Streit W R, Joseph C M, Phillips D A
Department of Agronomy and Range Science, University of California, Davis 95616, USA.
Mol Plant Microbe Interact. 1996 Jul;9(5):330-8. doi: 10.1094/mpmi-9-0330.
Rhizosphere growth limitations imposed on Rhizobium meliloti by availability of biotin, thiamine, and riboflavin were overcome by adding nanomolar amounts of these vitamins. Studies done with R. meliloti 1021 showed that both synthesis and uptake of biotin promote colonization of alfalfa roots. Two lines of evidence indicated that plant-derived biotin normally promotes root colonization: (i) adding avidin significantly (P < or = 0.01) reduced rhizosphere growth of R meliloti 1021, and (ii) growth of Tn5-induced biotin auxotrophs still increased 10-fold in the rhizosphere. Synthesis, however, is the more important source of biotin for R. meliloti 1021 because in root colonization tests biotin auxotrophs competed very poorly with the parent strain. Mutations conferring biotin auxotrophy were closely linked on a single restriction fragment, and one was complemented with the Escherichia coli bio operon. Initial nucleotide sequencing and DNA-DNA hybridization tests showed the biotin synthesis genes in R. meliloti are quite different from those in E. coli.
通过添加纳摩尔量的生物素、硫胺素和核黄素，克服了因这些维生素的可利用性对苜蓿根瘤菌施加的根际生长限制。对苜蓿根瘤菌1021进行的研究表明，生物素的合成和摄取均促进了苜蓿根的定殖。有两条证据表明，植物来源的生物素通常促进根定殖：（i）添加抗生物素蛋白显著（P≤0.01）降低了苜蓿根瘤菌1021的根际生长，以及（ii）转座子Tn5诱导的生物素营养缺陷型在根际的生长仍增加了10倍。然而，对于苜蓿根瘤菌1021而言，合成是生物素更重要的来源，因为在根定殖试验中，生物素营养缺陷型与亲本菌株的竞争能力非常弱。赋予生物素营养缺陷型的突变紧密连锁在一个单一的限制片段上，并且其中一个突变被大肠杆菌生物素操纵子互补。初步的核苷酸测序和DNA-DNA杂交试验表明，苜蓿根瘤菌中的生物素合成基因与大肠杆菌中的生物素合成基因有很大不同。
