unit, Agricultural Research Service, U. S. Department of Agriculture, and Department of Soil Science, University of Minnesota, St. Paul, Minnesota 55108.
Appl Environ Microbiol. 1993 Jun;59(6):1762-6. doi: 10.1128/aem.59.6.1762-1766.1993.
IncP plasmid r68.45, which carries several antibiotic resistance genes, and IncP plasmid pJP4, which contains genes for mercury resistance and 2,4-dichlorophenoxyacetic acid degradation, were evaluated for their ability to transfer to soil populations of rhizobia. Transfer of r68.45 was detected in nonsterile soil by using Bradyrhizobium japonicum USDA 123 as the plasmid donor and several Bradyrhizobium sp. strains as recipients. Plasmid transfer frequencies ranged up to 9.1 x 10 in soil amended with 0.1% soybean meal and were highest after 7 days with strain 3G4b4-RS as the recipient. Transconjugants were detected in 7 of 500 soybean nodules tested, but the absence of both parental strains in these nodules suggests that plasmid transfer had occurred in the soil, in the rhizosphere, or on the root surface. Transfer of degradative plasmid pJP4 was also evaluated in nonsterile soil by using B. japonicum USDA 438 as the plasmid donor and several Bradyrhizobium sp. strains as recipients. Plasmid pJP4 was transferred only when strains USDA 110-ARS and 3G4b4-RS were the recipients. The plasmid transfer frequency was highest for strain 3G4b4-RS (up to 7.4 x 10). Mercury additions to soil, ranging from 10 to 50 mug/g of soil, did not affect population levels of parental strains or the plasmid transfer frequency.
IncP 质粒 r68.45 携带多种抗生素抗性基因，IncP 质粒 pJP4 则含有抗汞和 2,4-二氯苯氧乙酸降解基因，研究了它们向土壤根瘤菌种群转移的能力。使用大豆根瘤菌 USDA123 作为质粒供体和几种根瘤菌菌株作为受体，在非无菌土壤中检测到 r68.45 的转移。在添加 0.1%豆粕的土壤中，质粒转移频率高达 9.1×10-5，在以 3G4b4-RS 为受体的 7 天后最高。在 500 个大豆根瘤中检测到 7 个转化体，但这些根瘤中没有亲株的存在，表明质粒转移发生在土壤中、根际或根表面。使用大豆根瘤菌 USDA438 作为质粒供体和几种根瘤菌菌株作为受体，在非无菌土壤中也评估了降解质粒 pJP4 的转移。只有当菌株 USDA110-ARS 和 3G4b4-RS 为受体时，质粒 pJP4 才能转移。对于 3G4b4-RS 菌株，质粒转移频率最高（高达 7.4×10-5）。向土壤中添加汞，范围从 10 到 50 微克/克土壤，不会影响亲株的种群水平或质粒转移频率。
