Beneficial Effect of Acetic Acid on the Xylose Utilization and Bacterial Cellulose Production by Gluconacetobacter xylinus

Identification of Gluconacetobacter xylinus LYP25 and application to bacterial cellulose production in biomass hydrolysate with acetic acid

Bacterial cellulose (BC) is a remarkable biomacromolecule with potential applications in food, biomedical, and other industries. However, the low economic feasibility of BC production processes hinders its industrialization. In our previous work, we obtained candidate strains with improved BC production through random mutations in Gluconacetobacter. In this study, the molecular identification of LYP25 strain with significantly improved productivity, the development of chestnut pericarp (CP) hydrolysate medium, and its application in BC fermentation were performed for cost-effective BC production process. As a result, the mutant strain was identified as Gluconacetobacter xylinus. The CP hydrolysate (CPH) medium contained 30 g/L glucose with 0.4 g/L acetic acid, whereas other candidates known to inhibit fermentation were not detected. Although acetic acid is generally known as a fermentation inhibitor, it improves the BC production by G. xylinus when present within about 5 g/L in the medium. Fermentation of G. xylinus LYP25 in CPH medium resulted in 17.3 g/L BC, a 33 % improvement in production compared to the control medium, and BC from the experimental and control groups had similar physicochemical properties. Finally, the overall process of BC production from biomass was evaluated and our proposed platform showed the highest yield (17.9 g BC/100 g biomass).

Potential use of olive oil mill wastewater for bacterial cellulose production

In this study, olive oil mill wastewater (OOMW), an important waste in the Mediterranean basin, was evaluated to produce bacterial cellulose (BC). For this purpose, the effects of different ratios of OOMW fractions (25–100%) and some additional nutrients (yeast extract, peptone and Hestrin-Schramm medium (HS) components) on BC productions were investigated. Unsupplemented OOMW medium (75% and 100%) yielded as much as BC obtained in HS medium (0.65 g/L), while enrichment of OOMW medium (%100) with yeast extract (5 g/L) and peptone (5 g/L) increased the amount of BC by 5.5 times, reaching to 5.33 g/L. In addition, produced BCs were characterized by FT-IR, TGA, XRD and SEM analyses. BC from OOMW medium (100% OOMW with supplementation) has a high thermal decomposition temperature (316.8°C), whereas it has lower crystallinity index (57%). According to the FT-IR analysis, it was observed that the components of OOMW might be absorbed by BCs. Thus, higher yield productions of BCs from OOMW media compared to BC obtained from HS medium indicate that olive oil industry wastes can be integrated into BC production for industrial applications.

Ultrasound-assisted dilute acid hydrolysis for production of essential oils, pectin and bacterial cellulose via a citrus processing waste biorefinery

An orange peel waste biorefinery was developed employing a design of experiments approach to optimize the ultrasound-assisted dilute acid hydrolysis process applied for production of useful commodities. Central composite design-based response surface methodology was used to approximate the combined effects of process parameters in simultaneous production of essential oils, pectin and a sugar-rich hydrolyzate. Application of a desirability function determined the optimal conditions required for maximal production efficiency of essential oils, pectin and sugars as 5.75% solid loading, 1.21% acid concentration and 34.2 min duration. Maximum production yields of 0.12% w/w essential oils, 45% w/w pectin and 40% w/w sugars were achieved under optimized conditions in lab- and pilot-scale facilities. The hydrolyzate formed was applied in bacterial cellulose fermentations producing 5.82 g biopolymer per 100 g waste. Design of experiments was efficient for process analysis and optimization providing a systems platform for the study of biomass-based biorefineries.

Bacterial cellulose: From production optimization to new applications

Bacterial cellulose (BC) is a biopolymer of great significance to the medical, pharmaceutical, and food industries. However, a high concentration of carbon sources (mainly glucose) and other culture media components is usually required to promote a significant yield of BC, which increases the bioprocess cost. Thus, optimization strategies (conventional or statistical) have become relevant for the cost-effective production of bacterial cellulose. Additionally, this biopolymer may present new properties through modifications with exogenous compounds. The present review, explores and discusses recent studies (last five years) that report the optimization of BC production and its yield as well as in situ and ex situ modifications, resulting in improved mechanical, antioxidant, and antimicrobial properties of BC for new applications.

Insights into Bacterial Cellulose Biosynthesis from Different Carbon Sources and the Associated Biochemical Transformation Pathways in Komagataeibacter sp. W1

Cellulose is the most abundant and widely used biopolymer on earth and can be produced by both plants and micro-organisms. Among bacterial cellulose (BC)-producing bacteria, the strains in genus Komagataeibacter have attracted wide attention due to their particular ability in furthering BC production. Our previous study reported a new strain of genus Komagataeibacter from a vinegar factory. To evaluate its capacity for BC production from different carbon sources, the present study subjected the strain to media spiked with 2% acetate, ethanol, fructose, glucose, lactose, mannitol or sucrose. Then the BC productivity, BC characteristics and biochemical transformation pathways of various carbon sources were fully investigated. After 14 days of incubation, strain W1 produced 0.040⁻1.529 g L-1 BC, the highest yield being observed in fructose. Unlike BC yields, the morphology and microfibrils of BCs from different carbon sources were similar, with an average diameter of 35⁻50 nm. X-ray diffraction analysis showed that all membranes produced from various carbon sources had 1⁻3 typical diffraction peaks, and the highest crystallinity (i.e., 90%) was found for BC produced from mannitol. Similarly, several typical spectra bands obtained by Fourier transform infrared spectroscopy were similar for the BCs produced from different carbon sources, as was the Iα fraction. The genome annotation and Kyoto Encyclopedia of Genes and Genomes analysis revealed that the biochemical transformation pathways associated with the utilization of and BC production from fructose, glucose, glycerol, and mannitol were found in strain W1, but this was not the case for other carbon sources. Our data provides suggestions for further investigations of strain W1 to produce BC by using low molecular weight sugars and gives clues to understand how this strain produces BC based on metabolic pathway analysis.

Biochemical and cellular properties of Gluconacetobacter xylinus cultures exposed to different modes of rotating magnetic field

The aim of the present study was to evaluate the impact of a rotating magnetic field (RMF) on cellular and biochemical properties of Gluconacetobacter xylinus during the process of cellulose synthesis by these bacteria. The application of the RMF during bacterial cellulose (BC) production intensified the biochemical processes in G. xylinus as compared to the RMF-unexposed cultures. Moreover, the RMF had a positive impact on the growth of cellulose-producing bacteria. Furthermore, the application of RMF did not increase the number of mutants unable to produce cellulose. In terms of BC production efficacy, the most favorable properties were found in the setting where RMF generator was switched off for the first 72 h of cultivation and switched on for the further 72 h. The results obtained can be used in subsequent studies concerning the optimization of BC production using different types of magnetic fields including RMF, especially.

Using In situ Dynamic Cultures to Rapidly Biofabricate Fabric-Reinforced Composites of Chitosan/Bacterial Nanocellulose for Antibacterial Wound Dressings

Bacterial nano-cellulose (BNC) is considered to possess incredible potential in biomedical applications due to its innate unrivaled nano-fibrillar structure and versatile properties. However, its use is largely restricted by inefficient production and by insufficient strength when it is in a highly swollen state. In this study, a fabric skeleton reinforced chitosan (CS)/BNC hydrogel with high mechanical reliability and antibacterial activity was fabricated by using an efficient dynamic culture that could reserve the nano-fibrillar structure. By adding CS in culture media to 0.25-0.75% (w/v) during bacterial cultivation, the CS/BNC composite hydrogel was biosynthesized in situ on a rotating drum composed of fabrics. With the proposed method, BNC biosynthesis became less sensitive to the adverse antibacterial effects of CS and the production time of the composite hydrogel with desirable thickness could be halved from 10 to 5 days as compared to the conventional static cultures. Although, its concentration was low in the medium, CS accounted for more than 38% of the CS/BNC dry weight. FE-SEM observation confirmed conservation of the nano-fibrillar networks and covering of CS on BNC. ATR-FTIR showed a decrease in the degree of intra-molecular hydrogen bonding and water absorption capacity was improved after compositing with CS. The fabric-reinforced CS/BNC composite exhibited bacteriostatic properties against Escherichia coli and Staphylococcus aureus and significantly improved mechanical properties as compared to the BNC sheets from static culture. In summary, the fabric-reinforced CS/BNC composite constitutes a desired candidate for advanced wound dressings. From another perspective, coating of BNC or CS/BNC could upgrade the conventional wound dressings made of cotton gauze to reduce pain during wound healing, especially for burn patients.

Evaluating the possibility of using acetone-butanol-ethanol (ABE) fermentation wastewater for bacterial cellulose production by Gluconacetobacter xylinus

To reduce the cost of bacterial cellulose (BC) production, the possibility of using acetone-butanol-ethanol (ABE) fermentation wastewater with high COD value (18 050 mg l(-1) ) for BC production by Gluconacetobacter xylinus was evaluated. After 7 days of fermentation, the highest BC yield (1·34 g l(-1) ) was obtained. The carbon sources including sugars (glucose and xylose), organic acids (acetic acid and butyric acid) and alcohol compounds (ethanol and butanol) were utilized by G. xylinus simultaneously during fermentation. Although the COD decrease ratio (about 14·7%) was low, the highest BC yield on COD consumption (56·2%, g g(-1) ) was relatively high and the remaining wastewater could be used for further BC fermentation. Besides, the environment of ABE fermentation wastewater showed small influence on the BC structure by comparison with the BC products obtained in traditional HS medium using field emission scanning electron microscope (FE-SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Overall, ABE fermentation wastewater is one promising substrate for BC production.

SIGNIFICANCE AND IMPACT OF THE STUDY

The possibility of using acetone-butanol-ethanol (ABE) fermentation wastewater for bacterial cellulose (BC) production by Gluconacetobacter xylinus was evaluated in this study. This is the first time that ABE fermentation wastewater was used as substrate for BC fermentation. The results provide detail information of metabolism of G. xylinus in ABE fermentation wastewater and the influence of wastewater environment on the structure of BC samples. Overall, this bioconversion could reduce the cost of BC production greatly.

Utilization of corncob acid hydrolysate for bacterial cellulose production by Gluconacetobacter xylinus

In this study, corncob acid hydrolysate was used as a substrate for bacterial cellulose (BC) production by Gluconacetobacter xylinus. After 2 weeks' static fermentation, a BC yield of 4 g/L could be obtained. Both effects of medium composition and fermentation condition on the BC production were evaluated. Most extra substrates (carbon and nitrogen sources) except mannitol, butyric acid, and levulinic acid showed no effect on the improvement of BC yield. Fermentation condition including fermentation mode, inoculation concentration, and initial pH showed certain influence on the BC yield and thus should be well controlled. The analysis by field emission scanning electron microscope (FE-SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) showed that the BC sample had obvious nano-network structure, clear functional groups that were found in cellulose, and relatively high crystallinity and crystallinity index value. Moreover, the BC sample had great water-holding capacity. Overall, corncob acid hydrolysate could be one promising substrate for BC production.