Increased Hepatitis B surface antigen production by recombinant Aspergillus niger through the optimization of agitation and dissolved oxygen concentration

Bioprocess Optimisation for High Cell Density Endoinulinase Production from Recombinant Aspergillus niger

Endoinulinase gene was expressed in recombinant Aspergillus niger for selective and high-level expression using an exponential fed-batch fermentation. The effects of the growth rate (μ), glucose feed concentration, nitrogen concentration and fungal morphology on enzyme production were evaluated. A recombinant endoinulinase with a molecular weight of 66 kDa was secreted. Endoinulinase production was growth associated at μ> 0.04 h-1, which is characteristic of the constitutive gpd promoter used for the enzyme production. The highest volumetric activity (670 U/ml) was achieved at a growth rate of 93% of μmax (0.07 h-1), while enzyme activity (506 U/ml) and biomass substrate yield (0.043 gbiomassDW/gglucose) significantly decreased at low μ (0.04 h-1). Increasing the feed concentration resulted in high biomass concentrations and viscosity, which necessitated high agitation to enhance the mixing efficiency and oxygen. However, the high agitation and low DO levels (ca. 8% of saturation) led to pellet disruption and growth in dispersed morphology. Enzyme production profiles, product (Yp/s) and biomass (Yx/s) yield coefficients were not affected by feed concentration and morphological change. The gradual increase in the concentration of nitrogen sources showed that, a nitrogen limited culture was not suitable for endoinulinase production in recombinant A. niger. Moreover, the increase in enzyme volumetric activity was still directly related to an increase in biomass concentration. An increase in nitrogen concentration, from 3.8 to 12 g/L, resulted in volumetric activity increase from 393 to 670 U/ml, but the Yp/s (10053 U/gglucose) and Yx/s (0.049 gbiomasDWs/gglucose) did not significantly change. The data demonstrated the potential of recombinant A. niger and high cell density fermentation for the development of large-scale endoinulinase production system.

Design of a high-efficiency synthetic system for l-asparaginase production in Bacillus subtilis

l-asparaginase has high application value in medicine and food industry, but the low yield limits its application. In this study, we designed a synthetic system in Bacillus subtilis to produce l-asparaginase by improving gene expression and optimizing the fermentation agitation speed. Gene expression was improved by respectively increasing transcription levels and translation speeds through screening promoters and RBS sequences. With the optimal promoter, P43, and the synthetic RBS sequence, the yield obtained in a shake flask was 371.87 U/mL, which was 2.09 times that with the original strain. To further enhance production in a 5-L fermenter, a multistage agitation speed control strategy was adopted, involving agitation at 600 rpm for the first 12 h, followed by a gradual increase in speed to 900 rpm, which resulted in the highest yield of l-asparaginase, 5321 U/mL, after 42 h of fermentation.

Bioprocess development for the production of sonorensin by Bacillus sonorensis MT93 and its application as a food preservative

Media composition and environmental conditions were optimized using statistical tools, Plackett Burman design and response surface methodology, to maximize the yield of a bacteriocin, named as sonorensin, from a new marine isolate Bacillus sonorensis MT93 showing broad spectrum of antimicrobial activity. Under optimized conditions, MT93 produced 15-fold higher yield of sonorensin compared to that under initial fermentation conditions. As oxygen supply is a critical parameter controlling growth and product formation in aerobic bioprocesses and used as a parameter for bioprocess scale up, the effects of oxygen transfer, in terms of volumetric oxygen transfer coefficient (kLa), on production of sonorensin was investigated using optimized medium composition in a bioreactor. Studies on effectiveness of sonorensin against Staphylococcus aureus and Listeria monocytogenes in fruit juice and as a preservative in pasteurized milk demonstrated its potential as a biopreservative in fruit products and shelf life extender of the pasteurized milk.

Enhanced riboflavin production by recombinant Bacillus subtilis RF1 through the optimization of agitation speed

Dissolved oxygen is one of the most important bioprocess parameters that could affect cell growth and product formation, and it is easy to control by changing agitation speed. In this work, the effects of agitation speed on the performance of riboflavin production by recombinant Bacillus subtilis RF1 was investigated in fed-batch fermentation. The lower agitation speed (600 rpm) was beneficial for cell growth and riboflavin biosynthesis in the initial phase of fermentation process. While, during the later phase, higher agitation speed (900 rpm) was favor for cell growth and riboflavin biosynthesis. Thus, a two-stage agitation speed control strategy was proposed based on kinetic analysis, in which the agitation speed was controlled at 600 rpm in the first 26 h and then switched to 900 rpm to maintain high μ for cell growth and high q(p) for riboflavin production during the entire fermentation process. However, it was observed that a sharp increase of agitation speed resulted in an adverse effect on cell growth and riboflavin synthesis within a short time. To avoid this phenomenon, a multi-stage agitation speed control strategy was set up based on the two-stage control strategy, the maximum concentration of riboflavin reached 9.4 g l(-1) in 48 h with the yield of 0.051 g g(-1) by applying this strategy, which were 20.5 and 21.4% over the best results controlled by constant agitation speeds.

Virus-like particles in vaccine development

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome, potentially yielding safer and cheaper vaccine candidates. A handful of prophylactic VLP-based vaccines is currently commercialized worldwide: GlaxoSmithKline's Engerix (hepatitis B virus) and Cervarix (human papillomavirus), and Merck and Co., Inc.'s Recombivax HB (hepatitis B virus) and Gardasil (human papillomavirus) are some examples. Other VLP-based vaccine candidates are in clinical trials or undergoing preclinical evaluation, such as, influenza virus, parvovirus, Norwalk and various chimeric VLPs. Many others are still restricted to small-scale fundamental research, despite their success in preclinical tests. This article focuses on the essential role of VLP technology in new-generation vaccines against prevalent and emergent diseases. The implications of large-scale VLP production are discussed in the context of process control, monitorization and optimization. The main up- and down-stream technical challenges are identified and discussed accordingly. Successful VLP-based vaccine blockbusters are briefly presented concomitantly with the latest results from clinical trials and the recent developments in chimeric VLP-based technology for either therapeutic or prophylactic vaccination.