Optimization of carbon source and glucose feeding strategy for improvement of L-isoleucine production by Escherichia coli

Strategic nutrient sourcing for biomanufacturing intensification

The successful design of economically viable bioprocesses can help to abate global dependence on petroleum, increase supply chain resilience, and add value to agriculture. Specifically, bioprocessing provides the opportunity to replace petrochemical production methods with biological methods and to develop novel bioproducts. Even though a vast range of chemicals can be biomanufactured, the constraints on economic viability, especially while competing with petrochemicals, are severe. There have been extensive gains in our ability to engineer microbes for improved production metrics and utilization of target carbon sources. The impact of growth medium composition on process cost and organism performance receives less attention in the literature than organism engineering efforts, with media optimization often being performed in proprietary settings. The widespread use of corn steep liquor as a nutrient source demonstrates the viability and importance of "waste" streams in biomanufacturing. There are other promising waste streams that can be used to increase the sustainability of biomanufacturing, such as the use of urea instead of fossil fuel-intensive ammonia and the use of struvite instead of contributing to the depletion of phosphate reserves. In this review, we discuss several process-specific optimizations of micronutrients that increased product titers by twofold or more. This practice of deliberate and thoughtful sourcing and adjustment of nutrients can substantially impact process metrics. Yet the mechanisms are rarely explored, making it difficult to generalize the results to other processes. In this review, we will discuss examples of nutrient sourcing and adjustment as a means of process improvement.

ONE-SENTENCE SUMMARY

The potential impact of nutrient adjustments on bioprocess performance, economics, and waste valorization is undervalued and largely undercharacterized.

Control algorithms and strategies of feeding for fed-batch fermentation of Escherichia coli: a review of 40 years of experience

Fed-batch cultivation is a well-known type of submerged fermentation that is frequently used in manufacture of recombinant proteins and various kinds of enzymes, owing to its ability to produce products with high concentrations and high efficiency. In fed-batch culture, several issues must be considered; most of them are also presented in batch culture. However, feed flow rate calculation only corresponds to fed-batch fermentation and its value has a significant impact on productivity, efficiency, final concentration of product, formation of by-products, and viscosity of the culture. From this background, the present review article is an effort to gather the information on feeding strategies for fed-batch cultivation of Escherichia coli, which is a well-known microorganism in the production of recombinant proteins and industrial enzymes, especially for therapeutic applications. Moreover, this review is an aid to comprehend and compare the fundamental concept of different feeding strategies and their advantages and drawbacks.

Improved production of D-pantothenic acid in Escherichia coli by integrated strain engineering and fermentation strategies

D-pantothenic acid (D-PA) is an essential vitamin that has been widely used in medicine, food, and animal feed. Microbial production of D-PA from natural renewable resources is attractive and challenging. In this study, both strain improvements and fermentation process strategies were applied to achieve high-level D-PA production in Escherichia coli. First, a D-PA-producing strain was developed through deletion of the aceF and mdh genes combined with the overexpression of the gene ppnk. The obtained engineered E. coli DPA02/pT-ppnk accumulated 6.89 ± 0.11 g/L of D-PA in shake flask fermentation, which was 79.9 % higher than the control strain. Moreover, the cultivation process contributed greatly to D-PA production with respect to titer and productivity by betaine supplementation and dissolved oxygen (DO)-feedback feeding framework. Under optimal conditions, 68.3 g/L of D-PA, the specific productivity of 0.794 g/L h and the yield of 0.36 g/g glucose in 5 L fermenter were achieved. Overall, this research successfully exploited advanced strategies to lay the foundation for bio-based D-PA production in industrial applications.

Overproduction of D-pantothenic acid via fermentation conditions optimization and isoleucine feeding from recombinant Escherichia coli W3110

D-pantothenic acid (D-PA), as a crucial vitamin, is widely used in food, animal feed, cosmetics, and pharmaceutical industries. In our previous work, recombinant Escherichia coli W3110 for production of D-PA was constructed through metabolic pathway modification. In this study, to enhance D-PA production, statistical optimization techniques including Plackett-Burman (PB) design and Box-Behnken design (BBD) first were adopted to optimize the culture condition. The results showed that the glucose, β-alanine and (NH₄)₂SO₄ have the most significant effects on D-PA biosynthesis. The response surface model based on BBD predicted that the optimal concentration is glucose 56.0 g/L, β-alanine 2.25 g/L and (NH4)₂SO₄ 11.8 g/L, the D-PA titer increases from 3.2 g/L to 6.73 g/L shake flask fermentation. For the fed-batch fermentation in 5 L fermenter, the isoleucine feeding strategy greatly increased the titer and productivity of D-PA. As a result, titer (31.6 g/L) and productivity (13.2 g/L·d) of D-PA were achieved, they increased by 4.66 times and 2.65 times, respectively, compared with batch culture. At the same time, the accumulation of acetate reduced from 29.79 g/L to 8.55 g/L in the fed-batch fermentation. These results demonstrated that the optimization of medium composition and the cell growth rate are important to increase the concentration of D-PA for microbial fermentation. This work laid the foundation for further research on the application of D-PA microbial synthesis.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02773-0.

Metabolic engineering of Corynebacterium glutamicum WM001 to improve l-isoleucine production

In this study, l-isoleucine production in Corynebacterium glutamicum WM001 was improved by deleting three genes in the genome, replacing the native promoter of ilvA in the genome, and overexpression of five genes in an alr-based auxotrophic complementation expression system. The three genes deleted in the genome are alaT, brnQ, and alr. Deletion of alaT improved l-isoleucine production by increasing the supply of pyruvate, whereas deletion of brnQ improved l-isoleucine production by blocking the uptake of extracellular l-isoleucine. Exchange of the native promoter of ilvA with promoter tac or tacM could contribute to l-isoleucine production by increasing 2-ketobutyric acid; tac is better than tacM for improving l-isoleucine yield. Different combinations of the genes ilvBN, ppnK, lrp, and brnFE were overexpressed in an alr-based auxotrophic complementation expression system to further improve l-isoleucine production, and the best yield after 72-H flask fermentation was obtained from the strain WM005/pYCW-1-ilvBN2-ppnK1. Without addition of any antibiotics, WM005/pYCW-1-ilvBN2-ppnK1 could produce 32.1 g/L l-isoleucine after 72-H fed-batch fermentation, which is 34.3% increase compared with the original strain WM001.

Exploring the fermentation characteristics of a newly isolated marine bacteria strain, Gordonia terrae TWRH01 for carotenoids production

Carotenoids serve as one of the most important group of naturally-occurring lipid-soluble pigments which exhibit great biological activities such as antioxidant, anti-inflammatory and provitamin A activities. Owing to their advantageous health effects, carotenoids are widely applied in various industries. Microbial carotenoids synthesis therefore has attracted increasing attention in recent years. In the present study, a marine microorganism originally isolated from seawater in northern Taiwan was determined to be a strain of Gordonia terrae based on its 16S rRNA gene sequence. The strain G. terrae TWRH01 has the ability to synthesize and accumulate the intracellular pigments was identified by gas chromatography-mass spectrometry (GC-MS). The biochemical production characteristics of this strain were studied by employing different fermentation strategies. Findings suggested that G. terrae TWRH01 can actively grow and efficiently synthesize carotenoids in medium adjusted to pH 7 containing 16 g L^-1 sucrose as the carbon source, 16 g L^-1 yeast extract as the nitrogen source, 0.6 M NaCl concentration, and supplemented with 0.45% (v/v) 1 M CaCl₂. Results revealed that the optimization of fermentation yielded 15.29 g L^-1 dry biomass and 10.58 μmol L^-1 relative β-carotene concentration. According to GC-MS analysis, the orange-red colored pigments produced were identified as carotenoid derivatives, mainly echinenone and adonixanthin 3'-β-d-glucoside. Therefore, the new bacterial strain showed a highly potential bioresource for the commercial production of natural carotenoids.

Vitreoscilla hemoglobin promotes biofilm expansion and mitigates sporulation in Bacillus subtilis DK1042

Biofilm formation is considered as a stress combating strategy adopted by bacteria in response to variety of cellular and environmental signals. Impaired respiration due to low oxygen concentrations is one such signal that triggers wrinkling and robust biofilm formation in Bacillus subtilis. Vitreoscilla hemoglobin (VHb) improves microaerobic growth and bioproduct synthesis in a variety of bacteria by supplying oxygen to the respiratory chain. Present study was carried out to determine the effect of VHb on multicellularity of B. subtilis. Thus, B. subtilis DK1042 (WT) was genetically modified to express vgb and gfp genes under the control of P43 promoter at amyE locus by double cross over events. Biofilm formation by the integrant NRM1113 and WT was monitored on Lysogeny broth (LB) and LB containing glycerol and manganese (LBGM) medium. The WT produced more wrinkled colonies than NRM1113 on LB and LBGM medium. Concomitantly, biofilm-associated sporulation and production of pulcherriminic acid was decreased in NRM1113 as compared to WT on LB as well as LBGM. Expression studies of genes encoding structural components of biofilms revealed ~ 70% down-regulation of bslA gene in NRM1113 on both LB and LBGM which is correlated with reduced wrinkling in NRM1113. Moreover, NRM1113 showed increased colony expansion compared to WT in LB, LBGM and high osmolarity conditions. VHb expression alters various processes in different host cells, our study represents that VHb modulates biofilm formation, sporulation and pulcherriminic acid formation in B. subtilis DK1042.

Novel technologies provide more engineering strategies for amino acid-producing microorganisms

Traditionally, amino acid-producing strains were obtained by random mutagenesis and subsequent selection. With the development of genetic and metabolic engineering techniques, various microorganisms with high amino acid production yields are now constructed by rational design of targeted biosynthetic pathways. Recently, novel technologies derived from systems and synthetic biology have emerged and open a new promising avenue towards the engineering of amino acid production microorganisms. In this review, these approaches, including rational engineering of rate-limiting enzymes, real-time sensing of end-products, pathway optimization on the chromosome, transcription factor-mediated strain improvement, and metabolic modeling and flux analysis, were summarized with regard to their application in microbial amino acid production.