Constitutive expression of Vitreoscilla haemoglobin in Sphingomonas elodea to improve gellan gum production.

摘要

Aims. To improve a commercially used strain for gellan production by exogenous Vitreoscilla haemoglobin (VHb). Methods and Results. VHb gene was expressed in Sphingomonas elodea under the control of constitutive bla promoter. Biochemical activity of expressed VHb was confirmed by CO-difference spectra analysis that exhibited a characteristic absorption maximum at 419 nm. During cultivation, not only enhanced cell growth was detected, but also 20% improvement in gellan production was observed after 48 h of incubation, with a maximum yield of 16.82 g l--1. Moreover, maximum sucrose conversion efficiency (g gellan per g sucrose) was 57.8, 20% higher than that of the parental strain. We further examined the polysaccharide production of VHb-expressing strain at different aeration levels in Erlenmeyer flasks. Again, in all cases, a significant enhancement of gellan production was observed, and the enhancement was more significant under oxygen-limiting conditions (up to 26.8%). Conclusions. VHb exhibited positive effect on cell growth and gellan yield of S. elodea, especially under hypoxic conditions. Significance and Impact of the Study. This is the first application of VHb as an effective metabolic engineering strategy in S. elodea to regulate cell growth and optimize gellan yield.