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Lu J, Lv X, Yu W, Zhang J, Lu J, Liu Y, Li J, Du G, Chen J, Liu L. Reshaping Phosphatase Substrate Preference for Controlled Biosynthesis Using a "Design-Build-Test-Learn" Framework. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024; 11:e2309852. [PMID: 38504470 PMCID: PMC11165480 DOI: 10.1002/advs.202309852] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 02/29/2024] [Indexed: 03/21/2024]
Abstract
Biosynthesis is the application of enzymes in microbial cell factories and has emerged as a promising alternative to chemical synthesis. However, natural enzymes with limited catalytic performance often need to be engineered to meet specific needs through a time-consuming trial-and-error process. This study presents a quantum mechanics (QM)-incorporated design-build-test-learn (DBTL) framework to rationally design phosphatase BT4131, an enzyme with an ambiguous substrate spectrum involved in N-acetylglucosamine (GlcNAc) biosynthesis. First, mutant M1 (L129Q) is designed using force field-based methods, resulting in a 1.4-fold increase in substrate preference (kcat/Km) toward GlcNAc-6-phosphate (GlcNAc6P). QM calculations indicate that the shift in substrate preference is caused by a 13.59 kcal mol-1 reduction in activation energy. Furthermore, an iterative computer-aided design is conducted to stabilize the transition state. As a result, mutant M4 (I49Q/L129Q/G172L) with a 9.5-fold increase in kcat-GlcNAc6P/Km-GlcNAc6P and a 59% decrease in kcat-Glc6P/Km-Glc6P is highly desirable compared to the wild type in the GlcNAc-producing chassis. The GlcNAc titer increases to 217.3 g L-1 with a yield of 0.597 g (g glucose)-1 in a 50-L bioreactor, representing the highest reported level. Collectively, this DBTL framework provides an easy yet fascinating approach to the rational design of enzymes for industrially viable biocatalysts.
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Affiliation(s)
- Jiangong Lu
- Key Laboratory of Carbohydrate Chemistry and BiotechnologyMinistry of EducationJiangnan UniversityWuxi214122China
- Science Center for Future FoodsJiangnan UniversityWuxi214122China
| | - Xueqin Lv
- Key Laboratory of Carbohydrate Chemistry and BiotechnologyMinistry of EducationJiangnan UniversityWuxi214122China
- Science Center for Future FoodsJiangnan UniversityWuxi214122China
| | - Wenwen Yu
- Key Laboratory of Carbohydrate Chemistry and BiotechnologyMinistry of EducationJiangnan UniversityWuxi214122China
- Science Center for Future FoodsJiangnan UniversityWuxi214122China
| | - Jianing Zhang
- Key Laboratory of Carbohydrate Chemistry and BiotechnologyMinistry of EducationJiangnan UniversityWuxi214122China
- Science Center for Future FoodsJiangnan UniversityWuxi214122China
| | - Jianxing Lu
- Shandong Runde Biotechnology co., LTDTaian271200China
| | - Yanfeng Liu
- Key Laboratory of Carbohydrate Chemistry and BiotechnologyMinistry of EducationJiangnan UniversityWuxi214122China
- Science Center for Future FoodsJiangnan UniversityWuxi214122China
| | - Jianghua Li
- Science Center for Future FoodsJiangnan UniversityWuxi214122China
| | - Guocheng Du
- Key Laboratory of Carbohydrate Chemistry and BiotechnologyMinistry of EducationJiangnan UniversityWuxi214122China
- Science Center for Future FoodsJiangnan UniversityWuxi214122China
| | - Jian Chen
- Science Center for Future FoodsJiangnan UniversityWuxi214122China
| | - Long Liu
- Key Laboratory of Carbohydrate Chemistry and BiotechnologyMinistry of EducationJiangnan UniversityWuxi214122China
- Science Center for Future FoodsJiangnan UniversityWuxi214122China
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Choi JW, Song NE, Hong SP, Rhee YK, Hong HD, Cho CW. Engineering Bacillus subtilis J46 for efficient utilization of galactose through adaptive laboratory evolution. AMB Express 2024; 14:14. [PMID: 38282124 PMCID: PMC10822834 DOI: 10.1186/s13568-024-01666-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Accepted: 01/08/2024] [Indexed: 01/30/2024] Open
Abstract
Efficient utilization of galactose by microorganisms can lead to the production of valuable bio-products and improved metabolic processes. While Bacillus subtilis has inherent pathways for galactose metabolism, there is potential for enhancement via evolutionary strategies. This study aimed to boost galactose utilization in B. subtilis using adaptive laboratory evolution (ALE) and to elucidate the genetic and metabolic changes underlying the observed enhancements. The strains of B. subtilis underwent multiple rounds of adaptive laboratory evolution (approximately 5000 generations) in an environment that favored the use of galactose. This process resulted in an enhanced specific growth rate of 0.319 ± 0.005 h-1, a significant increase from the 0.03 ± 0.008 h-1 observed in the wild-type strains. Upon selecting the evolved strain BSGA14, a comprehensive whole-genome sequencing revealed the presence of 63 single nucleotide polymorphisms (SNPs). Two of them, located in the coding sequences of the genes araR and glcR, were found to be the advantageous mutations after reverse engineering. The strain with these two accumulated mutations, BSGALE4, exhibited similar specific growth rate on galactose to the evolved strain BSGA14 (0.296 ± 0.01 h-1). Furthermore, evolved strain showed higher productivity of protease and β-galactosidase in mock soybean biomass medium. ALE proved to be a potent tool for enhancing galactose metabolism in B. subtilis. The findings offer valuable insights into the potential of evolutionary strategies in microbial engineering and pave the way for industrial applications harnessing enhanced galactose conversion.
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Affiliation(s)
- Jae Woong Choi
- Research Group of Traditional Food, Korea Food Research Institute, 245, Nongsaengmyeong-ro, Iseo-myeon, Wanju-gun, 55365, Republic of Korea
| | - Nho-Eul Song
- Research Group of Traditional Food, Korea Food Research Institute, 245, Nongsaengmyeong-ro, Iseo-myeon, Wanju-gun, 55365, Republic of Korea
| | - Sang-Pil Hong
- Research Group of Traditional Food, Korea Food Research Institute, 245, Nongsaengmyeong-ro, Iseo-myeon, Wanju-gun, 55365, Republic of Korea
| | - Young Kyoung Rhee
- Research Group of Traditional Food, Korea Food Research Institute, 245, Nongsaengmyeong-ro, Iseo-myeon, Wanju-gun, 55365, Republic of Korea
| | - Hee-Do Hong
- Research Group of Traditional Food, Korea Food Research Institute, 245, Nongsaengmyeong-ro, Iseo-myeon, Wanju-gun, 55365, Republic of Korea
| | - Chang-Won Cho
- Research Group of Traditional Food, Korea Food Research Institute, 245, Nongsaengmyeong-ro, Iseo-myeon, Wanju-gun, 55365, Republic of Korea.
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Herrmann LW, Letti LAJ, Penha RDO, Soccol VT, Rodrigues C, Soccol CR. Bacillus genus industrial applications and innovation: First steps towards a circular bioeconomy. Biotechnol Adv 2024; 70:108300. [PMID: 38101553 DOI: 10.1016/j.biotechadv.2023.108300] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2023] [Revised: 12/06/2023] [Accepted: 12/07/2023] [Indexed: 12/17/2023]
Abstract
In recent decades, environmental concerns have directed several policies, investments, and production processes. The search for sustainable and eco-friendly strategies is constantly increasing to reduce petrochemical product utilization, fossil fuel pollution, waste generation, and other major ecological impacts. The concepts of circular economy, bioeconomy, and biorefinery are increasingly being applied to solve or reduce those problems, directing us towards a greener future. Within the biotechnology field, the Bacillus genus of bacteria presents extremely versatile microorganisms capable of producing a great variety of products with little to no dependency on petrochemicals. They are able to grow in different agro-industrial wastes and extreme conditions, resulting in healthy and environmentally friendly products, such as foods, feeds, probiotics, plant growth promoters, biocides, enzymes, and bioactive compounds. The objective of this review was to compile the variety of products that can be produced with Bacillus cells, using the concepts of biorefinery and circular economy as the scope to search for greener alternatives to each production method and providing market and bioeconomy ideas of global production. Although the genus is extensively used in industry, little information is available on its large-scale production, and there is little current data regarding bioeconomy and circular economy parameters for the bacteria. Therefore, as this work gathers several products' economic, production, and environmentally friendly use information, it can be addressed as one of the first steps towards those sustainable strategies. Additionally, an extensive patent search was conducted, focusing on products that contain or are produced by the Bacillus genus, providing an indication of global technology development and direction of the bacteria products. The Bacillus global market represented at least $18 billion in 2020, taking into account only the products addressed in this article, and at least 650 patent documents submitted per year since 2017, indicating this market's extreme importance. The data we provide in this article can be used as a base for further studies in bioeconomy and circular economy and show the genus is a promising candidate for a greener and more sustainable future.
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Affiliation(s)
- Leonardo Wedderhoff Herrmann
- Bioprocess Engineering and Biotechnology Department, Federal University of Paraná, Francisco H. dos Santos Street, CP 19011, Centro Politécnico, Curitiba, Paraná, 81531-980, Brazil.
| | - Luiz Alberto Junior Letti
- Bioprocess Engineering and Biotechnology Department, Federal University of Paraná, Francisco H. dos Santos Street, CP 19011, Centro Politécnico, Curitiba, Paraná, 81531-980, Brazil
| | - Rafaela de Oliveira Penha
- Bioprocess Engineering and Biotechnology Department, Federal University of Paraná, Francisco H. dos Santos Street, CP 19011, Centro Politécnico, Curitiba, Paraná, 81531-980, Brazil
| | - Vanete Thomaz Soccol
- Bioprocess Engineering and Biotechnology Department, Federal University of Paraná, Francisco H. dos Santos Street, CP 19011, Centro Politécnico, Curitiba, Paraná, 81531-980, Brazil
| | - Cristine Rodrigues
- Bioprocess Engineering and Biotechnology Department, Federal University of Paraná, Francisco H. dos Santos Street, CP 19011, Centro Politécnico, Curitiba, Paraná, 81531-980, Brazil
| | - Carlos Ricardo Soccol
- Bioprocess Engineering and Biotechnology Department, Federal University of Paraná, Francisco H. dos Santos Street, CP 19011, Centro Politécnico, Curitiba, Paraná, 81531-980, Brazil
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An update on the review of microbial synthesis of glucosamine and N-acetylglucosamine. World J Microbiol Biotechnol 2023; 39:93. [PMID: 36754899 DOI: 10.1007/s11274-023-03531-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Accepted: 01/19/2023] [Indexed: 02/10/2023]
Abstract
Glucosamine (GlcN) is a natural amino monosaccharide in which a hydroxyl group of glucose is substituted by an amino group. It belongs to functional amino sugar compounds. In the traditional preparation process, GlcN and GlcNAc are obtained by hydrolyzing the cell wall of shrimp and crab. There are many potential problems with this method, such as geographical and seasonal restrictions on the supply of raw materials, serious environmental pollution and potential allergic reactions. Microbial fermentation has the advantages of mild conditions, low environmental pollution, high production intensity, and product safety. It can effectively solve the problem of shrimp and crab hydrolysis process, attracting many researchers to participate in the research of microbial fermentation production of GlcN. This paper mainly summarizes the research on strain construction method, metabolic pathway design and fermentation condition optimization in microbial fermentation, which has certain guiding significance for the further production, research and production of glucosamine.
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Ling M, Wu Y, Tian R, Liu Y, Yu W, Tao G, Lv X, Li J, Du G, Amaro RL, Liu L. Combinatorial pathway engineering of Bacillus subtilis for production of structurally defined and homogeneous chitooligosaccharides. Metab Eng 2022; 70:55-66. [PMID: 35033656 DOI: 10.1016/j.ymben.2022.01.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Revised: 12/30/2021] [Accepted: 01/12/2022] [Indexed: 11/16/2022]
Abstract
Chitooligosaccharides (COSs) have a widespread range of biological functions and an incredible potential for various pharmaceutical and agricultural applications. Although several physical, chemical, and biological techniques have been reported for COSs production, it is still a challenge to obtain structurally defined COSs with defined polymerization (DP) and acetylation patterns, which hampers the specific characterization and application of COSs. Herein, we achieved the de novo production of structurally defined COSs using combinatorial pathway engineering in Bacillus subtilis. Specifically, the COSs synthase NodC from Azorhizobium caulinodans was overexpressed in B. subtilis, leading to 30 ± 0.86 mg/L of chitin oligosaccharides (CTOSs), the homo-oligomers of N-acetylglucosamine (GlcNAc) with a well-defined DP lower than 6. Then introduction of a GlcNAc synthesis module to promote the supply of the sugar acceptor GlcNAc, reduced CTOSs production, which suggested that the activity of COSs synthase NodC and the supply of sugar donor UDP-GlcNAc may be the limiting steps for CTOSs synthesis. Therefore, 6 exogenous COSs synthase candidates were examined, and the nodCM from Mesorhizobium loti yielded the highest CTOSs titer of 560 ± 16 mg/L. Finally, both the de novo pathway and the salvage pathway of UDP-GlcNAc were engineered to further promote the biosynthesis of CTOSs. The titer of CTOSs in 3-L fed-batch bioreactor reached 4.82 ± 0.11 g/L (85.6% CTOS5, 7.5% CTOS4, 5.3% CTOS3 and 1.6% CTOS2), which was the highest ever reported. This is the first report proving the feasibility of the de novo production of structurally defined CTOSs by synthetic biology, and provides a good starting point for further engineering to achieve the commercial production.
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Affiliation(s)
- Meixi Ling
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China; Science Center for Future Foods, Jiangnan University, Wuxi, 214122, China
| | - Yaokang Wu
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China; Science Center for Future Foods, Jiangnan University, Wuxi, 214122, China
| | - Rongzhen Tian
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China; Science Center for Future Foods, Jiangnan University, Wuxi, 214122, China
| | - Yanfeng Liu
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China; Science Center for Future Foods, Jiangnan University, Wuxi, 214122, China
| | - Wenwen Yu
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China; Science Center for Future Foods, Jiangnan University, Wuxi, 214122, China
| | - Guanjun Tao
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, 214122, China
| | - Xueqin Lv
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China; Science Center for Future Foods, Jiangnan University, Wuxi, 214122, China
| | - Jianghua Li
- Science Center for Future Foods, Jiangnan University, Wuxi, 214122, China
| | - Guocheng Du
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China; Science Center for Future Foods, Jiangnan University, Wuxi, 214122, China.
| | - Rodrigo Ledesma Amaro
- Department of Bioengineering and Centre for Synthetic Biology, Imperial College London, London, SW7 2AZ, UK
| | - Long Liu
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China; Science Center for Future Foods, Jiangnan University, Wuxi, 214122, China.
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Wang K, Wang X, Luo H, Wang Y, Wang Y, Tu T, Qin X, Bai Y, Huang H, Yao B, Su X, Zhang J. Synergetic Fermentation of Glucose and Glycerol for High-Yield N-Acetylglucosamine Production in Escherichia coli. Int J Mol Sci 2022; 23:ijms23020773. [PMID: 35054959 PMCID: PMC8775389 DOI: 10.3390/ijms23020773] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Revised: 12/28/2021] [Accepted: 01/09/2022] [Indexed: 01/13/2023] Open
Abstract
N-acetylglucosamine (GlcNAc) is an amino sugar that has been widely used in the nutraceutical and pharmaceutical industries. Recently, microbial production of GlcNAc has been developed. One major challenge for efficient biosynthesis of GlcNAc is to achieve appropriate carbon flux distribution between growth and production. Here, a synergistic substrate co-utilization strategy was used to address this challenge. Specifically, glycerol was utilized to support cell growth and generate glutamine and acetyl-CoA, which are amino and acetyl donors, respectively, for GlcNAc biosynthesis, while glucose was retained for GlcNAc production. Thanks to deletion of the 6-phosphofructokinase (PfkA and PfkB) and glucose-6-phosphate dehydrogenase (ZWF) genes, the main glucose catabolism pathways of Escherichia coli were blocked. The resultant mutant showed a severe defect in glucose consumption. Then, the GlcNAc production module containing glucosamine-6-phosphate synthase (GlmS*), glucosamine-6-phosphate N-acetyltransferase (GNA1*) and GlcNAc-6-phosphate phosphatase (YqaB) expression cassettes was introduced into the mutant, to drive the carbon flux from glucose to GlcNAc. Furthermore, co-utilization of glucose and glycerol was achieved by overexpression of glycerol kinase (GlpK) gene. Using the optimized fermentation medium, the final strain produced GlcNAc with a high stoichiometric yield of 0.64 mol/mol glucose. This study offers a promising strategy to address the challenge of distributing carbon flux in GlcNAc production.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | - Xiaoyun Su
- Correspondence: (X.S.); (J.Z.); Tel.: +86-10-62599910 (X.S. & J.Z.)
| | - Jie Zhang
- Correspondence: (X.S.); (J.Z.); Tel.: +86-10-62599910 (X.S. & J.Z.)
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Mao X, Huang Z, Sun G, Zhang H, Lu W, Liu Y, Lv X, Du G, Li J, Liu L. High level production of diacetylchitobiose deacetylase by refactoring genetic elements and cellular metabolism. BIORESOURCE TECHNOLOGY 2021; 341:125836. [PMID: 34469820 DOI: 10.1016/j.biortech.2021.125836] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2021] [Revised: 08/21/2021] [Accepted: 08/21/2021] [Indexed: 06/13/2023]
Abstract
Diacetylchitobiose deacetylase (Dac) from Pyrococcus horikoshii can realize the one-step production of glucosamine (GlcN). The efficient expression and secretion of Dac play a central role in the green production of GlcN. In this study, Bacillus subtilis WB600 was used as the expression host. Firstly, we screened 12 signal peptides, among which signal peptide NprB had the strongest ability of guiding Dac secretion. Further optimization of the functional region showed that the extracellular Dac activity of NprB mutant was increased to 3682.2 U/mL. Next, the extracellular Dac activity was increased to 4807.6 U/mL by RBS sequence optimization. Then we got a new recombinant B. subtilis C6 for plasmid-free expression of Dac by integrating comK gene and silencing bpr, nprB, aprE, mpr and nprE genes. Finally, the extracellular Dac activity of genome-integrating strain reached 6357.38 U/mL, which was the highest level reported so far.
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Affiliation(s)
- Xinzhu Mao
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi 214122, PR China; Science Center for Future Foods, Jiangnan University, Wuxi 214122, PR China
| | - Ziyang Huang
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi 214122, PR China; Science Center for Future Foods, Jiangnan University, Wuxi 214122, PR China
| | - Guoyun Sun
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi 214122, PR China; Science Center for Future Foods, Jiangnan University, Wuxi 214122, PR China
| | - Hongzhi Zhang
- Shandong Runde Biotechnology Co., Ltd., Tai'an 271000, PR China
| | - Wei Lu
- Shandong Runde Biotechnology Co., Ltd., Tai'an 271000, PR China
| | - Yanfeng Liu
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi 214122, PR China; Science Center for Future Foods, Jiangnan University, Wuxi 214122, PR China
| | - Xueqin Lv
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi 214122, PR China; Science Center for Future Foods, Jiangnan University, Wuxi 214122, PR China
| | - Guocheng Du
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi 214122, PR China; Science Center for Future Foods, Jiangnan University, Wuxi 214122, PR China
| | - Jianghua Li
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi 214122, PR China; Science Center for Future Foods, Jiangnan University, Wuxi 214122, PR China
| | - Long Liu
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi 214122, PR China; Science Center for Future Foods, Jiangnan University, Wuxi 214122, PR China.
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Production of proteins and commodity chemicals using engineered Bacillus subtilis platform strain. Essays Biochem 2021; 65:173-185. [PMID: 34028523 DOI: 10.1042/ebc20210011] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 05/02/2021] [Accepted: 05/06/2021] [Indexed: 12/19/2022]
Abstract
Currently, increasing demand of biochemicals produced from renewable resources has motivated researchers to seek microbial production strategies instead of traditional chemical methods. As a microbial platform, Bacillus subtilis possesses many advantages including the generally recognized safe status, clear metabolic networks, short growth cycle, mature genetic editing methods and efficient protein secretion systems. Engineered B. subtilis strains are being increasingly used in laboratory research and in industry for the production of valuable proteins and other chemicals. In this review, we first describe the recent advances of bioinformatics strategies during the research and applications of B. subtilis. Secondly, the applications of B. subtilis in enzymes and recombinant proteins production are summarized. Further, the recent progress in employing metabolic engineering and synthetic biology strategies in B. subtilis platform strain to produce commodity chemicals is systematically introduced and compared. Finally, the major limitations for the further development of B. subtilis platform strain and possible future directions for its research are also discussed.
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