Hyaluronan production and molecular weight is enhanced in pathway-engineered strains of lactate dehydrogenase-deficient Lactococcus lactis

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.

Advances in hyaluronic acid production: Biosynthesis and genetic engineering strategies based on Streptococcus - A review

Hyaluronic acid (HA), which is a highly versatile glycosaminoglycan, is widely applied across the fields of food, cosmetics, and pharmaceuticals. It is primary produced through Streptococcus fermentation, but the product presents inherent challenges concerning consistency and potential pathogenicity. However, recent strides in molecular biology have paved the way for genetic engineering, which facilitates the creation of high-yield, nonpathogenic strains adept at synthesizing HA with specific molecular weights. This comprehensive review extensively explores the molecular biology underpinning pivotal HA synthase genes, which elucidates the intricate mechanisms governing HA synthesis. Moreover, it delineates various strategies employed in engineering HA-producing strains.

Reprogramming Metabolic Flux in Escherichia Coli to Enhance Chondroitin Production

Reprogramming metabolic flux is a promising approach for constructing efficient microbial cell factories (MCFs) to produce chemicals. However, how to boost the transmission efficiency of metabolic flux is still challenging in complex metabolic pathways. In this study, metabolic flux is systematically reprogrammed by regulating flux size, flux direction, and flux rate to build an efficient MCF for chondroitin production. The ammoniation pool for UDP-GalNAc synthesis and the carbonization pool for UDP-GlcA synthesis are first enlarged to increase flux size for providing enough precursors for chondroitin biosynthesis. Then, the ammoniation pool and the carbonization pool are rematched using molecular valves to shift flux direction from cell growth to chondroitin biosynthesis. Next, the adaptability of polymerization pool with the ammoniation and carbonization pools is fine-tuned by dynamic and static valve-based adapters to accelerate flux rate for polymerizing UDP-GalNAc and UDP-GlcA to produce chondroitin. Finally, the engineered strain E. coli F51 is able to produce 9.2 g L-1 chondroitin in a 5-L bioreactor. This strategy shown here provides a systematical approach for regulating metabolic flux in complex metabolic pathways for efficient biosynthesis of chemicals.

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.

Progress and prospects of biopolymers production strategies

In recent decades, biopolymers have garnered significant attention owing to their aptitude as an environmentally approachable precursor for an extensive application. In addition, due to their alluring assets and widespread use, biopolymers have made significant strides in their production based on various sources and forms. This review focuses on the most recent improvements and breakthroughs that have been made in the manufacturing of biopolymers, via sections focusing the most frequented and preferred routes like micro-macro, algae apart from focusing on microbials routes with special attention to bacteria and the synthetic biology avenue of biopolymer production. For ensuring the continued growth of the global polymer industry, promising research trends must be pursued, as well as methods for overcoming obstacles that arise in exploiting the beneficial properties exhibited by a variety of biopolymers.

Development of In Situ Product Recovery (ISPR) System Using Amberlite IRA67 for Enhanced Biosynthesis of Hyaluronic Acid by Streptococcus zooepidemicus

High broth viscosity due to the accumulation of hyaluronic acid (HA) causes a limited yield of HA. It is a major problem of HA production using Streptococcus zooepidemicus. Extractive fermentation via in situ product recovery (ISPR) was utilized to enhance the HA production. Resins from Amberlite: IRA400 Cl; IRA900 Cl; IRA410 Cl; IRA402 Cl; and IRA67 were tested for the HA adsorption. IRA67 showed high adsorption capacity on HA. The study of the adsorption via a 2 L stirred tank bioreactor of S. zooepidemicus fermentation was investigated to elucidate the adsorption of HA onto IRA67 in dispersed and integrated internal column systems. The application of a dispersed IRA67 improved the HA production compared to the fermentation without resin addition by 1.37-fold. The HA production was further improved by 1.36-fold with an internal column (3.928 g/L) over that obtained with dispersed IRA67. The cultivation with an internal column shows the highest reduction of viscosity value after the addition of IRA67 resin: from 58.8 to 23.7 (mPa·s), suggesting the most effective ISPR of HA. The improved biosynthesis of HA indicated that an extractive fermentation by ISPR adsorption is effective and may streamline the HA purification.

Enhanced Stability and Function of Probiotic Streptococcus thermophilus with Self-Encapsulation by Increasing the Biosynthesis of Hyaluronan

The harsh conditions of the gastrointestinal tract limit the potential health benefits of oral probiotics. It is promising that oral bioavailability is improved by strengthening the self-protection of probiotics. Here, we report the encapsulation of a probiotic strain by endogenous production of hyaluronan to enhance the effects of oral administration of the strain. The traditional probiotic Streptococcus thermophilus was engineered to produce hyaluronan shells by using traceless genetic modifications and clustered regularly interspaced short palindromic repeat interference. After oral delivery to mice in the form of fermented milk, hyaluronan-coated S. thermophilus (204.45 mg/L hyaluronan in the milk) exhibited greater survival and longer colonization time in the gut than the wild-type strain. In particular, the engineered probiotic strain could also produce hyaluronan after intestinal colonization. Importantly, S. thermophilus self-encapsulated with hyaluronan increased the number of goblet cells, mucus production, and abundance of the microorganisms related to the biosynthesis of short-chain fatty acids, resulting in the enhancement of the intestinal barrier. The coating formed by endogenous hyaluronan provides an ideal reference for the effective oral administration of probiotics.

Real-time metabolic heat-based specific growth rate soft sensor for monitoring and control of high molecular weight hyaluronic acid production by Streptococcus zooepidemicus

This present investigation addressing the metabolic bottleneck in synthesis of high MW HA by Streptococcus zooepidemicus and illustrates the application of calorimetric fed-batch control of µ at a narrower range. Feedforward (FF) and feedback (FB) control was devised to improve the molecular weight (MW) of HA production by S. zooepidemicus. Metabolic heat measurements (Fermentation calorimetry) were modeled to decipher real-time specific growth rate, [Formula: see text] was looped into the PID circuit, envisaged to control [Formula: see text] to their desired setpoint values 0.05 [Formula: see text], 0.1 [Formula: see text], and 0.15 [Formula: see text] respectively. Similarly, a predetermined exponential feed rate irrespective of real-time µ was carried out in FF strategy. The developed FB strategy established a robust control capable of maintaining the specific growth rate (µ) close to the [Formula: see text] value with a minimal tracking error. Exponential feed rate carried out with a lowest [Formula: see text] of 0.05 [Formula: see text] showed an improved MW of HA to 2.98 MDa and 2.94 MDa for the FF and FB-based control strategies respectively. An optimal HA titer of 4.73 g/L was achieved in FF control strategy at [Formula: see text]. Superior control of µ at low [Formula: see text] value was observed to influence HA polymerization positively by yielding an improved MW and desired polydispersity index (PDI) of HA. PID control offers advantage over conventional fed-batch method to synthesize HA at an improved MW. Calorimetric signal-based µ control by PID negates adverse effects due to the secretion of other end products albeit maintaining regular metabolic activities. KEY POINTS: First report to compare HA productivities by feedforward and feedback control strategy. Inherent merits of regulating µ at narrower range were entailed. Relationship between operating µ and HA molecular weight was discussed.

Primary recovery of hyaluronic acid produced in Streptococcus equi subsp. zooepidemicus using PEG-citrate aqueous two-phase systems

Given its biocompatibility, rheological, and physiological properties, hyaluronic acid (HA) has become a biomaterial of increasing interest with multiple applications in medicine and cosmetics. In recent decades, microbial fermentations have become an important source for the industrial production of HA. However, due to its final applications, microbial HA must undergo critical and long purification processes to ensure clinical and cosmetic grade purity. Aqueous two-phase systems (ATPS) have proven to be an efficient technique for the primary recovery of high-value biomolecules. Nevertheless, their implementation in HA downstream processing has been practically unexplored. In this work, polyethylene glycol (PEG)–citrate ATPS were used for the first time for the primary recovery of HA produced with an engineered strain of Streptococcus equi subsp. zooepidemicus. The effects of PEG molecular weight (MW), tie-line length (TLL), volume ratio (V_R), and sample load on HA recovery and purity were studied with a clarified fermentation broth as feed material. HA was recovered in the salt-rich bottom phase, and its recovery increased when a PEG MW of 8000 g mol⁻¹ was used. Lower V_R values (0.38) favoured HA recovery, whereas purity was enhanced by a high V_R (3.50). Meanwhile, sample load had a negative impact on both recovery and purity. The ATPS with the best performance was PEG 8000 g mol⁻¹, TLL 43% (w/w), and V_R 3.50, showing 79.4% HA recovery and 74.5% purity. This study demonstrated for the first time the potential of PEG–citrate ATPS as an effective primary recovery strategy for the downstream process of microbial HA.

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.

Absorption, distribution, metabolism and excretion of hyaluronic acid during pregnancy: a matter of molecular weight

INTRODUCTION

For many years hyaluronic acid (HA) was mainly used for its hydrating properties. However, new applications have recently arisen, considering the biological properties of HA and its molecular weight. Clinical application of low molecular weight HA (LMW-HA) initially was supported by specific absorption data. The identification of high molecular weight HA (HMW-HA) absorption pathways and the knowledge of its physiological role allowed to evaluate its clinical application. Based on the immunomodulatory properties of HMW-HA and its physiological involvement as signaling molecule, pregnancy represents an interesting context of application.

AREA COVERED

This expert opinion includes in-vitro, in-vivo, ex-vivo and clinical studies on gestational models. It provides an overview of the physiological and the therapeutic role of HMW-HA in pregnancy starting from its metabolism. Indeed, HMW-HA is widely involved in several physiological processes as implantation, immune response, uterine quiescence and cervical remodeling, and therefore is an essential molecule for a successful pregnancy.

EXPERT OPINION

Available evidence suggests that HMW-HA administration can support physiological pregnancy, favoring blastocyst adhesion and development, preventing miscarriage and pre-term birth. For this reason, supplementation in pregnancy should be evaluated.

Versatile strategies for bioproduction of hyaluronic acid driven by synthetic biology

Owing to its outstanding water-retention ability, viscoelasticity, biocompatibility and non-immunogenicity, Hyaluronic acid (HA), a natural linear polymer alternating linked by d-glucuronic acid and N-acetylglucosamine, has been widely employed in cosmetic, medical and clinical applications. With the development of synthetic biology and bioprocessing optimization, HA production via microbial fermentation is an economical and sustainable alternative over traditional animal extraction methods. Indeed, recently Streptococci and other recombinant systems for HA synthesis has received increasing interests due to its technical advantages. This review summarizes the production of HA by microorganisms and demonstrates its synthesis mechanism, focusing on the current status in various production systems, as well as common synthetic biology strategies include driving more carbon flux into HA biosynthesis and regulating the molecular weight (MW), and finally discusses the major challenges and prospects.

Evaluation of Ogataea (Hansenula) polymorpha for Hyaluronic Acid Production

Hyaluronic acid (HA) is a biopolymer formed by UDP-glucuronic acid and UDP-N-acetyl-glucosamine disaccharide units linked by β-1,4 and β-1,3 glycosidic bonds. It is widely employed in medical and cosmetic procedures. HA is synthesized by hyaluronan synthase (HAS), which catalyzes the precursors’ ligation in the cytosol, elongates the polymer chain, and exports it to the extracellular space. Here, we engineer Ogataea (Hansenula) polymorpha for HA production by inserting the genes encoding UDP-glucose 6-dehydrogenase, for UDP-glucuronic acid production, and HAS. Two microbial HAS, from Streptococcus zooepidemicus (hasAs) and Pasteurella multocida (hasAp), were evaluated separately. Additionally, we assessed a genetic switch using integrases in O. polymorpha to uncouple HA production from growth. Four strains were constructed containing both has genes under the control of different promoters. In the strain containing the genetic switch, HA production was verified by a capsule-like layer around the cells by scanning electron microscopy in the first 24 h of cultivation. For the other strains, the HA was quantified only after 48 h and in an optimized medium, indicating that HA production in O. polymorpha is limited by cultivation conditions. Nevertheless, these results provide a proof-of-principle that O. polymorpha is a suitable host for HA production.

Biological strategies for oligo/polysaccharide synthesis: biocatalyst and microbial cell factory

Oligosaccharides and polysaccharides constitute the principal components of carbohydrates, which are important biomacromolecules that demonstrate considerable bioactivities. However, the variety and structural complexity of oligo/polysaccharides represent a major challenge for biological and structural explorations. To access structurally defined oligo/polysaccharides, biological strategies using glycoenzyme biocatalysts have shown remarkable synthetic potential attributed to their regioselectivity and stereoselectivity that allow mild, structurally controlled reaction without addition of protecting groups necessary in chemical strategies. This review summarizes recent biotechnological approaches of oligo/polysaccharide synthesis, which mainly includes in vitro enzymatic synthesis and cell factory synthesis. We have discussed the important factors involved in the production of nucleotide sugars. Furthermore, the strategies established in the cell factory and enzymatic syntheses are summarized, and we have highlighted concepts like metabolic flux rebuilding and regulation, enzyme engineering, and route design as important strategies. The research challenges and prospects are also outlined and discussed.

Role of membrane proteins in bacterial synthesis of hyaluronic acid and their potential in industrial production

Hyaluronic acid (HA) is a glycosaminoglycan polymer found in various parts of human body and is required for functions like lubrication, water homeostasis etc. Hyaluronic acid is mostly produced industrially by bacterial fermentation for pharmaceutical and cosmetic applications. This review discusses on the role of membrane proteins involved in synthesis and transport of bacterial HA, since HA is a transmembrane product. The different types of membrane proteins involved, their transcriptional control in wild type bacteria and the expression of those proteins in various recombinant hosts have been discussed. The role of phospholipids and metal ions on membrane proteins activity, HA yield and size of HA have also been discussed. Today with an estimated market of US$ 8.3 billion and which is expected to grow to US$ 15.25 billion in 2026, it is essential to increase the efficiency of the industrial HA production process. So this review also proposes on how those membrane proteins and cellular mechanisms like the transcriptional control can be utilised to develop efficient industrial strains that enhance the yield and size of HA produced.

Eliminating the capsule-like layer to promote glucose uptake for hyaluronan production by engineered Corynebacterium glutamicum

Hyaluronan is widely used in cosmetics and pharmaceutics. Development of robust and safe cell factories and cultivation approaches to efficiently produce hyaluronan is of many interests. Here, we describe the metabolic engineering of Corynebacterium glutamicum and application of a fermentation strategy to manufacture hyaluronan with different molecular weights. C. glutamicum is engineered by combinatorial overexpression of type I hyaluronan synthase, enzymes of intermediate metabolic pathways and attenuation of extracellular polysaccharide biosynthesis. The engineered strain produces 34.2 g L⁻¹ hyaluronan in fed-batch cultures. We find secreted hyaluronan encapsulates C. glutamicum, changes its cell morphology and inhibits metabolism. Disruption of the encapsulation with leech hyaluronidase restores metabolism and leads to hyper hyaluronan productions of 74.1 g L⁻¹. Meanwhile, the molecular weight of hyaluronan is also highly tunable. These results demonstrate combinatorial optimization of cell factories and the extracellular environment is efficacious and likely applicable for the production of other biopolymers.

Bioproduction of hyaluronan needs increases in yield and greater diversity of the molecular weights. Here, the author increases hyaluronan production and diversifies the molecular weights through engineering the hyaluronan biosynthesis pathway and disruption of Corynebacterium glutamicum encapsulation caused by secreted hyaluronan.

Inhibitory activity of traditional plants against Mycobacterium smegmatis and their action on Filamenting temperature sensitive mutant Z (FtsZ)-A cell division protein

The study was designed to assess whether plant extracts / phytochemical (D-Pinitol) synergistically combine with antituberculosis drugs and act on Mycobacterium smegmatis (M. smegmatis) as well as assess their mode of action on Mycobacterium tuberculosis (M.tb) Filamenting temperature sensitive mutant Z (FtsZ) protein. Resazurin microtitre plate assay (Checker board) was performed to analyze the activity of plant extracts against M. smegmatis. Synergistic behaviour of plant extracts / D-Pinitol with Isoniazid (INH) and Rifampicin (RIF) were determined by time–kill and checker board assays. Elongation of M. smegmatis cells due to this treatment was determined by light microscopy. The effect of Hexane methanol extract (HXM) plant extracts on cell viability was determined using PI/SYTO9 dual dye reporter Live/Dead assay. Action of HXM plant extracts / D-Pinitol on inhibition of FtsZ protein was done using Guanosine triphosphatase (GTPase) light scattering assay and quantitative Polymerase Chain Reaction (qPCR). The Hexane-methanolic plant extract of Acacia nilotica, Aegle marmelos and Glycyrrhiza glabra showed antimycobacterial activity at 1.56 ± 0.03, 1.32 ± 0.02 and 1.25 ± 0.03 mg/mL respectively and that of INH and RIF were 4.00 ± 0.06 μg/mL and 2.00 ± 0.04 μg/mL respectively. These plant extracts and major phytochemical exudate D-Pinitol was found to act synergistically with antimycobacterial drugs INH and RIF with an FIC index ~ 0.20. Time-Kill kinetics studies indicate that, these plant extracts were bacteriostatic in nature. D-Pinitol in conjunction with INH and RIF exhibited a 2 Log reduction in the growth of viable cells compared to untreated. Attempt to elucidate their mode of action through phenotypic analysis indicated that these plant extracts and D-Pinitol was found to interfere in cell division there by leading to an abnormal elongated cellular morphology. HXM extracts and D-Pinitol synergistically combined with the first line tuberculosis drugs, INH and RIF, to act on M. smegmatis. The increase in the length of M. smegmatis cells on treatment with D-Pinitol and HXM extract of the plants indicated that they hinder the cell division mechanism thereby leading to a filamentous phenotype, and finally leading to cell death. In addition, the integrity of the bacterial cell membrane is also altered causing cell death. Further gene expression analysis showed that these plant extracts and D-Pinitol hampers with function of FtsZ protein which was confirmed through in vitro inhibition of FtsZ–GTPase enzymatic activity.

Harnessing Adaptive Evolution to Achieve Superior Mannitol Production by Lactococcus lactis Using Its Native Metabolism

Mannitol can be obtained as a by-product of certain heterolactic lactic acid bacteria, when grown on substrates containing fructose. Lactococcus lactis, a homolactic lactic acid bacterium, normally does not form mannitol but can be persuaded into doing so by expressing certain foreign enzyme activities. In this study, we find that L. lactis has an inherent capacity to form mannitol from glucose. By adaptively evolving L. lactis or derivatives blocked in NAD⁺ regenerating pathways, we manage to accelerate growth on mannitol. When cells of the adapted strains are resuspended in buffer containing glucose, 4-58% of the glucose metabolized is converted into mannitol, in contrast to nonadapted strains. The highest conversion was obtained for a strain lacking all major NAD⁺ regenerating pathways. Mannitol had an inhibitory effect on the conversion, which we speculated was due to the mannitol uptake system. After its inactivation, 60% of the glucose was converted into mannitol by cells suspended in glucose buffer. Using a two-stage setup, where biomass first was accumulated by aerated culturing, followed by a nonaerated phase (static conditions), it was possible to obtain 6.1 g/L mannitol, where 60% of the glucose had been converted into mannitol, which is the highest yield reported for L. lactis.

Enhancement of acetyl-CoA by acetate co-utilization in recombinant Lactococcus lactis cultures enables the production of high molecular weight hyaluronic acid

The molecular weight of hyaluronic acid (HA) is a critical property which determines its usage in various biomedical applications. This study investigates the correlation between the availability of a critical cofactor, acetyl-CoA, the concentration of a limiting precursor, UDP-N-acetylglucosamine (UDP-GlcNAc), and the molecular weight of HA (MW_HA) produced by recombinant Lactococcus lactis MKG6 cultures. This strain expressed three heterologous HA-pathway genes obtained from the has operon of Streptococcus zooepidemicus in an ldh-mutant host strain, L. lactis NZ9020. A flux balance analysis, performed using the L. lactis genome-scale metabolic network, showed a positive correlation of acetyl-CoA flux with the UDP-GlcNAc flux and the experimental data on HA productivity. To increase the intracellular levels of acetyl-CoA, acetate was supplemented as a pulse feed in anaerobic batch cultures. However, acetate is effectively utilized only in the presence of glucose and exhaustion of glucose resulted in decreasing the final MW_HA (1.5 MDa). Co-supplementation of acetate resulted in enhancing the acetyl-CoA and UDP-GlcNAc levels as well as the MW_HA to 2.5 MDa. This logic was extended to fed-batch cultures, designed with a pH-based feedback control of glucose feeding and pulse acetate supplementation. When the glucose feed concentration was optimally adjusted to prevent glucose exhaustion or accumulation, the acetate utilization was found to be high, resulting in significantly enhanced levels of acetyl-CoA and UDP-GlcNAc as well as a MW_HA of 3.4 MDa, which was sustained at this value throughout the process. This study provides the possibility of commercially producing high MW_HA using recombinant L. lactis strains.

Uncovering Novel Pathways for Enhancing Hyaluronan Synthesis in Recombinant Lactococcus lactis: Genome-Scale Metabolic Modeling and Experimental Validation

Hyaluronan (HA), a glycosaminoglycan with important medical applications, is commercially produced from pathogenic microbial sources. The metabolism of HA-producing recombinant generally regarded as safe (GRAS) systems needs to be more strategically engineered to achieve yields higher than native producers. Here, we use a genome-scale model (GEM) to account for the entire metabolic network of the cell while predicting strategies to improve HA production. We analyze the metabolic network of Lactococcus lactis adapted to produce HA and identify non-conventional strategies to enhance HA flux. We also show experimental verification of one of the predicted strategies. We thus identified an alternate route for enhancement of HA synthesis, originating from the nucleoside inosine, that can function in parallel with the traditionally known route from glucose. Adopting this strategy resulted in a 2.8-fold increase in HA yield. The strategies identified and the experimental results show that the cell is capable of involving a larger subset of metabolic pathways in HA production. Apart from being the first report to use a nucleoside to improve HA production, we demonstrate the role of experimental validation in model refinement and strategy improvisation. Overall, we point out that well-constructed GEMs could be used to derive efficient strategies to improve the biosynthesis of high-value products.

Hyaluronic Acid in the Third Millennium

Since its first isolation in 1934, hyaluronic acid (HA) has been studied across a variety of research areas. This unbranched glycosaminoglycan consisting of repeating disaccharide units of N-acetyl-d-glucosamine and d-glucuronic acid is almost ubiquitous in humans and in other vertebrates. HA is involved in many key processes, including cell signaling, wound reparation, tissue regeneration, morphogenesis, matrix organization and pathobiology, and has unique physico-chemical properties, such as biocompatibility, biodegradability, mucoadhesivity, hygroscopicity and viscoelasticity. For these reasons, exogenous HA has been investigated as a drug delivery system and treatment in cancer, ophthalmology, arthrology, pneumology, rhinology, urology, aesthetic medicine and cosmetics. To improve and customize its properties and applications, HA can be subjected to chemical modifications: conjugation and crosslinking. The present review gives an overview regarding HA, describing its history, physico-chemical, structural and hydrodynamic properties and biology (occurrence, biosynthesis (by hyaluronan synthases), degradation (by hyaluronidases and oxidative stress), roles, mechanisms of action and receptors). Furthermore, both conventional and recently emerging methods developed for the industrial production of HA and its chemical derivatization are presented. Finally, the medical, pharmaceutical and cosmetic applications of HA and its derivatives are reviewed, reporting examples of HA-based products that currently are on the market or are undergoing further investigations.

Directed Evolution of Hyaluronic Acid Synthase from Pasteurella multocida towards High-Molecular-Weight Hyaluronic Acid

Hyaluronic acid (HA), with diverse cosmetic and medical applications, is the natural glycosaminoglycan product of HA synthases. Although process and/or metabolic engineering are used for industrial HA production, the potential of protein engineering has barely been realised. Herein, knowledge-gaining directed evolution (KnowVolution) was employed to generate an HA synthase variant from Pasteurella multocida (pmHAS) with improved chain-length specificity and a twofold increase in mass-based turnover number. Seven improved pmHAS variants out of 1392 generated by error-prone PCR were identified; eight prospective positions were saturated and the most beneficial amino acid substitutions were recombined. After one round of KnowVolution, the longest HA polymer (<4.7 MDa), through an engineered pmHAS variant in a cell-free system, was synthesised. Computational studies showed that substitutions from the best variant (T40L, V59M and T104A) are distant from the glycosyltransferase sites and increase the flexibility of the N-terminal region of pmHAS. Taken together, these findings suggest that the N terminus may be involved in HA synthesis and demonstrate the potential of protein engineering towards improved HA synthase activity.

An Effective Translation: The Development of Hyaluronan-Based Medical Products From the Physicochemical, and Preclinical Aspects

This review shows the steps toward material selection focalized on the design and development of medical devices based on hyaluronan (HA). The selection is based on chemical and mechanical properties, biocompatibility, sterilization, safety, and scale-up costs. These facts play a vital role in the industrialization process. Approved medical devices containing-HA are illustrated to identify key parameters. The first part of this work involves the steps toward a complete characterization of chemical and mechanical aspects, reproducibility of the processes and scale up. In a second stage, we aimed to describe the preclinical in vitro and in vivo assays and selected examples of clinical trials. Furthermore, it is important to keep in mind the regulatory affairs during the research and development (R&D) using standardization (ISO standards) to achieve the main goal, which is the functionality and safety of the final device. To keep reproducible experimental data to prepare an efficient master file for the device, based on quality and recorded manufacturing data, and a rigorous R&D process may help toward clinical translation. A strong debate is still going on because the denominated basic research in HA field does not pay attention to the purity and quality of the raw materials used during the development. So that, to achieve the next generation of devices is needed to overcome the limitations of state of art in terms of efficacy, biodegradability, and non-toxicity.

Synthetic biology strategies for improving microbial synthesis of "green" biopolymers

Polysaccharide-based biopolymers have many material properties relevant to industrial and medical uses, including as drug delivery agents, wound-healing adhesives, and food additives and stabilizers. Traditionally, polysaccharides are obtained from natural sources. Microbial synthesis offers an attractive alternative for sustainable production of tailored biopolymers. Here, we review synthetic biology strategies for select "green" biopolymers: cellulose, alginate, chitin, chitosan, and hyaluronan. Microbial production pathways, opportunities for pathway yield improvements, and advances in microbial engineering of biopolymers in various hosts are discussed. Taken together, microbial engineering has expanded the repertoire of green biological chemistry by increasing the diversity of biobased materials.

Enhanced Biosynthesis of Hyaluronic Acid Using Engineered Corynebacterium glutamicum Via Metabolic Pathway Regulation

Hyaluronic acid (HA) is a polysaccharide used in many industries such as medicine, surgery, cosmetics, and food. To avoid potential pathogenicity caused by its native producer, Streptococcus, efforts have been made to create a recombinant host for HA production. In this work, a GRAS (generally recognized as safe) strain, Corynebacterium glutamicum, is engineered for enhanced biosynthesis of HA via metabolic pathway regulation. Five enzymes (HasA-HasE) involved in the HA biosynthetic pathway are highlighted, and eight diverse operon combinations, including HasA, HasAB, HasAC, HasAD, HasAE, HasABC, HasABD, and HasABE, are compared. HasAB and HasABC are found to be optimal for HA biosynthesis in C. glutamicum. To meet the energy demand for HA synthesis, the metabolic pathway that produces lactate is blocked by knocking out the lactate dehydrogenase (LDH) gene using single crossover homologous recombination. Engineered C. glutamicum/Δldh-AB is superior and had a significantly higher HA titer than C. glutamicum/Δldh-ABC. Batch and fed-batch cultures of C. glutamicum/Δldh-AB are performed in a 5-L fermenter. Using glucose feeding, the maximum HA titer reached 21.6 g L^-1 , more than threefolds of that of the wild-type Streptococcus. This work provides an efficient, safe, and novel recombinant HA producer, C. glutamicum/Δldh-AB, via metabolic pathway regulation.