Further investigation of the mechanism of Vitreoscilla hemoglobin (VHb) protection from oxidative stress in Escherichia coli

Coexpression of VHb and MceG genes in Mycobacterium sp. Strain LZ2 enhances androstenone production via immobilized repeated batch fermentation

Androstenone production is limited by low-efficiency substrate transport and dissolved oxygen levels during fermentation. In this study, the coexpression of the optimized Vitreoscilla hemoglobin (VHb) and sterol transporter ATPase (MceG) genes in Mycobacterium sp. LZ2 (Msp) was investigated to alleviate dissolved oxygen and mass transfer limitations. Results revealed that Msp-vgb/mceG effectively improved the growth, production, and adaptation to dissolved oxygen compared with those of Msp. The increased catalase activity and reduced intracellular ROS levels enhanced cell viability and promoted transcription of genes critical for phytosterol metabolism. Bagasse as an immobilization carrier increased the productivity of Msp-vgb/mceG by 56%. Immobilized repeat batch fermentation reduced the biotransformation period from 60 days to 37 days and improved the productivity from 0.039 g/L/h to 0.069 g/L/h. To the best of our knowledge, this work is the first study on the immobilization of recombinant mycobacteria on bagasse for androstenone production.

The Discovery of Vitreoscilla Hemoglobin and Early Studies on Its Biochemical Functions, the Control of Its Expression, and Its Use in Practical Applications

In 1986, the surprising identification of a hemoglobin (VHb) in the bacterium Vitreoscilla greatly extended the range of taxa in which this oxygen binding protein functions. Elucidation of many of its biochemical properties and relation to overall cell physiology, as well as the sequence of the gene encoding it and aspects of control of its expression were determined in the following years. In addition, during the early years following its discovery, strategies were developed to use its expression in heterologous microbial hosts to enhance processes of practical usefulness. The VHb discovery also served as the foundation for what has become the fascinatingly rich field of bacterial hemoglobins. VHb's position as the first known bacterial hemoglobin and its extensive use in biotechnological applications, which continue today, make a review of the early studies of its properties and uses an appropriate and interesting topic thirty-five years after its discovery.

Potential probiotic Escherichia coli 16 harboring the Vitreoscilla hemoglobin gene improves gastrointestinal tract colonization and ameliorates carbon tetrachloride induced hepatotoxicity in rats

The present study describes the beneficial effects of potential probiotic E. coli 16 (pUC8:16gfp) expressing Vitreoscilla hemoglobin (vgb) gene, associated with bacterial respiration under microaerobic condition, on gastrointestinal (GI) colonization and its antioxidant activity on carbon tetrachloride (CCl₄) induced toxicity in Charles Foster rats. In vitro, catalase activity in E. coli 16 (pUC8:16gfp) was 1.8 times higher compared to E. coli 16 (pUC-gfp) control. In vivo, E. coli 16 (pUC8:16gfp) not only was recovered in the fecal matter after 70 days of oral administration but also retained antibacterial activities, whereas E. coli 16 (pUC-gfp) was not detected. Oral administration of 200 and 500 μL/kg body weight of CCl₄ to rats at weekly interval resulted in elevated serum glutamyl pyruvate transaminase (SGPT) and serum glutamyl oxalacetate transaminase (SGOT) levels compared to controls. Rats prefed with E. coli 16 (pUC8:16gfp) demonstrated near to normal levels for SGPT and SGOT, whereas the liver homogenate catalase activity was significantly increased compared to CCl₄ treated rats. Thus, pUC8:16gfp plasmid encoding vgb improved the growth and GI tract colonization of E. coli 16. In addition, it also enhanced catalase activity in rats harboring E. coli 16 (pUC8:16gfp), thereby preventing the absorption of CCl₄ to GI tract.