Cheese whey: A cost-effective alternative for hyaluronic acid production by Streptococcus zooepidemicus

Bacterial Cellulose for Scalable and Sustainable Bio-Gels in the Circular Economy

Microbial-derived materials are emerging for applications in biomedicine, sensors, food, cosmetics, construction, and fashion. They offer considerable structural properties and process reproducibility compared to other bio-based materials. However, challenges related to efficient and sustainable large-scale production of microbial-derived materials must be addressed to exploit their potential fully. This review analyzes the synergistic contribution of circular, sustainable, and biotechnological approaches to enhance bacterial cellulose (BC) production and fine-tune its physico-chemical properties. BC was chosen as an ideal example due to its mechanical strength and chemical stability, making it promising for industrial applications. The review discusses upcycling strategies that utilize waste for microbial fermentation, simultaneously boosting BC production. Additionally, biotechnology techniques are identified as key to enhance BC yield and tailor its physico-chemical properties. Among the different areas where cellulose-based materials are employed, BC shows promise for mitigating the environmental impact of the garment industry. The review emphasizes that integrating circular and biotechnological approaches could significantly improve large-scale production and enhance the tunability of BC properties. Additionally, these approaches may simultaneously provide environmental benefits, depending on their future progresses. Future advancements should prioritize circular fermentation and biotechnological techniques to expand the potential of BC for sustainable industrial applications.

CRISPRi-assisted metabolic engineering of cyanobacteria for photosynthetic hyaluronic acid from CO2

BACKGROUND

Hyaluronic acid (HA) is widely used in pharmaceuticals, medicine, and cosmetics. Sustainable production has shifted to microbial fermentation using engineered GRAS strains. Diverse carbon sources and CO2 conversion via engineered microorganisms enhance HA production. Herein we applied advances in CRISPR technologies and tools to optimize metabolic pathway by redirecting carbon portioning in cyanobacterium Synechoccous elongatus PCC 7942, demonstrating enhanced HA production.

RESULTS

S. elongatus PCC 7942 lacking hyaluronan synthase (HAS) required pathway engineering for HA production. By expressing heterologous Class I HAS, a modular gene expression system was employed, incorporating hasB and hasC for the HA-GlcA module and glmU, glmM, and glmS for the GlcNAc module. This approach resulted in construction of four engineered cyanobacterial strains. Optimizing metabolic pathway involving the HA-GlcA and GlcNAc modules led to SeHA220 (wild-type with HA-GlcA and GlcNAc modules) producing 2.4 ± 0.85 mg/L HA at 21 d, a 27.5-fold increase compared to the control. Targeting F6P and G6P metabolic nodes via CRISPR interference to repress zwf and pfk genes further improved production, with SeHA226 (SeHA220 with a gene repression module) achieving 5.0 ± 0.3 mg/L HA from CO2 at 15 d. Notably, SeHA226 produced photosynthetic HA with a molecular weight (Mw) of 4.2 MDa, comparable to native producers, emphasizing the importance of precursor balance and growth conditions.

CONCLUSIONS

This study engineered cyanobacteria for efficient HA biosynthesis using modular gene expression and CRISPR-interference systems. Optimizing heterologous metabolic pathway was key to achieving high-molecular-weight photosynthetic HA production from CO2. The findings provide insights into tunable HA production, with future efforts aimed at scaling up photosynthetic HA production for larger-scale applications.

Microbial production of hyaluronic acid: The current advances, engineering strategies and trends

Hyaluronic acid (HA) is a versatile biomolecule with applications in medicine, cosmetics, and pharmaceuticals. While traditionally extracted from animal tissues, HA is now predominantly produced through microbial fermentation. Microbial fermentation using strains such as Streptococcus zooepidemicus, Corynebacterium glutamicum, and Bacillus subtilis offers a more scalable and sustainable alternative to chemical and animal extraction methods. Recent studies reveal promising yields from engineered strains of Corynebacterium glutamicum and Bacillus subtilis, utilizing advanced metabolic and genetic techniques. Recent advancements in genetic and metabolic engineering, as well as synthetic biology, have addressed some challenges related to molecular weight, viscosity, and by-product formation. This review focuses on the microbial production of HA using engineered strains, encompassing producer organisms, metabolic engineering strategies, industrial-scale production, and key factors influencing molecular weight. Furthermore, it addresses the challenges and potential solutions associated with HA production. Additional research is necessary to develop more efficient and robust engineered strains that exhibit resistance to contamination and can utilize low-cost substrates, such as Pseudomonas putida and Halomonas spp. By overcoming these challenges, researchers can advance the industrial production of HA and expand its applications, thereby contributing to the growth of the HA market.

Hyaluronic acid production by Streptococcus zooepidemicus MW26985 using potato peel waste hydrolyzate

In this research, we examined the production of hyaluronic acid (HA) by Streptococcus zooepidemicus strain MW26985 using different substrates and potato peel waste (PPW) as an affordable substrate. First, culture medium components, including carbon and nitrogen sources, were optimized for bacterial HA production. Five different carbon sources (glucose, sucrose, lactose, sago starch, and potato starch, at a concentration of 30 g/L) and three distinct nitrogen sources (peptone, yeast extract, and ammonium sulfate, at a concentration of 10 g/L) were investigated. Glucose, among the carbon sources, and yeast extract, among nitrogen sources, produced the most HA which was determined as 1.41 g/L. Afterward, potato peel sugars were extracted by dilute acid and enzymatic hydrolysis and then employed as a cost-effective carbon source for the growth of S. zooepidemicus. Based on the results, the fermentation process yielded 0.59 g/L HA from potato peel sugars through acid hydrolysis and 0.92 g/L HA from those released by enzymatic hydrolysis. The supplementation of both hydrolyzates with glucose as an additional carbon source enhanced HA production to 0.95 g/L and 1.18 g/L using acidic and enzymatic hydrolyzates, respectively. The cetyltrimethylammonium bromide (CTAB) turbidimetric method was used to evaluate the concentration of HA in the fermentation broth using the colorimetric method. Also, the peaks observed by Fourier transform infrared (FTIR) spectroscopy confirmed that the exopolysaccharide (EPS) was composed of HA. These observations demonstrate that potato peel residues can be a novel alternative as a carbon source for the economical production of HA by S. zooepidemicus.

Fractionation of Extracellular Polymeric Substances by Aqueous Three-Phase Partitioning Systems

Extracellular polymeric substances (EPS) are natural polymers secreted by microorganisms and represent a key chemical for the development of a range of circular economy applications. The production of EPS comes with notable challenges such as downstream processing. In this work, a three-phase partitioning (TPP) system was investigated as a fractionation technique for the separation of polysaccharides and proteins, both present in the EPS culture broth. The effect of the type of phase-forming compounds (alcohol, polymer, or ionic liquid, in combination with salt) and its concentration were evaluated and compared to the results previously obtained with model systems. The recyclability of phase-forming compounds used to form the fractionation platform was assessed by ultrafiltration. The best fractionation of EPS was achieved using a TPP system composed of 23 wt % ethanol and 25% K3C6H5O7 as 82% EPS-PS partitioned to the salt-rich/bottom phase, and 76% EPS-PN was recovered as an interfacial precipitate, which could be readily resolubilized in water. This represented an increase of 1.24 and 2.83-fold in the purity of EPS-PS and EPS-PN, respectively, in relation to the initial feed concentration. Finally, high recovery yields of phase-forming compounds (>99%) and fractionated EPS (>80%) were obtained using ultrafiltration/diafiltration (UF/DF) as the regeneration technique. The substantial fractionation yields, selectivity, and recyclability of the phase-forming compounds confirm the potential of TPP systems in combination with UF/DF as the separation method for real biopolymer mixtures. Key contributions of this study include the demonstration of the applicability of a readily scalable and cost-effective separation technique for the fractionation of EPS from real EPS-containing broths, while also the limitations of prescreening with model systems became clear through the observed deviating trends between model system studies and real broth studies.

Tapping on the Potential of Hyaluronic Acid: from Production to Application

The manufacture, purification, and applications of hyaluronic acid (HA) are discussed in this article. Concerning the growing need for affordable, high-quality HA, it is essential to consider diverse production techniques using renewable resources that pose little risk of cross-contamination. Many microorganisms can now be used to produce HA without limiting the availability of raw materials and in an environmentally friendly manner. The production of HA has been associated with Streptococci A and C, explicitly S. zooepidemicus and S. equi. Different fermentation techniques, including the continuous, batch, fed-batch, and repeated batch culture, have been explored to increase the formation of HA, particularly from S. zooepidemicus. The topic of current interest also involves a complex broth rich in metabolites and residual substrates, intensifying downstream processes to achieve high recovery rates and purity. Although there are already established methods for commercial HA production, the anticipated growth in trade and the diversification of application opportunities necessitate the development of new procedures to produce HA with escalated productivity, specified molecular weights, and purity. In this report, we have enacted the advancement of HA technical research by analyzing bacterial biomanufacturing elements, upstream and downstream methodologies, and commercial-scale HA scenarios.

Biotechnological advances in the synthesis of modified chondroitin towards novel biomedical applications

Chondroitin sulfate (CS) is a well-known glycosaminoglycan present in a large variety of animal tissues, with an outstanding structural heterogeneity mainly related to molecular weight and sulfation pattern. Recently, few microorganisms, eventually engineered, proved able to synthesize the CS biopolymer backbone, composed of d-glucuronic acid and N-acetyl-d-galactosamine linked through alternating β-(1-3)- and β-(1-4)-glycosidic bonds, and secrete the biopolymers generally unsulfated and possibly decorated with other carbohydrates/molecules. Enzyme catalyzed/assisted methods and chemical tailored protocols allowed to obtain a variety of macromolecules not only resembling the natural extractive ones, but even enlarging the access to unnatural structural features. These macromolecules have been investigated for their bioactivity in vitro and in vivo establishing their potentialities in an array of novel applications in the biomedical field. This review aims to present an overview of the advancements in: i) the metabolic engineering strategies and the biotechnological processes towards chondroitin manufacturing; ii) the chemical approaches applied to obtain specific structural features and targeted decoration of the chondroitin backbone; iii) the biochemical and biological properties of the diverse biotechnological-sourced chondroitin polysaccharides reported so far, unraveling novel fields of applications.

System metabolic engineering of Escherichia coli W for the production of 2-ketoisovalerate using unconventional feedstock

Replacing traditional substrates in industrial bioprocesses to advance the sustainable production of chemicals is an urgent need in the context of the circular economy. However, since the limited degradability of non-conventional carbon sources often returns lower yields, effective exploitation of such substrates requires a multi-layer optimization which includes not only the provision of a suitable feedstock but the use of highly robust and metabolically versatile microbial biocatalysts. We tackled this challenge by means of systems metabolic engineering and validated Escherichia coli W as a promising cell factory for the production of the key building block chemical 2-ketoisovalerate (2-KIV) using whey as carbon source, a widely available and low-cost agro-industrial waste. First, we assessed the growth performance of Escherichia coli W on mono and disaccharides and demonstrated that using whey as carbon source enhances it significantly. Second, we searched the available literature and used metabolic modeling approaches to scrutinize the metabolic space of E. coli and explore its potential for overproduction of 2-KIV identifying as basic strategies the block of pyruvate depletion and the modulation of NAD/NADP ratio. We then used our model predictions to construct a suitable microbial chassis capable of overproducing 2-KIV with minimal genetic perturbations, i.e., deleting the pyruvate dehydrogenase and malate dehydrogenase. Finally, we used modular cloning to construct a synthetic 2-KIV pathway that was not sensitive to negative feedback, which effectively resulted in a rerouting of pyruvate towards 2-KIV. The resulting strain shows titers of up to 3.22 ± 0.07 g/L of 2-KIV and 1.40 ± 0.04 g/L of L-valine in 24 h using whey in batch cultures. Additionally, we obtained yields of up to 0.81 g 2-KIV/g substrate. The optimal microbial chassis we present here has minimal genetic modifications and is free of nutritional autotrophies to deliver high 2-KIV production rates using whey as a non-conventional substrate.

Bridging biotechnology and nanomedicine to produce biogreen whey-nanovesicles for intestinal health promotion

New intestinal health-promoting biotechnological nanovesicles were manufactured by combining the main environmental pollutant generated from the cheese-making process, whey, with phospholipid, sodium hyaluronate and dextrin, thus overcoming environmental and medical challenges. An efficient, consolidated and eco-friendly preparation method was employed to manufacture the vesicles and the bioactive whey was obtained by mesophilic dark fermentation without external inoculum through a homolactic pathway, which was operated in such a way as to maximize the production of lactic acid. The biotechnological nutriosomes and hyalonutriosomes were relatively small (∼100 nm) and characterized by the net negative surface charge (>-30 mV). The addition of maltodextrin to the liposomes and especially to the hyalurosomes significantly stabilized the vesicles under acidic conditions, simulating the gastric environment, as their size and polydispersity index were significantly lower (p < 0.05) than those of the other formulations. The vesicles were effectively internalized by Caco-2 cells and protected them against oxidative stress. Nutriosomes promoted the proliferation of Streptococcus salivarius, a human commensal bacterium, to a better extent (p < 0.05) than liposomes and hyalurosomes, as a function of the concentration tested. These findings could open a new horizon in intestinal protection and health promotion by integrating biotechnology, nanomedicine, sustainability principles and bio-circular economy.

Microbial Hyaluronic Acid Production: A Review

Microbial production of hyaluronic acid (HA) is an area of research that has been gaining attention in recent years due to the increasing demand for this biopolymer for several industrial applications. Hyaluronic acid is a linear, non-sulfated glycosaminoglycan that is widely distributed in nature and is mainly composed of repeating units of N-acetylglucosamine and glucuronic acid. It has a wide and unique range of properties such as viscoelasticity, lubrication, and hydration, which makes it an attractive material for several industrial applications such as cosmetics, pharmaceuticals, and medical devices. This review presents and discusses the available fermentation strategies to produce hyaluronic acid.

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.

A Concise Review of Extraction and Characterization of Chondroitin Sulphate from Fish and Fish Wastes for Pharmacological Application

Chondroitin sulphate (CS) is one of the most predominant glycosaminoglycans (GAGs) available in the extracellular matrix of tissues. It has many health benefits, including relief from osteoarthritis, antiviral properties, tissue engineering applications, and use in skin care, which have increased its commercial demand in recent years. The quest for CS sources exponentially increased due to several shortcomings of porcine, bovine, and other animal sources. Fish and fish wastes (i.e., fins, scales, skeleton, bone, and cartilage) are suitable sources of CS as they are low cost, easy to handle, and readily available. However, the lack of a standard isolation and characterization technique makes CS production challenging, particularly concerning the yield of pure GAGs. Many studies imply that enzyme-based extraction is more effective than chemical extraction. Critical evaluation of the existing extraction, isolation, and characterization techniques is crucial for establishing an optimized protocol of CS production from fish sources. The current techniques depend on tissue hydrolysis, protein removal, and purification. Therefore, this study critically evaluated and discussed the extraction, isolation, and characterization methods of CS from fish or fish wastes. Biosynthesis and pharmacological applications of CS were also critically reviewed and discussed. Our assessment suggests that CS could be a potential drug candidate; however, clinical studies should be conducted to warrant its effectiveness.

A Review on Current Strategies for Extraction and Purification of Hyaluronic Acid

Since it is known that hyaluronic acid contributes to soft tissue growth, elasticity, and scar reduction, different strategies of producing HA have been explored in order to satisfy the current demand of HA in pharmaceutical products and formulations. The current interest deals with production via bacterial and yeast fermentation and extraction from animal sources; however, the main challenge is the right extraction technique and strategy since the original sources (e.g., fermentation broth) represent a complex system containing a number of components and solutes, which complicates the achievement of high extraction rates and purity. This review sheds light on the main pathways for the production of HA, advantages, and disadvantages, along with the current efforts in extracting and purifying this high-added-value molecule from different sources. Particular emphasis has been placed on specific case studies attempting production and successful recovery. For such works, full details are given together with their relevant outcomes.

Hyaluronic acid production and purification techniques: a review

Hyaluronic acid (HA) is an exopolysaccharide extracted from several sources such as rooster combs, umbilical cords and microorganisms. A system that controls temperature, agitation and aeration of bacterial cultures could make the HA production autonomous. Therefore, HA of microbial origin is set to take over alternative methods of production. Furthermore, the use of different nutrient sources in the culture medium and the purification stage applied in the process can cause physicochemical alterations on the bioproduct. For instance, structural modifications that change the molecular weight of HA may alter its elastic and viscoelastic properties. As a result, HA synthesized by microbes has applications in pharmacology, biotechnology, and tissue engineering. Our aim here, is to show the vast range of applications by compiling articles and patents on the culture media or genetic modifications of microorganisms that synthesize HA.

Heterologous production of chondroitin

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Chondroitin sulfate (CS) is a glycosaminoglycan with a growing variety of applications.

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CS can be produced from microbial fermentation of native or engineered strains.

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Synthetic biology tools are being used to improve CS yields in different hosts.

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Integrated polymerization and sulfation can generate cost-effective CS.

Chondroitin sulfate (CS) is a glycosaminoglycan with a broad range of applications being a popular dietary supplement for osteoarthritis. Usually, CS is extracted from animal sources. However, the known risks of animal products use have been driving the search for alternative methods and sources to obtain this compound. Several pathogenic bacteria naturally produce chondroitin-like polysaccharides through well-known pathways and, therefore, have been the basis for numerous studies that aim to produce chondroitin using non-pathogenic hosts. However, the yields obtained are not enough to meet the high demand for this glycosaminoglycan. Metabolic engineering strategies have been used to construct improved heterologous hosts. The identification of metabolic bottlenecks and regulation points, and the screening for efficient enzymes are key points for constructing microbial cell factories with improved chondroitin yields to achieve industrial CS production. The recent advances on enzymatic and microbial strategies to produce non-animal chondroitin are herein reviewed. Challenges and prospects for future research are also discussed.

Bored Coffee Beans for Production of Hyaluronic Acid by Streptococcus zooepidemicus

Bored coffee beans (BCBs) are the residues left from the pest Hypothenemus hampei that attacks coffee crops, resulting in enormous economic losses. The bioconversion of monosaccharides from BCBs into hyaluronic acid (HA) is appealing both for using the residues and given the high commercial value of HA. This study dealt with the production of HA using Streptococcus zooepidemicus by employing either acid (AcH) or enzymatic (EnH) hydrolyzates from BCBs. The highest release of monosaccharides (evaluated using surface response methodology) was obtained with EnH (36.4 g/L); however, S. zooepidemicus produced more HA (1.5 g/L) using AcH compared to EnH. Hydrolyzates from acetone-extracted BCBs yielded 2.7 g/L of HA, which is similar to the amount obtained using a synthetic medium (2.8 g/L). This report demonstrates the potential of hydrolyzates from bored coffee beans to produce HA by S. zooepidemicus.

Physicochemical characterization and in vitro antioxidant activity of hyaluronic acid produced by Streptococcus zooepidemicus CCT 7546

Hyaluronic acid (HA) is a biopolymer with applications in different areas such as medicine and cosmetics. HA is currently either isolated from animal sources or produced by microbial fermentation. Animal HA presents some disadvantages such as high cost and risk of viral cross-species or another infectious agent. In the present study, we evaluated the physicochemical characteristics and in vitro antioxidant capacity of HA produced by Streptococcus zooepidemicus CCT 7546. In addition, commercial sodium hyaluronate (SH) from an animal source was used as control. The microbial HA yield after purification was 69.8 mg/L. According to Fourier transform infrared spectroscopy, it was seen that bacterial and animal HA spectra are overlapped. The thermogravimetric analysis revealed that microbial HA was more stable than its equivalent from the animal source. However, scanning electron microscopy indicates that the purification method used in the animal product was more effective. Microbial HA showed activity in total antioxidant capacity (14.02 ± 0.38%), reducing power (18.18 ± 6.43%), DPPH radical-scavenging (5.57 ± 0.23 kmol TE/g), and hydroxyl radical-scavenging (28.39 ± 2.40%) tests. Therefore, in vitro antioxidant tests demonstrated that the antioxidant action mechanism occurs through scavenging reactive oxygen species (ROS) and donating electrons/hydrogen atoms.

Sucrose-modified iron nanoparticles for highly efficient microbial production of hyaluronic acid by Streptococcus zooepidemicus

Nanoparticles (NPs) were hypothesized to enhance fermentation processes and assist microorganisms in producing valuable biopolymers. Donors of trace iron, i.e., FeSO₄·7H₂O, zero-valence iron nanoparticles (Fe NPs), and ferric oxide nanoparticles (α-Fe₂O₃ NPs), were tested to study the impact on hyaluronic acid (HA) production. The bioprocess with the addition of 30 mg/L Fe NPs produced higher HA than the other groups. However, Fe NPs were limited by the synergistic effect of geomagnetism and high surface energy, resulting in obvious agglomeration behavior. To address this, we developed novel sucrose-modified iron nanoparticles (SM-Fe NPs), which showed effective improvement of dispersion and agglomeration. Concerning the SM-Fe NP additives, an adequate supply of nutrients and trace elements provided sufficient substrates and energy for the reproduction of Streptococcus zooepidemicus. Furthermore, the highest HA production with the addition of 30 mg/L SM-Fe NPs was 0.226 g/L, and the dry weight of the produced HA increased 3.28 times compared with the control group (0.069 g/L). This work significantly improved HA production and presented promising opportunities for industrial production.

Cheese whey permeate fermentation by Kluyveromyces lactis: a combined approach to wastewater treatment and bioethanol production

Cheese whey is a dairy industry by-product responsible for serious environmental problems. Its fermentation would allow reducing its environmental impact and producing, at the same time, high-value products, hence ensuring cleaner production. Batch fermentations of cheese whey permeate, either as such or 1.5-fold or twice-concentrated, by Kluyveromyces lactis CBS2359 were performed in flasks with or without agitation to select the best conditions to produce simultaneously ethanol and biomass with high β-galactosidase activity. In shake cultures, the highest ethanol concentration (15.0 g L^-1), yield on consumed lactose (0.47 g g^-1) and productivity (0.31 g L^-1 h^-1), were obtained on cheese whey permeate as such, corresponding to 87.4% fermentation efficiency, but β-galactosidase activity was disappointing (449.3-680.0 U g^-1). In static cultures on twice-concentrated whey permeate, despite a decrease in fermentation efficiency and yield, ethanol production increased by 48% and β-galactosidase activity by no less than 209-367%. Therefore, cheese whey should be considered an alternative feedstock rather than an undesirable dairy industry by-product.

Bioconversion of Fish Discards through the Production of Lactic Acid Bacteria and Metabolites: Sustainable Application of Fish Peptones in Nutritive Fermentation Media

In the current work, we study the capacity of 30 peptones obtained by enzyme proteolysis of ten discarded fish species (hake, megrim, red scorpionfish, pouting, mackerel, gurnard, blue whiting, Atlantic horse mackerel, grenadier, and boarfish) to support the growth and metabolite production of four lactic acid bacteria (LAB) of probiotic and technological importance. Batch fermentations of Lactobacillus plantarum, L. brevis, L. casei, and Leuconostoc mesenteroides in most of the media formulated with fish peptones (87% of the cases) led to similar growths (quantified as dry-weight biomass and viable cells) and metabolites (mainly lactic acid) than in commercial control broth (MRS). Comparisons among cultures were performed by means of the parameters obtained from the mathematical fittings of experimental kinetics to the logistic equation. Modelling among experimental and predicted data from each bioproduction was generally accurate. A simple economic assessment demonstrated the profitability achieved when MRS is substituted by media formulated with fish discards: a 3-4-fold reduction of costs for LAB biomass, viable cells formation, and lactic and acetic acid production. Thus, these fish peptones are promising alternatives to the expensive commercial peptones as well as a possible solution to valorize discarded fish biomasses and by-products.

Deciphering the role of dissolved oxygen and N-acetyl glucosamine in governing higher molecular weight hyaluronic acid synthesis in Streptococcus zooepidemicus cell factory

The present study is focused on systematic process and kinetic investigation of hyaluronic acid (HA) production strategy unraveling the role of dissolved oxygen (DO) and N-acetyl glucosamine (GlcNAc) towards the enhancement of HA titer and its molecular weight. Maintaining excess DO levels (10-40% DO) through DO-stat control and the substitution of GlcNAc at a range (5-20 g/L) with glucose (Glc) critically influenced HA production. DO-stat control strategy yielded a promising HA titer (2.4 g/L) at 40% DO concentration. Controlling DO level at 20% (DO-stat) was observed to be optimum resulting in a significant HA production (2.1 g/L) and its molecular weight ranging 0.98-1.45 MDa with a consistent polydispersity index (PDI) (1.57-1.69). Substitution of GlcNAc with Glc at different proportions explicitly addressed the metabolic trade-off between HA titer and its molecular weight. GlcNAc substitution positively influenced the molecular weight of HA. The highest HA molecular weight (2.53 MDa) of two-fold increase compared with glucose as sole carbon substrate and narrower PDI (1.35 ± 0.18) was achieved for the 10:20 (Glc:GlcNAc) proportion. A novice attempt on modeling the uptake of dual substrates (Glc and GlcNAc) by Streptococcus zooepidemicus for HA production was successfully accomplished using double Andrew's growth model and the kinetic parameters were estimated reliably.

Growth profiling, kinetics and substrate utilization of low-cost dairy waste for production of β-cryptoxanthin by Kocuria marina DAGII

The dairy industry produces enormous amount of cheese whey containing the major milk nutrients, but this remains unutilized all over the globe. The present study investigates the production of β-cryptoxanthin (β-CRX) by Kocuria marina DAGII using cheese whey as substrate. Response surface methodology (RSM) and an artificial neural network (ANN) approach were implemented to obtain the maximum β-CRX yield. Significant factors, i.e. yeast extract, peptone, cheese whey and initial pH, were the input variables in both the optimizing studies, and β-CRX yield and biomass were taken as output variables. The ANN topology of 4-9-2 was found to be optimum when trained with a feed-forward back-propagation algorithm. Experimental values of β-CRX yield (17.14 mg l-1) and biomass (5.35 g l-1) were compared and ANN predicted values (16.99 mg l-1 and 5.33 g l-1, respectively) were found to be more accurate compared with RSM predicted values (16.95 mg l-1 and 5.23 g l-1, respectively). Detailed kinetic analysis of cellular growth, substrate consumption and product formation revealed that growth inhibition took place at substrate concentrations higher than 12% (v/v) of cheese whey. The Han and Levenspiel model was the best fitted substrate inhibition model that described the cell growth in cheese whey with an R2 and MSE of 0.9982% and 0.00477%, respectively. The potential importance of this study lies in the development, optimization and modelling of a suitable cheese whey supplemented medium for increased β-CRX production.

Efficient production of high-molecular-weight hyaluronic acid with a two-stage fermentation

A two-stage fermentation process with a segmented control strategy provides high-level synthesis in both HA titer and molecular weight.

Engineering aspects of microbial exopolysaccharide production

Although the ability to secrete exopolysaccharides (EPS) is widespread among microorganisms, only a few bacterial (e.g. xanthan, levan, dextran) and fungal (e.g. pullulan) EPS have reached full commercialization. During the last years, other microbial EPS producers have been the subject of extensive research, including endophytes, extremophiles, microalgae and Cyanobacteria, as well as mixed microbial consortia. Those studies have demonstrated the great potential of such microbial systems to generate biopolymers with novel chemical structures and distinctive functional properties. In this work, an overview of the bioprocesses developed for EPS production by the wide diversity of reported microbial producers is presented, including their development and scale-up. Bottlenecks that currently hinder microbial EPS development are identified, along with future prospects for further advancement.

Glycosaminoglycans from marine sources as therapeutic agents

Glycosaminoglycans (GAGs) in marine animals are different to those of terrestrial organisms, mainly in terms of molecular weight and sulfation. The therapeutic properties of GAGs are related to their ability to interact with proteins, which is very much influenced by sulfation position and patterns. Since currently GAGs cannot be chemically synthesized, they are sourced from natural products, with high intra- but also inter-species variability, in terms of chain length, disaccharide composition and sulfation pattern. Consequently, sulfated GAGs are the most interesting molecules in the marine environment and constitute the focus of the present review. In particular, chondroitin sulfate (CS) appears as the most promising compound. CS-E chains [GlcA-GalNAc(4S,6S)] extracted from squid possess antiviral and anti-metastatic activities and seem to impart signalling properties and improve the mechanical performance of cartilage engineering constructs; Squid CS-E and octopus CS-K [GlcA(3S)-GalNAc(4S)], dermatan sulfate (DS) from sea squirts [-iK units, IdoA(3S)-GalNAc(4S)] and sea urchins [-iE units, IdoA-GalNAc(4S,6S)] and hybrids CS/DS from sharks (-B/iB [GlcA/IdoA(2S)-GalNAc(4S)], -D/iD [GlcA/IdoA(2S)-GalNAc(6S)] and -E/iE units [GlcA/IdoA-GalNAc(4S,6S)]) promote neurite outgrowth and could be valuable materials for nerve regeneration. Also displaying antiviral and anti-metastatic properties, a rare CS with fucosylated branches isolated from sea cucumbers is an anticoagulant and anti-inflammatory agent. In this same line, marine heparin extracted from shrimp and sea squirt has proven anti-inflammatory properties, with the added advantage of decreased risk of bleeding because of its low anticoagulant activity.

Enhancement and inhibition effects on the corneal permeability of timolol maleate: Polymers, cyclodextrins and chelating agents

This study investigates how both bioadhesive polymers (chitosan, hyaluronic acid and alginate) and permeability enhancers (ethylene glycol- bis(2-aminoethylether)- N, N, N', N'- tetraacetic acid (EGTA) and hydroxypropyl-ß-cyclodextrin) influence the permeability of the anti-glaucoma drug timolol maleate through ex vivo bovine corneas. Our results showed that only the permeability enhancers alone were able to increase drug permeability, whereas the polymers significantly reduced drug permeation, and however, they increased the pre-corneal residence of timolol. Ternary systems (polymer-enhancer-drug) showed a reduced drug permeability compared to the polymers alone. Fluorescence microscopy analysis of the epithelium surface confirmed there was no evidence of epithelial disruption caused by these formulations, suggesting that polymer-enhancer interactions reduce drug solubilization and counteract the disruptive effect of the permeability enhancers on the surface of the cornea. Further mucoadhesive tests, revealed a stable interaction of chitosan and hyaluronic acid with the epithelium, while alginate showed poor mucoadhesive properties. The differences in mucoadhesion correlated with the permeability of timolol maleate observed, i.e. formulations containing mucoadhesive polymers showed lower drug permeabilities. The results of the present study indicate polymers acting as an additional barrier towards drug permeability which is even more evident in the presence of permeability enhancers like EGTA and hydroxypropyl-ß-cyclodextrin. Then, this study highlights the need to adequately select additives intended for ocular applications since interactions between them can have opposite results to what expected in terms of drug permeability.

Improvement Production of Hyaluronic Acid by Streptococcus zooepidemicus in Sugarcane Molasses

Microbial hyaluronic acid (HA) production has been preferred rather than extraction from animal tissue for medical and cosmetic applications. In this context, to obtain an economically competitive HA production by Streptococcus zooepidemicus, culture conditions were studied to improve the polymer production in sugarcane molasses. The highest HA production by S. zooepidemicus ATCC 39920 achieved was 2.825 g. L^-1 in a 4.5 L bioreactor with controlled pH (8.0) and medium containing molasses (85.35 g.L^-1 total sugar) pretreated with activated charcoal and yeast extract (50 g.L^-1). The HA produced exhibited a high molecular weight of 1.35 × 10³ kDa and the DPPH radical scavenging activity of the polymer at 1 g.L^-1 was 41 %. The FTIR and UV-Vis spectra showed no substantial differences in the spectral pattern between produced and standard HA. This study is a promising strategy for sugarcane molasses application by producing high value-added products such as hyaluronic acid.