Top E, Mergeay M, Springael D, Verstraete W
Laboratory of Microbial Ecology, Faculty of Agricultural Sciences, State University of Ghent, Belgium.
Appl Environ Microbiol. 1990 Aug;56(8):2471-9. doi: 10.1128/aem.56.8.2471-2479.1990.
Conjugal transfer from Escherichia coli to Alcaligenes eutrophus of the A. eutrophus genes coding for plasmid-borne resistance to cadmium, cobalt, and zinc (czc genes) was investigated on agar plates and in soil samples. This czc fragment is not expressed in the donor strain, E. coli, but it is expressed in the recipient strain, A. eutrophus. Hence, expression of heavy metal resistance by cells plated on a medium containing heavy metals represents escape of the czc genes. The two plasmids into which this DNA fragment has been cloned previously and which were used in these experiments are the nonconjugative, mobilizable plasmid pDN705 and the nonconjugative, nonmobilizable plasmid pMOL149. In plate matings at 28 to 30 degrees C, the direct mobilization of pDN705 occurred at a frequency of 2.4 x 10(-2) per recipient, and the mobilization of the same plasmid by means of the IncP1 conjugative plasmids RP4 or pULB113 (present either in a third cell [triparental cross] or in the recipient strain itself [retromobilization]) occurred at average frequencies of 8 x 10(-4) and 2 x 10(-5) per recipient, respectively. The czc genes cloned into the Tra- Mob- plasmid pMOL149 were transferred at a frequency of 10(-7) to 10(-8) and only by means of plasmid pULB113. The direct mobilization of pDN705 was further investigated in sandy, sandy-loam, and clay soils. In sterile soils, transfer frequencies at 20 degrees C were highest in the sandy-loam soil (10(-5) per recipient) and were enhanced in all soils by the addition of easily metabolizable nutrients.(ABSTRACT TRUNCATED AT 250 WORDS)
在琼脂平板和土壤样品中研究了编码质粒介导的对镉、钴和锌抗性的嗜碱产碱杆菌基因（czc基因）从大肠杆菌向嗜碱产碱杆菌的接合转移。这个czc片段在供体菌株大肠杆菌中不表达，但在受体菌株嗜碱产碱杆菌中表达。因此，接种在含重金属培养基上的细胞对重金属的抗性表达代表了czc基因的逃逸。先前已将该DNA片段克隆到其中并用于这些实验的两个质粒是非接合、可移动的质粒pDN705和非接合、不可移动的质粒pMOL149。在28至30摄氏度的平板交配中，pDN705的直接转移频率为每受体2.4×10⁻²，通过IncP1接合质粒RP4或pULB113（存在于第三个细胞中[三亲本杂交]或存在于受体菌株本身中[反向转移]）对同一质粒的转移频率分别为每受体平均8×10⁻⁴和2×10⁻⁵。克隆到Tra⁻Mob⁻质粒pMOL149中的czc基因仅通过质粒pULB113以10⁻⁷至10⁻⁸的频率转移。在沙质、沙壤土和粘土中进一步研究了pDN705的直接转移。在无菌土壤中，20摄氏度时的转移频率在沙壤土中最高（每受体10⁻⁵），并且通过添加易代谢的养分在所有土壤中都有所提高。（摘要截短于250字）
