Growth Phase Influence the Gene Expression and Metabolite Production Related to Indole-3-Acetic Acid (IAA) Biosynthesis by Serratia plymuthica UBCF_13.

Abstract

<b>Background and Objective:</b> The optimization of the indole-3-acetic acid (IAA) producing capability of <i>Serratia plymuthica</i> UBCF_13 has been intensively studied. This work tried to reveal the effect of growth phases on IAA production, gene expression and metabolite synthesis related to the IAA biosynthesis pathway. <b>Materials and Methods:</b> The growth curve and IAA production were measured every 3 hrs. The putative IAA biosynthesis pathway was investigated based on the UBCF_13 genome. To identify the possible pathway of IAA biosynthesis in UBCF_13, we applied the Quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR) and High-Performance Liquid Chromatography (HPLC) analysis to measure the transcript levels of each gene and indole metabolite production based on tryptophan treatment at different times of incubation. <b>Results:</b> The optimal IAA production on colorimetric assay was at 9 hrs of incubation (initial stationary phase). The level expression of <i>puuC</i>, <i>DDC</i>, <i>oxdA</i>, <i>amiE</i>, <i>nthA</i> and <i>nthB</i> have been upregulated maximum in 3 hrs of culture time (lag phase), except <i>tyrB</i> and <i>ipdC</i>. The highest transcript level of the genes was found in nitrile hydratase genes (<i>nthA</i> and <i>nthB</i>) and indole-3- acetamide (IAM) has been detected as the only intermediate in the crude extract of UBCF_13 thus the IAM pathway may be used to produce IAA. The maximum IAA production on HPLC analysis was found at 21 hrs of incubation (late stationary phase). <b>Conclusion:</b> This study gives a new insight that the best time to measure gene expression and intermediates related to the IAA biosynthetic pathway in bacteria was found at a specific growth phase.