Indole acetic acid (IAA) has been an important compound for plant growth and is widely known to be produced by plant growth-promoting rhizobacteria (PGPR). The isolate producing the maximum amount of IAA from the Korea shooting range soil was identified as Pseudarthrobacter sp. NIBRBAC000502770, using 16S rRNA gene sequencing. IAA production was determined in Luria-Bertani (LB) broth and optimized using different temperatures, agitation rates, L-tryptophan concentrations, carbon and nitrogen sources, and inorganic salts. The strain NIBRBAC000502770 showed better production of IAA at temperature 30 °C (29.47 mg·L-1) and at an agitation rate of 200 rpm (32.65 mg·L-1). Maltose (0.5%) was found to be the best carbon source for the strain (yielding 36.48 mg·L-1 IAA). IAA yield was 19.17 mg·L-1 and 24.73 mg·L-1 at 1% yeast extract and 1% tryptone as nitrogen sources, respectively. qRT-PCR showed the transcript levels of amiE and aldH genes, which had been predicted to encode indole-3-acetamide hydrolase and indole-3-acetaldehyde dehydrogenase, to be significantly upregulated in response to tryptophan. This study has examined that NIBRBAC000502770 has significant effects as a biological agent such as plant growth promotion, and development of optimal medium could significantly reduce the cost of mass production of microorganisms.
Keywords: Indole-3-acetic acid (IAA); Optimization; Plant growth-promoting rhizobacteria (PGPR); Pseudarthrobacter sp.
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