Enhancing single-cell hyaluronic acid biosynthesis by microbial morphology engineering

Unraveling the intricacies of glycosaminoglycan biosynthesis: Decoding the molecular symphony in understanding complex polysaccharide assembly

Glycosaminoglycans (GAGs) are extensively utilized in clinical, cosmetic, and healthcare field, as well as in the treatment of thrombosis, osteoarthritis, rheumatism, and cancer. The biological production of GAGs is a strategy that has garnered significant attention due to its numerous advantages over traditional preparation methods. In this review, we embark on a journey to decode the intricate molecular symphony that orchestrates the biosynthesis of glycosaminoglycans. By unraveling the complex interplay of related enzymes and thorough excavation of the intricate metabolic cascades involved, GAGs chain aggregation and transportation, which efficiently and controllably modulate GAGs sulfation patterns involved in biosynthetic pathway, we endeavor to offer a thorough comprehension of how these remarkable GAGs are intricately assembled and pushes the boundaries of our understanding in GAGs biosynthesis.

Mid-Long Chain Dicarboxylic Acid Production via Systems Metabolic Engineering: Progress and Prospects

Mid-to-long-chain dicarboxylic acids (DCAi, i ≥ 6) are organic compounds in which two carboxylic acid functional groups are present at the terminal position of the carbon chain. These acids find important applications as structural components and intermediates across various industrial sectors, including organic compound synthesis, food production, pharmaceutical development, and agricultural manufacturing. However, conventional petroleum-based DCA production methods cause environmental pollution, making sustainable development challenging. Hence, the demand for eco-friendly processes and renewable raw materials for DCA production is rising. Owing to advances in systems metabolic engineering, new tools from systems biology, synthetic biology, and evolutionary engineering can now be used for the sustainable production of energy-dense biofuels. Here, we explore systems metabolic engineering strategies for DCA synthesis in various chassis via the conversion of different raw materials into mid-to-long-chain DCAs. Subsequently, we discuss the future challenges in this field and propose synthetic biology approaches for the efficient production and successful commercialization of these acids.

Fine-tuning the cell morphology of Corynebacterium glutamicum via dual-valve regulation for enhanced hyaluronic acid production

Enhanced synthesis of hyaluronic acid (HA) with recombinant Corynebacterium glutamicum as production host was achieved in this work. Hyaluronan synthase (HAS), which is a membrane protein acting as a key enzyme in HA biosynthesis, impacts both HA yield and its molecular weight. Cell morphology, which includes size, shape, and surface area, has a large impact on the expression and activity of HAS. Therefore, deliberate regulation of cell morphology holds the potential to enhance HA production. Here, we constructed three modules, namely the transporter module, the morphology tuning module and the HA synthesis module. The transporter module contains a strong constitutive promoter Ptuf and arabinose transport protein was used to control the maximum amount of inducer entering the cell, thus reducing excessive cell deformation. The morphology tuning module contains an arabinose-inducible weak promoter PBAD and a cell-division-relevant gene was used to sense intracellular inducer concentrations and achieve different degrees of change in cell size. These two modules worked together, described as a dual-valve regulation, to achieve fine-tuning of cell morphology, resulting in a 1.87-fold increase in cell length and a 2.08-fold increase in cell membrane. When combined with the HA synthesis module, the HA titer reached 16.0 g/L, which was 1.6 times the yield reported in the previous morphology-engineered strain. Hence, for the first time, a morphologically engineered strain resulting in both high cell density and HA titer was constructed.

Production of different molecular weight glycosaminoglycans with microbial cell factories

Glycosaminoglycans (GAGs) are naturally occurring acidic polysaccharides with wide applications in pharmaceuticals, cosmetics, and health foods. The diverse biological activities and physiological functions of GAGs are closely associated with their molecular weights and sulfation patterns. Except for the non-sulfated hyaluronan which can be synthesized naturally by group A Streptococcus, all the other GAGs such as heparin and chondroitin sulfate are mainly acquired from animal tissues. Microbial cell factories provide a more effective platform for the production of structurally homogeneous GAGs. Enhancing the production efficiency of polysaccharides, accurately regulating the GAGs molecular weight, and effectively controlling the sulfation degree of GAGs represent the major challenges of developing GAGs microbial cell factories. Several enzymatic, metabolic engineering, and synthetic biology strategies have been developed to tackle these obstacles and push forward the industrialization of biotechnologically produced GAGs. This review summarizes the recent advances in the construction of GAGs synthesis cell factories, regulation of GAG molecular weight, and modification of GAGs chains. Furthermore, the challenges and prospects for future research in this field are also discussed.

Comprehensive review on biosynthesis of hyaluronic acid with different molecular weights and its biomedical applications

Hyaluronic acid (HA), an anionic and nonsulfated glycosaminoglycan, is the main structural component of various tissues and plays an important role in various biological processes. Given the promising properties of HA, such as high cellular compatibility, moisture retention, antiaging, proper interaction with cells, and CD44 targeting, HA can be widely used extensively in drug delivery, tissue engineering, wound healing, and cancer therapy. HA can obtain from animal tissues and microbial fermentation, but its applications depend on its molecular weight. Microbial fermentation is a common method for HA production on an industrial scale and S. zooepidemicus is the most frequently used strain in HA production. Culture conditions including pH, temperature, agitation rate, aeration speed, shear stress, dissolved oxygen, and bioreactor type significantly affect HA biosynthesis properties. In this review all the HA production methods and purification techniques to improve its physicochemical and biological properties for various biomedical applications are discussed in details. In addition, we showed that how HA molecular weight can significantly affect its properties and applications.

Microbial synthesis of glycosaminoglycans and their oligosaccharides

Compared with chemical synthesis and tissue extraction methods, microbial synthesis of glycosaminoglycans (GAGs) is attractive because of the advantages of eco-friendly processes, production safety, and sustainable development. However, boosting the efficiency of microbial cell factories, precisely regulating GAG molecular weights, and rationally controlling the sulfation degree of GAGs remain challenging. To address these issues, various strategies, including genetic, enzymatic, metabolic, and fermentation engineering, have been developed. In this review, we summarize the recent progress in the construction of efficient GAG-producing microbial cell factories, regulation of the molecular weight of GAGs, and modification of GAG chains. Moreover, future studies, remaining challenges, and potential solutions in this field are discussed.

Biomimetic natural biomaterials for tissue engineering and regenerative medicine: new biosynthesis methods, recent advances, and emerging applications

Biomimetic materials have emerged as attractive and competitive alternatives for tissue engineering (TE) and regenerative medicine. In contrast to conventional biomaterials or synthetic materials, biomimetic scaffolds based on natural biomaterial can offer cells a broad spectrum of biochemical and biophysical cues that mimic the in vivo extracellular matrix (ECM). Additionally, such materials have mechanical adaptability, microstructure interconnectivity, and inherent bioactivity, making them ideal for the design of living implants for specific applications in TE and regenerative medicine. This paper provides an overview for recent progress of biomimetic natural biomaterials (BNBMs), including advances in their preparation, functionality, potential applications and future challenges. We highlight recent advances in the fabrication of BNBMs and outline general strategies for functionalizing and tailoring the BNBMs with various biological and physicochemical characteristics of native ECM. Moreover, we offer an overview of recent key advances in the functionalization and applications of versatile BNBMs for TE applications. Finally, we conclude by offering our perspective on open challenges and future developments in this rapidly-evolving field.

Construction of an ultra-strong PtacM promoter via engineering the core-element spacer and 5' untranslated region for versatile applications in Corynebacterium glutamicum

As one of the most important synthetic biology elements in transcriptional regulation, promoters play irreplaceable roles in metabolic engineering. For the industrial microorganism Corynebacterium glutamicum, both the construction of a promoter library with gradient strength and the creation of ultra-strong promoters are essential for the production of target enzymes and compounds. In this work, the spacer sequence (both length and base) between the -35 and -10 regions, and the 5'-terminal untranslated region (5'UTR) were particularly highlighted to investigate their contributions to promoter strength. We constructed a series of artificially induced promoters based on the classical tac promoter using C. glutamicum ATCC13032 as the host. Here, we explored the effect of sequence length between the -35 and -10 regions on the strength of the tac promoter, and found that the mutant with 15 nt spacer length (PtacL15) was transcriptionally stronger than the classic Ptac (16 nt); subsequently, based on PtacL15, we explored the effect of the nucleotide sequence in the spacer region on transcriptional strength, and screened the strongest PtacL15m-110 (GAACAGGCTTTATCT), and PtacL15m-87 (AGTCGCTAAGACTCA); finally, we investigated the effect of the length of the 5'-terminal untranslated region (5'UTR) and screened out the optimal PtacM4 mutant with a 5'UTR length of 32 nt. Based on our new findings on the optimal spacer length (15 nt), nucleotide sequence (AGTCGCTAAGACTCA), and 5'UTR (truncated 32 nt), an ultra-strong PtacM, whose transcriptional strength was about 3.25 times that of the original Ptac, was obtained. We anticipate that these promoters with gradient transcriptional strength and the ultra-strong PtacM will play an important role in the construction of recombinant strains and industrial production.

Prospective bacterial and fungal sources of hyaluronic acid: A review

The unique biological and rheological properties make hyaluronic acid a sought-after material for medicine and cosmetology. Due to very high purity requirements for hyaluronic acid in medical applications, the profitability of streptococcal fermentation is reduced. Production of hyaluronic acid by recombinant systems is considered a promising alternative. Variations in combinations of expressed genes and fermentation conditions alter the yield and molecular weight of produced hyaluronic acid. This review is devoted to the current state of hyaluronic acid production by recombinant bacterial and fungal organisms.

Remodeling Bacillus amyloliquefaciens Cell Wall Rigidity to Reduce Cell Lysis and Increase the Yield of Heterologous Proteins

Bacillus amyloliquefaciens has great potential as a host for heterologous protein production, but its severe autolytic behavior has precluded its industrial application to date. Because d,l-endopeptidase activity-guided cell wall rigidity is considered essential for autolysis resistance, we investigated the effects of d,l-endopeptidase genes lytE, lytF, cwlO, and cwlS play on the growth, lysis, and morphology remodeling of B. amyloliquefaciens strain TCCC11018. Individual and combinatorial deletion of lytE, lytF, and cwlS enhanced the cell growth and delayed cell lysis. For the best mutant with the lytF and cwlS double deletion, the viable cell number at 24 h increased by 11.90% and the cell wall thickness at 6 h increased by 25.87%. Transcriptomic and proteomic analyses indicated that the improvement was caused by enhanced peptidoglycan synthesis. With the lytF and cwlS double deletion, the extracellular green fluorescent protein and phospholipase D expression levels increased by 113 and 55.89%, respectively. This work broadens our understanding of the relationship between d,l-endopeptidases and B. amyloliquefaciens cell characteristics, which provides an effective strategy to improve the heterologous protein expression in B. amyloliquefaciens-based cell factories.

Designing Microbial Cell Factories for the Production of Chemicals

The sustainable production of chemicals from renewable, nonedible biomass has emerged as an essential alternative to address pressing environmental issues arising from our heavy dependence on fossil resources. Microbial cell factories are engineered microorganisms harboring biosynthetic pathways streamlined to produce chemicals of interests from renewable carbon sources. The biosynthetic pathways for the production of chemicals can be defined into three categories with reference to the microbial host selected for engineering: native-existing pathways, nonnative-existing pathways, and nonnative-created pathways. Recent trends in leveraging native-existing pathways, discovering nonnative-existing pathways, and designing de novo pathways (as nonnative-created pathways) are discussed in this Perspective. We highlight key approaches and successful case studies that exemplify these concepts. Once these pathways are designed and constructed in the microbial cell factory, systems metabolic engineering strategies can be used to improve the performance of the strain to meet industrial production standards. In the second part of the Perspective, current trends in design tools and strategies for systems metabolic engineering are discussed with an eye toward the future. Finally, we survey current and future challenges that need to be addressed to advance microbial cell factories for the sustainable production of chemicals.

Comprehensive review on biotechnological production of hyaluronic acid: status, innovation, market and applications

The growing, existing demand for low-cost and high-quality hyaluronic acid (HA) needs an outlook of different possible production strategies from renewable resources with the reduced possibility of cross-infections. Recently, the possibility of producing HA from harmless microorganisms appeared, which offers the opportunity to make HA more economical, without raw material limitations, and environmentally friendly. HA production is mainly reported with Lancefield Streptococci A and C, particularly from S. equi and S. zooepidemicus. Various modes of fermentation such as batch, repeated batch, fed-batch, and continuous culture have been investigated to optimize HA production, particularly from S. zooepidemicus, obtaining a HA yield of 2.5 g L⁻¹ – 7.0 g L⁻¹. Among the different utilized DSP approaches of HA production, recovery with cold ethanol (4°C) and cetylpyridinium chloride is the ideal strategy for lab-scale HA production. On the industrial scale, besides using isopropanol, filtration (0.22 um), ultrafiltration (100 kDa), and activated carbon absorption are employed to obtain HA of low molecular weight and additional ultrafiltration to purify HA of higher MW. Even though mature technologies have already been developed for the industrial production of HA, the projections of increased sales volume and the expansion of application possibilities require new processes to obtain HA with higher productivity, purity, and specific molecular weights. In this review, we have put forth the progress of HA technological research by discussing the microbial biosynthetic aspects, fermentation and downstream strategies, industrial-scale scenarios of HA, and the prospects of HA production to meet the current and ongoing market demands.

Microbial cell surface engineering for high-level synthesis of bio-products

Microbial cell surface layers, which mainly include the cell membrane, cell wall, periplasmic space, outer membrane, capsules, S-layers, pili, and flagella, control material exchange between the cell and the extracellular environment, and have great impact on production titers and yields of various bio-products synthesized by microbes. Recent research work has made exciting achievements in metabolic engineering using microbial cell surface components as novel regulation targets without direct modifications of the metabolic pathways of the desired products. This review article will summarize the accomplishments obtained in this emerging field, and will describe various engineering strategies that have been adopted in bacteria and yeasts for the enhancement of mass transfer across the cell surface, improvement of protein expression and folding, modulation of cell size and shape, and re-direction of cellular resources, all of which contribute to the construction of more efficient microbial cell factories toward the synthesis of a variety of bio-products. The existing problems and possible future directions will also be discussed.

Indirect Pathway Metabolic Engineering Strategies for Enhanced Biosynthesis of Hyaluronic Acid in Engineered Corynebacterium glutamicum

Hyaluronic acid (HA) is composed of alternating d-glucuronic acid and N-acetyl-d-glucosamine, with excellent biocompatibility and water retention capacity. To achieve heterologous biosynthesis of HA, Corynebacterium glutamicum, a safe GRAS (generally recognized as safe) host, was utilized and metabolically engineered previously. In this work, to achieve further enhancement of HA yield, four strategies were proposed and performed separately first, i.e., (1) improvement of glucose uptake via iolR gene knockout, releasing the inhibition of transporter IolT1/IolT2 and glucokinases; (2) intensification of cardiolipin synthesis through overexpression of genes pgsA1/pgsA2/cls involved in cardiolipin synthesis; (3) duly expressed Vitreoscilla hemoglobin in genome, enhancing HA titer coupled with more ATP and improved NAD⁺/NADH (>7.5) ratio; and (4) identification of the importance of glutamine for HA synthesis through transcriptome analyses and then enhancement of the HA titer via its supplement. After that, we combined different strategies together to further increase the HA titer. As a result, one of the optimal recombinant strains, Cg-dR-CLS, yielded 32 g/L of HA at 60 h in a fed-batch culture, which was increased by 30% compared with that of the starting strain. This high value of HA titer will enable the industrial production of HA via the engineered C. glutamicum.

Synthetic Biology Toolkits and Metabolic Engineering Applied in Corynebacterium glutamicum for Biomanufacturing

Corynebacterium glutamicum is an important workhorse in industrial white biotechnology. It has been widely applied in the producing processes of amino acids, fuels, and diverse value-added chemicals. With the continuous disclosure of genetic regulation mechanisms, various strategies and technologies of synthetic biology were used to design and construct C. glutamicum cells for biomanufacturing and bioremediation. This study mainly aimed to summarize the design and construction strategies of C. glutamicum-engineered strains, which were based on genomic modification, synthetic biological device-assisted metabolic flux optimization, and directed evolution-based engineering. Then, taking two important bioproducts (N-acetylglucosamine and hyaluronic acid) as examples, the applications of C. glutamicum cell factories were introduced. Finally, we discussed the current challenges and future development trends of C. glutamicum-engineered strain construction.

Genetic strategies for improving hyaluronic acid production in recombinant bacterial culture

Hyaluronic acid (HA) is a biopolymer of repeating units of glucuronic acid and N-acetylglucosamine. Its market was valued at USD 8.9 billion in 2019. Traditionally, HA has been obtained from rooster comb-like animal tissues and fermentative cultures of attenuated pathogenic streptococci. Various attempts have been made to engineer a safe micro-organism for HA synthesis; however, the HA titres obtained from these attempts are in general still lower than those achieved by natural, pathogenic producers. In this scenario, ways to increase HA molecule length and titres in already constructed strains are gaining attention in the last years, but no recent publication has reviewed the main genetic strategies applied to improve HA production on heterologous hosts. In light of that, we hereby compile the advances made in the engineering of micro-organisms to improve HA synthesis.