Insights into the structure and assembly of a bacterial cellulose secretion system

Bacterial cellulose in cosmetic innovation: A review

Bacterial cellulose (BC) emerges as a versatile biomaterial with a myriad of industrial applications, particularly within the cosmetics sector. The absence of hemicellulose, lignin, and pectin in its pure cellulose structure enables favorable interactions with both hydrophilic and hydrophobic biopolymers. This enhances compatibility with active ingredients commonly employed in cosmetics, such as antioxidants, vitamins, and botanical extracts. Recent progress in BC-based materials, which encompasses membranes, films, gels, nanocrystals, and nanofibers, highlights its significant potential in cosmetics. In this context, BC not only serves as a carrier for active ingredients but also plays a crucial role as a structural agent in formulations. The sustainability of BC production and processing is a central focus, highlighting the need for innovative approaches to strengthen scalability and cost-effectiveness. Future research endeavors, including the exploration of novel cultivation strategies and functionalization techniques, aim to maximize BC's therapeutic potential while broadening its scope in personalized skincare regimes. Therefore, this review emphasizes the crucial contribution of BC to the cosmetics sector, underlining its role in fostering innovation, sustainability, and ethical skincare practices. By integrating recent research findings and industry trends, this review proposes a fresh approach to advancing both skincare science and environmental responsibility in the cosmetics industry.

Bacterial synthase-dependent exopolysaccharide secretion: a focus on cellulose

Bacterial biofilms are a prevalent multicellular life form in which individual members can undergo significant functional differentiation and are typically embedded in a complex extracellular matrix of proteinaceous fimbriae, extracellular DNA, and exopolysaccharides (EPS). Bacteria have evolved at least four major mechanisms for EPS biosynthesis, of which the synthase-dependent systems for bacterial cellulose secretion (Bcs) represent not only key biofilm determinants in a wide array of environmental and host-associated microbes, but also an important model system for the studies of processive glycan polymerization, cyclic diguanylate (c-di-GMP)-dependent synthase regulation, and biotechnological polymer applications. The secreted cellulosic chains can be decorated with additional chemical groups or can pack with various degrees of crystallinity depending on dedicated enzymatic complexes and/or cytoskeletal scaffolds. Here, I review recent progress in our understanding of synthase-dependent EPS biogenesis with a focus on common and idiosyncratic molecular mechanisms across diverse cellulose secretion systems.

Nanocellulose-based hydrogels as versatile materials with interesting functional properties for tissue engineering applications

Tissue engineering has emerged as a remarkable field aiming to restore or replace damaged tissues through the use of biomimetic constructs. Among the diverse materials investigated for this purpose, nanocellulose-based hydrogels have garnered attention due to their intriguing biocompatibility, tunable mechanical properties, and sustainability. Over the past few years, numerous research works have been published focusing on the successful use of nanocellulose-based hydrogels as artificial extracellular matrices for regenerating various types of tissues. The review emphasizes the importance of tissue engineering, highlighting hydrogels as biomimetic scaffolds, and specifically focuses on the role of nanocellulose in composites that mimic the structures, properties, and functions of the native extracellular matrix for regenerating damaged tissues. It also summarizes the types of nanocellulose, as well as their structural, mechanical, and biological properties, and their contributions to enhancing the properties and characteristics of functional hydrogels for tissue engineering of skin, bone, cartilage, heart, nerves and blood vessels. Additionally, recent advancements in the application of nanocellulose-based hydrogels for tissue engineering have been evaluated and documented. The review also addresses the challenges encountered in their fabrication while exploring the potential future prospects of these hydrogel matrices for biomedical applications.

CslA and GlxA from Streptomyces lividans form a functional cellulose synthase complex

Filamentous growth of streptomycetes coincides with the synthesis and deposition of an uncharacterized protective glucan at hyphal tips. Synthesis of this glucan depends on the integral membrane protein CslA and the radical copper oxidase GlxA, which are part of a presumably large multiprotein complex operating at growing tips. Here, we show that CslA and GlxA interact by forming a protein complex that is sufficient to synthesize cellulose in vitro. Mass spectrometry analysis revealed that the purified complex produces cellulose chains with a degree of polymerization of at least 80 residues. Truncation analyses demonstrated that the removal of a significant extracellular segment of GlxA had no impact on complex formation, but significantly diminished activity of CslA. Altogether, our work demonstrates that CslA and GlxA form the active core of the cellulose synthase complex and provide molecular insights into a unique cellulose biosynthesis system that is conserved in streptomycetes.

IMPORTANCE

Cellulose stands out as the most abundant polysaccharide on Earth. While the synthesis of this polysaccharide has been extensively studied in plants and Gram-negative bacteria, the mechanisms in Gram-positive bacteria have remained largely unknown. Our research unveils a novel cellulose synthase complex formed by the interaction between the cellulose synthase-like protein CslA and the radical copper oxidase GlxA from Streptomyces lividans, a soil-dwelling Gram-positive bacterium. This discovery provides molecular insights into the distinctive cellulose biosynthesis machinery. Beyond expanding our understanding of cellulose biosynthesis, this study also opens avenues for exploring biotechnological applications and ecological roles of cellulose in Gram-positive bacteria, thereby contributing to the broader field of microbial cellulose biosynthesis and biofilm research.

Molecular insights into phosphoethanolamine cellulose formation and secretion

Phosphoethanolamine (pEtN) cellulose is a naturally occurring modified cellulose produced by several Enterobacteriaceae. The minimal components of the E. coli cellulose synthase complex include the catalytically active BcsA enzyme, an associated periplasmic semicircle of hexameric BcsB, as well as the outer membrane (OM)-integrated BcsC subunit containing periplasmic tetratricopeptide repeats (TPR). Additional subunits include BcsG, a membrane-anchored periplasmic pEtN transferase associated with BcsA, and BcsZ, a conserved periplasmic cellulase of unknown biological function. While events underlying the synthesis and translocation of cellulose by BcsA are well described, little is known about its pEtN modification and translocation across the cell envelope. We show that the N-terminal cytosolic domain of BcsA positions three copies of BcsG near the nascent cellulose polymer. Further, the terminal subunit of the BcsB semicircle tethers the N-terminus of a single BcsC protein to establish a trans-envelope secretion system. BcsC's TPR motifs bind a putative cello-oligosaccharide near the entrance to its OM pore. Additionally, we show that only the hydrolytic activity of BcsZ but not the subunit itself is necessary for cellulose secretion, suggesting a secretion mechanism based on enzymatic removal of mislocalized cellulose. Lastly, we introduce pEtN modification of cellulose in orthogonal cellulose biosynthetic systems by protein engineering.

[New Advances in the Application of Bacterial Cellulose Composite Materials in the Field of Bone Tissue Engineering]

Bacterial cellulose (BC) is a type of extracellular polymeric nanomaterial secreted by microorganisms over the course of their growth. It has gained significant attention in the field of bone tissue engineering due to its unique structure of three-dimensional fibrous network, excellent biocompatibility, biodegradability, and exceptional mechanical properties. Nevertheless, BC still has some weaknesses, including low osteogenic activity, a lack of antimicrobial properties, small pore size, issues with the degradation rate, and a mismatch in bone tissue regeneration, limiting its standalone use in the field of bone tissue engineering. Therefore, the modification of BC and the preparation of BC composite materials have become a recent research focus. Herein, we summarized the relationships between the production, modification, and bone repair applications of BC. We introduced the methods for the preparation and the modification of BC. Additionally, we elaborated on the new advances in the application of BC composite materials in the field of bone tissue engineering. We also highlighted the existing challenges and future prospects of BC composite materials.

Transcriptomic Insights into Metabolism-Dependent Biosynthesis of Bacterial Nanocellulose

Bacterial nanocellulose (BNC) is an attractive green-synthesized biomaterial for biomedical applications and various other applications. However, effective engineering of BNC production has been limited by our poor knowledge of the related metabolic processes. In contrast to the traditional perception that genome critically determines biosynthesis behaviors, here we discover that the glucose metabolism could also drastically affect the BNC synthesis in Gluconacetobacter hansenii. The transcriptomic profiles of two model BNC-producing strains, G. hansenii ATCC 53582 and ATCC 23769, which have highly similar genomes but drastically different BNC yields, were compared. The results show that their BNC synthesis capacities were highly related to metabolic activities such as ATP synthesis, ion transport protein assembly, and carbohydrate metabolic processes, confirming an important role of metabolism-related transcriptomes in governing the BNC yield. Our findings provide insights into the microbial biosynthesis behaviors from a transcriptome perspective, potentially guiding cellular engineering for biomaterial synthesis.

A convergent evolutionary pathway attenuating cellulose production drives enhanced virulence of some bacteria

Bacteria adapt to selective pressure in their immediate environment in multiple ways. One mechanism involves the acquisition of independent mutations that disable or modify a key pathway, providing a signature of adaptation via convergent evolution. Extra-intestinal pathogenic Escherichia coli (ExPEC) belonging to sequence type 95 (ST95) represent a global clone frequently associated with severe human infections including acute pyelonephritis, sepsis, and neonatal meningitis. Here, we analysed a publicly available dataset of 613 ST95 genomes and identified a series of loss-of-function mutations that disrupt cellulose production or its modification in 55.3% of strains. We show the inability to produce cellulose significantly enhances ST95 invasive infection in a rat model of neonatal meningitis, leading to the disruption of intestinal barrier integrity in newborn pups and enhanced dissemination to the liver, spleen and brain. Consistent with these observations, disruption of cellulose production in ST95 augmented innate immune signalling and tissue neutrophil infiltration in a mouse model of urinary tract infection. Mutations that disrupt cellulose production were also identified in other virulent ExPEC STs, Shigella and Salmonella, suggesting a correlative association with many Enterobacteriaceae that cause severe human infection. Together, our findings provide an explanation for the emergence of hypervirulent Enterobacteriaceae clones.

Effects of hydrolysis conditions on the morphology of cellulose II nanocrystals (CNC-II) derived from mercerized microcrystalline cellulose

The properties of cellulose nanocrystals with allomorph II (CNC-II) vary with the sources and the treatments received. In this work, the influences of hydrolysis time, temperature, and the applied acid concentration on the crystal size of CNC-II were investigated by the surface response experimental design. The results showed that temperature was the most significant factor affecting the crystal size of CNC-II during hydrolysis from mercerized cellulose. Then the morphology and colloidal properties of CNC-II were revealed by dynamic laser scattering (DLS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), etc. XRD results indicated that CNC-II had slightly lower crystallinity (80.89 % vs 82.7 %) and larger crystallite size (5.21 vs. 5.13 nm) than CNC-I. TEM and AFM results showed that the morphology of CNC-II were disc-like and rod-like particles, with an average diameter of 14.6 ± 4.7 nm (TEM) and a thickness of 4- 8 nm (AFM). TG and XPS revealed the reduced thermal stability was due to the introduced sulfate groups in CNC-II during hydrolysis. This investigation has addressed the features of CNC-II derived from mercerized cellulose, and it would be promising in fabricating advanced materials.

Structural biology: Proteobacterial accessories for diverse cellulose synthesis

BcsD is broadly present throughout Proteobacteria and is predicted to contribute to cellulose crystallinity via interaction with BcsH. However, new work shows that, in non-crystalline forming Proteobacteria, BcsD contains an amino-terminal a1-helix, forms a tetrahedron-like structure, and interacts with alternative proline-rich protein partners.

Structures and roles of BcsD and partner scaffold proteins in proteobacterial cellulose secretion

Cellulose is the world's most abundant biopolymer, and similar to its role as a cell wall component in plants, it is a prevalent constituent of the extracellular matrix in bacterial biofilms. Although bacterial cellulose (BC) was first described in the 19th century, it was only recently revealed that it is produced by several distinct types of Bcs secretion systems that feature multiple accessory subunits in addition to a catalytic BcsAB synthase tandem. We recently showed that crystalline cellulose secretion in the Gluconacetobacter genus (α-Proteobacteria) is driven by a supramolecular BcsH-BcsD scaffold-the "cortical belt"-which stabilizes the synthase nanoarrays through an unexpected inside-out mechanism for secretion system assembly. Interestingly, while bcsH is specific for Gluconacetobacter, bcsD homologs are widespread in Proteobacteria. Here, we examine BcsD homologs and their gene neighborhoods from several plant-colonizing β- and γ-Proteobacteria proposed to secrete a variety of non-crystalline and/or chemically modified cellulosic polymers. We provide structural and mechanistic evidence that through different quaternary structure assemblies BcsD acts with proline-rich BcsH, BcsP, or BcsO partners across the proteobacterial clade to form synthase-interacting intracellular scaffolds that, in turn, determine the biofilm strength and architecture in species with strikingly different physiology and secreted biopolymers.

Large Complexes: Cloning Strategy, Production, and Purification

With few exceptions-such as myxobacteria, filamentous cyanobacteria, and actinomycetes (Rokas, Annu Rev Genet 42:235-251, 2008)-bacteria are defined as unicellular prokaryotes or single, self-sufficient cells containing all the genetic material necessary for their physiology and reproduction, while maintaining none or a minimum of intracellular organelles for pathway compartmentalization. The latter is therefore primarily achieved through the assembly of macromolecular complexes that can secure spatiotemporal control of a plethora of physiological processes, such as precise midcell division, assembly of diverse motility organelles and chemotaxis sensory arrays, metabolic channeling of substrates and toxic intermediates, localized signal transduction via soluble intracellular second messengers or the secretion of signaling molecules, competition effectors, and extracellular matrix components (Cornejo et al., Curr Opin Cell Biol 26:132-138, 2014; de Lorenzo et al., FEMS Microbiol Rev 39:96-119, 2015; Krasteva and Sondermann, Nat Chem Biol 13:350-359, 2017; Abidi et al., FEMS Microbiol Rev 46(2):fuab051, 2022; Altinoglu et al., PLoS Genet 18:e1009991, 2022). Oftentimes, pathway-specific components are encoded by clusters of co-regulated genes (Lawrence, Annu Rev Microbiol 57:419-440, 2003), which not only allows for facilitated macrocomplex assembly and rapid physiological adaptation in cellulo but can also be harnessed for the recombinant coexpression and purification of intact multicomponent nanomachines for structure-function studies of medical or biotechnological relevance. Important examples are synthase-dependent exopolysaccharide secretion systems that provide key biofilm matrix components in a vast variety of free-living or pathogenic species and at the molecular level secure the physical conduit, protection, chemical modifications and energetics for the processive extrusion of hydrophilic biopolymers through the complex bacterial envelope (Abidi et al., FEMS Microbiol Rev 46(2):fuab051, 2022). Here, we present cloning, expression, and purification strategies for the structure-function studies of macromolecular assemblies involved in bacterial cellulose secretion (Bcs) (Krasteva et al. Nat Commun 8:2065, 2017; Abidi et al. Sci Adv 7:eabd8049, 2021) that can be adapted to a variety of multicomponent cytosolic or membrane-embedded assemblies.

Genotypic variations and interspecific interactions modify gene expression and biofilm formation of Xanthomonas retroflexus

Multispecies biofilms are important models for studying the evolution of microbial interactions. Co-cultivation of Xanthomonas retroflexus (XR) and Paenibacillus amylolyticus (PA) systemically leads to the appearance of an XR wrinkled mutant (XRW), increasing biofilm production. The nature of this new interaction and the role of each partner remain unclear. We tested the involvement of secreted molecular cues in this interaction by exposing XR and XRW to PA or its supernatant and analysing the response using RNA-seq, colony-forming unit (CFU) estimates, biofilm quantification, and microscopy. Compared to wild type, the mutations in XRW altered its gene expression and increased its CFU number. These changes matched the reported effects for one of the mutated genes: a response regulator part of a two-component system involved in environmental sensing. When XRW was co-cultured with PA or its supernatant, the mutations effects on XRW gene expression were masked, except for genes involved in sedentary lifestyle, being consistent with the higher biofilm production. It appears that the higher biofilm production was the result of the interaction between the genetic context (mutations) and the biotic environment (PA signals). Regulatory genes involved in environmental sensing need to be considered to shed further light on microbial interactions.

Pseudomonas aeruginosa AlgF is a protein-protein interaction mediator required for acetylation of the alginate exopolysaccharide

Enzymatic modifications of bacterial exopolysaccharides enhance immune evasion and persistence during infection. In the Gram-negative opportunistic pathogen Pseudomonas aeruginosa, acetylation of alginate reduces opsonic killing by phagocytes and improves reactive oxygen species scavenging. Although it is well known that alginate acetylation in P. aeruginosa requires AlgI, AlgJ, AlgF, and AlgX, how these proteins coordinate polymer modification at a molecular level remains unclear. Here, we describe the structural characterization of AlgF and its protein interaction network. We characterize direct interactions between AlgF and both AlgJ and AlgX in vitro and demonstrate an association between AlgF and AlgX, as well as AlgJ and AlgI, in P. aeruginosa. We determine that AlgF does not exhibit acetylesterase activity and is unable to bind to polymannuronate in vitro. Therefore, we propose that AlgF functions to mediate protein-protein interactions between alginate acetylation enzymes, forming the periplasmic AlgJFXK (AlgJ-AlgF-AlgX-AlgK) acetylation and export complex required for robust biofilm formation.

Synthesis, Properties, and Applications of Nanocomposite Materials Based on Bacterial Cellulose and MXene

MXene exhibits impressive characteristics, including flexibility, mechanical robustness, the capacity to cleanse liquids like water through MXene membranes, water-attracting nature, and effectiveness against bacteria. Additionally, bacterial cellulose (BC) exhibits remarkable qualities, including mechanical strength, water absorption, porosity, and biodegradability. The central hypothesis posits that the incorporation of both MXene and bacterial cellulose into the material will result in a remarkable synthesis of the attributes inherent to MXene and BC. In layered MXene/BC coatings, the presence of BC serves to separate the MXene layers and enhance the material's integrity through hydrogen bond interactions. This interaction contributes to achieving a high mechanical strength of this film. Introducing cellulose into one layer of multilayer MXene can increase the interlayer space and more efficient use of MXene. Composite materials utilizing MXene and BC have gained significant traction in sensor electronics due to the heightened sensitivity exhibited by these sensors compared to usual ones. Hydrogel wound healing bandages are also fabricated using composite materials based on MXene/BC. It is worth mentioning that MXene/BC composites are used to store energy in supercapacitors. And finally, MXene/BC-based composites have demonstrated high electromagnetic interference (EMI) shielding efficiency.

Recent advances and perspectives in nucleotide second messenger signaling in bacteria

Nucleotide second messengers act as intracellular 'secondary' signals that represent environmental or cellular cues, i.e. the 'primary' signals. As such, they are linking sensory input with regulatory output in all living cells. The amazing physiological versatility, the mechanistic diversity of second messenger synthesis, degradation, and action as well as the high level of integration of second messenger pathways and networks in prokaryotes has only recently become apparent. In these networks, specific second messengers play conserved general roles. Thus, (p)ppGpp coordinates growth and survival in response to nutrient availability and various stresses, while c-di-GMP is the nucleotide signaling molecule to orchestrate bacterial adhesion and multicellularity. c-di-AMP links osmotic balance and metabolism and that it does so even in Archaea may suggest a very early evolutionary origin of second messenger signaling. Many of the enzymes that make or break second messengers show complex sensory domain architectures, which allow multisignal integration. The multiplicity of c-di-GMP-related enzymes in many species has led to the discovery that bacterial cells are even able to use the same freely diffusible second messenger in local signaling pathways that can act in parallel without cross-talking. On the other hand, signaling pathways operating with different nucleotides can intersect in elaborate signaling networks. Apart from the small number of common signaling nucleotides that bacteria use for controlling their cellular "business," diverse nucleotides were recently found to play very specific roles in phage defense. Furthermore, these systems represent the phylogenetic ancestors of cyclic nucleotide-activated immune signaling in eukaryotes.

Diverse mechanisms of polysaccharide biosynthesis, assembly and secretion across kingdoms

Polysaccharides are essential biopolymers produced in all kingdoms of life. On the cell surface, they represent versatile architectural components, forming protective capsules and coats, cell walls, or adhesives. Extracellular polysaccharide (EPS) biosynthesis mechanisms differ based on the cellular localization of polymer assembly. Some polysaccharides are first synthesized in the cytosol and then extruded by ATP powered transporters [1]. In other cases, the polymers are assembled outside the cell [2], synthesized and secreted in a single step [3], or deposited on the cell surface via vesicular trafficking [4]. This review focuses on recent insights into the biosynthesis, secretion, and assembly of EPS in microbes, plants and vertebrates. We focus on comparing the sites of biosynthesis, secretion mechanisms, and higher-order EPS assemblies.

Unraveling the Supramolecular Structure and Nanoscale Dislocations of Bacterial Cellulose Ribbons Using Correlative Super-Resolution Light and Electron Microscopy

Cellulose is a structural linear polysaccharide that is naturally produced by plants and bacteria, making it the most abundant biopolymer on Earth. The hierarchical structure of cellulose from the nano- to microscale is intimately linked to its biosynthesis and the ability to process this sustainable resource for materials applications. Despite this, the morphology of bacterial cellulose microfibrils and their assembly into higher order structures, as well as the structural origins of the alternating crystalline and disordered supramolecular structure of cellulose, have remained elusive. In this work, we employed high-resolution transmission electron and atomic force microscopies to study the morphology of bacterial cellulose ribbons at different levels of its structural hierarchy and provide direct visualization of nanometer-wide microfibrils. The non-persistent twisting of cellulose ribbons was characterized in detail, and we found that twists are associated with nanostructural defects at the bundle and microfibril levels. To investigate the structural origins of the persistent disordered regions that are present along cellulose ribbons, we employed a correlative super-resolution light and electron microscopy workflow and observed that the disordered regions that can be seen in super-resolution fluorescence microscopy largely correlated with the ribbon twisting observed in electron microscopy. Unraveling the hierarchical assembly of bacterial cellulose and the ultrastructural basis of its disordered regions provides insights into its biosynthesis and susceptibility to hydrolysis. These findings are important to understand the cell-directed assembly of cellulose, develop new cellulose-based nanomaterials, and develop more efficient biomass conversion strategies.

Effects of Fluticasone Propionate on Klebsiella pneumoniae and Gram-Negative Bacteria Associated with Chronic Airway Disease

Inhaled corticosteroids (ICS) are commonly prescribed first-line treatments for asthma and chronic obstructive pulmonary disease (COPD). Recent evidence has shown that ICS use is associated with changes in the airway microbiome, which may impact clinical outcomes such as potential increased risk for pneumonia in COPD. Although the immunomodulatory effects of corticosteroids are well appreciated, whether ICS could directly influence the behavior of respiratory tract bacteria has been unknown. In this pilot study we explored the effects of fluticasone proprionate, a commonly prescribed inhaled corticosteroid, on respiratory bacteria with an expanded focus on Klebsiella pneumoniae, a species previously implicated in fluticasone-associated pneumonia in COPD. We observed significant effects of fluticasone proprionate on growth responses of K. pneumoniae, as well as other bacterial species isolated from asthmatic patients. Fluticasone-exposed K. pneumoniae displayed altered expression of several bacterial genes and reduced the metabolic activity of bronchial epithelial cells and their expression of human β-defensin 2. Targeted assays identified a fluticasone metabolite from fluticasone-exposed K. pneumoniae cells, suggesting this species may be capable of metabolizing fluticasone proprionate. Collectively, these observations support the hypothesis that specific members of the airway microbiota possess the functional repertoire to respond to or potentially utilize corticosteroids in their microenvironment. These findings lay a foundation for novel research directions into the potential direct effects of ICS, often prescribed long term to patients, on the broader airway microbial community and on the behavior of specific microbial species implicated in asthma and COPD outcomes. IMPORTANCE Inhaled corticosteroids are widely prescribed for many respiratory diseases, including asthma and COPD. While they benefit many patients, corticosteroids can also have negative effects. Some patients do not improve with treatment and even experience adverse side effects. Recent studies have shown that inhaled corticosteroids can change the make-up of bacteria in the human respiratory tract. However, whether these medications can directly impact the behavior of such bacteria has been unknown. Here, we explored the effects of fluticasone propionate, a commonly prescribed inhaled corticosteroid, on Klebsiella pneumoniae and other airway bacteria of interest, including primary species isolated from adult asthma patients. We provide evidence of growth responses to direct fluticasone exposure in culture and further examined fluticasone's effects on K. pneumoniae, including gene expression changes and effects of fluticasone-exposed bacteria on airway cells. These findings indicate that members of the human airway bacterial community possess the functional ability to respond to corticosteroids, which may have implications for the heterogeneity of treatment response observed clinically.

Structure prediction-based insights into the patatin family of Mycobacterium tuberculosis

Despite its genome sequencing more than two decades ago, the majority of the genes of Mycobacterium tuberculosis remain functionally uncharacterized. Patatins are one such class of proteins that, despite undergoing an expansion in this pathogenic species compared to their non-pathogenic cousins, remain largely unstudied. Recent advances in protein structure prediction using machine learning tools such as AlphaFold2 have provided high-confidence predicted structures for all M. tuberculosis proteins. Here we present detailed analyses of the patatin family of M. tuberculosis using AlphaFold-predicted structures, providing insights into likely modes of regulation, membrane interaction and substrate binding. Regulatory domains within this family of proteins include cyclic nucleotide binding, lid-like domains and other helical domains. Using structural homologues, we identified the likely membrane localization mechanisms and substrate-binding sites. These analyses reveal diversity in their regulatory capacity, mechanisms of membrane binding and likely length of fatty acid substrates. Together, this analysis suggests unique roles for the eight predicted patatins of M. tuberculosis.

Building a Cell House from Cellulose: The Case of the Soil Acidobacterium Acidisarcina polymorpha SBC82T

Acidisarcina polymorpha SBC82T is a recently described representative of the phylum Acidobacteriota from lichen-covered tundra soil. Cells of this bacterium occur within unusual saccular chambers, with the chamber envelope formed by tightly packed fibrils. These extracellular structures were most pronounced in old cultures of strain SBC82T and were organized in cluster-like aggregates. The latter were efficiently destroyed by incubating cell suspensions with cellulase, thus suggesting that they were composed of cellulose. The diffraction pattern obtained for 45-day-old cultures of strain SBC82T by using small angle X-ray scattering was similar to those reported earlier for mature wood samples. The genome analysis revealed the presence of a cellulose biosynthesis locus bcs. Cellulose synthase key subunits A and B were encoded by the bcsAB gene whose close homologs are found in genomes of many members of the order Acidobacteriales. More distant homologs of the acidobacterial bcsAB occurred in representatives of the Proteobacteria. A unique feature of bcs locus in strain SBC82T was the non-orthologous displacement of the bcsZ gene, which encodes the GH8 family glycosidase with a GH5 family gene. Presumably, these cellulose-made extracellular structures produced by A. polymorpha have a protective function and ensure the survival of this acidobacterium in habitats with harsh environmental conditions.

Bacterial Cellulose as a Versatile Biomaterial for Wound Dressing Application

Chronic ulcers are among the main causes of morbidity and mortality due to the high probability of infection and sepsis and therefore exert a significant impact on public health resources. Numerous types of dressings are used for the treatment of skin ulcers-each with different advantages and disadvantages. Bacterial cellulose (BC) has received enormous interest in the cosmetic, pharmaceutical, and medical fields due to its biological, physical, and mechanical characteristics, which enable the creation of polymer composites and blends with broad applications. In the medical field, BC was at first used in wound dressings, tissue regeneration, and artificial blood vessels. This material is suitable for treating various skin diseases due its considerable fluid retention and medication loading properties. BC membranes are used as a temporary dressing for skin treatments due to their excellent fit to the body, reduction in pain, and acceleration of epithelial regeneration. BC-based composites and blends have been evaluated and synthesized both in vitro and in vivo to create an ideal microenvironment for wound healing. This review describes different methods of producing and handling BC for use in the medical field and highlights the qualities of BC in detail with emphasis on biomedical reports that demonstrate its utility. Moreover, it gives an account of biomedical applications, especially for tissue engineering and wound dressing materials reported until date. This review also includes patents of BC applied as a wound dressing material.

Biomedical engineering aspects of nanocellulose: a review

Cellulose is one of the most abundant renewable biopolymer in nature and is present as major constituent in both plant cell walls as well as synthesized by some microorganisms as extracellular products. In both the systems, cellulose self-assembles into a hierarchical ordered architecture to form micro to nano-fibrillated structures, on basis of which it is classified into various forms. Nanocellulose (NCs) exist as rod-shaped highly crystalline cellulose nanocrystals to high aspect ratio cellulose nanofibers, micro-fibrillated cellulose and bacterial cellulose (BC), depending upon the origin, structural and morphological properties. Moreover, NCs have been processed into diversified products ranging from composite films, coatings, hydrogels, aerogels, xerogels, organogels, rheological modifiers, optically active birefringent colored films using traditional-to-advanced manufacturing techniques. With such versatility in structure-property, NCs have profound application in areas of healthcare, packaging, cosmetics, energy, food, electronics, bioremediation, and biomedicine with promising commercial potential. Herein this review, we highlight the recent advancements in synthesis, fabrication, processing of NCs, with strategic chemical modification routes to tailor its properties for targeted biomedical applications. We also study the basic mechanism and models for biosynthesis of cellulose in both plant and microbial systems and understand the structural insights of NC polymorphism. The kinetics study for both enzymatic/chemical modifications of NCs and microbial growth behavior of BC under various reactor configurations are studied. The challenges associated with the commercial aspects as well as industrial scale production of pristine and functionalized NCs to meet the growing demands of market are discussed and prospective strategies to mitigate them are described. Finally, post chemical modification evaluation of biological and inherent properties of NC are important to determine their efficacy for development of various products and technologies directed for biomedical applications.

Genomic attributes differ between Vibrio parahaemolyticus environmental and clinical isolates including pathotypes

Vibrio parahaemolyticus is a marine bacterium and causes opportunistic gastroenteritis in humans. Clinical strains of V. parahaemolyticus contain haemolysin and type III secretion systems (T3SS) that define their pathotype. A growing number of strains isolated recently from the environment have acquired these virulence genes constituting a pool of potential pathogens. This study used comparative genomics to identify genetic factors that delineate environmental and clinical V. parahaemolyticus population and understand the similarities and differences between the T3SS2 phylotypes. The comparative analysis revealed the presence of a cluster of genes belonging to bacterial cellulose synthesis (bcs) in isolates of environmental origin. This cluster, previously unreported in V. parahaemolyticus, exhibit significant similarity to that of Aliivibrio fischeri, and might dictate a potentially new mechanism of its environmental adaptation and persistence. The study also identified many genes predicted in silico to be T3SS effectors that are unique to T3SS2β of tdh^- trh⁺ and tdh⁺ trh⁺ pathotype and having no identifiable homologue in tdh⁺ trh^- T3SS2α. Overall, these findings highlight the importance of understanding the genes and strategies V. parahaemolyticus utilize for the myriad interactions with its hosts, either marine invertebrates or humans.

Bacterial protein secretion systems: Game of types

Protein trafficking across the bacterial envelope is a process that contributes to the organisation and integrity of the cell. It is the foundation for establishing contact and exchange between the environment and the cytosol. It helps cells to communicate with one another, whether they establish symbiotic or competitive behaviours. It is instrumental for pathogenesis and for bacteria to subvert the host immune response. Understanding the formation of envelope conduits and the manifold strategies employed for moving macromolecules across these channels is a fascinating playground. The diversity of the nanomachines involved in this process logically resulted in an attempt to classify them, which is where the protein secretion system types emerged. As our knowledge grew, so did the number of types, and their rightful nomenclature started to be questioned. While this may seem a semantic or philosophical issue, it also reflects scientific rigour when it comes to assimilating findings into textbooks and science history. Here I give an overview on bacterial protein secretion systems, their history, their nomenclature and why it can be misleading for newcomers in the field. Note that I do not try to suggest a new nomenclature. Instead, I explore the reasons why naming could have escaped our control and I try to reiterate basic concepts that underlie protein trafficking cross membranes.

Acetobacter senegalensis Isolated from Mango Fruits: Its Polyphasic Characterization and Adaptation to Protect against Stressors in the Industrial Production of Vinegar: A Review

It has been more than a decade since Acetobacter senegalensis was isolated, identified, and described as a thermotolerant strain of acetic acid bacteria. It was isolated from mango fruits in Senegal and used for industrial vinegar production in developing countries, mainly in sub-Saharan Africa. The strain was tested during several spirit vinegar fermentation processes at relatively high temperatures in accordance with African acclimation. The upstream fermentation process had significant stress factors, which are highlighted in this review so that the fermentation process can be better controlled. Due to its high industrial potential, this strain was extensively investigated by diverse industrial microbiologists worldwide; they concentrated on its microbiological, physiological, and genomic features. A research group based in Belgium proposed an important project for the investigation of the whole-genome sequence of A. senegalensis. It would use a 454-pyrosequencing technique to determine and corroborate features that could give this strain significant diverse bioindustrial applications. For instance, its application in cocoa bean fermentation has made it a more suitable acetic acid bacterium for the making of chocolate than Acetobacter pasteurianus. Therefore, in this paper, we present a review that summarizes the current research on A. senegalensis at its microbial and genomic levels and also its specific bioindustrial applications, which can provide economic opportunities for African agribusiness.

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.

A Bacterial Two-Hybrid System for In Vivo Assays of Protein-Protein Interactions and Drug Discovery

The bacterial adenylate cyclase-based two-hybrid (BACTH) system is a robust and simple genetic assay used to monitor protein-protein interactions in vivo. This system is based on functional complementation between two fragments from the catalytic domain of Bordetella pertussis adenylate cyclase (AC) to reconstitute a cyclic AMP (cAMP)-signaling cascade in Escherichia coli. Interactions between two chimeric proteins result in the synthesis of cAMP, which activates the transcription of various catabolite operons, leading to selectable phenotypes. One advantageous feature of this signaling cascade is that the physical association between the two interacting hybrid proteins is spatially separated from the transcriptional activation readout. Consequently, the BACTH system can detect protein-protein interactions occurring at various subcellular localizations. The system has been used to characterize interactions between soluble or membrane proteins of prokaryotic, eukaryotic, or viral origin. The BACTH assay can be used to uncover the region(s), domain(s), or amino acid residue(s) of a protein involved in an interaction with a specific partner. The BACTH system can also be adapted for the high-throughput screening of small molecules able to interfere with protein-protein interactions.

A New Sugar for an Old Phage: a c-di-GMP-Dependent Polysaccharide Pathway Sensitizes Escherichia coli for Bacteriophage Infection

Bacteriophages are ubiquitous parasites of bacteria and major drivers of bacterial ecology and evolution. Despite an ever-growing interest in their biotechnological and therapeutic applications, detailed knowledge of the molecular mechanisms underlying phage-host interactions remains scarce. Here, we show that bacteriophage N4 exploits a novel surface glycan (NGR) as a receptor to infect its host Escherichia coli. We demonstrate that this process is regulated by the second messenger c-di-GMP and that N4 infection is specifically stimulated by the diguanylate cyclase DgcJ, while the phosphodiesterase PdeL effectively protects E. coli from N4-mediated killing. PdeL-mediated protection requires its catalytic activity to reduce c-di-GMP and includes a secondary role as a transcriptional repressor. We demonstrate that PdeL binds to and represses the promoter of the wec operon, which encodes components of the enterobacterial common antigen (ECA) exopolysaccharide pathway. However, only the acetylglucosamine epimerase WecB but none of the other ECA components is required for N4 infection. Based on this, we postulate that NGR is an N-acetylmannosamine-based carbohydrate polymer that is produced and exported to the cell surface of E. coli in a c-di-GMP-dependent manner, where it serves as a receptor for N4. This novel carbohydrate pathway is conserved in E. coli and other bacterial pathogens, serves as the primary receptor for various bacteriophages, and is induced at elevated temperature and by specific amino acid-based nutrients. These studies provide an entry point into understanding how bacteria use specific regulatory mechanisms to balance costs and benefits of highly conserved surface structures.

Capsules and Extracellular Polysaccharides in Escherichia coli and Salmonella

Escherichia coli and Salmonella isolates produce a range of different polysaccharide structures that play important roles in their biology. E. coli isolates often possess capsular polysaccharides (K antigens), which form a surface structural layer. These possess a wide range of repeat-unit structures. In contrast, only one capsular polymer (Vi antigen) is found in Salmonella, and it is confined to typhoidal serovars. In both genera, capsules are vital virulence determinants and are associated with the avoidance of host immune defenses. Some isolates of these species also produce a largely secreted exopolysaccharide called colanic acid as part of their complex Rcs-regulated phenotypes, but the precise function of this polysaccharide in microbial cell biology is not fully understood. E. coli isolates produce two additional secreted polysaccharides, bacterial cellulose and poly-N-acetylglucosamine, which play important roles in biofilm formation. Cellulose is also produced by Salmonella isolates, but the genes for poly-N-acetylglucosamine synthesis appear to have been lost during its evolution toward enhanced virulence. Here, we discuss the structures, functions, relationships, and sophisticated assembly mechanisms for these important biopolymers.

Bio-conversion of kitchen waste into bacterial cellulose using a new multiple carbon utilizing Komagataeibacter rhaeticus: Fermentation profiles and genome-wide analysis

A cellulose-producing bacterium Komagataeibacter rhaeticus K15 was isolated from kombucha tea, and its metabolic pathways and cellulose synthesis operon were analyzed by genome sequencing. Different from the reported K. rhaeticus, the K15 produced little gluconic acid (2.26 g/L) when glucose was the sole carbon source and has the capacity for high cellulose production (4.76 g/L) with other carbon sources. Furthermore, six nitrogen-fixing genes were found to be responsible for the survival of K15 on a nitrogen-free medium. Based on its fermentation characteristics, K15 was cultured in a kitchen waste medium as a strategy for green and sustainable bacterial cellulose production. The SEM, XRD, and FTIR results indicated that synthesized cellulose has a mean diameter of 40-50 nm nanofiber, good crystallinity, and the same chemical structure. The K15 strain provides a highly viable alternative strategy to reduce the costs of bacterial cellulose production using agro-industrial residues as nutrient sources.

Emergent Biological Endurance Depends on Extracellular Matrix Composition of Three-Dimensionally Printed Escherichia coli Biofilms

Biofilms are three-dimensional (3D) bacterial communities that exhibit a highly self-organized nature in terms of their composition and complex architecture. Bacteria in biofilms display emergent biological properties, such as resistance to antimicrobials and disinfectants that the individual planktonic cells lack. Bacterial biofilms possess specialized architectural features including unique extracellular matrix compositions and a distinct spatially patterned arrangement of cells and matrix components within the biofilm. It is unclear which of these architectural elements of bacterial biofilms lead to the development of their emergent biological properties. Here, we report a 3D printing-based technique for studying the emergent resistance behaviors of Escherichia coli biofilms as a function of their architecture. Cellulose and curli are the major extracellular-matrix components in E. coli biofilms. We show that 3D-printed biofilms expressing either curli alone or both curli and cellulose in their extracellular matrices show higher resistance to exposure against disinfectants than 3D prints expressing either cellulose alone or no biofilm-matrix components. The 3D-printed biofilms expressing cellulose and/or curli also show thicker anaerobic zones than nonbiofilm-forming E. coli 3D prints. Thus, the matrix composition plays a crucial role in the emergent spatial patterning and biological endurance of 3D-printed biofilms. In contrast, initial spatial distribution of bacterial density or curli-producing cells does not have an effect on biofilm resistance phenotypes. Further, these 3D-printed biofilms could be reversibly attached to different surfaces (bacterial cellulose, glass, and polystyrene) and display resistance to physical distortions by retaining their shape and structure. This physical robustness highlights their potential in applications including bioremediation, protective coatings against pathogens on medical devices, or wastewater treatment, among many others. This new understanding of the emergent behavior of bacterial biofilms could aid in the development of novel engineered living materials using synthetic biology and materials science approaches.

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.

Regulation of Biofilm Exopolysaccharide Production by Cyclic Di-Guanosine Monophosphate

Many bacterial species in nature possess the ability to transition into a sessile lifestyle and aggregate into cohesive colonies, known as biofilms. Within a biofilm, bacterial cells are encapsulated within an extracellular polymeric substance (EPS) comprised of polysaccharides, proteins, nucleic acids, lipids, and other small molecules. The transition from planktonic growth to the biofilm lifecycle provides numerous benefits to bacteria, such as facilitating adherence to abiotic surfaces, evasion of a host immune system, and resistance to common antibiotics. As a result, biofilm-forming bacteria contribute to 65% of infections in humans, and substantially increase the energy and time required for treatment and recovery. Several biofilm specific exopolysaccharides, including cellulose, alginate, Pel polysaccharide, and poly-N-acetylglucosamine (PNAG), have been shown to play an important role in bacterial biofilm formation and their production is strongly correlated with pathogenicity and virulence. In many bacteria the biosynthetic machineries required for assembly of these exopolysaccharides are regulated by common signaling molecules, with the second messenger cyclic di-guanosine monophosphate (c-di-GMP) playing an especially important role in the post-translational activation of exopolysaccharide biosynthesis. Research on treatments of antibiotic-resistant and biofilm-forming bacteria through direct targeting of c-di-GMP signaling has shown promise, including peptide-based treatments that sequester intracellular c-di-GMP. In this review, we will examine the direct role c-di-GMP plays in the biosynthesis and export of biofilm exopolysaccharides with a focus on the mechanism of post-translational activation of these pathways, as well as describe novel approaches to inhibit biofilm formation through direct targeting of c-di-GMP.

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.

Bacterial Multicellularity: The Biology of Escherichia coli Building Large-Scale Biofilm Communities

Biofilms are a widespread multicellular form of bacterial life. The spatial structure and emergent properties of these communities depend on a polymeric extracellular matrix architecture that is orders of magnitude larger than the cells that build it. Using as a model the wrinkly macrocolony biofilms of Escherichia coli, which contain amyloid curli fibers and phosphoethanolamine (pEtN)-modified cellulose as matrix components, we summarize here the structure, building, and function of this large-scale matrix architecture. Based on different sigma and other transcription factors as well as second messengers, the underlying regulatory network reflects the fundamental trade-off between growth and survival. It controls matrix production spatially in response to long-range chemical gradients, but it also generates distinct patterns of short-range matrix heterogeneity that are crucial for tissue-like elasticity and macroscopic morphogenesis. Overall, these biofilms confer protection and a potential for homeostasis, thereby reducing maintenance energy, which makes multicellularity an emergent property of life itself. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Genome Features of Asaia sp. W12 Isolated from the Mosquito Anopheles stephensi Reveal Symbiotic Traits

Asaia bacteria commonly comprise part of the microbiome of many mosquito species in the genera Anopheles and Aedes, including important vectors of infectious agents. Their close association with multiple organs and tissues of their mosquito hosts enhances the potential for paratransgenesis for the delivery of antimalaria or antivirus effectors. The molecular mechanisms involved in the interactions between Asaia and mosquito hosts, as well as Asaia and other bacterial members of the mosquito microbiome, remain underexplored. Here, we determined the genome sequence of Asaia strain W12 isolated from Anopheles stephensi mosquitoes, compared it to other Asaia species associated with plants or insects, and investigated the properties of the bacteria relevant to their symbiosis with mosquitoes. The assembled genome of strain W12 had a size of 3.94 MB, the largest among Asaia spp. studied so far. At least 3585 coding sequences were predicted. Insect-associated Asaia carried more glycoside hydrolase (GH)-encoding genes than those isolated from plants, showing their high plant biomass-degrading capacity in the insect gut. W12 had the most predicted regulatory protein components comparatively among the selected Asaia, indicating its capacity to adapt to frequent environmental changes in the mosquito gut. Two complete operons encoding cytochrome bo₃-type ubiquinol terminal oxidases (cyoABCD-1 and cyoABCD-2) were found in most Asaia genomes, possibly offering alternative terminal oxidases and allowing the flexible transition of respiratory pathways. Genes involved in the production of 2,3-butandiol and inositol have been found in Asaia sp. W12, possibly contributing to biofilm formation and stress tolerance.

Deciphering Legionella effector delivery by Icm/Dot secretion system reveals a new role for c-di-GMP signaling

Secretion of bacterial effector proteins into host cells plays a key role in bacterial virulence. Yet, the dynamics of the secretion systems activity remains poorly understood, especially when machineries deal with the export of numerous effectors. We address the question of multi-effector secretion by focusing on the Legionella pneumophila Icm/Dot T4SS that translocates a record number of 300 effectors. We set up a kinetic translocation assay, based on the β-lactamase translocation reporter system combined with the effect of the protonophore CCCP. When used for translocation analysis of Icm/Dot substrates constitutively produced by L. pneumophila, this assay allows a fine monitoring of the secretion activity of the T4SS, independently of the expression control of the effectors. We observed that effectors are translocated with a specific timing, suggesting a control of their docking/translocation by the T4SS. Their delivery is accurately organized to allow effective manipulation of the host cell, as exemplified by the sequential translocation of effectors targeting Rab1, namely SidM/DrrA, LidA, LepB. Remarkably, the timed delivery of effectors does not depend only on their interaction with chaperone proteins but implies cyclic-di-GMP signaling, as the diguanylate cyclase Lpl0780/Lpp0809, contributes to the timing of translocation.

A SNP in the Cache 1 Signaling Domain of Diguanylate Cyclase STM1987 Leads to Increased In Vivo Fitness of Invasive Salmonella Strains

Nontyphoidal Salmonella (NTS) strains are associated with gastroenteritis worldwide but are also the leading cause of bacterial bloodstream infections in sub-Saharan Africa. The invasive NTS (iNTS) strains that cause bloodstream infections differ from standard gastroenteritis-causing strains by >700 single-nucleotide polymorphisms (SNPs). These SNPs are known to alter metabolic pathways and biofilm formation and to contribute to serum resistance and are thought to signify iNTS strains becoming human adapted, similar to typhoid fever-causing Salmonella strains. Identifying SNPs that contribute to invasion or increased virulence has been more elusive. In this study, we identified a SNP in the cache 1 signaling domain of diguanylate cyclase STM1987 in the invasive Salmonella enterica serovar Typhimurium type strain D23580. This SNP was conserved in 118 other iNTS strains analyzed and was comparatively absent in global S Typhimurium isolates associated with gastroenteritis. STM1987 catalyzes the formation of bis-(3',5')-cyclic dimeric GMP (c-di-GMP) and is proposed to stimulate production of cellulose independent of the master biofilm regulator CsgD. We show that the amino acid change in STM1987 leads to a 10-fold drop in cellulose production and increased fitness in a mouse model of acute infection. Reduced cellulose production due to the SNP led to enhanced survival in both murine and human macrophage cell lines. In contrast, loss of CsgD-dependent cellulose production did not lead to any measurable change in in vivo fitness. We hypothesize that the SNP in stm1987 represents a pathoadaptive mutation for iNTS strains.

Molecular organization of the E. coli cellulose synthase macrocomplex

Cellulose is frequently found in communities of sessile bacteria called biofilms. Escherichia coli and other enterobacteriaceae modify cellulose with phosphoethanolamine (pEtN) to promote host tissue adhesion. The E. coli pEtN cellulose biosynthesis machinery contains the catalytic BcsA-B complex that synthesizes and secretes cellulose, in addition to five other subunits. The membrane-anchored periplasmic BcsG subunit catalyzes pEtN modification. Here we present the structure of the roughly 1 MDa E. coli Bcs complex, consisting of one BcsA enzyme associated with six copies of BcsB, determined by single-particle cryo-electron microscopy. BcsB homo-oligomerizes primarily through interactions between its carbohydrate-binding domains as well as intermolecular beta-sheet formation. The BcsB hexamer creates a half spiral whose open side accommodates two BcsG subunits, directly adjacent to BcsA's periplasmic channel exit. The cytosolic BcsE and BcsQ subunits associate with BcsA's regulatory PilZ domain. The macrocomplex is a fascinating example of cellulose synthase specification.

High-Specificity Local and Global c-di-GMP Signaling

The striking multiplicity, signal input diversity, and output specificity of c-di-GMP signaling proteins in many bacteria has brought second messenger signaling back onto the agenda of contemporary microbiology. How can several signaling pathways act in parallel in a specific manner if all of them use the same diffusible second messenger present at a certain global cellular concentration? Recent research has now shown that bacteria achieve this by flexibly combining modes of local and global c-di-GMP signaling in complex signaling networks. Three criteria have to be met to define local c-di-GMP signaling: specific knockout phenotypes, direct interactions between proteins involved, and actual cellular c-di-GMP levels remaining below the K_d of effectors. Adaptive changes in signaling network architecture can further enhance signaling flexibility.

Biomedical Applications of Bacterial Exopolysaccharides: A Review

Bacterial exopolysaccharides (EPSs) are an essential group of compounds secreted by bacteria. These versatile EPSs are utilized individually or in combination with different materials for a broad range of biomedical field functions. The various applications can be explained by the vast number of derivatives with useful properties that can be controlled. This review offers insight on the current research trend of nine commonly used EPSs, their biosynthesis pathways, their characteristics, and the biomedical applications of these relevant bioproducts.

Engineering Halomonas bluephagenesis as a chassis for bioproduction from starch

Halomonas bluephagenesis has been successfully engineered to produce multiple products under open unsterile conditions utilizing costly glucose as the carbon source. It would be highly interesting to investigate if H. bluephagenesis, a chassis for the Next Generation Industrial Biotechnology (NGIB), can be reconstructed to become an extracellular hydrolytic enzyme producer replacing traditional enzyme producer Bacillus spp. If successful, cost of bulk hydrolytic enzymes such as amylase and protease, can be significantly reduced due to the contamination resistant and robust growth of H. bluephagenesis. This also allows H. bluephagenesis to be able to grow on low cost substrates such as starch. The modularized secretion machinery was constructed and fine-tuned in H. bluephagenesis using codon-optimized gene encoding α-amylase from Bacillus lichenifomis. Screening of suitable signal peptides and linkers based on super-fold green fluorescence protein (sfGFP) for enhanced expression in H. bluephagenesis resulted in a 7-fold enhancement of sfGFP secretion in the recombinant H. bluephagenesis. When the gene encoding sfGFP was replaced by α-amylase encoding gene, recombinant H. bluephagenesis harboring this amylase secretory system was able to produce poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), ectoine and L-threonine utilizing starch as the growth substrate, respectively. Recombinant H. bluephagenesis TN04 expressing genes encoding α-amylase and glucosidase on chromosome and plasmid-based systems, respectively, was able to grow on corn starch to approximately 10 g/L cell dry weight containing 51% PHB when grown in shake flasks. H. bluephagenesis was demonstrated to be a chassis for productions of extracellular enzymes and multiple products from low cost corn starch.

Recent Advances and Applications of Bacterial Cellulose in Biomedicine

Bacterial cellulose (BC) is an extracellular polymer produced by Komagateibacter xylinus, which has been shown to possess a multitude of properties, which makes it innately useful as a next-generation biopolymer. The structure of BC is comprised of glucose monomer units polymerised by cellulose synthase in β-1-4 glucan chains which form uniaxially orientated BC fibril bundles which measure 3-8 nm in diameter. BC is chemically identical to vegetal cellulose. However, when BC is compared with other natural or synthetic analogues, it shows a much higher performance in biomedical applications, potable treatment, nano-filters and functional applications. The main reason for this superiority is due to the high level of chemical purity, nano-fibrillar matrix and crystallinity. Upon using BC as a carrier or scaffold with other materials, unique and novel characteristics can be observed, which are all relatable to the features of BC. These properties, which include high tensile strength, high water holding capabilities and microfibrillar matrices, coupled with the overall physicochemical assets of bacterial cellulose makes it an ideal candidate for further scientific research into biopolymer development. This review thoroughly explores several areas in which BC is being investigated, ranging from biomedical applications to electronic applications, with a focus on the use as a next-generation wound dressing. The purpose of this review is to consolidate and discuss the most recent advancements in the applications of bacterial cellulose, primarily in biomedicine, but also in biotechnology.

Bioengineering of Bordetella pertussis Adenylate Cyclase Toxin for Vaccine Development and Other Biotechnological Purposes

The adenylate cyclase toxin, CyaA, is one of the key virulent factors produced by Bordetella pertussis, the causative agent of whooping cough. This toxin primarily targets innate immunity to facilitate bacterial colonization of the respiratory tract. CyaA exhibits several remarkable characteristics that have been exploited for various applications in vaccinology and other biotechnological purposes. CyaA has been engineered as a potent vaccine vehicle to deliver antigens into antigen-presenting cells, while the adenylate cyclase catalytic domain has been used to design a robust genetic assay for monitoring protein-protein interactions in bacteria. These two biotechnological applications are briefly summarized in this chapter.

Molecular Dynamics Simulation of Cellulose Synthase Subunit D Octamer with Cellulose Chains from Acetic Acid Bacteria: Insight into Dynamic Behaviors and Thermodynamics on Substrate Recognition

The present study reports the building of a computerized model and molecular dynamics (MD) simulation of cellulose synthase subunit D octamer (CesD) from Komagataeibacter hansenii. CesD was complexed with four cellulose chains having DP = 12 (G12) by model building, which revealed unexpected S-shaped pathways with bending regions. Combined conventional and accelerated MD simulations of CesD complex models were carried out, while the pyranose ring conformations of the glucose residues were restrained to avoid undesirable deviations of the ring conformation from the ⁴C₁ form. The N-terminal regions and parts of the secondary structures of CesD established appreciable contacts with the G12 chains. Hybrid quantum mechanical (QM) and molecular mechanical (MM) simulations of the CesD complex model were performed. Glucose residues located at the pathway bends exhibited reversible changes to the ring conformation into either skewed or boat forms, which might be related to the function of CesD in regulating microfibril production.

Structure of the Bacterial Cellulose Ribbon and Its Assembly-Guiding Cytoskeleton by Electron Cryotomography

This work’s relevance for the microbiology community is twofold. It delivers for the first time high-resolution near-native snapshots of Gluconacetobacter spp. (previously Komagataeibacter spp.) in the process of cellulose ribbon synthesis, in their native biofilm environment.

Cellulose is a widespread component of bacterial biofilms, where its properties of exceptional water retention, high tensile strength, and stiffness prevent dehydration and mechanical disruption of the biofilm. Bacteria in the genus Gluconacetobacter secrete crystalline cellulose, with a structure very similar to that found in plant cell walls. How this higher-order structure is produced is poorly understood. We used cryo-electron tomography and focused-ion-beam milling of native bacterial biofilms to image cellulose-synthesizing Gluconacetobacter hansenii and Gluconacetobacter xylinus bacteria in a frozen-hydrated, near-native state. We confirm previous results suggesting that cellulose crystallization occurs serially following its secretion along one side of the cell, leading to a cellulose ribbon that can reach several micrometers in length and combine with ribbons from other cells to form a robust biofilm matrix. We were able to take direct measurements in a near-native state of the cellulose sheets. Our results also reveal a novel cytoskeletal structure, which we have named the cortical belt, adjacent to the inner membrane and underlying the sites where cellulose is seen emerging from the cell. We found that this structure is not present in other cellulose-synthesizing bacterial species, Agrobacterium tumefaciens and Escherichia coli 1094, which do not produce organized cellulose ribbons. We therefore propose that the cortical belt holds the cellulose synthase complexes in a line to form higher-order cellulose structures, such as sheets and ribbons.

IMPORTANCE This work’s relevance for the microbiology community is twofold. It delivers for the first time high-resolution near-native snapshots of Gluconacetobacter spp. (previously Komagataeibacter spp.) in the process of cellulose ribbon synthesis, in their native biofilm environment. It puts forward a noncharacterized cytoskeleton element associated with the side of the cell where the cellulose synthesis occurs. This represents a step forward in the understanding of the cell-guided process of crystalline cellulose synthesis, studied specifically in the Gluconacetobacter genus and still not fully understood. Additionally, our successful attempt to use cryo-focused-ion-beam milling through biofilms to image the cells in their native environment will drive the community to use this tool for the morphological characterization of other studied biofilms.

Racing to build a wall: glycoconjugate assembly in Gram-positive and Gram-negative bacteria

The last two years have seen major advances in understanding the structural basis of bacterial cell envelope glycoconjugate biosynthesis, including capsules, lipopolysaccharide, teichoic acid, cellulose, and peptidoglycan. The recent crystal and cryo-electron microscopy structures of proteins involved in the initial glycosyltransferase steps in the cytoplasm, the transport of large and small lipid-linked glycoconjugates across the inner membrane, the polymerization of glycans in the periplasm, and the export of molecules from the cell have shed light on the mechanisms by which cell envelope glycoconjugates are made. We discuss these recent advances and highlight remaining unanswered questions.

Architecture and regulation of an enterobacterial cellulose secretion system

Many free-living and pathogenic enterobacteria secrete biofilm-promoting cellulose using a multicomponent, envelope-embedded Bcs secretion system under the control of intracellular second messenger c-di-GMP. The molecular understanding of system assembly and cellulose secretion has been largely limited to the crystallographic studies of a distantly homologous BcsAB synthase tandem and a low-resolution reconstruction of an assembled macrocomplex that encompasses most of the inner membrane and cytosolic subunits and features an atypical layered architecture. Here, we present cryo-EM structures of the assembled Bcs macrocomplex, as well as multiple crystallographic snapshots of regulatory Bcs subcomplexes. The structural and functional data uncover the mechanism of asymmetric secretion system assembly and periplasmic crown polymerization and reveal unexpected subunit stoichiometry, multisite c-di-GMP recognition, and ATP-dependent regulation.