de Weert Sandra, Vermeiren Hans, Mulders Ine H M, Kuiper Irene, Hendrickx Nico, Bloemberg Guido V, Vanderleyden Jos, De Mot René, Lugtenberg Ben J J
Leiden University, Institute of Molecular Plant Sciences, The Netherlands.
Mol Plant Microbe Interact. 2002 Nov;15(11):1173-80. doi: 10.1094/MPMI.2002.15.11.1173.
Motility is a major trait for competitive tomato root-tip colonization by Pseudomonas fluorescens. To test the hypothesis that this role of motility is based on chemotaxis toward exudate components, cheA mutants that were defective in flagella-driven chemotaxis but retained motility were constructed in four P. fluorescens strains. After inoculation of seedlings with a 1:1 mixture of wild-type and nonmotile mutants all mutants had a strongly reduced competitive root colonizing ability after 7 days of plant growth, both in a gnotobiotic sand system as well as in nonsterile potting soil. The differences were significant on all root parts and increased from root base to root tip. Significant differences at the root tip could already be detected after 2 to 3 days. These experiments show that chemotaxis is an important competitive colonization trait. The best competitive root-tip colonizer, strain WCS365, was tested for chemotaxis toward tomato root exudate and its major identified components. A chemotactic response was detected toward root exudate, some organic acids, and some amino acids from this exudate but not toward its sugars. Comparison of the minimal concentrations required for a chemotactic response with concentrations estimated for exudates suggested that malic acid and citric acid are among major chemo-attractants for P. fluorescens WCS365 cells in the tomato rhizosphere.
运动性是荧光假单胞菌在番茄根尖定殖竞争中的一个主要特性。为了验证运动性这一作用是基于对渗出物成分的趋化性这一假设,在四株荧光假单胞菌菌株中构建了鞭毛驱动趋化性有缺陷但仍保留运动性的cheA突变体。在用野生型和非运动性突变体的1:1混合物接种幼苗后,在植物生长7天后,所有突变体在无菌沙质系统以及非无菌盆栽土壤中的根定殖竞争能力都大幅降低。在所有根段上差异都很显著,且从根基部到根尖逐渐增加。在2至3天后就能在根尖检测到显著差异。这些实验表明趋化性是一种重要的定殖竞争特性。对最佳的根尖定殖菌株WCS365进行了针对番茄根渗出物及其主要鉴定成分的趋化性测试。检测到对根渗出物、一些有机酸以及该渗出物中的一些氨基酸有趋化反应,但对其糖类没有趋化反应。将趋化反应所需的最低浓度与渗出物估计浓度进行比较表明,苹果酸和柠檬酸是荧光假单胞菌WCS365细胞在番茄根际的主要化学引诱剂。