Production exopolysaccharide from Kosakonia cowanii LT-1 through solid-state fermentation and its application as a plant growth promoter.

• This study was the first to report EPS synthesis by K. cowanii LT-1 through SSF. • Comparative transcriptome reveals the mechanism of NaNO 3 promoting EPS production. • A maximum EPS production of 41.62 mg/gds was achieved in single batch SSF. • Fermented SSF substrate increased seed germination and growth vigor of maize. Exopolysaccharide has the activity of promoting plants growth. Herein, several agro-industrial residues were used for EPS biosynthesis through solid-state fermentation (SSF) using an EPS producing stain Kosakonia cowanii LT-1. Then the influences of cane molasses powder (CMP), NaNO 3 and temperature on EPS biosynthesis through SSF were studied using response surface methodology. Maximum EPS yield (41.62 mg/gds) was obtained in a mixed substrate composed of cane bagasse and broadbean seed capsule (2:1, w/w) supplemented with CMP (5.09%, w/w) and NaNO 3 (4.16‰, w/w), which achieved about 30.43% cost savings for substrates. Transcriptomic analysis explained the mechanism of NaNO 3 promoting EPS production. Repeated batch SSF was performed eight times with 10% substrate as the seeds of the next SSF cycle successfully. Therefore, the fermented SSF substrate containing K. cowanii LT-1 and its EPS was applied in maize growth, which could promote seed germination rate and growth vigor of maize. Hence, fermented SSF substrates would be an ideal candidate for application as a plant growth promoter in agriculture field. [ABSTRACT FROM AUTHOR]