Halverson L J, Clayton M K, Handelsman J
Department of Plant Pathology, University of Wisconsin, Madison 53706.
Mol Ecol. 1993 Apr;2(2):65-78. doi: 10.1111/j.1365-294x.1993.tb00001.x.
We compared the stability of antibiotic-resistance markers in strains derived from Bacillus cereus UW85 in culture media and in the soybean rhizosphere in a growth chamber and in the field. We studied two independent, spontaneous mutants resistant to neomycin, three independent, spontaneous mutants resistant to streptomycin, and strains carrying plasmid pBC16, which encodes tetracycline resistance. Antibiotic-resistance markers were maintained in populations of all UW85 derivatives in culture and in the rhizosphere of soybeans grown in soil in a growth chamber. In two field experiments, antibiotic resistance was substantially lost in rhizosphere populations of B. cereus as early as 14 or as late as 116 days after planting. To distinguish between death of the inoculated strain and loss of its marker, we tested populations of B. cereus for other phenotypes (orange pigmentation, plasmid-borne resistance to tetracycline, and biocontrol activity) that are typical of UW85-derivatives used as inoculum, but atypical of the indigenous populations of B. cereus, and these phenotypes were maintained in populations from which the marker was lost. In general, neomycin-resistance markers were maintained at a higher frequency than streptomycin-resistance markers, and maintenance of antibiotic-resistance markers varied with position on the root and with the year of the experiment. In a semi-defined medium, the UW85 derivatives grew at the same rate as the wild type at 28 degrees C, but most grew more slowly than the wild type at 16 degrees C, demonstrating that antibiotic resistance can affect fitness under some conditions. The results suggest that the stability of antibiotic-resistance markers should be assessed in the ecosystems in which they will be studied.
我们比较了蜡样芽孢杆菌UW85衍生菌株中的抗生素抗性标记在培养基、生长室中的大豆根际以及田间条件下的稳定性。我们研究了两个独立的对新霉素耐药的自发突变体、三个独立的对链霉素耐药的自发突变体，以及携带编码四环素抗性的质粒pBC16的菌株。抗生素抗性标记在所有UW85衍生物培养群体以及生长室土壤中种植的大豆根际中得以维持。在两项田间试验中，早在种植后14天或晚至116天，蜡样芽孢杆菌根际群体中的抗生素抗性就大幅丧失。为了区分接种菌株的死亡与其标记的丧失，我们检测了蜡样芽孢杆菌群体的其他表型（橙色色素沉着、质粒介导的四环素抗性以及生物防治活性），这些表型是用作接种物的UW85衍生物所特有的，但并非蜡样芽孢杆菌土著群体所具有的典型表型，并且这些表型在标记丧失的群体中得以维持。一般来说，新霉素抗性标记比链霉素抗性标记维持的频率更高，并且抗生素抗性标记的维持情况因根的位置和试验年份而异。在半限定培养基中，UW85衍生物在28℃时与野生型生长速率相同，但在16℃时大多数比野生型生长得更慢，这表明抗生素抗性在某些条件下会影响适应性。结果表明，抗生素抗性标记的稳定性应在其将被研究的生态系统中进行评估。
