Enhanced Production of Bacterial Cellulose in Komagataeibacter xylinus Via Tuning of Biosynthesis Genes with Synthetic RBS

Engineering of Pseudomonas putida to produce medium-chain-length polyhydroxyalkanoate from crude glycerol

The development of biodegradable polymers is crucial for addressing environmental issues and waste management challenges, and a medium-chain-length polyhydroxyalkanoate(MCL-PHA) exhibits significant application potential in diverse industrial and environmental contexts owing to its versatility and biodegradability. Here, Pseudomonas putida was metabolically engineered to produce MCL-PHA from crude glycerol. To increase the precursor pool, we first deleted the phaC1ZC2 operon and introduced a plasmid-based overexpression of phaC2 and phaG, and the MCL-PHA content derived from glycerol increased to 18.27 wt% at 60 h. Subsequently, by optimizing the acoA expression through promoter selection and UTR design, the MCL-PHA content further increased to 19.93 wt% at 72 h. Additionally, a notable increase in MCL-PHA production was achieved using PhaC2 designed to have no substrate-trapping effect (PhaC2A477A478). This improvement was guided by filling structural data gaps using AlphaFold2 and docking simulations that revealed the substrate-trapping phenomenon. High-level production of MCL-PHA was achieved through fed-batch fermentation using the final engineered P. putida from refined glycerol, which yielded 34.9 g/L of MCL-PHA with 44.64 wt% at 180 h. Furthermore, using crude glycerol as the sole carbon source enabled the production of 49.5 g/L of MCL-PHA with 45.41 wt% at 180 h in fed-batch culture.

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).

Engineering the next generation of theranostic biomaterials with synthetic biology

Biomaterials have evolved from inert materials to responsive entities, playing a crucial role in disease diagnosis, treatment, and modeling. However, their advancement is hindered by limitations in chemical and mechanical approaches. Synthetic biology enabling the genetically reprograming of biological systems offers a new paradigm. It has achieved remarkable progresses in cell reprogramming, engineering designer cells for diverse applications. Synthetic biology also encompasses cell-free systems and rational design of biological molecules. This review focuses on the application of synthetic biology in theranostics, which boost rapid development of advanced biomaterials. We introduce key fundamental concepts of synthetic biology and highlight frontier applications thereof, aiming to explore the intersection of synthetic biology and biomaterials. This integration holds tremendous promise for advancing biomaterial engineering with programable complex functions.

Production of Bacterial Exopolysaccharides: Xanthan and Bacterial Cellulose

Recently, degradable biopolymers have become increasingly important as potential environmentally friendly biomaterials, providing a wide range of applications in various fields. Bacterial exopolysaccharides (EPSs) are biomacromolecules, which due to their unique properties have found applications in biomedicine, foodstuff, textiles, cosmetics, petroleum, pharmaceuticals, nanoelectronics, and environmental remediation. One of the important commercial polysaccharides produced on an industrial scale is xanthan. In recent years, the range of its application has expanded significantly. Bacterial cellulose (BC) is another unique EPS with a rapidly increasing range of applications. Due to the great prospects for their practical application, the development of their highly efficient production remains an important task. The present review summarizes the strategies for the cost-effective production of such important biomacromolecules as xanthan and BC and demonstrates for the first time common approaches to their efficient production and to obtaining new functional materials for a wide range of applications, including wound healing, drug delivery, tissue engineering, environmental remediation, nanoelectronics, and 3D bioprinting. In the end, we discuss present limitations of xanthan and BC production and the line of future research.

In-situ CBM3-modified bacterial cellulose film with improved mechanical properties

Cellulose materials have poor wet strength and are susceptible to acidic or basic environments. Herein, we developed a facile strategy to modify bacterial cellulose (BC) with a genetically engineered Family 3 Carbohydrate-Binding Module (CBM3). To assess the effect of BC films, water adsorption rate (WAR), water holding capacity (WHC), water contact angle (WCA), and mechanical and barrier properties were determined. The results showed that CBM3-modified BC film exhibited significant strength and ductility improvement, reflecting improved mechanical properties of the film. The excellent wet strength (both in the acidic and basic environment), bursting strength, and folding endurance of CBM3-BC films were due to the strong interaction between CBM3 and fiber. The toughness of CBM3-BC films reached 7.9, 28.0, 13.3, and 13.6 MJ/m³, which were 6.1, 1.3, 1.4, and 3.0 folds over the control for conditions of dry, wet, acidic, and basic, respectively. In addition, its gas permeability was reduced by 74.3 %, and folding times increased by 56.8 % compared with the control. The synthesized CBM3-BC films may hold promise for future applications in food packaging, paper straw, battery separator, and other fields. Finally, the in situ modification strategy used to BC can be successfully applied in other functional modifications for BC materials.

Bacterial cellulose: Strategies for its production in the context of bioeconomy

Bacterial cellulose has advantages over plant-derived cellulose, which make its use for industrial applications easier and more profitable. Its intrinsic properties have been stimulating the global biopolymer market, with strong growth expectations in the coming years. Several bacterial species are capable of producing bacterial cellulose under different culture conditions; in this context, strategies aimed at metabolic engineering and several possibilities of carbon sources have provided opportunities for the bacterial cellulose's biotechnological exploration. In this article, an overview of biosynthesis pathways in different carbon sources for the main producing microorganisms, metabolic flux under different growth conditions, and their influence on the structural and functional characteristics of bacterial cellulose is provided. In addition, the main industrial applications and ways to reduce costs and optimize its production using alternative sources are discussed, contributing to new insights on the exploitation of this biomaterial in the context of the bioeconomy.

Dynamic and balanced regulation of the thrABC operon gene for efficient synthesis of L-threonine

L-threonine is an essential amino acid used widely in food, cosmetics, animal feed and medicine. The thrABC operon plays an important role in regulating the biosynthesis of L-theronine. In this work, we systematically analyzed the effects of separating thrAB and thrC in different proportions on strain growth and L-threonine production in Escherichia coli firstly. The results showed that higher expression of thrC than thrAB enhanced cell growth and L-threonine production; however, L-threonine production decreased when the thrC proportion was too high. The highest L-threonine production was achieved when the expression intensity ratio of thrAB to thrC was 3:5. Secondly, a stationary phase promoter was also used to dynamically regulate the expression of engineered thrABC. This strategy improved cell growth and shortened the fermentation period from 36 h to 24 h. Finally, the acetate metabolic overflow was reduced by deleting the ptsG gene, leading to a further increase in L-threonine production. With these efforts, the final strain P _2.1 -2901ΔptsG reached 40.06 g/L at 60 h fermentation, which was 96.85% higher than the initial control strain TH and the highest reported titer in shake flasks. The maximum L-threonine yield and productivity was obtained in reported fed-batch fermentation, and L-threonine production is close to the highest titer (127.30 g/L). In this work, the expression ratio of genes in the thrABC operon in E. coli was studied systematically, which provided a new approach to improve L-threonine production and its downstream products.

Microbial Production of Bacterial Cellulose Using Chestnut Shell Hydrolysates by Gluconacetobacter xylinus ATCC 53524

Bacterial cellulose (BC) is gaining attention as a carbon-neutral alternative to plant cellulose, and as a means to prevent deforestation and achieve a carbon-neutral society. However, the high cost of fermentation media for BC production is a barrier to its industrialization. In this study, chestnut shell (CS) hydrolysates were used as a carbon source for the BC-producing bacteria strain, Gluconacetobacter xylinus ATCC 53524. To evaluate the suitability of the CS hydrolysates, major inhibitors in the hydrolysates were analyzed, and BC production was profiled during fermentation. CS hydrolysates (40 g glucose/l) contained 1.9 g/l acetic acid when applied directly to the main medium. As a result, the BC concentration at 96 h using the control group and CS hydrolysates was 12.5 g/l and 16.7 g/l, respectively (1.3-fold improved). In addition, the surface morphology of BC derived from CS hydrolysates revealed more densely packed nanofibrils than the control group. In the microbial BC production using CS, the hydrolysate had no inhibitory effect during fermentation, suggesting it is a suitable feedstock for a sustainable and eco-friendly biorefinery. To the best of our knowledge, this is the first study to valorize CS by utilizing it in BC production.

Enhancing bacterial cellulose production with hypoxia-inducible factors

Komagataeibacter xylinus is an aerobic strain that produces bacterial cellulose (BC). Oxygen levels play a critical role in regulating BC synthesis in K. xylinus, and an increase in oxygen tension generally means a decrease in BC production. Fumarate nitrate reduction protein (FNR) and aerobic respiration control protein A (ArcA) are hypoxia-inducible factors, which can signal whether oxygen is present in the environment. In this study, FNR and ArcA were used to enhance the efficiency of oxygen signaling in K. xylinus, and globally regulate the transcription of the genome to cope with hypoxic conditions, with the goal of improving growth and BC production. FNR and ArcA were individually overexpressed in K. xylinus, and the engineered strains were cultivated under different oxygen tensions to explore how their overexpression affects cellular metabolism and regulation. Although FNR overexpression did not improve BC production, ArcA overexpression increased BC production by 24.0% and 37.5% as compared to the control under oxygen tensions of 15% and 40%, respectively. Transcriptome analysis showed that FNR and ArcA overexpression changed the way K. xylinus coped with oxygen tension changes, and that both FNR and ArcA overexpression enhanced the BC synthesis pathway. The results of this study provide a new perspective on the effect of oxygen signaling on growth and BC production in K. xylinus and suggest a promising strategy for enhancing BC production through metabolic engineering. KEY POINTS: • K. xylinus BC production increased after overexpression of ArcA • The young's modulus is enhanced by the ArcA overexpression • ArcA and FNR overexpression changed how cells coped with changes in oxygen tension.

Developments in bioprocess for bacterial cellulose production

Bacterial cellulose (BC) represents a novel bio-origin nonomaterial with its unique properties having diverse applications. Increased market demand and low yield are the major reason for its higher cost. Bacteria belonging to Komagataeibacter sp are the most exploited ones for BC production. Development of a cost-effective bioprocess for higher BC production is desirable. Though static fermentation modes have been majorly employed for BC production using tray fermenters, agitated mode has also been employed successfully with air-lift fermenters as well as stirred tank reactors. Bioprocess advances in recent years has led BC production to an upper level; however, challenges of aeration requirement and labor cost towards the higher end is associated with static cultivation at large scale. We have discussed the bioprocess development for BC production in recent years along with the challenges associated and the path forward.

Bacterial Nanocellulose Fortified with Antimicrobial and Anti-Inflammatory Natural Products from Chelidonium majus Plant Cell Cultures

In this work we developed a bi-functional Bacterial-Nano-Cellulose (BNC) carrier system for cell cultures of Chelidonium majus-a medicinal plant producing antimicrobial compounds. The porous BNC was biosynthesized for 3, 5 or 7 days by the non-pathogenic Komagataeibacter xylinus bacteria and used in three forms: (1) Without removal of K. xylinus cells, (2) partially cleaned up from the remaining K. xylinus cells using water washing and (3) fully purified with NaOH leaving no bacterial cells remains. The suspended C. majus cells were inoculated on the BNC pieces in liquid medium and the functionalized BNC was harvested and subjected to scanning electron microscopy observation and analyzed for the content of C. majus metabolites as well as to antimicrobial assays and tested for potential proinflammatory irritating activity in human neutrophils. The highest content and the most complex composition of pharmacologically active substances was found in 3-day-old, unpurified BNC, which was tested for its bioactivity. The assays based on the IL-1β, IL-8 and TNF-α secretion in an in vitro model showed an anti-inflammatory effect of this particular biomatrix. Moreover, 3-day-old-BNC displayed antimicrobial and antibiofilm activity against Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. The results of the research indicated a possible application of such modified composites, against microbial pathogens, especially in local surface infections, where plant metabolite-enriched BNC may be used as the occlusive dressing.

Weaving of bacterial cellulose by the Bcs secretion systems

Cellulose is the most abundant biological compound on Earth and while it is the predominant building constituent of plants, it is also a key extracellular matrix component in many diverse bacterial species. While bacterial cellulose was first described in the 19th century, it was not until this last decade that a string of structural works provided insights into how the cellulose synthase BcsA, assisted by its inner-membrane partner BcsB, senses c-di-GMP to simultaneously polymerize its substrate and extrude the nascent polysaccharide across the inner bacterial membrane. It is now established that bacterial cellulose can be produced by several distinct types of cellulose secretion systems and that in addition to BcsAB, they can feature multiple accessory subunits, often indispensable for polysaccharide production. Importantly, the last years mark significant progress in our understanding not only of cellulose polymerization per se but also of the bigger picture of bacterial signaling, secretion system assembly, biofilm formation and host tissue colonization, as well as of structural and functional parallels of this dominant biosynthetic process between the bacterial and eukaryotic domains of life. Here, we review current mechanistic knowledge on bacterial cellulose secretion with focus on the structure, assembly and cooperativity of Bcs secretion system components.

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.

On the way toward regulatable expression systems in acetic acid bacteria: target gene expression and use cases

Acetic acid bacteria (AAB) are valuable biocatalysts for which there is growing interest in understanding their basics including physiology and biochemistry. This is accompanied by growing demands for metabolic engineering of AAB to take advantage of their properties and to improve their biomanufacturing efficiencies. Controlled expression of target genes is key to fundamental and applied microbiological research. In order to get an overview of expression systems and their applications in AAB, we carried out a comprehensive literature search using the Web of Science Core Collection database. The Acetobacteraceae family currently comprises 49 genera. We found overall 6097 publications related to one or more AAB genera since 1973, when the first successful recombinant DNA experiments in Escherichia coli have been published. The use of plasmids in AAB began in 1985 and till today was reported for only nine out of the 49 AAB genera currently described. We found at least five major expression plasmid lineages and a multitude of further expression plasmids, almost all enabling only constitutive target gene expression. Only recently, two regulatable expression systems became available for AAB, an N-acyl homoserine lactone (AHL)-inducible system for Komagataeibacter rhaeticus and an L-arabinose-inducible system for Gluconobacter oxydans. Thus, after 35 years of constitutive target gene expression in AAB, we now have the first regulatable expression systems for AAB in hand and further regulatable expression systems for AAB can be expected. KEY POINTS: • Literature search revealed developments and usage of expression systems in AAB. • Only recently 2 regulatable plasmid systems became available for only 2 AAB genera. • Further regulatable expression systems for AAB are in sight.

Engineering Bacterial Cellulose by Synthetic Biology

Synthetic biology is an advanced form of genetic manipulation that applies the principles of modularity and engineering design to reprogram cells by changing their DNA. Over the last decade, synthetic biology has begun to be applied to bacteria that naturally produce biomaterials, in order to boost material production, change material properties and to add new functionalities to the resulting material. Recent work has used synthetic biology to engineer several Komagataeibacter strains; bacteria that naturally secrete large amounts of the versatile and promising material bacterial cellulose (BC). In this review, we summarize how genetic engineering, metabolic engineering and now synthetic biology have been used in Komagataeibacter strains to alter BC, improve its production and begin to add new functionalities into this easy-to-grow material. As well as describing the milestone advances, we also look forward to what will come next from engineering bacterial cellulose by synthetic biology.