•S. sp. carrying of vgb was constructed to improve welan gum yield.•An increase of 34.6 g/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 25.3 g/L to 34.6 g/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.

•M-TiO2 was modified by ε-poly-l-lysine successfully.•ε-Poly-l-lysine played an important role in increasing enzymes loading on carriers.•Immobilized SIase showed superior activity, stability and longer half-life.•Generation of isomaltulose from sucrose using immobilized SIase.Sucrose isomerase (SIase) is the key enzyme in the enzymatic synthesis of isomaltulose. Mesoporous titanium dioxide (M-TiO2) and ε-poly-l-lysine-functionalized M-TiO2 (EPL-M-TiO2) were prepared as carriers for immobilizing SIase. SIase was effectively immobilized on EPL-M-TiO2 (SI-EPL-M-TiO2) with an enzyme activity of 39.41 U/g, and the enzymatic activity recovery rate up to 93.26%. The optimal pH and temperature of immobilized SIase were 6.0 and 30 °C, respectively. SI-EPL-M-TiO2 was more stable in pH and thermal tests than SIase immobilized on M-TiO2 and free SIase. Km of SI-EPL-M-TiO2 was 204.92 mmol/L, and vmax was 45.7 μmol/L/s. Batch catalysis reaction of sucrose by SI-EPL-M-TiO2 was performed under the optimal conditions. The half-life period of SI-EPL-M-TiO2 under continuous reaction was 114 h, and the conversion rate of sucrose after 16 batches consistently remained at around 95%, which indicates that SI-EPL-M-TiO2 has good operational stability. Thus, SI-EPL-M-TiO2 can be used as a biocatalyst in food industries.

d-Tagatose, a functional sweetener, is commonly transformed from d-galactose by l-arabinose isomerase (l-AI). In this study, a novel type of biocatalyst, l-AI from Lactobacillus fermentum CGMCC2921 displayed on the spore surface of Bacillus subtilis 168, was developed for producing d-tagatose. The anchored l-AI, exhibiting the relatively high bioactivity, suggested that the surface display system using CotX as the anchoring protein was successfully constructed. The stability of the anchored l-AI was significantly improved. Specifically, the consolidation of thermal stability representing 87% of relative activity was retained even at 80 °C for 30 min, which remarkably favored the production of d-tagatose. Under the optimal conditions, the robust spores can convert 75% d-galactose (100 g/L) into d-tagatose after 24 h, and the conversion rate remained at 56% at the third cycle. Therefore, this biocatalysis system, which could express the target enzyme on the food-grade vector, was an alternative method for the value-added production of d-tagatose.

•Sucrose isomerase was firstly expressed in B. subtilis WB800.•Cane molasses as low-cost food waste was firstly used to isomaltulose production.•B. subtilis WB800, a GRAS microbe, was firstly used for isomaltulose synthesis.•BMR system exhibited great operational stability for isomaltulose production.A green process and environmentally benign process is highly desirable in the development of enzymatic catalysis. In this work, the shuttle plasmid pHA01 was constructed and the sucrose isomerase (SIase) was expressed in Bacillus subtilis WB800. The optimal nitrogen and carbon sources for SIase expression were yeast extract (15 g/L) and un-pretreated cane molasses (UCM, 20 g/L), respectively. After the UCM fed, the whole cell activity reached 5.2 U/mL in a 7.5 L fermentor. Optimum catalytic temperature and pH of whole cell were 35 °C and 5.5, respectively. Although the biologic membrane reactor (BMR) system consecutively worked for 12 batches, the sucrose conversion remained higher than 90%, indicating the BMR system had a greater operational stability. Furthermore, isomaltulose production using the BMR system with low-cost cane molasses as its substrate not only reduces the production cost and mediates environmental pollution, but also solves the genetic background problem of the non-food-grade strains.