Journal of Bioprocessing & Biotechniques

The aromatic polyketide antibiotic oxytetracycline (OTC) is produced by Streptomyces rimosus as an important secondary metabolite. Enhancement of self-resistance is one effective way to improve antibiotic production in Streptomyces spp. In the present study, we aimed to improve the production of OTC by introducing extra copies of the OTC resistance genes, otrA and otrB, into the chromosome of the industrial strain of S. rimosus (SRI). First, otrA and otrB were cloned and ligated with pSET152 to generate the recombinant plasmids pSET152-otrA/otrB, the demethylated pSET152-otrA/otrB by Escherichia coli ET12567(pUZ8002) were then introduced into SRI to yield otrA/ otrB knock-in mutants: SRI-A (otrA) and SRI-B (otrB). Ten selected mutants and the parent SRI strain were cultured in shake flasks. Production of OTC was increased by 67% in one SRI-B mutant compared with the parent strain, suggesting that the enhancement of resistance gene otrB in the antibiotic producer is an effective way to improve OTC biosynthesis. However, introduction of extra copy of otrB could retard growth of mutant cells.

The response surface optimization strategy was used to enhance the lipase production by Rhizopus arrhizus MTCC 2233 in submerged fermentation. Various vegetable oils were experimented as an inducer using the optimized medium to study the influence on lipase production, and corn oil was found to be the best inducer for lipase production by Rhizopus arrhizus. The optimization of fermentation conditions, temperature, initial pH and agitation speed was carried out using corn oil as the inducer. Statistical analysis of the experimental data showed that the temperature, agitation speed, quadratic effects of temperature, initial pH and agitation speed and interactive effects of temperature and agitation speed are significant parameters that affect lipase production. The optimum fermentation conditions were achieved at 32°C; pH 6.0 and agitation speed of 107 rpm with the maximum lipase activity of 4.32 U/mL. Artificial neural network model was used to predict the lipase activity and cell mass production under various fermentation conditions. Unstructured kinetic models, Logistic model, Luedeking-Piret model and modified Luedeking-Piret model were used to describe the cell biomass, lipase production and glucose utilization kinetics respectively.

Stilbenes are natural phenolic compounds which function as antimicrobial phytoalexins in plants and affect human health as cardioprotective, antibaceteria, antioxidative and antineoplastic agents . In this review, the progresses of study on relevant enzymes, genes and regulation mechanism in biosynthesis pathway of stilbenes are described. Here we introduce a holistic and systematic method of researching relevant enzymes, genes and other regulatory factors in biosynthesis pathway of stilbenes - Systems biology. The application of knowledge of relative enzymes, genes and regulation mechanisms in stilbenes biosynthesis in metabolic engineering which is used as a tool of improving the disease resistance of plants and health caring quality of crops is also discussed.

Fish processing waste can be used to produce valuable by-products such as chymotrypsin which has applications in the food, leather, chemical and clinical industries. In this study, a reverse micelles system of AOT/isooctane was used to extract chymotrypsin from crude aqueous extract of red perch intestine. The effects of pH and KCl concentration of the backward extraction step on the total volume (TV), volume ratio (VR), total activity (TA), enzyme activity (AE), specific activity (SA), purification fold (PF), protein concentration (Cp) and recovery yield (RY) were studied. Changing the pH from 6.5 to 8.5 and the KCl concentration from 0.5 to 2.0 M during the backward extraction step had no effects on the TV or VR. Increasing the pH from 6.5 to 7.5 increased AE, SA, Cp, PF and RY by up to 47.06%, 30.0%, 27.0%, 26.9% and 18.47%, respectively but they all then declined with further increases in the pH. Similar trends were observed when the KCl concentration was increased from 0.5 to 1.5 M. The decreases in these parameters were due to the denaturation of protein under high pH. The highest AE, Cp and RY were achieved with pH 7.5 and 1.0 M KCl concentration while the highest SA and PF were achieved with pH 7.5 and 1.5 M KCl concentration. Addition of isobutyl alcohol in the backward extraction step increased the TV, AE, TA, Cp, SA, PF and RY by 13.6%, 336.4%, 342.6%, 81.1%, 146.4%, 146.2% and 345.8%, respectively. Alcohol reduced the interfacial resistance for the reverse micelles and, thus, destroyed the reverse micelles structure. The values of AE, TA, SA, PF and RY obtained with reverse micelles methods were much higher (2.3 fold) than those obtained with the ammonium sulphate method.