Indole-3-acetic Acid Production from Alginate by Vibrio sp. dhg: Physiology and Characteristics

The production of indole-3-acetic acid (IAA) by bacteria has attracted considerable attention in plant studies due to its significant role as a plant growth regulator. In this study, it was confirmed that Vibrio sp. dhg, a novel microbial platform capable of assimilating alginate, can naturally synthesize IAA. The effects of L-tryptophan and the carbon sources obtained from brown algae (glucose, mannitol, and alginate) were also examined to characterize the IAA biosynthesis in Vibrio sp. dhg. The highest IAA production (9.32 ± 0.25 mg/L) was observed in the alginate medium containing 0.8 g/L of L-tryptophan. Interestingly, alginate was found to be a favorable option for IAA production due to the rapid uptake of L-tryptophan during the exponential phase. By adding external NADH, this study demonstrated that the low net reducing equivalents in the alginate medium were linked to this phenomenon. This study is the first to provide alginate as the sole carbon source for IAA production and to propose that the oxidoreduction potentials of the carbon source can affect bacterial IAA biosynthesis.