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

Abstract

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.

Structural Characterization and Bioactivity of Exopolysaccharide Synthesized by Geobacillus sp. TS3-9 Isolated from Radioactive Radon Hot Spring

“…Microbial exopolysaccharide (EPS) has a wide range of industrial (such as textiles, oil recovery, food additives, cosmetic and pharmaceutical) and medical applications. The collection of diverse products from different microorganisms include: xanthan from Xanthomonas [1], gellan from Sphingomonas [2], heparason from E. coli [3], glucans from Leuconostoc, Streptococcus and Lactobacillus [4], cellulose from Acetobacter [5], hyaluronan from Pseudomonas and Streptococci group A and C. In recent years there has been an increased interest in EPS for pharmaceutical applications such as antioxidants, antitumor agents and immunostimulants [6].…”

Enhanced Coproduction of Cell-Bound Zeaxanthin and Secreted Exopolysaccharides by Sphingobium sp. via Metabolic Engineering and Optimized Fermentation

“…Most zeaxanthin-producing organisms are unable to synthesize EPS. Sphingomonas species have been used to produce EPS. ,− Here, we showed that Sphingobium sp. could accumulate as high amounts of EPS as its relatives, Sphingomonas species.…”

Enhancement of Gellan Production in Sphingomonas paucimobilis JLJ by Heterogeneous Expression of Vitreoscilla Hemoglobin

“…However, inadequate oxygenation, resulting in poor cell growth and reduced product yields, is one major limitation encountered in large-scale bioreactors. Gellan production was reported to almost completely cease when the dissolved oxygen (DO) concentration was adjusted to zero [4]. Furthermore, the DO also played a critical role in the viscosity and molecular weight of the polymer produced, which was closely related to the rheological properties and applications of gellan gum.…”