土壤中质粒pLV1016 在快生型大豆根瘤菌间的水平转移

在滤膜、液体培养基和土壤微宇宙3种系统中,研究了接合型质粒pLV1016 由快生型大豆根瘤菌(Rhizobiumfredii)QB1131 向R.frediilux Lux3的水平转移及pLV1016 由QB1131 向土著细菌的转移.接合培养1d后,分别计算供、受体菌的生长速率和质粒转移速率常数(γ).结果表明,相同接种浓度下,滤膜接合时γ值最高,土壤中γ值最低,γ值不受土壤是否灭菌和是否有大豆植株的影响,γ值与初始接种浓度负相关,与供、受体的生长速率正相关.在未灭菌土中检测到pLV1016 可转移到土著细菌,土著接合子分别属于根瘤菌属和假单胞菌属.

Horizontal transfer of plasmid pLV1016 among Rhizobium fredii strains in soil

Broadhost range conjugative plasmid transfer between R.fredii QB1131 (pLV1016) and lux3 or between QB1131(pLV1016) and indigenous bacteria on filter,in broth,and in microcosms containing sterile or nonsterile soil,planted with or without soybean were studied. The donors,recipients and transconjugants were enumerated on selective media 1 day after inoculation,and the growth rates of donor and recipient as well as the transfer rate constants (γ) of plasmid were calculated for three initial parental densities in each system.At the same initial density, γ value was the highest in filter mating and the lowest in soil microcosm mating,which was not influenced by soybean spermosphere or by soil sterilization or nonsterilization.But in microcosm experiments,it was inversely related to initial parental density and directly related to donor growth rates.In nonsterile soil,plasmid pLV1016 could transfer from R.fredii to indigenous bacteria Rhizobium sp.or Pseudomonas sp.