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•pH-stat fed-batch fermentation with high density culture of engineered E. coli for increased NMN production.•The highest NMN concentration of 22.5 g/L and productivity of 1.13 g/L/h ...were achieved.•Highest titer and productivity of NMN using pH-stat fed-batch culture.
Nicotinamide mononucleotide (NMN), a naturally occurring nucleotide with various biological activities, has recently attracted significant interest for its potential applications in pharmaceutical and nutraceutical products. In this study, a genetically engineered E. coli via pH-stat fed batch fermentation produced a high concentration of intracellular NMN. The production process involved pH-stat glucose feeding and continuous feeding of nicotinamide (NAM). Various cumulative NAM concentrations of 6.4, 8.4, 10.4, and 14 g/L produced NMN of 16.7, 21.2, 22.5, and 10.7 g/L, respectively. Furthermore, the highest intracellular NMN concentration of 22.5 g/L was produced with 10.4 g/L of total cumulative NAM concentration along with a productivity of 1.13 g/L/h. This is the highest intracellular NMN titer and productivity achieved through optimized fed-batch fermentation to date. This also demonstrates that a high cell density approach through pH-stat feeding offers the potential to produce high quality, substantial NMN at a reasonable cost.
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•A high rhamnolipids titer (150g/L) was obtained using sequential fed-batch culture.•A high rhamnolipids productivity was well-maintained as 0.4g/Lh for 17 d.•Cell components play ...major role in this high-performance fermentation strategy.•This process has a great prospect in high-efficiency rhamnolipids production.
Rhamnolipids are the most promising biosurfactants, have widespread applications in many fields. However, low yield and productivity in fermentation caused a high production cost and thus prohibited the bulk applications of rhamnolipids in industry. In this study, a sequential fed-batch fermentation process with fill-and-draw operation was developed to improve rhamnolipids production. By utilizing this strategy, the total produced rhamnolipids reached over 150g/L, had a 163% and 102% increase over the traditional batch and fed-batch processes, respectively. This remarkable high production efficiency was achieved by the well-maintained high productivity of 0.4g/Lh for a period of 17 d. Astonishingly, the conversion yield was high as 84%, while this value was only 53.2% and 42.7% in the traditional batch and fed-batch process, respectively. The high-efficiency rhamnolipids production in this sequential fed-batch fermentation could be largely explained by a high presence of cell coupled with the replenishment of nutrients and dilution of toxic byproducts via fill-and-draw operation. In all, this validated fermentation strategy offers a great prospect for high-efficiency production of rhamnolipids in industry.
•A majority of industrial fermentation processes are operated in fed-batch mode.•The rate of feed addition to the fed-batch process is a focus for optimising the process operation.•This review covers ...strategies for controlling the feed rate to a fed-batch fermentation process.
A majority of industrial fermentation processes are operated in fed-batch mode. In this case, the rate of feed addition to the system is a focus for optimising the process operation, as it directly impacts metabolic activity, as well as directly affecting the volume dynamics in the system. This review covers a range of strategies which have been employed to use the feed rate as a manipulated variable in a control strategy. The feed rate is chosen as the focus for this review, as it is seen that this variable may be used towards many different objectives depending on the process of interest, the characteristics of the strain, or the product being produced, which leads to different drivers for process optimisation. This review summarises the methods, as well as focusing on the different objectives for the controllers, and the choice of measured variables involved in the strategy. The discussion includes a summary of considerations for control strategy development.
Using microalgae as a feedstock for biofuel is a method to reduce carbon dioxide emissions.
Nannochloropsis
is among the most promising microalgal taxa for biofuel production. To improve the lipid ...productivity of the marine microalga
Nannochloropsis
sp. SCSIO-45217 a novel method involving phosphate (NaH
2
PO
4
·2H
2
O) adjustment was established. First, the effects of phosphorous concentration on the lipid accumulation and biochemical composition of
Nannochloropsis
sp. SCSIO-45217 was studied in a batch culture. Subsequently, to enhance lipid productivity, a fed-batch cultivation mode was established with an initial phosphate concentration of 8 mg L
−1
and continuous supplementation with 1, 2 and 3 mg L
−1
phosphate, respectively, beginning on the 4
th
day. In batch culture the lipid content increased gradually from 27.45 to 46.15% DW with decreasing phosphate concentrations. Along with the decrease in phosphate concentrations, the contents of neutral lipids, eicosapentaenoic acid (EPA) and polyunsaturated fatty acids (PUFAs) increased from 50.87 to 70.07%, 2.06 to 7.30% and 2.91 to 11.73% of the total lipid content, respectively. Lipid productivity was enhanced up to 127.20 mg L
−1
day
−1
in fed-batch culture, which was approximately threefold-fold higher than that of the low phosphate group (8 mg L
−1
). The productivity was 43.2% higher than that of the high phosphate group (40 mg L
−1
). These results indicated that
Nannochloropsis
sp. SCSIO-45217 can be a promising source for PUFAs and the optimized supply of phosphate in fed-batch cultivation is a suitable cultivation strategy for microalgal lipid production.
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•Use of constitutive PGK promoter for CalB production in Pichia pastoris.•Study of specific growth rate effect in CalB production by Pichia pastoris.•Comparison between chemostat and ...fed-batch culture modes.•Theoretical best operational strategy over a 6-weeks period.
In this work, continuous and fed-batch operational modes for producing the recombinant protein lipase B from Candida antarctica under the new constitutive promoter PGK in the cell factory Pichia pastoris was assessed. For this purpose, the influence of the specific growth rate (μ) was examined from 0.05 to 0.16 h−1 on various key bioprocess parameters.
The overall biomass-to-substrate yield YX/S and specific substrate uptake rate (qs) were found to be independent of the particular operational mode. However, the μ-dependence of specific production rate (qp) differed with the cultivation strategy used. Thus, qp was linearly related in the continuous mode but suggested saturation in fed-batch cultures.
The highest volumetric and specific productivity were obtained at the highest μlevels in the continuous mode, which provided volumetric and specific productivities (QP and Qe, respectively) roughly 1.5 and 3 times greater than the fed-batch mode. The continuous mode also proved more effective in the long rung; thus, CalB production after 6 weeks was estimated to be about 5.8 times greater than with the fed-batch mode.
Continuous operation with the novel constitutive promoter PGK is thus a realistic alternative to the standard fed-batch cultivation at a high cell density typically used in industrial bioprocesses for heterologous protein production in Pichia pastoris.
•A proposal for obtaining smooth control profiles in fed-batch processes is given.•Proposal relies on parameterization of control vector by sinusoidal functions.•Sinusoidal based parameterization ...requires less number of parameters.•Application of proposed parameterization may avoid substrate shock in bioprocesses.•Approach leads to maximal productivity by using smooth-continuous feeding profiles.
In this work, a new approach for smooth control profiles parameterization (requiring a small number of parameters) is presented and especially recommended for bioprocess applications because of the smoothness of the profiles obtained, which are not only continuous time functions but also differentiable along the whole control interval. The importance of smooth profiles relays on the fact that abrupt changes in the cells’ environment may affect the metabolism of the cell, usually leading to a decrease in the process productivity. The parameterization proposed in this work is based on sinusoidal functions, which not only describe smooth functions but also are flexible and naturally constrained. Two very well-known bioprocess case studies have been successfully addressed by using the new parameterization approach.
•A multistage substrate feeding strategy independent from an organic substrate was developed for PHB production.•The developed feeding strategy is sensitive, robust, cheap and independent of the ...carbon source.•Glucose and glycerol concentrations were controlled within its optimal range.•Maximal cell and PHB concentrations of 164 and 125g/L were obtained from glucose and 104.7 and 65.6g/L from waste glycerol.
A three-stage control strategy independent of the organic substrate was developed for automated substrate feeding in a two-phase fed-batch culture of Cupriavidus necator DSM 545 for the production of the biopolymer polyhydroxybutyrate (PHB). The optimal feeding strategy was determined using glucose as the substrate. A combined substrate feeding strategy consisting of exponential feeding and a novel method based on alkali-addition monitoring resulted in a maximal cell concentration in the biomass growth phase. In the PHB accumulation phase, a constant substrate feeding strategy based on the estimated amount of biomass produced in the first phase and a specific PHB accumulation rate was implemented to induce PHB under limiting nitrogen at different biomass concentrations. Maximal cell and PHB concentrations of 164 and 125g/L were obtained when nitrogen feeding was stopped at 56g/L of residual biomass; the glucose concentration was maintained within its optimal range. The developed feeding strategy was validated using waste glycerol as the sole carbon source for PHB production, and the three-stage control strategy resulted in a PHB concentration of 65.6g/L and PHB content of 62.7% while keeping the glycerol concentration constant. It can thus be concluded that the developed feeding strategy is sensitive, robust, inexpensive, and applicable to fed-batch culture for PHB production independent of the carbon source.
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