Serratia plymuthica UBCF_13 is one of the bacteria that can increase plant growth [plant growth-promoting bacteria] by producing IAA [Indole-3-Acetic Acid]. S. plymuthica UBCF_13 is a strain of Andalas University Biotechnology Laboratory Collection which can produce IAA and increase the growth of Solanaceae plants. Optimization of culture media needs to be analyzed to increase IAA production on UBCF_13. Optimization can be done by adding tryptophan as a precursor, using various types of media, adding wall affecting agents, and certain metal ions. In this study, optimization was carried out by testing the type of media [TSB, NB, YM, and King’s B], adding tryptophan [0, 100, 200, 300 μg/mL], differences in pH [5, 6, 7, 8], giving wall affecting agent [SDS 0.1 μg / mL, EDTA 0.1 μg/mL], and metal ions [Ca, Fe, K, Mg at a concentration of 0.05% and 0.1%]. The highest IAA production was obtained in the combination treatment of YM media and tryptophan 300 μg/mL. Meanwhile, the treatment of differences in pH and wall affecting agents did not have a significant effect on the increase in the production of IAA UBCF_13. Testing of metal types on IAA production showed that calcium was able to increase the production of IAA UBCF_13 by 12-14 μg/mL. Serratia plymuthica UBCF_13 produced the highest IAA on YM media combined with the addition of 300 μg/mL of tryptophan and 0.1% calcium ion.
Background and Objective: The optimization of the indole-3-acetic acid (IAA) producing capability of Serratia plymuthica UBCF̲13 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. Materials and Methods: The growth curve and IAA production were measured every 3 hrs. The putative IAA biosynthesis pathway was investigated based on the UBCF̲13 genome. To identify the possible pathway of IAA biosynthesis in UBCF̲13, 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. Results: The optimal IAA production on colorimetric assay was at 9 hrs of incubation (initial stationary phase). The level expression of puuC, DDC, oxdA, amiE, nthA and nthB have been upregulated maximum in 3 hrs of culture time (lag phase), except tyrB and ipdC. The highest transcript level of the genes was found in nitrile hydratase genes (nthA and nthB) and indole-3-acetamide (IAM) has been detected as the only intermediate in the crude extract of UBCF̲13 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). Conclusion: 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.
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