Enhanced ultrafine nanofibril biosynthesis of bacterial nanocellulose using a low-cost material by the adapted strain of Komagataeibacter xylinus MSKU 12

Better under stress: Improving bacterial cellulose production by Komagataeibacter xylinus K2G30 (UMCC 2756) using adaptive laboratory evolution

Among naturally produced polymers, bacterial cellulose is receiving enormous attention due to remarkable properties, making it suitable for a wide range of industrial applications. However, the low yield, the instability of microbial strains and the limited knowledge of the mechanisms regulating the metabolism of producer strains, limit the large-scale production of bacterial cellulose. In this study, Komagataeibacter xylinus K2G30 was adapted in mannitol based medium, a carbon source that is also available in agri-food wastes. K. xylinus K2G30 was continuously cultured by replacing glucose with mannitol (2% w/v) for 210 days. After a starting lag-phase, in which no changes were observed in the utilization of mannitol and in bacterial cellulose production (cycles 1–25), a constant improvement of the phenotypic performances was observed from cycle 26 to cycle 30, accompanied by an increase in mannitol consumption. At cycle 30, the end-point of the experiment, bacterial cellulose yield increased by 38% in comparision compared to cycle 1. Furthermore, considering the mannitol metabolic pathway, D-fructose is an intermediate in the bioconversion of mannitol to glucose. Based on this consideration, K. xylinus K2G30 was tested in fructose-based medium, obtaining the same trend of bacterial cellulose production observed in mannitol medium. The adaptive laboratory evolution approach used in this study was suitable for the phenotypic improvement of K. xylinus K2G30 in bacterial cellulose production. Metabolic versatility of the strain was confirmed by the increase in bacterial cellulose production from D-fructose-based medium. Moreover, the adaptation on mannitol did not occur at the expense of glucose, confirming the versatility of K2G30 in producing bacterial cellulose from different carbon sources. Results of this study contribute to the knowledge for designing new strategies, as an alternative to the genetic engineering approach, for bacterial cellulose production.

Conversion of golden oyster mushroom, Pleurotus citrinopileatus to sugar syrup using enzymatic hydrolysis as a substrate for novel bacterial cellulose (Nata) fermentation

Enzymatic hydrolysis of the golden oyster mushroom (Pleurotus citrinopileatus) generated a new bacterial cellulose (BC). The sugar syrup obtained from the hydrolysis of mushroom powder by commercial enzymes gave maximum total soluble solids (TSS) content at 8.83 ± 0.29°Brix, while 8.82 ± 0.06 mg GAE/g substrate of total phenolic content (TPC) was obtained when using initial substrate and enzyme concentrations at 125 g/L and 5.0%, respectively. Glutamic acid, aspartic acid, alanine and valine were determined as the main amino acids found in P. citrinopileatus hydrolysis at 524.74 ± 0.03, 247.09 ± 0.04, 176.82 ± 0.07 and 174.57 ± 0.01 mg/100 g sample, respectively. Thin-layer chromatography revealed that the obtained sugar syrup was glucose. The hydrolyzed mushroom fermented with Komagataeibacter xylinus AGR 60 at 30 ± 2 °C for 9 days produced optimal conditions at 4.0°Brix of the initial mushroom syrup and 12.0% (v/v) of the starter culture. Maximum BC thickness was 0.88 ± 0.03 cm with 7.90 ± 0.07 g dry weight, equivalent to 39.50 ± 0.35 g/L and 4.39 ± 0.04 g/L/day for BC production (P) and BC production rate (R p), respectively. The obtained BC was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, small-angle X-ray scattering and wide-angle X-ray diffraction. These showed the structure and functional properties as a natural source of fiber from the fermentation of a novel substrate.

Bioprocess development for bacterial cellulose biosynthesis by novel Lactiplantibacillus plantarum isolate along with characterization and antimicrobial assessment of fabricated membrane

Bacterial cellulose (BC) is an ecofriendly biopolymer with diverse commercial applications. Its use is limited by the capacity of bacterial production strains and cost of the medium. Mining for novel organisms with well-optimized growth conditions will be important for the adoption of BC. In this study, a novel BC-producing strain was isolated from rotten fruit samples and identified as Lactiplantibacillus plantarum from 16S rRNA sequencing. Culture conditions were optimized for supporting maximal BC production using one variable at a time, Plackett–Burman design, and Box Behnken design approaches. Results indicated that a modified Yamanaka medium supported the highest BC yield (2.7 g/l), and that yeast extract, MgSO₄, and pH were the most significant variables influencing BC production. After optimizing the levels of these variables through Box Behnken design, BC yield was increased to 4.51 g/l. The drug delivery capacity of the produced BC membrane was evaluated through fabrication with sodium alginate and gentamycin antibiotic at four different concentrations. All membranes (normal and fabricated) were characterized by scanning electron microscope, Fourier transform-infrared spectroscopy, X-ray diffraction, and mechanical properties. The antimicrobial activity of prepared composites was evaluated by using six human pathogens and revealed potent antibacterial activity against Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, and Streptococcus mutans, with no detected activity against Pseudomonas aeruginosa and Candida albicans.

Influence of cellulose nanocrystal addition on the production and characterization of bacterial nanocellulose

Bacterial nanocellulose (BNC) is characterized by high purity and excellent mechanical properties; however, its production is constrained by low yield. Therefore, efforts aimed at improving its yield and material properties are imperative. This study investigated the effect of adding different concentrations (0%, 0.5%, and 1.0%) of cellulose nanocrystal (CNC) in Hestrin-Schramm modified medium on the yield and properties of BNC produced by Komagataeibacter sp. SFCB22-18. The BNC yield increased as following an increase in added CNC concentration. Also, the morphology, structure, crystallinity, thermal stability, and mechanical properties of BNC improved after CNC incorporation. A low CNC concentration (0.1%) favored mechanical strength, whereas 0.5% gave the optimum morphology, structural, and thermal stability. These results showed that modifying BNC with CNC could help increase yield and improve its properties, and thus; the potentiality of BNC in various applications would be much enhanced.

Research progress of the biosynthetic strains and pathways of bacterial cellulose

Bacterial cellulose is a glucose biopolymer produced by microorganisms and widely used as a natural renewable and sustainable resource in the world. However, few bacterial cellulose-producing strains and low yield of cellulose greatly limited the development of bacterial cellulose. In this review, we summarized the 30 cellulose-producing bacteria reported so far, including the physiological functions and the metabolic synthesis mechanism of bacterial cellulose, and the involved three kinds of cellulose synthases (type I, type II, and type III), which are expected to provide a reference for the exploration of new cellulose-producing microbes.

The role of genetic manipulation and in situ modifications on production of bacterial nanocellulose: A review

Natural polysaccharides are well-known biomaterials because of their availability and low-cost, with applications in diverse fields. Cellulose, a renowned polysaccharide, can be obtained from different sources including plants, algae, and bacteria, but recently much attention has been paid to the microorganisms due to their potential of producing renewable compounds. In this regard, bacterial nanocellulose (BNC) is a novel type of nanocellulose material that is commercially synthesized mainly by Komagataeibacter spp. Characteristics such as purity, porosity, and remarkable mechanical properties made BNC a superior green biopolymer with applications in pharmacology, biomedicine, bioprocessing, and food. Genetic manipulation of BNC-producing strains and in situ modifications of the culturing conditions can lead to BNC with enhanced yield/productivity and properties. This review mainly highlights the role of genetic engineering of Komagataeibacter strains and co-culturing of bacterial strains with additives such as microorganisms and nanomaterials to synthesize BNC with improved functionality and productivity rate.

Application of raw starch degrading enzyme from Laceyella sacchari LP175 for development of bacterial cellulose fermentation using colored rice as substrate

Brown and black rice substrates were applied for sugar syrup production by the hydrolysis of raw starch degrading enzyme (RSDE) from Laceyella sacchari LP175 (300 U/mL) and commercial glucoamylase (GA, 2.0 U/mL) at 50 °C for 12 h using a simplex centroid mixture design. Results indicated that 300 g/L of substrates, consisting of 255 g/L Leum Pua glutinous rice and 45 g/L Black Jasmine rice, gave the highest sugar syrup production at 124.6 ± 2.52 g/L with 2.00 ± 0.05 mg GAE/mL of total phenolic content (TPC), equivalent to 0.42 ± 0.01 g/g rice sample and 6.67 ± 0.15 mg GAE/g rice sample, respectively. The obtained sugar syrup was used as the substrate for production of bacterial cellulose (Nata) by Komagataeibacter xylinus AGR 60 in a plastic tray at room temperature for 9 days. The fermentation medium containing 200 mL of rice syrup (25 g/L), 2.0 g of ammonium sulfate [(NH₄)₂SO₄] and 0.4 mL glacial acetic acid yielded 1.1 ± 0.08 cm thickness with 8.15 ± 0.12 g of dry weight. The obtained bacterial cellulose from colored rice was characterized compared with bacterial cellulose from the conventional coconut juice by scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FTIR) which demonstrated that the sugar syrup from colored rice could use as substrate for a novel bacterial cellulose as a healthy product in the future through microbial enzyme technological process.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02673-3.

TEMPO-oxidized cellulose nanofibril film from nano-structured bacterial cellulose derived from the recently developed thermotolerant Komagataeibacter xylinus C30 and Komagataeibacter oboediens R37-9 strains

Bacterial cellulose (BC), prepared from two recently developed thermotolerant bacterial strains (Komagataeibacter xylinus C30 and Komagataeibacter oboediens R37-9), were used as a raw material to synthesize nanofibril films. Field-emission scanning electron microscope (FE-SEM) observations confirmed the ultrafine nano-structure of BC pellicle (BCP) with average fibril widths between 50 and 60 nm. The BC was directly oxidized in a TEMPO/NaBr/NaClO system at pH of 10 for 2 h. TEMPO-oxidized bacterial cellulose nanofibrils (TOBCN) were obtained by a mild mechanical treatment and the TOBCN films were prepared through heat-drying. The oxidation yielded a recovery ratio between 70 and 80% by weight with an increase in the carboxylate content of 0.9-1.0 mmol g ^-1. Nanofibrillation yields were more than 90% and the resulting high aspect ratio TOBCNs were ~6 nm in average width with >800 nm in lengths, when observed under transmission electron microscope (TEM). TOBCN film of K. xylinus C30 exhibited high transparency (79%), tensile strength (142 MPa), Young's modulus (7.13 GPa), elongation around failure (3.89%), and work of fracture (2.29 MJ m^-3), when compared to the TOBCN films of K. oboediens R37-9 at 23 °C and 50% RH. Coefficients of thermal expansion of both the TOBCN films were low at around 6 ppm K^-1.

Characterization of bacterial cellulose nanocrystals: Effect of acid treatments and neutralization

In this study, bacterial cellulose nanocrystals (BCNCs) were obtained from bacterial cellulose nanofibers (BCNFs) by controlled hydrolysis of sulfuric and hydrochloric acids. The influence of hydrolysis temperature and acid type with the addition of the post-treatment step was studied. The obtained BCNCs were analyzed based on the structural characterization and the properties of the nanocrystals. The BCNCs crystallinity increased, and the size of nanocrystals decreased with increasing 10 °C hydrolysis temperature for both acid hydrolysis conditions. Hydrolysis conditions with neutralization post-treatment did not alter the thermal stability of nanocrystals, and BCNCs had high thermal stability like raw BCNFs. Elemental analysis results indicated that sulfur content (S %) was very low for sulfuric acid hydrolyzed samples, and X-ray results did not show any sulfate salt peaks. Thermal stable BCNCs with high crystallinity were successfully produced to meet the process requirements in various applications, especially in the food industry.