Dekkers L C, van der Bij A J, Mulders I H, Phoelich C C, Wentwoord R A, Glandorf D C, Wijffelman C A, Lugtenberg B J
Leiden University, Institute of Molecular Plant Sciences, Clusius Laboratory, The Netherlands.
Mol Plant Microbe Interact. 1998 Aug;11(8):763-71. doi: 10.1094/MPMI.1998.11.8.763.
Colonization-defective, transposon-induced mutants of the efficient root colonizer Pseudomonas fluorescens WCS365 were identified with a gnotobiotic system. Most mutants were impaired in known colonization traits, i.e., prototrophy for amino acids, motility, and synthesis of the O-antigen of LPS (lipopolysaccharide). Mutants lacking the O-antigen of LPS were impaired in both colonization and competitive growth whereas one mutant (PCL1205) with a shorter O-antigen chain was defective only in colonization ability, suggesting a role for the intact O-antigen of LPS in colonization. Eight competitive colonization mutants that were not defective in the above-mentioned traits colonized the tomato root tip well when inoculated alone, but were defective in competitive root colonization of tomato, radish, and wheat, indicating they contained mutations affecting host range. One of these eight mutants (PCL1201) was further characterized and contains a mutation in a gene that shows homology to the Escherichia coli nuo4 gene, which encodes a subunit of one of two known NADH:ubiquinone oxidoreductases. Competition experiments in an oxygen-poor medium between mutant PCL1201 and its parental strain showed a decreased growth rate of mutant PCL1201. The requirement of the nuo4 gene homolog for optimal growth under conditions of oxygen limitation suggests that the root-tip environment is micro-aerobic. A mutant characterized by a slow growth rate (PCL1216) was analyzed further and contained a mutation in a gene with similarity to the E. coli HtrB protein, a lauroyl transferase that functions in lipid A biosynthesis.
利用无菌系统鉴定了高效定殖于根部的荧光假单胞菌WCS365的定殖缺陷型转座子诱导突变体。大多数突变体在已知的定殖特性方面存在缺陷，即氨基酸原养型、运动性以及脂多糖（LPS）O抗原的合成。缺乏LPS O抗原的突变体在定殖和竞争性生长方面均受损，而一个O抗原链较短的突变体（PCL1205）仅在定殖能力方面存在缺陷，这表明完整的LPS O抗原在定殖中发挥作用。八个在上述特性方面无缺陷的竞争性定殖突变体，单独接种时能很好地定殖于番茄根尖，但在番茄、萝卜和小麦的竞争性根定殖中存在缺陷，这表明它们含有影响宿主范围的突变。对这八个突变体中的一个（PCL1201）进行了进一步表征，发现其一个基因发生了突变，该基因与大肠杆菌nuo4基因具有同源性，大肠杆菌nuo4基因编码两种已知的NADH：泛醌氧化还原酶之一的一个亚基。突变体PCL1201与其亲本菌株在缺氧培养基中的竞争实验表明，突变体PCL1201的生长速率降低。在氧气限制条件下，nuo4基因同源物对最佳生长的需求表明根尖环境是微需氧的。对一个生长速率缓慢的突变体（PCL1216）进行了进一步分析，发现其一个基因发生了突变，该基因与大肠杆菌HtrB蛋白相似，HtrB蛋白是一种在脂质A生物合成中起作用的月桂酰转移酶。
