Indole-3-acetic acid (IAA) is an important plant hormone, and many types of bacteria interact with plants by producing or degrading IAA in the rhizosphere. The iac (indole-3-acetic acid catabolism) gene locus in Acinetobacter baumannii ATCC19606 was previously associated with IAA degradative capability, and in this study, transcriptome analysis results derived from A. baumannii cultured with IAA showed that the expression of catechol-degrading and phenylacetate-degrading genes was elevated, indicating that IAA is likely degraded through these pathways. This study further found that A. baumannii also has IAA productive capability, primarily involving the ipdC gene, and transcriptome and spent media analysis of wild-type and mutant cultures grown in minimal media revealed that A. baumannii likely produces IAA through the indole-3-pyruvic acid (IPyA) pathway. Exogenously applied IAA improved tolerance against oxidative stress in wild-type A. baumannii and iacA mutants unable to degrade IAA, but not in ipdC mutants incapable of producing IAA, suggesting that endogenous IAA is important for stress tolerance. Meanwhile, ipdC mutants also had reduced virulence against human A549 epithelial cells as compared to wild-type. Endogenously produced IAA was found to enhance root growth in A. baumannii and kidney bean plant co-cultures, indicating that A. baumannii can interact with plants through the production and degradation of IAA. Taken together, this study sheds light on the biosynthesis pathways and functional significance of IAA in A. baumannii, and may be useful in exploring other IAA-mediated plant-microbe interactions as well.

吲哚-3-乙酸（IAA）是一种重要的植物激素，许多细菌通过在根际中产生或降解IAA与植物相互作用。鲍曼不动杆菌ATCC19606中的iac（吲哚-3-乙酸分解代谢）基因位点以前与IAA的降解能力有关，在这项研究中，从IAA培养的鲍曼不动杆菌得到的转录组分析结果表明，儿茶酚降解和苯乙酸酯降解基因升高，表明IAA可能通过这些途径降解。这项研究进一步发现鲍曼不动杆菌还具有IAA生产能力，主要涉及ipdC。基因，转录组和用培养基进行的野生型和突变型培养基的基本培养基分析表明，鲍曼不动杆菌可能通过吲哚-3-丙酮酸（IPyA）途径产生IAA。在野生型鲍曼不动杆菌和无法降解IAA的iacA突变体中，外源施用IAA改善了其对氧化应激的耐受性，但在不能产生IAA的ipdC突变体中却没有，这表明内源IAA对于胁迫耐受性很重要。同时，与野生型相比，ipdC突变体对人A549上皮细胞的毒性也有所降低。发现内源产生的IAA可增强鲍曼不动杆菌的根生长和芸豆植物的共培养，表明鲍曼不动杆菌可以通过IAA的产生和降解与植物相互作用。综上所述，本研究揭示了鲍曼不动杆菌中IAA的生物合成途径和功能意义，也可能有助于探索其他IAA介导的植物-微生物相互作用。