Gene regulation of IAA metabolism in Acinetobacter baumannii

We found two gene clusters with the function for IAA degradation. One of the gene cluster revealed that IacA is the enzyme for IAA degradation. This gene cluster were regulated by IacR, a MarR family regulatory protein. IacR repressed iacA gene expression while there was no IAA available. IAA binding to IacR removed it from the promoter for RNA polymerase binding. While IAA was degraded by IacA, IacR will bind to promoter region of iacA again. (H-Y Shu, L-C Lin, T-K Lin, H-P Chen, H-H Yang, K-C Peng, G-H Lin*. Transcriptional regulation of the iac locus from Acinetobacter baumannii by the phytohormone indole-3-acetic acid. Antonie van Leeuwenhoek. 2015(107):1237-1247.)Lin G-H, H-P Chen, J-H Huang, T-T Liu, T-K Lin, S-J Wang, C-H Tseng and H-YShu. Identification and characterization of an indigo-producing oxygenase involved in indole 3-acetic acid utilization by Acinetobacter baumanni. 2012. Antonie van Leeuwenhoek. 101:881-890.)

While we are working with the IAA metabolism, we are wondering why A. baumannii with the ability to degrade IAA. Where is the IAA in the environment available for bacteria? By using LC-MS/MS as a tools, we found that this bacteria can produce IAA for raining days. We also found that it produced IAA via IpyA pathway. (G-H,Lin, C-Y Chang, H-R Lin*,Systematic profiling of indole-3-acetic acid biosynthesis in bacteria using LC–MS/MS. Journal of Chromatography B. 2015 (988): 53-58.)

The most will studied habitat for A. baumannii is the human. It will cause antibiotic resistance and death of patient in ICU. However, the nature habitat of this bacteria is soil. It will colonize in rhizosphere and using tryptophan from plant to produce IAA. IAA will serve as growth hormone for plants. Bacteria will use IAA back into bacteria as nutrient source while there is no other nutrient available. (H-R Lin, H-Y Shu, G-H Lin*. 2018. Biological roles of indole-3-acetic acid in Acinetobacter baumannii. Microbiological Research. (Nov) 216:30-39.)

Gene regulation of tert-butylhydroperoxide resistance in Acinetobacter baumannii

Host produced orgainc hydroperoxide (OHP) to kill bacteria. Bacteria will generate OHP while agitation and encounter with antibiotic. The expression of Ohr will increase antibiotic resistance ability of bacteria indirectly. In this study, we found A. baumannii ATCC19606 with two pairs of ohrR-ohr gene cluster. The one on chromosome contributed more important role for tert-butyl hydroperoxide resistance. (S.-J. Chen, H.-Y. Shu, G.-H. Lin*. 2021. Regulation of tert-butyl hydroperoxide resistance by chromosomal OhrR in A. baumannii ATCC19606. Microorganisms. DOI: 10.3390/microorganisms9030629)