Pseudomonas putida 1290 is a model organism for the study of bacterial degradation of the plant hormone indole-3-acetic acid (IAA). This property is encoded by the iac gene cluster. Insertional inactivation and/or deletion of individual iac genes and heterologous expression of the gene cluster in Escherichia coli were combined with mass spectrometry to demonstrate that iac-based degradation of IAA is likely to involve 2-hydroxy-IAA, 3-hydroxy-2-oxo-IAA, and catechol as intermediates. The first gene of the cluster, iacA encodes for the first step in the pathway, and also can convert indole to indoxyl to produce the blue pigment indigo. Transcriptional profiling of iac genes in P. putida 1290 revealed that they were induced in the presence of IAA. Based on results with an iacR knockout, we propose that this gene codes for a repressor of iacA expression and that exposure to IAA relieves this repression. Transformation of P. putida KT2440 (which cannot degrade IAA) with the iac gene cluster conferred the ability to grow on IAA as a sole source of carbon and energy, but not the ability to chemotaxi towards IAA. We could show such tactic response for P. putida 1290, thus representing the first demonstration of bacterial chemotaxis towards IAA. We discuss the ecological significance of our findings, and specifically the following question: under what circumstances do bacteria with the ability to degrade, recognize, and move towards IAA have a selective advantage?
假单胞菌1290是研究植物激素
吲哚-3-
乙酸(
IAA)细菌降解的模型
生物。这种特性由iac
基因簇编码。通过质谱分析,我们发现,在大肠杆菌中,单个iac
基因的插入失活和/或缺失以及
基因簇的异源表达表明,基于iac的
IAA降解可能涉及2-羟基-
IAA、3-羟基-2-氧代-
IAA和
儿茶酚作为中间产物。
基因簇的第一个
基因iacA编码该途径的第一步,并且还可以将吲