High-yield production of indole-3-acetic acid by Enterobacter sp. DMKU-RP206, a rice phyllosphere bacterium that possesses plant growth-promoting traits

Abstract

Enterobacter sp. DMKU-RP206 was isolated from rice leaves in Thailand and identified by the 16S rRNA gene and multilocus sequence (gyrB, rpoB, atpD, and infB genes) analysis. The bacterium was assessed on plant growth-promoting traits including indole-3-acetic acid (IAA) production. Phosphate solubilization, ammonia production, and antagonism to fungal plant pathogens, as well as siderophore production, were shown by this bacterium. However, only IAA production was focused on. The production of IAA by Enterobacter sp. DMKU-RP206 was optimized by statistical methods. A Box-Behnken design was used for the investigation of interactions among the basic influencing factors and for the optimization of IAA production. The results showed that l-tryptophan had a significant importance in terms of IAA production. Enterobacter sp. DMKU-RP206 produced a higher amount of IAA than previously reported for the genus Enterobacter. 0.85% of lactose as a carbon source, 1.3% of yeast extract as a nitrogen source, 1.1% of l-tryptophan as a precursor, 0.4% of NaCl, an initial pH of 5.8, an incubation temperature at 30 °C, and a shaking speed of 200 rpm were found to be the optimum conditions for IAA production. In addition, IAA production was performed to scale up IAA production, and the highest amount, 5561.7 mg l^-1, was obtained. This study reported a 13.4-fold improvement in IAA production by Enterobacter sp. DMKU-RP206.

Keywords: Enterobacter sp.; Indole-3-acetic acid; Multilocus sequence analysis; Optimization; Phyllosphere bacteria; Plant growth-promoting traits.

Fig. 1

The phylogenetic relationships between strain DMKU-RP206 and the type strains of genus Enterobacter base on 16S rRNA gene sequences (a) and concatenated partial gyrB, rpoB, atpD, and infB gene sequences (b). The sequence of Erwinia aphidicola LMG 24877^T was used as an outgroup. Bootstrap values below 50% are not indicated

Fig. 2

Antagonism of Enterobacter sp. DMKU-RP206 against Curvularia lunata (a), Fusarium moniliforme (b), and Rhizoctonia solani (c), which causes disease in rice plants

Fig. 3

Effect of incubation time (a), carbon sources (b), and nitrogen sources (c) on IAA production by Enterobacter sp. DMKU-RP206. Bars with different letters are significantly different from each other (p < 0.05)

Fig. 4

Contour plot of significant interaction-terms on IAA production by Enterobacter sp. DMKU-RP206

Fig. 5

IAA (a), growth (b), and pH (c) during batch fermentation in 2 l stirred tank fermenter by Enterobacter sp. DMKU-RP206 with agitation speed of 200 rpm and varied aeration rates (0.6, 1.3, and 2.0 vvm)

Fig. 6

HPLC chromatogram of authentic indole-3-acetic acid (a) and culture supernatant of Enterobacter sp. DMKU-RP206 (b)