The facile and controllable synthesis of a bacterial cellulose/polyhydroxybutyrate composite by co-culturing Gluconacetobacter xylinus and Ralstonia eutropha

Toward biomanufacturing of next-generation bacterial nanocellulose (BNC)-based materials with tailored properties: A review on genetic engineering approaches

Bacterial nanocellulose (BNC) is a biopolymer that is drawing significant attention for a wide range of applications thanks to its unique structure and excellent properties, such as high purity, mechanical strength, high water holding capacity and biocompatibility. Nevertheless, the biomanufacturing of BNC is hindered due to its low yield, the instability of microbial strains and cost limitations that prevent it from being mass-produced on a large scale. Various approaches have been developed to address these problems by genetically modifying strains and to produce BNC-based biomaterials with added value. These works are summarized and discussed in the present article, which include the overexpression and knockout of genes related and not related with the nanocellulose biosynthetic operon, the application of synthetic biology approaches and CRISPR/Cas techniques to modulate BNC biosynthesis. Further discussion is provided on functionalized BNC-based biomaterials with tailored properties that are incorporated in-vivo during its biosynthesis using genetically modified strains either in single or co-culture systems (in-vivo manufacturing). This novel strategy holds potential to open the road toward cost-effective production processes and to find novel applications in a variety of technology and industrial fields.

Enhanced bacterial cellulose production by Komagataeibacter species and Hibiscus sabdariffa herbal tea

This study proposed Hibiscus sabdariffa as a novel substrate for BC production with Komagataeibacter species and their consortia. K. intermedius is found as the most efficient producer (5.98 g/L BC, 3.56 × 10-2 g-1 h-1 productivity rate) following K. maltaceti (4.44 g/L BC, 2.64 × 10-2 g-1 h-1 productivity rate) and K. nataicola (3.67 g/L BC, 2.18 × 10-2 g-1 h-1 productivity rate). Whereas agitation increased BC production with K. nataicola (1.22-fold, 4.49 g/L BC), K. maltaceti (1.24-fold, 5.52 g/L BC) and K. intermedius (1.27-fold, 7.63 g/L BC), irregular shaped BC was obtained. This could be a novel result as Komagataeibacter consortia increased BC production by 1.17-2.01-fold compared to monocultures resulting as 8.11 g/L BC through the co-cultivation of K. maltaceti-K. intermedius. Maximum increase was found to be 1.75-fold (1.79-fold WHC), occurring with monoculture of K. maltaceti, while 1.94-fold (1.26-fold WHC) with K. maltaceti-K. intermedius consortium when H. sabdariffa-based media compared Hestrin-Schramm media. Based on these results, this could be a novel result as H. sabdariffa-based media may replace the use of HS media in BC production by means of a bioactive content-rich plant and obtaining 3-D ultrafine porous structure with high thermal resistant (∼460-500 °C) BC with mono and co-cultivation of Komagataeibacter species to be used in industrial area.

In vitro degradation and antibacterial activity of bacterial cellulose deposited flax fabric reinforced with polylactic acid and polyhydroxybutyrate

The objective of this study was to prepare biocomposites through the solution casting method followed by compression moulding in which bacterial cellulose (BC) deposited flax fabric (FF) produced through fermentation is coated with minimal amount of polylactic acid (PLA) and polyhydroxybutyrate (PHB). Biocomposites incorporated with 60 % of PLA or PHB (% w/w) show enhanced tensile strength. Cross-sectional morphology showed good superficial interaction of these biopolymers with fibres of FF thereby filling up the gaps present between the fibres. The tensile strength of biocomposites at 60 % PLA and 60 % PHB improved from 37.97 MPa (i.e., BC deposited FF produced in presence of honey) to 67.17 MPa and 56.26 MPa, respectively. Further, 0.25 % of nalidixic acid (NA) (% w/w) and 6 % of oleic acid (OA) (% w/w) incorporation into the biocomposites imparted prolonged antibacterial activity against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The in vitro cytotoxicity of biocomposites was determined using L929 mouse fibroblast cells. The 3-(4,5-cime- thylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide cytotoxicity tests showed that the PHB derived biocomposites along with antibacterial compounds in it were non-toxic. In vitro degradation of biocomposites was measured for up to 8 weeks in the mimicked physiological environment that showed a gradual rate of degradation over the period.

Production of bacterial cellulose (BC)/nisin composite with enhanced antibacterial and mechanical properties through co-cultivation of Komagataeibacter xylinum and Lactococcus lactis subsp. lactis

By employing co-cultivation technique on Komagataeibacter xylinum and Lactococcus lactis subsp. lactis, bacterial cellulose (BC)/nisin films with improved antibacterial activity and mechanical properties were successfully produced. The findings demonstrated that increased nisin production is associated with an upregulation of gene expression. Furthermore, results from Scanning electronic microscopy (SEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and Thermogravimetric analysis (TG) confirmed the integration of nisin within BC. While being biocompatible with human cells, the BC/nisin composites exhibited antimicrobial activity. Moreover, mechanical property analyses showed a noticeable improvement in Young's modulus, tensile strength, and elongation at break by 161, 271, and 195 %, respectively. Additionally, the nisin content in fermentation broth was improved by 170 % after co-culture, accompanied by an 8 % increase in pH as well as 10 % decrease in lactate concentration. Real-time reverse transcription PCR analysis revealed an upregulation of 11 nisin-related genes after co-cultivation, with the highest increase in nisA (5.76-fold). To our knowledge, this is the first study which demonstrates that an increase in secondary metabolites after co-culturing is modulated by gene expression. This research offers a cost-effective approach for BC composite production and presents a technique to enhance metabolite concentration through the regulation of relevant genes.

From Nature to Lab: Sustainable Bacterial Cellulose Production and Modification with Synthetic Biology

Bacterial cellulose (BC) is a macromolecule with versatile applications in medicine, pharmacy, biotechnology, cosmetology, food and food packaging, ecology, and electronics. Although many bacteria synthesize BC, the most efficient BC producers are certain species of the genera Komagataeibacter and Novacetimonas. These are also food-grade bacteria, simplifying their utilization at industrial facilities. The basic principles of BC synthesis are known from studies of Komagataeibacter xylinus, which became a model species for studying BC at genetic and molecular levels. Cellulose can also be of plant origin, but BC surpasses its purity. Moreover, the laboratory production of BC enables in situ modification into functionalized material with incorporated molecules during its synthesis. The possibility of growing Komagataeibacter and Novacetimonas species on various organic substrates and agricultural and food waste compounds also follows the green and sustainable economy principles. Further intervention into BC synthesis was enabled by genetic engineering tools, subsequently directing it into the field of synthetic biology. This review paper presents the development of the fascinating field of BC synthesis at the molecular level, seeking sustainable ways for its production and its applications towards genetic modifications of bacterial strains for producing novel types of living biomaterials using the flexible metabolic machinery of bacteria.

Efficient microbial cellulose/Fe3O4 nanocomposite for photocatalytic degradation by advanced oxidation process of textile dyes

Fenton-type advanced oxidative processes (AOP) have been employed to treat textile dyes in aqueous solution and industrial effluent. The work focused on assisting the limitations still presented by the Fenton process regarding the use of suspended iron catalysts. Soon, a nanocomposite of bacterial cellulose (BC) and magnetite (Fe₃O₄) was developed. It has proven to be superior to those available in the literature, exhibiting purely catalytic properties and high reusability. Its successful production was verified through analytical characterization, while its catalytic potential was investigated in the treatment of different textile matrices. In initial tests, the photo-Fenton process irradiated and catalyzed by sunlight and BC/Fe₃O₄ discolored 92.19% of an aqueous mixture of four textile dyes. To improve the efficiency, the design of experiments technique evaluated the influence of the variables pH, [H₂O₂], and the number of BC/Fe₃O₄ membranes. 99.82% of degradation was obtained under optimized conditions using pH 5, 150 mg L^-1 of H₂O₂, and 11 composite membranes. Reaction kinetics followed a pseudo-first-order model, effectively reducing the organic matter (COD = 83.24% and BOD = 88.13%). The composite showed low iron leaching (1.60 ± 0.08 mg L^-1) and high stability. It was recovered and reused for 15 consecutive cycles, keeping the treatment efficiency at over 90%. As for the industrial wastewater, the photo-Fenton/sunlight/BC/Fe₃O₄ system showed better results when combined with the physical-chemical coagulation/flocculation process previously used in the industry's WWTP. Together they reduced COD by 77.77%, also meeting the color standards (DFZ scale) for the wavelengths of 476 nm (<3 m^-1), 525 nm (<5 m^-1), and 620 nm (<7 m^-1). Thus, the results obtained demonstrated that employing the BC/Fe₃O₄ composite as an iron catalyst is a suitable alternative to materials employed in suspension. This is mainly due to the high catalytic activity and power of reuse, which will reduce treatment costs.

Removal of heavy metal vanadium from aqueous solution by nanocellulose produced from Komagataeibacter europaeus employing pineapple waste as carbon source

Environmental concerns have taken a center stage in our lives driving the society towards biorefinery. Bioprocess development to produce valuable products utilizing waste has its own significance in circular bioeconomy and environmental sustainability. In the present study, production of bacterial cellulose using pineapple waste as carbon source by Komagataeibacter europaeus was undertaken and it was applied for removal of vanadium, a heavy metal which is generated as waste by semiconductors industry in Taiwan. Highest yield of bacterial cellulose (BC) e.i. 5.04 g/L was obtained with pineapple core hydrolysate (HS-PC) replacing glucose in HS medium. The vanadium adsorption capacity by BC produced by HS medium was 5.24 mg/g BC at pH 4 and 2.85 mg/g BC was observed on PCH medium. BC was characterised via SEM, FTIR and XRD.

Bacterial cellulose flakes loaded with Bi2MoO6 nanoparticles and quantum dots for the photodegradation of antibiotic and dye pollutants

Effective strategies to improve charge separation in semiconductor particles are critical for improving the photodegradation of organic pollutants at levels sufficient for environmental applications. Herein, Bi₂MoO₆ (BMO_MOF), comprising both nanoparticles (NPs) and quantum dots (QDs), was synthesized from a bismuth-based metal-organic framework (Bi-MOF) precursor. Surface defects on BMO_MOF, the combination of NPs and QDs, and modified energy band edges improved photogenerated charge separation and facilitated redox reactions. When compared to BMO derived from uncoordinated Bi, the BMO_MOF photocatalyst (PC) was more efficient at photodegrading tetracycline hydrochloride (TCH) and ciprofloxacin (CIP), two widely-used antibiotics ubiquitous in wastewater, as well as the carcinogenic pollutant rhodamine B (RhB). BMO_MOF was then loaded on the biopolymer bacterial cellulose (BC) to further enhance photocatalytic performance and facilitate the recovery of the PC after water treatment processes. The novel BMO_MOF/BC photocatalytic flakes were significantly larger than pure BMO_MOF, and thus easier to recuperate. Furthermore, anchoring BMO_MOF on BC flakes augmented significantly the photodegradation of TCH, CIP, and RhB, mainly because hydroxyl groups in BC act as hole traps facilitating photogenerated electron-hole separation. Results obtained with BMO_MOF/BC highlight promising approaches to develop optimal PCs for aqueous pollutants degradation.

Gaining control of bacterial cellulose colonization by polyhydroxyalkanoate-producing microorganisms to develop bioplasticized ultrathin films

Synergistic methodological strategies based on the fields of microbial biotechnology and materials science open up an enormous range of possibilities for the sustainable production of advanced materials with predictable properties. This study shows how naturally produced polyhydroxyalkanoate (PHA) particles are introduced into bacterial cellulose (BC) driven by their bacterial producers. Thanks to an extensive knowledge of the internal structure of BC, it was possible to control the colonization process, i.e. loading and localization of PHA. A subsequent acid treatment favored the PHA-BC bonding at the position reached by the bacteria. These biodegradable films showed improved mechanical and barrier properties even with respect to reference plastic films 8 times thicker, reaching a Young's modulus 4.25 times higher and an oxygen permeability 3 times lower than those of polyethylene terephthalate (PET) films. Owing to the versatility of the method, a wide variety of materials can be developed for very diverse fields of application.

Biocatalysts in Synthesis of Microbial Polysaccharides: Properties and Development Trends

Polysaccharides synthesized by microorganisms (bacterial cellulose, dextran, pullulan, xanthan, etc.) have a set of valuable properties, such as being antioxidants, detoxifying, structuring, being biodegradable, etc., which makes them suitable for a variety of applications. Biocatalysts are the key substances used in producing such polysaccharides; therefore, modern research is focused on the composition and properties of biocatalysts. Biocatalysts determine the possible range of renewable raw materials which can be used as substrates for such synthesis, as well as the biochemistry of the process and the rate of molecular transformations. New biocatalysts are being developed for participating in a widening range of stages of raw material processing. The functioning of biocatalysts can be optimized using the following main approaches of synthetic biology: the use of recombinant biocatalysts, the creation of artificial consortia, the combination of nano- and microbiocatalysts, and their immobilization. New biocatalysts can help expand the variety of the polysaccharides’ useful properties. This review presents recent results and achievements in this field of biocatalysis.

A two-stage process for the autotrophic and mixotrophic conversion of C1 gases into bacterial cellulose

Gas fermentation is a well-established process for the conversion of greenhouse gases from industrial wastes into valuable multi-carbon chemicals. Here, a two-stage process was developed to expand the product range of gas fermentation and synthesized the versatile biopolymer bacterial cellulose (BC). In the first stage, the acetogen Clostridium autoethanogenum was cultivated with H₂:CO:CO₂ and produced ethanol and acetate. In the second stage, BC-synthesizing Komagataeibacter sucrofermentans was grown in the spent medium from gas fermentation. K. sucrofermentans was able to produce BC autotrophically from gas-derived metabolites alone as well as mixotrophically with the addition of exogenous glucose. In these circumstances, 1.31 g/L BC was synthesized with a major energetic contribution from C1 gas fermentation products. Mixotrophic BC characterization reveals unique properties including augmented mechanical strength, porosity, and crystallinity. This proof-of-concept process demonstrates that BC can be produced from gases and holds good potential for the efficient conversion of C1 wastes.

Advanced "Green" Prebiotic Composite of Bacterial Cellulose/Pullulan Based on Synthetic Biology-Powered Microbial Coculture Strategy

Bacterial cellulose (BC) is a biopolymer produced by different microorganisms, but in biotechnological practice, Komagataeibacter xylinus is used. The micro- and nanofibrillar structure of BC, which forms many different-sized pores, creates prerequisites for the introduction of other polymers into it, including those synthesized by other microorganisms. The study aims to develop a cocultivation system of BC and prebiotic producers to obtain BC-based composite material with prebiotic activity. In this study, pullulan (PUL) was found to stimulate the growth of the probiotic strain Lactobacillus rhamnosus GG better than the other microbial polysaccharides gellan and xanthan. BC/PUL biocomposite with prebiotic properties was obtained by cocultivation of Komagataeibacter xylinus and Aureobasidium pullulans, BC and PUL producers respectively, on molasses medium. The inclusion of PUL in BC is proved gravimetrically by scanning electron microscopy and by Fourier transformed infrared spectroscopy. Cocultivation demonstrated a composite effect on the aggregation and binding of BC fibers, which led to a significant improvement in mechanical properties. The developed approach for "grafting" of prebiotic activity on BC allows preparation of environmentally friendly composites of better quality.

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.