Improvement of welan gum biosynthesis and transcriptional analysis of the genes responding to enhanced oxygen transfer by oxygen vectors in Sphingomonas sp.

Abstract

Oxygen transfer (kLa) is one of the most essential factors affecting microbial cell growth and metabolite formation. In this study, low-cost methods capable of effectively enhancing oxygen transfer were investigated by adding oxygen vectors into the fermentation broth. Upon addition of n-dodecane and n-hexadecane, the kLa of the fermentation medium reached remarkably higher values than that of the control. In response to the enhanced oxygen transfer, welan gum concentration and yield reached maxima of 33.9±0.56g/L and 0.761±0.010g/g, respectively. The DCW reached a maximum of 7.82±0.18g/L with n-dodecane addition. Welan gum productivity and yield were significantly affected by kLa under n-hexadecane addition because of the promotion of the highest transcriptional levels of genes in the metabolic flux for welan gum biosynthesis. In addition, transcription levels of TCA and electron transfer chain (ETC) genes exhibited maximum up-regulation under n-dodecane, which resulted in enhanced cell growth. These results suggest a mechanism for enhanced kLa using oxygen vectors to improve welan gum biosynthesis through regulation of transcriptional levels of ETC, TCA, and metabolic pathways for welan gum biosynthesis genes during fermentation.