Genetic regulation, biosynthesis and applications of extracellular polysaccharides of the biofilm matrix of bacteria

Little alginates synthesized in EPS: Evidences from high-throughput community and metagenes

As a significant structure in activated sludge, extracellular polymeric substances (EPS) hold considerable value regarding resource recovery and applications. The present study aimed to elucidate the relationship between the microbial community and the composition and properties of EPS. A biological nutrient removal (BNR) reactor was set up in the laboratory and controlled under different solid retention times (SRT), altering microbial species within the system. Then EPS was extracted from activated and analyzed by chemical and spectroscopic methods. High-throughput sequencing and metagenomic approaches were employed to investigate bacterial community and metabolic pathways. The results showed that lower SRT with a higher abundance of the family-level Proteobacteria (27.7%-53.5%) favored EPS synthesis, while another dominant group Bacteroidetes (20.0%-32.6%) may not significantly affect EPS synthesis. Furthermore, the abundance of alginates-producing bacteria including Pseudomonas spp. and Azotobacter vinelandii was only 2.53%-6.76% and 1.98%-6.34%, respectively. The alginate synthesis pathway genes Alg8 and Alg44 were also present at very low levels (0.05‱-0.11‱, 0.01‱-0.02‱, respectively). Another important gene related to alginates operons, AlgK, was absent across all the SRT-operated reactors. These findings suggest an impossible and incomplete alginate synthesis pathway within sludge. In light of these results, it can be concluded that EPS does not necessarily contain alginate components.

Nanoscale zero-valent iron alleviated horizontal transfer of antibiotic resistance genes in soil: The important role of extracellular polymeric substances

Extracellular polymeric substances (EPS) are tightly related to the horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs), but often neglected in soil. In this study, nanoscale zero-valent iron (nZVI) was utilized for attenuation of ARGs in contaminated soil, with an emphasis on its effects on EPS secretion and HGT. Results showed during soil microbe cultivation exposed to tetracycline, more EPS was secreted and significant increase of tet was observed due to facilitated HGT. Notably, copies of EPS-tet accounted for 71.39 % of the total tet, implying vital effects of EPS on ARGs proliferation. When co-exposed to nZVI, EPS secretion was decreased by 38.36-71.46 %, for that nZVI could alleviate the microbial oxidative stress exerted by tetracycline resulting in downregulation of genes expression related to the c-di-GMP signaling system. Meanwhile, the abundance of EPS-tet was obviously reduced from 7.04 to 5.12-6.47 log unit, directly causing decrease of total tet from 7.19 to 5.68-6.69 log unit. For the reduced tet, it was mainly due to decreased EPS secretion induced by nZVI resulting in inhibition of HGT especially transformation of the EPS-tet. This work gives an inspiration for attenuation of ARGs dissemination in soil through an EPS regulation strategy.

Assessment of the Safety and Exopolysaccharide Synthesis Capabilities of Bacillus amyloliquefaciens D189 Based on Complete Genome and Phenotype Analysis

Exopolysaccharides (EPS) are natural macromolecular carbohydrates with good functional activity and physiological activities, which can be utilized as an emulsifier, viscosity enhancer, stabilizer, gelling agent, and water retention agent in a wide range of food products. In this study, the whole genome of Bacillus amyloliquefaciens D189, an EPS-producing bacteria, was sequenced. The result showed that D189 contains a single, circular chromosome of 3,963,356 bp with an average GC content of 45.74% and 3996 coding genes. The gene annotation results showed that D189 is a potentially safe strain and confirmed to be safe associated with hemolytic assay, and antibiotic resistance test. Meanwhile, D189 genome possessed 240 genes related to carbohydrate metabolism. More importantly, D189 could transport 9 sugars and contained a complete biosynthetic pathway for 8 nucleotide sugars. Based on the validation experiments, strain D189 could metabolize 8 sugars (glucose, sucrose, trehalose, fructose, cellobiose, maltose, mannitol, and N-acetyl-D-glucosamine) to produce EPS, with the highest yield of 1.212 g/L when sucrose was the carbon source. Therefore, the whole genome sequencing preliminarily elucidated the physiological mechanism of EPS, providing several pathways for engineering D189 to further enhance the yield of EPS.

Challenges and opportunities in bioprocessing of gellan gum: A review

Gellan gum (GG) - the microbial exopolysaccharide is increasingly being adopted into drug development, tissue engineering, and food and pharmaceutical products. In spite of the commercial importance and expanding application horizon of GG, little attention has been directed toward the exploration of novel microbial cultures, development of advanced screening protocols, strain engineering, and robust upstream or downstream processes. This comprehensive review not only attempts to summarize the existing knowledge pool on GG bioprocess but also critically assesses their inherent challenges. The process optimization design augmented with advanced machine learning modeling tools, widely adopted in other microbial bioprocesses, should be extended to GG. The unification of mechanistic insight into data-driven modeling would help to formulate optimal feeding and process control strategies.

Current strategies for monitoring and controlling bacterial biofilm formation on medical surfaces

Biofilms, intricate microbial communities that attach to surfaces, especially medical devices, form an exopolysaccharide matrix, which enables bacteria to resist environmental pressures and conventional antimicrobial agents, leading to the emergence of multi-drug resistance. Biofilm-related infections associated with medical devices are a significant public health threat, compromising device performance. Therefore, developing effective methods for supervising and managing biofilm growth is imperative. This in-depth review presents a systematic overview of strategies for monitoring and controlling bacterial biofilms. We first outline the biofilm creation process and its regulatory mechanisms. The discussion then progresses to advancements in biosensors for biofilm detection and diverse treatment strategies. Lastly, this review examines the obstacles and new perspectives associated with this domain to facilitate the advancement of innovative monitoring and control solutions. These advancements are vital in combating the spread of multi drug-resistant bacteria and mitigating public health risks associated with infections from biofilm formation on medical instruments.

Recent advances in the pathogenesis and prevention strategies of dental calculus

Dental calculus severely affects the oral health of humans and animal pets. Calculus deposition affects the gingival appearance and causes inflammation. Failure to remove dental calculus from the dentition results in oral diseases such as periodontitis. Apart from adversely affecting oral health, some systemic diseases are closely related to dental calculus deposition. Hence, identifying the mechanisms of dental calculus formation helps protect oral and systemic health. A plethora of biological and physicochemical factors contribute to the physiological equilibrium in the oral cavity. Bacteria are an important part of the equation. Calculus formation commences when the bacterial equilibrium is broken. Bacteria accumulate locally and form biofilms on the tooth surface. The bacteria promote increases in local calcium and phosphorus concentrations, which triggers biomineralization and the development of dental calculus. Current treatments only help to relieve the symptoms caused by calculus deposition. These symptoms are prone to relapse if calculus removal is not under control. There is a need for a treatment regime that combines short-term and long-term goals in addressing calculus formation. The present review introduces the mechanisms of dental calculus formation, influencing factors, and the relationship between dental calculus and several systemic diseases. This is followed by the presentation of a conceptual solution for improving existing treatment strategies and minimizing recurrence.

A typical acidic extracellular polysaccharide alludes to algae-bacteria-collaboration in microalgal-bacterial symbiosis

Microalgal-bacterial symbioses are prevalent in aquatic ecosystems and play a pivotal role in carbon sequestration, significantly contributing to global carbon cycling. The understanding of the contribution of exopolysaccharides (EPSs), a crucial carbon-based component, to the structural integrity of microalgal-bacterial symbioses remains insufficiently elucidated. To address this gap, our study aims to enhance our comprehension of the composition and primary structure of EPSs within a specific type of granular microalgal-bacterial symbiosis named microalgal-bacterial granular sludge (MBGS). Our investigation reveals that the acidic EPSs characteristic of this symbiosis have molecular weights ranging from several hundred thousand to over one million Daltons, including components like glucopyranose, galactopyranose, mannose, and rhamnose. Our elucidation of the backbone linkage of a representative exopolysaccharide revealed a →3)-β-D-Galp-(1→4)-β-D-Glcp-(1→ glycosidic linkage. This linear structure closely resembles bacterial xanthan, while the branched chain structure bears similarities to algal EPSs. Our findings highlight the collaborative synthesis of acidic EPSs by both microalgae and bacteria, emphasizing their joint contribution in the production of macromolecules within microalgal-bacterial symbiosis. This collaborative synthesis underscores the intricate molecular interactions contributing to the stability and function of these symbiotic relationships.

Decoding Microcystis aeruginosa quorum sensing through AHL-mediated transcriptomic molecular regulation mechanisms

Acyl-homoserine lactone (AHL) serves as a key signaling molecule for quorum sensing (QS) in bacteria. QS-related genes and physiological processes in Microcystis aeruginosa remain elusive. In this study, we elucidated the regulatory role of AHL-mediated QS in M. aeruginosa. Using AHL activity extract and transcriptomic analysis, we revealed significant effects of the AHL on growth and photosynthesis. AHL significantly increased chlorophyll a (Chl-a) content and accelerated photosynthetic rate thereby promoting growth. Transcriptome analysis revealed that AHL stimulated the up-regulation of photosynthesis-related genes (apcABF, petE, psaBFK, psbUV, etc.) as well as nitrogen metabolism and ribosomal metabolism. In addition, AHL-regulated pathways are associated with lipopolysaccharide and phenazine synthesis. Our findings deepen the understanding of the QS system in M. aeruginosa and are important for gaining insights into the role of QS in Microcystis bloom formation. It also provides new insights into the prevalence of M. aeruginosa in water blooms.

A novel acid-responsive polymer coating with antibacterial and antifouling properties for the prevention of biofilm-associated infections

Chronic infections caused by the pathogenic biofilms on implantable medical devices pose an increasing challenge. To combat long-term biofilm-associated infections, we developed a novel dual-functional polymer coating with antibacterial and antifouling properties. The coating consists of N-vinylpyrrolidone (NVP) and 3-(acrylamido)phenylboronic acid (APBA) copolymer brushes, which bind to curcumin (Cur) as antibacterial molecules through acid-responsive boronate ester bonds. In this surface design, the hydrophilic poly (N-vinylpyrrolidone) (PVP) component improved antifouling performance and effectively prevented bacterial adhesion and aggregation during the initial phases. The poly (3-(acrylamido) phenylboronic acid) (PAPBA, abbreviated PB) component provided binding sites for Cur by forming acid-responsive boronate ester bonds. When fewer bacteria overcame the anti-adhesion barrier and colonized, the surface responded to the decreased microenvironmental pH by breaking the boronate ester bonds and releasing curcumin. This responsive mechanism enabled Cur to interfere with biofilm formation and provide a multilayer anti-biofilm protection system. The coating showed excellent antibacterial properties against Escherichia coli and Staphylococcus aureus, preventing biofilm formation for up to 7 days. The coating also inhibited protein adsorption and platelet adhesion significantly. This coating also exhibited high biocompatibility with animal erythrocytes and pre-osteoblasts. This research offers a promising approach for developing novel smart anti-biofilm coating materials.

Non-filamentous bulking of activated sludge induced by graphene oxide: Insights from extracellular polymeric substances

Widespread use of nanomaterials raises concerns. The underlying mechanism by which graphene oxide (GO) nanoparticles causes poor settleability of activated sludge remains unclear. To explore this mechanism, three reactors with different GO concentrations were established. Extended Derjaguin-Landau-Verwey-Overbeek theory indicated that GO destroyed the property of extracellular polymeric substances (EPS), increasing the energy barrier between bacteria. Low levels of uronic acid and hydrogen bonding in exopolysaccharide weakened the EPS gelation increasing aggregation repulsion. Lager amounts of hydrophilic amino acid and looser structure of extracellular proteins for exposing inner hydrophilic groups significantly contributed to the hydrophilicity of EPS. Both changes implied deterioration in EPS structure under GO stress. Metagenome demonstrated a decrease in genes responsible for capsular polysaccharide colonization and genes regulated the translocation of loose proteins were increased, which increased repulsion between bacteria. This study elucidated that changes in EPS secretion under GO exposure are the underlying causes of poor settleability.

Bacteria contribute exopolysaccharides to an algal-bacterial joint extracellular matrix

Marine ecosystems are influenced by phytoplankton aggregation, which affects processes like marine snow formation and harmful events such as marine mucilage outbreaks. Phytoplankton secrete exopolymers, creating an extracellular matrix (ECM) that promotes particle aggregation. This ECM attracts heterotrophic bacteria, providing a nutrient-rich and protective environment. In terrestrial environments, bacterial colonization near primary producers relies on attachment and the formation of multidimensional structures like biofilms. Bacteria were observed attaching and aggregating within algal-derived exopolymers, but it is unclear if bacteria produce an ECM that contributes to this colonization. This study, using Emiliania huxleyi algae and Phaeobacter inhibens bacteria in an environmentally relevant model system, reveals a shared algal-bacterial ECM scaffold that promotes algal-bacterial aggregation. Algal exudates play a pivotal role in promoting bacterial colonization, stimulating bacterial exopolysaccharide (EPS) production, and facilitating a joint ECM formation. A bacterial biosynthetic pathway responsible for producing a specific EPS contributing to bacterial ECM formation is identified. Genes from this pathway show increased expression in algal-rich environments. These findings highlight the underestimated role of bacteria in aggregate-mediated processes in marine environments, offering insights into algal-bacterial interactions and ECM formation, with implications for understanding and managing natural and perturbed aggregation events.

Exopolysaccharide production by salt-tolerant bacteria: Recent advances, current challenges, and future prospects

Natural biopolymers derived from exopolysaccharides (EPSs) are considered eco-friendly and sustainable alternatives to available traditional synthetic counterparts. Salt-tolerant bacteria inhabiting harsh ecological niches have evolved a number of unique adaptation strategies allowing them to maintain cellular integrity and assuring their long-term survival; among these, producing EPSs can be adopted as an effective strategy to thrive under high-salt conditions. A great diversity of EPSs from salt-tolerant bacteria have attracted widespread attention recently. Because of factors such as their unique structural, physicochemical, and functional characteristics, EPSs are commercially valuable for the global market and their application potential in various sectors is promising. However, large-scale production and industrial development of these biopolymers are hindered by their low yields and high costs. Consequently, the research progress and future prospects of salt-tolerant bacterial EPSs must be systematically reviewed to further promote their application and commercialization. In this review, the structure and properties of EPSs produced by a variety of salt-tolerant bacterial strains isolated from different sources are summarized. Further, feasible strategies for solving production bottlenecks are discussed, which provides a scientific basis and direct reference for more scientific and rational EPS development.

Regulating bacterial biofilms in food and biomedicine: unraveling mechanisms and Innovating strategies

Bacterial biofilm has brought a lot of intractable problems in food and biomedicine areas. Conventional biofilm control mainly focuses on inactivation and removal of biofilm. However, with robust construction and enhanced resistance, the established biofilm is extremely difficult to eradicate. According to the mechanism of biofilm development, biofilm formation can be modulated by intervening in the key factors and regulatory systems. Therefore, regulation of biofilm formation has been proposed as an alternative way for effective biofilm control. This review aims to provide insights into the regulation of biofilm formation in food and biomedicine. The underlying mechanisms for early-stage biofilm establishment are summarized based on the key factors and correlated regulatory networks. Recent developments and applications of novel regulatory strategies such as anti/pro-biofilm agents, nanomaterials, functionalized surface materials and physical strategies are also discussed. The current review indicates that these innovative methods have contributed to effective biofilm control in a smart, safe and eco-friendly way. However, standard methodology for regulating biofilm formation in practical use is still missing. As biofilm formation in real-world systems could be far more complicated, further studies and interdisciplinary collaboration are still needed for simulation and experiments in the industry and other open systems.

Clostridioides difficile Biofilm

Clostridioides difficile infection (CDI), previously Clostridium difficile infection, is a symptomatic infection of the large intestine caused by the spore-forming anaerobic, gram-positive bacterium Clostridioides difficile. CDI is an important healthcare-associated disease worldwide, characterized by high levels of recurrence, morbidity, and mortality. CDI is observed at a higher rate in immunocompromised patients after antimicrobial therapy, with antibiotics disrupting the commensal microbiota and promoting C. difficile colonization of the gastrointestinal tract.A rise in clinical isolates resistant to multiple antibiotics and the reduced susceptibility to the most commonly used antibiotic molecules have made the treatment of CDI more complicated, allowing the persistence of C. difficile in the intestinal environment.Gut colonization and biofilm formation have been suggested to contribute to the pathogenesis and persistence of C. difficile. In fact, biofilm growth is considered as a serious threat because of the related antimicrobial tolerance that makes antibiotic therapy often ineffective. This is the reason why the involvement of C. difficile biofilm in the pathogenesis and recurrence of CDI is attracting more and more interest, and the mechanisms underlying biofilm formation of C. difficile as well as the role of biofilm in CDI are increasingly being studied by researchers in the field.Findings on C. difficile biofilm, possible implications in CDI pathogenesis and treatment, efficacy of currently available antibiotics in treating biofilm-forming C. difficile strains, and some antimicrobial alternatives under investigation will be discussed here.

Exploring the role of microbial proteins in controlling environmental pollutants based on molecular simulation

Molecular simulation has been widely used to study microbial proteins' structural composition and dynamic properties, such as volatility, flexibility, and stability at the microscopic scale. Herein, this review describes the key elements of molecular docking and molecular dynamics (MD) simulations in molecular simulation; reviews the techniques combined with molecular simulation, such as crystallography, spectroscopy, molecular biology, and machine learning, to validate simulation results and bridge information gaps in the structure, microenvironmental changes, expression mechanisms, and intensity quantification; illustrates the application of molecular simulation, in characterizing the molecular mechanisms of interaction of microbial proteins with four different types of contaminants, namely heavy metals (HMs), pesticides, dyes and emerging contaminants (ECs). Finally, the review outlines the important role of molecular simulations in the study of microbial proteins for controlling environmental contamination and provides ideas for the application of molecular simulation in screening microbial proteins and incorporating targeted mutagenesis to obtain more effective contaminant control proteins.

A growing battlefield in the war against biofilm-induced antimicrobial resistance: insights from reviews on antibiotic resistance

Biofilms are a common survival strategy employed by bacteria in healthcare settings, which enhances their resistance to antimicrobial and biocidal agents making infections difficult to treat. Mechanisms of biofilm-induced antimicrobial resistance involve reduced penetration of antimicrobial agents, increased expression of efflux pumps, altered microbial physiology, and genetic changes in the bacterial population. Factors contributing to the formation of biofilms include nutrient availability, temperature, pH, surface properties, and microbial interactions. Biofilm-associated infections can have serious consequences for patient outcomes, and standard antimicrobial therapies are often ineffective against biofilm-associated bacteria, making diagnosis and treatment challenging. Novel strategies, including antibiotics combination therapies (such as daptomycin and vancomycin, colistin and azithromycin), biofilm-targeted agents (such as small molecules (LP3134, LP3145, LP4010, LP1062) target c-di-GMP), and immunomodulatory therapies (such as the anti-PcrV IgY antibodies which target Type IIIsecretion system), are being developed to combat biofilm-induced antimicrobial resistance. A multifaceted approach to diagnosis, treatment, and prevention is necessary to address this emerging problem in healthcare settings.

Engineering extracellular polymer substrates biosynthesis and carbon felt-carbon nanotube hybrid electrode to promote biofilm electroactivity and bioelectricity production

Organic-rich thin stillage is a significant by-product of the liquor brewing industry, and its direct release into the environment can cause severe water pollution. Microbial fuel cells (MFCs) offer the possibility for converting organic matters in thin stillage into clean electricity. However, limited biofilm formation and conductivity are crucial bottlenecks in restricting the power harvest of MFCs. Here, to efficiently harvest electricity power from thin stillage of liquor industry, we adopted a modular engineering strategy to increase biofilm formation and conductivity of Shewanella oneidensis via enhancing the component biosynthesis of extracellular polymer substrates (EPS) matrix, regulating intracellular c-di-GMP level, and constructing of artificial hybrid system. The results showed that the constructed CNTs@CF-EnBF2 hybrid system with low charge-transfer resistance enabled a maximum output power density of 576.77 mW/m2 in lactate-fed MFCs. Also, to evaluate the capability of harvesting electricity from actual wastewater, the CNTs@CF-EnBF2 system was employed to treat actual thin stillage, obtaining a maximum output power density of 495.86 mW/m2, 3.3-fold higher than the wild-type strain. Our research suggested that engineering and regulating EPS biosynthesis effectively promoted bioelectricity harvest, providing a green and sustainable treatment strategy for thin stillage.

Overview of the effects and mechanisms of NO and its donors on biofilms

Microbial biofilm is undoubtedly a challenging problem in the food industry. It is closely associated with human health and life, being difficult to remove and antibiotic resistance. Therefore, an alternate method to solve these problems is needed. Nitric oxide (NO) as an antimicrobial agent, has shown great potential to disrupt biofilms. However, the extremely short half-life of NO in vivo (2 s) has facilitated the development of relatively more stable NO donors. Recent studies reported that NO could permeate biofilms, causing damage to cellular biomacromolecules, inducing biofilm dispersion by quorum sensing (QS) pathway and reducing intracellular bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) levels, and significantly improving the bactericidal effect without drug resistance. In this review, biofilm hazards and formation processes are presented, and the characteristics and inhibitory effects of NO donors are carefully discussed, with an emphasis on the possible mechanisms of NO resistance to biofilms and some advanced approaches concerning the remediation of NO donor deficiencies. Moreover, the future perspectives, challenges, and limitations of NO donors were summarized comprehensively. On the whole, this review aims to provide the application prospects of NO and its donors in the food industry and to make reliable choices based on these available research results.

Regulation of cadmium-induced biofilm formation by artificial polysaccharide-binding proteins for enhanced phytoremediation

Phytoremediation is an economic way to attenuate soil heavy metal pollution, but is frequently limited by its low pollutant-removing efficiency. Recently, we revealed the close relation between polysaccharide-based biofilm formation and cadmium removal. In this study, for improving the phytoremediation efficiency, an artificial polysaccharide-binding protein was designed by synthetic biology techniques to regulate biofilm formation. The artificial protein Syn contained two polysaccharide-binding domains from the Ruminococcus flavefaciens CttA and the Clostridium cellulolyticum CipC, preferentially binding polysaccharides exposed on both cadmium-treated bacteria and plant roots. Under cadmium stress, Syn remarkably promoted bacterial polysaccharide production from 99 mg/L to 237 mg/L, leading to 1.23-fold higher biofilm biomass. During treatment of the remediation plants with exogenous cadmium-capturing bacteria, Syn improved root biofilm formation, with the root surface polysaccharide contents increasing by 79%, and the Log10 CFU/g root increasing from 7.01 to 7.80. Meanwhile, Syn remodeled the rhizosphere microbiome, especially increasing the abundance of the bacterial groups involved in biofilm formation and stress tolerance, e.g., Pseudomonas, Enterobacter, etc. Consequently, Syn promoted plant cadmium adsorption, with the cadmium-removing efficiency increasing from 17.2% to 33.8%. This study sheds light on synthetic biology-based regulation of biofilm formation for enhanced phytoremediation.

Multifunctional magnetocaloric bone cement with a time-varying alkaline microenvironment for sequential bacterial inhibition, angiogenesis and osteogenesis

Repairing infected bone defects remains a severe challenge due to antibiotic abuse and recurrence. Hence, we modified magnetocaloric Fe3O4 nanoparticles and added them to magnesium calcium phosphate bone cement (MCPC) to fabricate multifunctional magnetic composites for sequential bacterial inhibition, angiogenesis and osteogenesis. Nevertheless, high doses of Mg ions and Fe ions were released from MCPC, which adversely affected osteogenesis. Thus, Fe3O4 was modified using gelatin according to the emulsification crosslinking method, which exhibited a controllable magnetocaloric effect and degradation behavior, and favorable anti-bacterial ability under the action of an alternating magnetic field (AMF). In the early stage, the residual MgO created a local strong alkaline microenvironment by hydrolysis, which inhibited the function and activity of S. aureus and E. coli. At the later stage, the MCPC composites were controllably degraded under the function of gelatin and maintained a long-term local slight alkaline microenvironment that promoted the osteogenic differentiation and mineralization of BMSCs. In vivo subcutaneous implantation experiments further indicated that MCPC composites showed good biocompatibility and facilitated angiogenesis, presenting a promising future in magnetic materials design and infectious bone defect repair.

Regulation on Pathway Metabolic Fluxes to Enhance Colanic Acid Production in Escherichia coli

Colanic acid (CA) is a natural polysaccharide macromolecule with rich and unique biological properties and is a promising candidate for use in food and cosmetics. To date, the efficient biosynthesis of CA and the influence of product accumulation on the strains used have yet to be precisely investigated. Herein, bottlenecks in the CA metabolic pathway were untangled by finely regulating the expression of manA, cpsG, fcl, and rcsA. Engineered strains produced CA at >1 g/L in shake flasks without dependence on cold temperatures, and it was verified in a 1 L bioreactor with a titer up to 18.64 g/L within 24 h. The accumulation of CA caused a decrease in the saturated fatty acid content (represented by C16:0 and C18:0) in the cell membrane. This study demonstrated pathway engineering for efficient CA production in cell factories and provided insights into the barriers and solutions faced in the biosynthesis of natural products.

Understanding resistance acquisition by Pseudomonas aeruginosa and possible pharmacological approaches in palliating its pathogenesis

Pseudomonas aeruginosa can utilize various virulence factors necessary for host infection and persistence. These virulence factors include pyocyanin, proteases, exotoxins, 2-heptyl-4-hydroxyquinoline N-oxide (HQNO), phospholipases, and siderophores that enable the bacteria to cause severe infections in immunocompromised individuals. P. aeruginosa falls into the category of nosocomial pathogens that are typically resistant to available antibiotics and therapeutic approaches. P. aeruginosa bio-film formation is a major concern in hospitals because it can cause chronic infection and increase the risk of mortality. Therefore, the development of new strategies to disrupt biofilm formation and improve antibiotic efficacy for the treatment of P. aeruginosa infections is crucial. Anti-biofilm and anti-quorum sensing (QS) activity can be viewed as an anti-virulence approach to control the infectious nature of P. aeruginosa. Inhibition of QS and biofilm formation can be achieved through pharmacological approaches such as phytochemicals and essential oils, which have shown promising results in laboratory studies. A regulatory protein called LasR plays a key role in QS signaling to coordinate gene expression. Designing an antagonist molecule that mimics the natural autoinducer might be the best approach for LasR inhibition. Here we reviewed the mechanism behind antibiotic resistance and alternative approaches to combat the pathogenicity of P. aeruginosa.

Genetic Basis and Expression Pattern Indicate the Biocontrol Potential and Soil Adaption of Lysobacter capsici CK09

Lysobacter species have attracted increasing attention in recent years due to their capacities to produce diverse secondary metabolites against phytopathogens. In this research, we analyzed the genomic and transcriptomic patterns of Lysobacter capsici CK09. Our data showed that L. capsici CK09 harbored various contact-independent biocontrol traits, such as fungal cell wall lytic enzymes and HSAF/WAP-8294A2 biosynthesis, as well as several contact-dependent machineries, including type 2/4/6 secretion systems. Additionally, a variety of hydrolytic enzymes, particularly extracellular enzymes, were found in the L. capsici CK09 genome and predicted to improve its adaption in soil. Furthermore, several systems, including type 4 pili, type 3 secretion system and polysaccharide biosynthesis, can provide a selective advantage to L. capsici CK09, enabling the species to live on the surface in soil. The expression of these genes was then confirmed via transcriptomic analysis, indicating the activities of these genes. Collectively, our research provides a comprehensive understanding of the biocontrol potential and soil adaption of L. capsici CK09 and implies the potential of this strain for application in the future.

Fabrication of ZnO/Gypsum/Gelatine nanocomposites films and their antibacterial mechanism against Staphylococcus aureus

Staphylococcus aureus (S. aureus) has long been acknowledged as being one of the most harmful bacteria for human civilization. It is the main contributor to skin and soft tissue infections. The gram positive pathogen also contributes to bloodstream infections, pneumonia, or bone and joint infections. Hence, developing an efficient and targeted treatment for these illnesses is greatly desired. Recently, studies on nanocomposites (NCs) have significantly increased due to their potent antibacterial and antibiofilm properties. These NCs provide an intriguing way to control the growth of bacteria without causing the development of resistance strains that come from improper or excessive use of the conventional antibiotics. In this context, we have demonstrated the synthesis of a NC system by precipitation of ZnO nanoparticles (NPs) on Gypsum followed by encapsulation with Gelatine, in the present study. Fourier transform infrared (FTIR) spectroscopy was used to validate the presence of ZnO NPs and Gypsum. The film was characterized by X-ray diffraction (XRD) spectroscopy and scanning electron microscopy (SEM). The system exhibited promising antibiofilm action and was effective in combating S. aureus and MRSA in concentrations between 10 and 50 ug/ml. The bactericidal mechanism by release of reactive oxygen species (ROS) was anticipated to be induced by the NC system. Studies on cell survival and in-vitro infection support the film's notable biocompatibility and its potential for treating Staphylococcus infections in the future.

The morphology and metabolic changes of Actinobacillus pleuropneumoniae during its growth as a biofilm

Actinobacillus pleuropneumoniae is an important swine respiratory pathogen. Previous studies have suggested that growth as a biofilm is a natural state of A. pleuropneumoniae infection. To understand the survival features involved in the biofilm state, the growth features, morphology and gene expression profiles of planktonic and biofilm A. pleuropneumoniae were compared. A. pleuropneumoniae in biofilms showed reduced viability but maintained the presence of extracellular polymeric substances (EPS) after late log-phase. Under the microscope, bacteria in biofilms formed dense aggregated structures that were connected by abundant EPS, with reduced condensed chromatin. By construction of Δpga and ΔdspB mutants, polymeric β-1,6-linked N-acetylglucosamine and dispersin B were confirmed to be critical for normal biofilm formation. RNA-seq analysis indicated that, compared to their planktonic counterparts, A. pleuropneumoniae in biofilms had an extensively altered transcriptome. Carbohydrate metabolism, energy metabolism and translation were significantly repressed, while fermentation and genes contributing to EPS synthesis and translocation were up-regulated. The regulators Fnr (HlyX) and Fis were found to be up-regulated and their binding motifs were identified in the majority of the differentially expressed genes, suggesting their coordinated global role in regulating biofilm metabolism. By comparing the transcriptome of wild-type biofilm and Δpga, the utilization of oligosaccharides, iron and sulfur and fermentation were found to be important in adhesion and aggregation during biofilm formation. Additionally, when used as inocula, biofilm bacteria showed reduced virulence in mouse, compared with planktonic grown cells. Thus, these results have identified new facets of A. pleuropneumoniae biofilm maintenance and regulation.

Anti-Bacterial Adhesion on Abiotic and Biotic Surfaces of the Exopolysaccharide from the Marine Bacillus licheniformis B3-15

The eradication of bacterial biofilm represents a crucial strategy to prevent a clinical problem associated with microbial persistent infection. In this study we evaluated the ability of the exopolysaccharide (EPS) B3-15, produced by the marine Bacillus licheniformis B3-15, to prevent the adhesion and biofilm formation of Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213 on polystyrene and polyvinyl chloride surfaces. The EPS was added at different times (0, 2, 4 and 8 h), corresponding to the initial, reversible and irreversible attachment, and after the biofilm development (24 or 48 h). The EPS (300 µg/mL) impaired the initial phase, preventing bacterial adhesion even when added after 2 h of incubation, but had no effects on mature biofilms. Without exerting any antibiotic activity, the antibiofilm mechanisms of the EPS were related to the modification of the (i) abiotic surface properties, (ii) cell-surface charges and hydrophobicity, and iii) cell-to-cell aggregation. The addition of EPS downregulated the expression of genes (lecA and pslA of P. aeruginosa and clfA of S. aureus) involved in the bacterial adhesion. Moreover, the EPS reduced the adhesion of P. aeruginosa (five logs-scale) and S. aureus (one log) on human nasal epithelial cells. The EPS could represent a promising tool for the prevention of biofilm-related infections.

Sustainable production of bioemulsifiers, a critical overview from microorganisms to promising applications

Microbial bioemulsifiers are molecules of amphiphilic nature and high molecular weight that are efficient in emulsifying two immiscible phases such as water and oil. These molecules are less effective in reducing surface tension and are synthesized by bacteria, yeast and filamentous fungi. Unlike synthetic emulsifiers, microbial bioemulsifiers have unique advantages such as biocompatibility, non-toxicity, biodegradability, efficiency at low concentrations and high selectivity under different conditions of pH, temperature and salinity. The adoption of microbial bioemulsifiers as alternatives to their synthetic counterparts has been growing in ongoing research. This article analyzes the production of microbial-based emulsifiers, the raw materials and fermentation processes used, as well as the scale-up and commercial applications of some of these biomolecules. The current trend of incorporating natural compounds into industrial formulations indicates that the search for new bioemulsifiers will continue to increase, with emphasis on performance improvement and economically viable processes.

Bacterial extracellular polymeric substances: Biosynthesis and interaction with environmental pollutants

Extracellular polymeric substances (EPS) are highly hydrated matrices produced by bacteria, containing various polymers such as polysaccharides, proteins, lipids, and DNA. Extracellular polymer concentrations, ions, and functional groups provide physical stability to the EPS. Constituents of EPS form the three-dimensional architecture and help acquire nutrition for the bacteria. Structural and functional diversity of the extracellular polymer depends on the specific glycosyltransferases, polymerase and transporter proteins. These enzymes are encoded by specific genes present in operons such as crd, alg, wca, and gum reported in Agrobacterium, Pseudomonas, Enterobacteriaceae, and Xanthomonas. The operons regulate the biosynthesis of extracellular polymers such as curdlan, alginate, colonic acid, and xanthan, respectively. Various functional groups in the EPS, such as carbonyl, hydroxyl, phosphoryl, and amide, provide the sorption site for interaction with environmental pollutants. Hydrophobic interactions and coordinate bonds mainly dominate the binding of EPS with environmental pollutants. EPS binds, emulsifies, and solubilizes the organic compounds, enhancing the degradation process. EPS binds with heavy metals through complexation, surface adsorption, precipitation, and ion exchange mechanisms. The biodegradability efficiency and nontoxicity properties of EPS make it an excellent biopolymer for decontaminating environmental pollutants. This review summarizes an overview of the biosynthetic mechanisms and interaction of the bacterial extracellular polymer with environmental pollutants. Interaction mechanisms of pollutants with EPS and EPS-mediated bioremediation will help develop removal applications. Moreover, understanding the genes responsible for EPS production, and implementation of new genetic methodology can be helpful for the enhanced biosynthesis of EPS to control pollution by sequestrating more environmental pollutants.

Oxidative Stress Response and E. coli Biofilm Formation under the Effect of Pristine and Modified Carbon Nanotubes

The article investigates the expression of oxyR and soxS oxidative stress genes in E. coli under the effect of pristine multi-walled carbon nanotubes (MWCNTs) and pristine single-walled carbon nanotubes (SWCNTs), MWCNTs and SWCNTs functionalized with carboxyl groups (MWCNTs-COOH and SWCNTs-COOH, respectively), SWCNTs functionalized with amino groups (SWCNTs-NH₂) and SWCNTs functionalized with octadecylamine (SWCNTs-ODA). Significant differences were found in the expression of the soxS gene, while no changes were observed in the expression level of the oxyR gene. The pro-oxidant effect of SWCNTs, SWCNTs-COOH, SWCNTs-NH₂, and SWCNTs-ODA is presented, and the contrary antioxidant effect of pristine MWCNTs and MWCNTs-COOH in the presence of methyl viologen hydrate (paraquat) is shown. The article shows that SWCNTs-COOH, SWCNTs-NH₂, and SWCNTs-ODA added to the medium generate the production of reactive oxygen species (ROS) in bacterial cells. SWCNTs-COOH intensified the E. coli biofilm formation, and the biofilm biomass exceeded the control by 25 times. Additionally, it is shown that the rpoS expression increased in response to MWCNTs-COOH and SWCNTs-COOH, and the effect of SWCNTs-COOH was more significant. SWCNTs-COOH and SWCNTs-NH₂ initiated an increase in ATP concentration in the planktonic cells and a decrease in the biofilm cells. The atomic force microscopy (AFM) method showed that the volume of E. coli planktonic cells after the exposure to carbon nanotubes (CNTs) decreased compared to that without exposure, mainly due to a decrease in cell height. The absence of a strong damaging effect of functionalized SWCNTs on E. coli K12 cells, both in suspension and in biofilms, is shown. Contact with functionalized SWCNTs initiated the aggregation of the polymeric substances of the biofilms; however, the cells did not lyse. Among the studied CNTs, SWCNTs-COOH caused an increased expression of the soxS and rpoS, the formation of ROS, and stimulation of the biofilm formation.

Potential and prospects of Actinobacteria in the bioremediation of environmental pollutants: Cellular mechanisms and genetic regulations

Increasing industrialization and anthropogenic activities have resulted in the release of a wide variety of pollutants into the environment including pesticides, polycyclic aromatic hydrocarbons (PAHs), and heavy metals. These pollutants pose a serious threat to human health as well as to the ecosystem. Thus, the removal of these compounds from the environment is highly important. Mitigation of the environmental pollution caused by these pollutants via bioremediation has become a promising approach nowadays. Actinobacteria are a group of eubacteria mostly known for their ability to produce secondary metabolites. The morphological features such as spore formation, filamentous growth, higher surface area to volume ratio, and cellular mechanisms like EPS secretion, and siderophore production in Actinobacteria render higher resistance and biodegradation ability. In addition, these bacteria possess several oxidoreductase systems (oxyR, catR, furA, etc.) which help in bioremediation. Actinobacteria genera including Arthrobacter, Rhodococcus, Streptomyces, Nocardia, Microbacterium, etc. have shown great potential for the bioremediation of various pollutants. In this review, the bioremediation ability of these bacteria has been discussed in detail. The utilization of various genera of Actinobacteria for the biodegradation of organic pollutants, including pesticides and PAHs, and inorganic pollutants like heavy metals has been described. In addition, the cellular mechanisms in these microbes which help to withstand oxidative stress have been discussed. Finally, this review explores the Actinobacteria mediated strategies and recent technologies such as the utilization of mixed cultures, cell immobilization, plant-microbe interaction, utilization of biosurfactants and nanoparticles, etc., to enhance the bioremediation of various environmental pollutants.

Comprehensive insights into the gallic acid assisted bioleaching process for spent LIBs: Relationships among bacterial functional genes, Co(III) reduction and metal dissolution behavior

Despite the growing demand for resource recovery from spent lithium-ion batteries (LIBs) by bioleaching, low Co leaching efficiency has hindered the development and application of this technology. Therefore, a novel process was designed, combining gallic acid (GA) and mixed culture bioleaching (MCB), to enhance the removal of metals from spent LIBs. Results indicated that the GA + MCB process achieved 98.03% Co and 98.02% Li leaching from spent LIBs, simultaneously reducing the biotoxicity, phytotoxicity and leaching toxicity of spent LIBs under optimal conditions. The results of mechanism analysis demonstrated that functional microorganisms adapted to the leaching system through various strategies, including oxidative stress reduction, DNA damage repair, heavy metal resistance and biofilm formation, maintaining normal physiological activities and the continuous production of biological acid. The biological acid erodes the surface of waste LIBs, causing some Co and a large amount of Li to be released, while also increasing the contact area between GA and Co(III). Therefore, GA is beneficial for reducing insoluble Co(III), forming soluble Co(II). Finally, biological acid can effectively promote Co(II) leaching. Collectively, the results of this study provide valuable insight into the simultaneous enhancement of metal extraction and the mitigation of environmental pollution from spent LIBs.

Biofilm control strategies in the light of biofilm-forming microorganisms

Biofilm is a complex consortium of microorganisms attached to biotic or abiotic surfaces and live in self-produced or acquired extracellular polymeric substances (EPSs). EPSs are mainly formed by lipids, polysaccharides, proteins, and extracellular DNAs. The adherence to the surface of microbial communities is seen in food, medical, dental, industrial, and environmental fields. Biofilm development in food processing areas challenges food hygiene, and human health. In addition, bacterial attachment and biofilm formation on medical implants inside human tissue can cause multiple critical chronic infections. More than 30 years of international research on the mechanisms of biofilm formation have been underway to address concerns about bacterial biofilm infections. Antibiofilm strategies contain cold atmospheric plasma, nanotechnological, phage-based, antimicrobial peptides, and quorum sensing inhibition. In the last years, the studies on environmentally-friendly techniques such as essential oils and bacteriophages have been intensified to reduce microbial growth. However, the mechanisms of the biofilm matrix formation are still unclear. This review aims to discuss the latest antibiofilm therapeutic strategies against biofilm-forming bacteria.

Temporin-GHb-Derived Peptides Exhibit Potent Antibacterial and Antibiofilm Activities against Staphylococcus aureus In Vitro and Protect Mice from Acute Infectious Pneumonia

With the continuous development of drug resistance in bacteria to traditional antibiotics, the demand for novel antibacterial agents is urgent. Antimicrobial peptides (AMPs) are promising candidates because of their unique mechanism of action and low tendency to induce drug resistance. Previously, we cloned temporin-GHb (hereafter referred to simply as "GHb") from Hylarana guentheri. In this study, a series of derived peptides were designed, namely, GHbR, GHbK, GHb3K, GHb11K, and GHbK4R. The five derived peptides had stronger antibacterial activities against Staphylococcus aureus than the parent peptide GHb and could effectively inhibit the formation of biofilms and eradicate mature biofilms in vitro. GHbR, GHbK, GHb3K, and GHbK4R exerted bactericidal effects by disrupting membrane integrity. However, GHb11K exhibited bacteriostatic efficacy with toroidal pore formation on the cell membrane. In comparison to GHbK4R, GHb3K showed much lower cytotoxicity against A549 alveolar epithelial cells, with an IC₅₀ > 200 μM, which was much higher than its minimal inhibitory concentration (MIC = 3.1 μM) against S. aureus. The anti-infection potential of GHbK4R and GHb3K was investigated in vivo. Compared with vancomycin, the two peptides displayed significant efficacy in a mouse model of acute pneumonia infected with S. aureus. Both GHbK4R and GHb3K also had no obvious toxicity to normal mice after intraperitoneal administration (15 mg/kg) for 8 days. Our results indicate that GHb3K and GHbK4R might be promising candidates for the treatment of bacterial pneumonia infected with S. aureus.

A Review of Biofilm Formation of Staphylococcus aureus and Its Regulation Mechanism

Bacteria can form biofilms in natural and clinical environments on both biotic and abiotic surfaces. The bacterial aggregates embedded in biofilms are formed by their own produced extracellular matrix. Staphylococcus aureus (S. aureus) is one of the most common pathogens of biofilm infections. The formation of biofilm can protect bacteria from being attacked by the host immune system and antibiotics and thus bacteria can be persistent against external challenges. Therefore, clinical treatments for biofilm infections are currently encountering difficulty. To address this critical challenge, a new and effective treatment method needs to be developed. A comprehensive understanding of bacterial biofilm formation and regulation mechanisms may provide meaningful insights against antibiotic resistance due to bacterial biofilms. In this review, we discuss an overview of S. aureus biofilms including the formation process, structural and functional properties of biofilm matrix, and the mechanism regulating biofilm formation.

eDNA, Amyloid Fibers and Membrane Vesicles Identified in Pseudomonas fluorescens SBW25 Biofilms

Pseudomonas fluorescens SBW25 is a model soil- and plant-associated bacterium capable of forming a variety of air-liquid interface biofilms in experimental microcosms and on plant surfaces. Previous investigations have shown that cellulose is the primary structural matrix component in the robust and well-attached Wrinkly Spreader biofilm, as well as in the fragile Viscous Mass biofilm. Here, we demonstrate that both biofilms include extracellular DNA (eDNA) which can be visualized using confocal laser scanning microscopy (CLSM), quantified by absorbance measurements, and degraded by DNase I treatment. This eDNA plays an important role in cell attachment and biofilm development. However, exogenous high-molecular-weight DNA appears to decrease the strength and attachment levels of mature Wrinkly Spreader biofilms, whereas low-molecular-weight DNA appears to have little effect. Further investigation with CLSM using an amyloid-specific fluorophore suggests that the Wrinkly Spreader biofilm might also include Fap fibers, which might be involved in attachment and contribute to biofilm strength. The robust nature of the Wrinkly Spreader biofilm also allowed us, using MALDI-TOF mass spectrometry, to identify matrix-associated proteins unable to diffuse out of the structure, as well as membrane vesicles which had a different protein profile compared to the matrix-associated proteins. CLSM and DNase I treatment suggest that some vesicles were also associated with eDNA. These findings add to our understanding of the matrix components in this model pseudomonad, and, as found in other biofilms, biofilm-specific products and material from lysed cells contribute to these structures through a range of complex interactions.

The variation on structure and immunomodulatory activity of polysaccharide during the longan pulp fermentation

In the current study, the effects of fermentation manners on the structure and immunomodulatory activity of polysaccharide in longan wine or vinegar were investigated. Compared to longan polysaccharide (CP1), polysaccharide in longan wine (CP2) or vinegar (CP3 and CP4) had smaller molecular weights, and was consisted of more mannose, arabinose, rhamnose, galactose and less glucose. After purification, the major fraction (P1-P4) was obtained from CP1-CP4, respectively. The structures and immunoregulatory activities of P1-P4 were characterized. Fermentation and purification were favorable to increase the immunoregulatory activities of P2-P4, which were contributed to their different structural features. The structure-activity relationship analysis indicated that molecular weight, mannose, rhamnose, glucuronic acid, glucose and arabinose were significantly associated with the cytokines secretion. Compared with other polysaccharides, P3 displayed better immunomodulatory activity due to its lower molecular weight, lower contents of rhamnose and glucose, and higher levels of mannose and arabinose by activating MAPK and PI3K/Akt signaling pathways.