Effect of Vitreoscilla hemoglobin on production of a chemotherapeutic enzyme, L-asparaginase, by Pseudomonas aeruginosa

Recent Advances in the Physicochemical Properties and Biotechnological Application of Vitreoscilla Hemoglobin

Vitreoscilla hemoglobin (VHb), the first discovered bacterial hemoglobin, is a soluble heme-binding protein with a faster rate of oxygen dissociation. Since it can enhance cell growth, product synthesis and stress tolerance, VHb has been widely applied in the field of metabolic engineering for microorganisms, plants, and animals. Especially under oxygen-limited conditions, VHb can interact with terminal oxidase to deliver enough oxygen to achieve high-cell-density fermentation. In recent years, with the development of bioinformatics and synthetic biology, several novel physicochemical properties and metabolic regulatory effects of VHb have been discovered and numerous strategies have been utilized to enhance the expression level of VHb in various hosts, which greatly promotes its applications in biotechnology. Thus, in this review, the new information regarding structure, function and expressional tactics for VHb is summarized to understand its latest applications and pave a new way for the future improvement of biosynthesis for other products.

Optimization of culture conditions and bench-scale production of anticancer enzyme L-asparaginase by submerged fermentation from Aspergillus terreus CCT 7693

L-Asparaginase amidohydrolase (EC 3.5.1.1) has received significant attention owing to its clinical use in acute lymphoblastic leukemia treatment and non-clinical applications in the food industry to reduce acrylamide (toxic compound) formation during the frying of starchy foods. In this study, a sequential optimization strategy was used to determine the best culture conditions for L-asparaginase production from filamentous fungus Aspergillus terreus CCT 7693 by submerged fermentation. The cultural conditions were studied using a 3-level, central composite design of response surface methodology, and biomass and enzyme production were optimized separately. The highest amount of biomass (22.0 g·L^-1) was obtained with modified Czapek-Dox medium containing glucose (14 g·L^-1), L-proline (10 g·L^-1), and ammonium nitrate (2 g·L^-1) fermented at 37.2 °C and pH 8.56; for maximum enzyme production (13.50 U·g^-1), the best condition was modified Czapek-Dox medium containing glucose (2 g·L^-1), L-proline (10 g·L^-1), and inoculum concentration of 4.8 × 10⁸ espore·mL^-1 adjusted to pH 9.49 at 34.6 °C. The L-asparaginase production profile was studied in a 7 L bench-scale bioreactor and a final specific activity of 13.81 U·g^-1 was achieved, which represents an increase of 200% in relation to the initial non-optimized conditions.

L-Asparaginase from Streptomyces griseus NIOT-VKMA29: optimization of process variables using factorial designs and molecular characterization of L-asparaginase gene

Marine actinobacteria are known to be a rich source for novel metabolites with diverse biological activities. In this study, a potential extracellular L-asparaginase was characterised from the Streptomyces griseus NIOT-VKMA29. Box-Behnken based optimization was used to determine the culture medium components to enhance the L-asparaginase production. pH, starch, yeast extract and L-asparagine has a direct correlation for enzyme production with a maximum yield of 56.78 IU mL(-1). A verification experiment was performed to validate the experiment and more than 99% validity was established. L-Asparaginase biosynthesis gene (ansA) from Streptomyces griseus NIOT-VKMA29 was heterologously expressed in Escherichia coli M15 and the enzyme production was increased threefold (123 IU mL(-1)) over the native strain. The ansA gene sequences reported in this study encloses several base substitutions with that of reported sequences in GenBank, resulting in altered amino acid sequences of the translated protein.

A study on L-asparaginase of Nocardia levis MK-VL_113

An enzyme-based drug, L-asparaginase, was produced by Nocardia levis MK-VL_113 isolated from laterite soils of Guntur region. Cultural parameters affecting the production of L-asparaginase by the strain were optimized. Maximal yields of L-asparaginase were recorded from 3-day-old culture grown in modified asparagine-glycerol salts broth with initial pH 7.0 at temperature 30°C. Glycerol (2%) and yeast extract (1.5%) served as good carbon and nitrogen sources for L-asparaginase production, respectively. Cell-disrupting agents like EDTA slightly enhanced the productivity of L-asparaginase. Ours is the first paper on the production of L-asparaginase by N. levis.

Production of L-DOPA and dopamine in recombinant bacteria bearing the Vitreoscilla hemoglobin gene

Given the well-established beneficial effects of Vitreoscilla hemoglobin (VHb) on heterologous organisms, the potential of this protein for the production of L-DOPA and dopamine in two bacteria, Citrobacter freundii and Erwinia herbicola, was investigated. The constructed recombinants bearing the VHb gene (vgb(+)) had substantially higher levels of cytoplasmic L-DOPA (112 mg/L for C. freundii and 97 mg/L for E. herbicola) than their respective hosts (30.4 and 33.8 mg/L) and the vgb(-) control strains (35.6 and 35.8 mg/L). Further, the vgb(+) recombinants of C. freundii and E. herbicola had 20-fold and about two orders of magnitude higher dopamine levels than their hosts, repectively. The activity of tyrosine phenol-lyase, the enzyme converting L-tyrosine to L-DOPA, was well-correlated to cytoplasmic L-DOPA levels. As cultures aged, higher tyrosine phenol-lyase activity of the vgb(+) strains was more apparent.

DevR-mediated adaptive response in Mycobacterium tuberculosis H37Ra: links to asparagine metabolism

The DevR transcriptional switch that defines the response of Mycobacterium tuberculosis to the lack of oxygen is now well established and likely helps the bacteria shift to a state of persistence. The M. tuberculosis two component signal transduction system (TCS), DevR-DevS, implicated in this transition to latency, is differentially expressed in H37Ra and H37Rv strains. Despite originating from the H37 ancestral strain, H37Ra and H37Rv have significant differences in their growth, physiology, and virulence. To further dissect the role of DevR in growth adaptive processes of M. tuberculosis, we investigated the hypoxic response of the avirulent H37Ra strain. Our results show that the DevR-DevS TCS in H37Ra is responsive to hypoxia and capable of target gene regulation, indicating similar DevR-DevS signaling pathways in H37Ra and H37Rv. A key finding of this study was the constitutive expression of the Rv3134c-devR-devS operon and a subset of sentinel DevR-regulated genes in aerobic cultures of H37Ra but not H37Rv grown in Dubos-Tween-albumin medium. Asparagine and/or catabolites of asparagine metabolism were implicated in aerobic induction of the DevR-DevS TCS in H37Ra. This is the first report of medium-specific constitutive expression of the DevR regulon in an avirulent strain and suggests a potential role for metabolite(s) in the activation of the DevR-DevS TCS.

L-Asparaginase: A Promising Chemotherapeutic Agent

This article comprises detailed information about L-asparaginase, encompassing topics such as microbial and plant sources of L-asparaginase, treatment with L-asparaginase, mechanism of action of L-asparaginase, production, purification, properties, expression and characteristics of l-asparaginase along with information about studies on the structure of L-asparaginase. Although L-asparaginase has been reviewed by Savitri and Azmi (2003), our effort has been to include recent and updated information about the enzyme covering new aspects such as structural modification and immobilization of L-asparaginase, recombinant L-asparaginase, resistance to L-asparaginase, methods of assay of L-asparagine and L-asparaginase activity using the biosensor approach, L-asparaginase activity in soil and the factors affecting it. Also, side-effects of L-asparaginase treatment in acute lymphoblastic leukemia (ALL) have been discussed in the current review. L-asparaginase has been and is still one of the most widely studied therapeutic enzymes by researchers and scientists worldwide.

L-asparaginase production by Streptomyces albidoflavus

Attempts were made to optimize the cultural conditions for the production of L-asparaginase by Streptomyces albidoflavus under submerged fermentations. Enhanced level of L-asparaginase was found in culture medium supplemented with maltose as carbon source. Yeast extract (2%) was served as good nitrogen source for the production of L-asparaginase. The optimum pH for enzyme production was 7.5 and temperature was 35°C. The release of L-asparaginase from the cells of S. albidoflavus was high when strain was treated with cell disrupting agents like EDTA and lysozyme. The enzyme produced by the strain was purifi ed by ammonium sulfate, Sephadex G-100 and CM-Sephadex C-50 gel fi ltration and the molecular weight was apparently determined as 112 kDa.