Appl Environ Microbiol. 1995 Aug;61(8):3136-41. doi: 10.1128/aem.61.8.3136-3141.1995.
Plasmid transfer rates for the conjugative plasmid R388::Tn1721 from Pseudomonas cepacia (donor) to Pseudomonas fluorescens (recipient) on agar media, in broth, and in microcosms containing sterile or nonsterile soil, in the presence or absence of germinating pea seeds, were determined. Donors, recipients, and transconjugants were enumerated on selective media after 1 day on agar or in broth culture and over a 7-day period in soil or pea spermosphere microcosms. Donor and recipient growth rates and plasmid transfer rate constants [(gamma), where (gamma) = transconjugants (middot) (donors (middot) recipients)(sup-1) (middot) h(sup-1)] were calculated for three initial parental densities (10(sup4), 10(sup6), or 10(sup8) CFU/g or ml) in each system. For all initial density levels, values of (gamma) in agar and broth matings were higher than those in soil or in the pea spermosphere-rhizosphere microcosms. Values of (gamma) were not influenced by the pea spermosphere or by sterile or nonsterile conditions of the soil. However, (gamma) values in microcosm experiments were inversely related to initial parental density and were directly related to donor growth rates. Values of (gamma) averaged 4 x 10(sup-10), 4 x 10(sup-12), and 3 x 10(sup-14) when initial donor and recipient cell densities were 10(sup4), 10(sup6), and 10(sup8) CFU/g, respectively. These results suggest that the plasmid transfer rate constant is independent of parental cell density only when parental growth is not limited. In a resource-limited environment, intra- or interspecific competition may reduce the transfer rate by limiting parental growth.
在琼脂培养基、培养液以及含有无菌或非无菌土壤的微宇宙中，测定了假单胞菌（供体）中 R388::Tn1721 可接合质粒向荧光假单胞菌（受体）的转移率，同时还研究了在有或没有发芽豌豆种子存在的情况下的转移率。在琼脂或培养液培养 1 天后以及在土壤或豌豆生境微宇宙中培养 7 天期间，在选择性培养基上对供体、受体和转导子进行了计数。针对三种初始亲本密度（10^4、10^6 或 10^8 CFU/g 或 ml），计算了每个系统中供体和受体的生长率和质粒转移率常数[γ，其中 γ=转导子（·）（供体（·）受体）^-1（·）h^-1]。对于所有初始密度水平，在琼脂和培养液中的γ值均高于土壤或豌豆生境-根际微宇宙中的值。豌豆生境或土壤的无菌或非无菌条件均不会影响γ值。然而，微宇宙实验中的γ值与初始亲本密度成反比，与供体生长率成正比。当初始供体和受体细胞密度分别为 10^4、10^6 和 10^8 CFU/g 时，γ值平均为 4×10^-10、4×10^-12 和 3×10^-14。这些结果表明，只有当亲本生长不受限制时，质粒转移率常数才与亲本细胞密度无关。在资源有限的环境中，种内或种间竞争可能通过限制亲本生长来降低转移率。
