Murat Elibol

Optimization of medium composition for actinorhodin production by Streptomyces coelicolor A3(2) with response surface methodology

Optimization of the fermentation medium for maximization of actinorhodin production by Streptomyces coelicolor A3(2) was carried out. Response surface methodology (RSM) was applied to optimize the medium constituents. A 24 full-factorial central composite design (CCD) was chosen to explain the combined effects of the four medium constituents, viz. sucrose, glucose, yeast extract (YE) and peptone, and to design a minimum number of experiments. The P-values of the coefficients for linear, quadratic and cross-product effect of sucrose and glucose concentration were <0.0001, suggesting that these were critical variables having the greatest effect on the production of actinorhodin in the complex medium. The optimized medium consisting of 339 g/l sucrose, 1 g/l glucose, 1.95 g/l YE and 2.72 g/l peptone predicted 195 mg/l of actinorhodin which was 32% higher than that of the unoptimized medium. The amounts of glucose, YE and peptone required were also reduced with RSM.

Influence of oxygen transfer on lipase production by Rhizopus arrhizus

Abstract The effect of oxygen on lipase production by Rhizopus arrhizus was studied under two operating modes, controlled dissolved oxygen concentration (DO) and controlled aeration rate. Lipase production depended more extensively on oxygen than cell growth. The intrinsic factor determining cell growth and lipase production was oxygen transfer rate (OTR) rather than DO concentration. Improvements in OTR, either by aeration or agitation or perfluorocarbon (PFC) inclusion resulted in an increase in lipase production. The formation of lipase could be described by a mixed-growth associated model. The overall productivity for the lipase which depended more strongly on agitation than aeration could be related to the volumetric oxygen transfer coefficient, k L a. Addition of 10% (v/v) PFC to the fermentation medium also resulted in higher lipase production.

Response surface methodological approach for inclusion of perfluorocarbon in actinorhodin fermentation medium

The combined effects of perfluorocarbon and glucose concentrations on actinorhodin production by Streptomyces coelicolor A3(2) were studied in a 2-l bioreactor using response surface methodology. A 22 full-factorial central composite design was employed for experimental design and analysis of the results. The optimum PFC and glucose concentrations were found to be 42.7% and 12.25 g/l, respectively. In these conditions, actinorhodin concentration of 60 mg/l with a biomass concentration of 1.9 g/l, a maximum volumetric oxygen uptake rate of 180 mgO2/l h and a glucose consumption rate of 0.110 g glucose/l h was attained. These results are in close agreement with the model predictions.

Response surface analysis of lipase production by freely suspended Rhizopus arrhizus

Abstract The combined effects of initial glucose concentration and inducer (corn oil) concentration on lipase production by freely suspended Rhizopus arrhizus were investigated using response surface methodology (RSM). A 2 2 full-factorial central composite design was employed for experimental design and analysis of the results. The optimum glucose and inducer concentrations were found to be 1.1 and 3.3 g/l, respectively. In these conditions, the biomass concentration of 2.4 g/l with a lipolytic activity of 370 μmol/l min was attained. These results are in close agreement with the model parameters.

Production of extracellular alkaline protease by immobilization of the marine bacterium Teredinobacter turnirae

Abstract Cells from a marine bacterium, Teredinobacter turnirae cells were immobilized in calcium alginate beads and used for alkaline protease production. The maximum protease activity was obtained at 3% (w/v) sodium alginate and 3% CaCl 2 concentrations with a 1/2 cell/alginate ratio, i.e. 2400 U/ml. There was no significant difference in the maximum protease activity between three bead sizes used. A drastic fall in protease production was observed when the beads were treated with glutaraldehyde. The beads were used for eight successive fermentation batches each lasting 72 h. It was also observed that there was a ∼3.5-fold increase in volumetric productivity of protease after the fourth cycle.

A KINETIC MODEL FOR ACTINORHODIN PRODUCTION BY STREPTOMYCES COELICOLOR A3(2)

Abstract The fermentation kinetics of an extracellular antibiotic, actinorhodin, by Streptomyces coelicolor were studied in a batch system. A simple model was proposed using the Logistic equation for growth, the Luedeking–Piret equation for actinorhodin production and Luedeking–Piret-like equations for glucose and oxygen consumptions. The model appeared to provide a reasonable description for each parameter during the growth phase.

Lipase production by immobilised Rhizopus arrhizus

Immobilisation of Rhizopus arrhizus cells on a solid support (polyurethane foam) for lipase production has been explored. Lipase biosynthesis was repressed at a high glucose level. Maximum productivity was recorded at 1 g l−1 glucose concentration. The inclusion of 0.5 g l−1 corn oil (as an inducer) in the fermentation medium resulted in 2.5-fold higher lipase production compared to the control where no oil was added. Repeated-batch experiments revealed that immobilised R. arrhizus cells demonstrated reproducible behaviour, producing the same amount of enzyme over a 120 h period. The storage stability of the enzyme was investigated and enzyme activity reduction was 26% within 160 h.

Production of actinorhodin by Streptomyces coelicolor in batch and fed-batch cultures

Abstract Fed-batch fermentations of Streptomyces coelicolor in chemically defined medium in a 20 litre bioreactor were used to produce actinorhodin. Concentrated solutions of phosphate and nitrate with or without glucose were fed intermittently or continuously. Continuous feeding of glucose alone was found to be the best strategy for actinorhodin production. In this case, the specific productivity was almost twice that obtained in conventional batch fermentation.

Mass transfer characteristics of yeast fermentation broth in the presence of pluronic F-68

Abstract A nonionic surfactant, Pluronic F-68, was used to investigate mass transfer characteristics of a fermentation medium in a 1 l bench-top bioreactor. At low flow rate (0.08 vvm), k L a did not change significantly with increasing agitation speed. In all air flow rates studied, pluronic caused a remarkable reduction in k L a . When an oxygen carrier such as perfluorocarbon (PFC) was added to the medium, k L a increased with increasing PFC concentration. Moreover, PFC emulsified with pluronic F-68 resulted in a significant increase in k L a values. The inclusion of 4 g l −1 pluronic in yeast fermentation medium resulted in a longer lag phase, while the final biomass concentration was almost unaffected.

Product shifting by controlling medium pH in immobilised Streptomyces coelicolor A3(2) culture

Actinorhodin production by Streptomyces coelicolor A3(2) immobilised naturally in a porous support material was investigated in a 20 l bioreactor. The effect of pH-control on actinorhodin fermentation was conducted by performing different strategies. The combination of pH-control and immobilisation of the cells produced a different result than pH-control with freely suspended cells. The control of pH at 7.2 in an immobilised cell system altered the physiology of the cells shifting the product, actinorhodin, to another pigmented secondary metabolite, undecylprodigiosin. Although the cells were biologically active in such an environment, they were unable to produce actinorhodin. In the freely suspended cell system, however, actinorhodin biosynthesis was not hindered by controlling the medium pH.