Enhancement of welan gum production in Sphingomonas sp. HT-1 via heterologous expression of Vitreoscilla hemoglobin gene

•S. sp. carrying of vgb was constructed to improve welan gum yield.•An increase of 34.6g/L welan gum was attained with VHb expression.•The rheological behavior of welan gum solutions had no change after vgb insertion.•VHb expression enhanced oxygen uptake rate and ATP level for welan gum production. Welan gum is a microbial polysaccharide produced by Sphingomonas sp. Its production is limited by the dissolved oxygen levels in the highly viscous fermentation. A strategy of heterologous expression of the Vitreoscilla hemoglobin gene in Sphingomonas sp. HT-1 was investigated to alleviate oxygen limitation and improve the yield of welan gum. Ultimately, the welan gum production increased from 25.3g/L to 34.6g/L, whereas the rheological behavior of welan gum solutions remained virtually unchanged. The transcriptional levels of the key genes in the electron transfer chain, TCA cycle and welan gum synthesis pathway, as well as ATP level revealed that the VHb expression in Sphingomonas sp. HT-1 enhanced welan gum biosynthesis by improving respiration and ATP supply. This study would pave the genetic manipulation way for enhancing welan gum yield, and it’s also of great importance for the industrial applications of welan gum under harsh conditions.