Dekkers L C, Phoelich C C, van der Fits L, Lugtenberg B J
Leiden University, Institute of Molecular Plant Sciences, Clusius Laboratory, Wassenaarseweg 64, 2333AL Leiden, The Netherlands.
Proc Natl Acad Sci U S A. 1998 Jun 9;95(12):7051-6. doi: 10.1073/pnas.95.12.7051.
A colonization mutant of the efficient root-colonizing biocontrol strain Pseudomonas fluorescens WCS365 is described that is impaired in competitive root-tip colonization of gnotobiotically grown potato, radish, wheat, and tomato, indicating a broad host range mutation. The colonization of the mutant is also impaired when studied in potting soil, suggesting that the defective gene also plays a role under more natural conditions. A DNA fragment that is able to complement the mutation for colonization revealed a multicistronic transcription unit composed of at least six ORFs with similarity to lppL, lysA, dapF, orf235/233, xerC/sss, and the largely incomplete orf238. The transposon insertion in PCL1233 appeared to be present in the orf235/233 homologue, designated orf240. Introduction of a mutation in the xerC/sss homologue revealed that the xerC/sss gene homologue rather than orf240 is crucial for colonization. xerC in Escherichia coli and sss in Pseudomonas aeruginosa encode proteins that belong to the lambda integrase family of site-specific recombinases, which play a role in phase variation caused by DNA rearrangements. The function of the xerC/sss homologue in colonization is discussed in terms of genetic rearrangements involved in the generation of different phenotypes, thereby allowing a bacterial population to occupy various habitats. Mutant PCL1233 is assumed to be locked in a phenotype that is not well suited to compete for colonization in the rhizosphere. Thus we show the importance of phase variation in microbe-plant interactions.
本文描述了高效定殖于根部的生防菌株荧光假单胞菌WCS365的一个定殖突变体,该突变体在无菌条件下生长的马铃薯、萝卜、小麦和番茄的根尖竞争性定殖中受损,表明这是一个具有广泛宿主范围的突变。在盆栽土壤中研究时,该突变体的定殖也受到损害,这表明缺陷基因在更自然的条件下也发挥作用。一个能够互补定殖突变的DNA片段揭示了一个多顺反子转录单元,该转录单元由至少六个与lppL、lysA、dapF、orf235/233、xerC/sss以及大部分不完整的orf238具有相似性的开放阅读框组成。PCL1233中的转座子插入似乎存在于orf235/233的同源物中,命名为orf240。在xerC/sss同源物中引入突变表明,xerC/sss基因同源物而非orf240对定殖至关重要。大肠杆菌中的xerC和铜绿假单胞菌中的sss编码属于位点特异性重组酶的λ整合酶家族的蛋白质,它们在由DNA重排引起的相变中发挥作用。从参与不同表型产生的基因重排角度讨论了xerC/sss同源物在定殖中的功能,从而使细菌群体能够占据各种生境。假定突变体PCL1233锁定在一种不太适合在根际竞争定殖的表型中。因此,我们证明了相变在微生物-植物相互作用中的重要性。