Affecting Biofilm Formation Research Articles

Enhancement of the anaerobic biodegradation efficiency of azo dye by anthraquinone-loaded biochar biofilm: factors affecting biofilm formation and the enhancement mechanism

Carbon-based materials that serve as microbial carriers, and the role of surface-formed biofilms in anaerobic digestion, merit further investigation. This study explored the role and mechanism behind the biodegradation enhancement of biofilms formed onto anthraquinone-loaded biochar (AQS-BC) surfaces through the anaerobic decolorization process of azo dye Reactive Red 2, and optimized the conditions for AQS-BC biofilm formation. The results indicated that the AQS-BC biofilm system exhibited high treatment efficiency and stability in RR2 anaerobic decolorization. RR2 led to the accumulation of volatile fatty acids (VFAs) and inhibition of methane production, while the presence of AQS increased methane production. The effects of sludge concentration, contact time, carbon source concentration, and RR2 concentration on biofilm maturity were also analyzed. Combining biochemical characteristics, electrochemical properties, surface structure, and microbial community analysis, a mechanism for the anaerobic decolorization of RR2 via AQS-BC as a microbial carrier was proposed. This study provides insights into the roles of biofilms in the anaerobic wastewater treatment processes.Graphical

MutL Significantly Regulates the Formation of Biofilms in Bacillus amyloliquefaciens YT1

The purpose of this study is to discover and excavate more key factors and signaling pathways that regulate the formation intensity of biofilms and to fully reveal the possible models affecting biofilm formation. By using gene homologous recombination and bioinformatics technology, a MutL protein-directed deletion mutant strain was successfully constructed. The growth status of the mutant strain was observed, and it was confirmed that, except for the change in cell morphology, there were no significant differences in growth and reproduction between the mutant strain and the wild-type strain. By using the induced biofilm formation technique, the significant decrease in biofilm formation in the MutL mutant strain was successfully verified. The plate confrontation test confirmed that the inhibitory ability of the mutant strain against rice blast fungus was not significantly different from that of the WT strain. The colonization ability of the mutant strain on rice stems was tested, and it was confirmed that the colonization ability of the mutant strain was significantly lower than that of the WT strain. In terms of the prevention and control effect of rice blast disease, the mutant strain showed a significant decrease. By using transcriptomic big data, the gene and pathway expression differences between the mutant strain and the WT strain during biofilm formation were analyzed. The analysis revealed no significant correlation with the previously reported spo0A and tapA-sipW-tasA pathways. The key factor capB of the polyglutamic acid signaling pathway, which affects the formation of the biological model, was found to have a significant decrease in expression. A mechanical hypothesis was proposed: MutL may participate in regulating the formation intensity of Bacillus biofilms by regulating the formation of glutamic acid to polyglutamic acid.

Antibiofilm activity and synergistic effects of DNase I and Lysostaphin against Staphylococcus aureus biofilms

Abstract In recent years, food safety has become the focus of global public health concerns. Microbial contamination is one of the most common food safety issues. Staphylococcus aureus is a common foodborne pathogen that can form biofilms on the surface of food processing equipment, leading to greater resistance to antimicrobial agents than occurs with planktonic bacteria. In this work, recombinant Escherichia coli BL21 (DE3) cells expressing optimised lysostaphin (Lst) were constructed, recombinant Lst was produced and purified, and Lst enzymatic assays were performed, followed by antimicrobial testing of Lst. Finally, a mixture of Lst and DNase I was tested for antibiofilm activity. The protein content of purified Lst was 0.6 mg/mL and the enzyme activity was 240 U/mL. The minimum inhibitory concentration (MIC) of Lst against S. aureus was 0.1 μg/mL. At 1 MIC, Lst exerted an effect on the growth, cell wall integrity and cell membrane permeability of S. aureus. Although Lst alone also showed good inhibition and disruption of S. aureus biofilms, inhibition and disruption of S. aureus biofilms was significantly greater when Lst was mixed with DNase I. This is probably because DNase I removes extracellular DNA, affecting biofilm formation and dispersing mature biofilms, and thereby facilitating penetration of Lst.

Amygdalin prevents multidrug-resistant Staphylococcus aureus-induced lung epithelial cell injury by regulating inflammation and oxidative stress.

Methicillin-resistant Staphylococcus aureus (MRSA) is an opportunistic pathogen that can cause severe bacterial pneumonia. Amygdalin is the main active pharmaceutical ingredient of bitter almond, which has broad-spectrum antibacterial, anti-inflammatory, anti-oxidation and immunomodulatory effects. It is also the main ingredient of Yinhua Pinggan granule, which is commonly used to moisten the lung and relieve cough. However, little is known about the effects of amygdalin on MRSA. In this study, we found that amygdalin exhibited good antimicrobial activity in vitro against MRSA. Amygdalin has a protective effect on MRSA infected cells, and the effect is better when combined with levofloxacin. It also can reduce the adhesion and invasion of MRSA to cells. Amygdalin has anti-inflammatory and antioxidant effects, which can significantly reduce the increase of inflammatory factors and the production of ROS caused by infection. The protective mechanism of amygdalin on cells may be related to inhibiting the expression of NLRP3, ASC and IL-1β pyroptosis pathways. Taken together, our study suggests that amygdalin exerts antibacterial effects by affecting biofilm formation, the expression of virulence factors, and drug resistance genes. Amygdalin combined with levofloxacin has a protective effect on A549 cells infected with MRSA, and the mechanism may be related to the inhibition of inflammatory response, oxidative damage and pyroptosis.

Factors affecting biofilm formation by bacteria on fabrics.

Fabrics act as fomites for microorganisms, thereby playing a significant role in infection transmission, especially in the healthcare and hospitality sectors. This study aimed to examine the biofilm formation ability of four nosocomial infection-causing bacteria (Acinetobacter calcoaceticus, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus) on cotton, polyester, polyester-cotton blend, silk, wool, viscose, and nylon, used frequently in the healthcare sector, by qualitative and quantitative methods. The impact of temperature, pH, and relative humidity(RH) on biofilm formation was also assessed. P. aeruginosa and S. aureus were strong biofilm producers, while E. coli produced weak biofilm. Wool (maximum roughness) showed the highest bacterial load, while silk (lowest roughness) showed the least. P. aeruginosa exhibited a higher load on all fabrics, than other test bacteria. Extracellular polymeric substances were characterized by infrared spectroscopy. Roughness of biofilms was assessed by atomic force microscopy. For biofilm formation, optimum temperature, pH, and RH were 30°C, 7.0, and 62%, respectively. MgCl2 and CaCl2 were the most effective in removing bacterial biofilm. In conclusion, biofilm formation was observed to be influenced by the type of fabric, bacteria, and environmental conditions. Implementing recommended guidelines for the effective disinfection of fabrics is crucial to curb the risk of nosocomial infections. In addition, designing modified healthcare fabrics that inhibit pathogen load could be an effective method to mitigate the transmission of infections.

Attenuation of biofilm and quorum sensing regulated virulence factors of an opportunistic pathogen Pseudomonas aeruginosa by phytofabricated silver nanoparticles

Green-synthesized nanoparticles provide an effective strategy for inhibiting microbial pathogenesis by affecting biofilm formation, quorum sensing (QS), and other surface properties of microorganisms. QS is a density-dependent communication signaling cascade that regulates biofilm formation and other pathogenic factors of Pseudomonas aeruginosa. In this context, the effect of phytofabricated silver nanoparticles (CC-AgNPs) synthesized using Cuphea carthagenensis extract on biofilm, QS, and QS-dependent virulence factors of P. aeruginosa were evaluated in this study. CC-AgNPs demonstrated significant attenuation of biofilm, QS, and QS-dependent virulence factors at sub-MICs. A significant inhibition of 88.39 ± 4.32 %, 79.64 ± 3.31 %, 73.07 ± 3.0 %, and 61.67 ± 1.5 % of biofilm formation, quorum sensing, pyocyanin, and LasB elastase, respectively was reported in the study at 20 μg/mL. The study also demonstrated a significant reduction of LasA Staphylolytic activity and 91.37 ± 1.05 % exoprotease production in comparison to untreated control. The lower concentrations of CC-AgNPs also demonstrated significant attenuation of biofilm and other virulence factors suggesting the strong potency of NPs against P. aeruginosa. XTT analysis reported the effect of CC-AgNPs on sessile cells of P. aeruginosa without impacting growth of planktonic cells at sub-MICs. Cell-proliferation study in human cell lines (HEK 293 and Caco-2 cells) demonstrated the safe nature of CC-AgNPs at tested concentrations. This study is novel in a way that environmentally friendly CC-AgNPs were used to inhibit QS at sub-MICs without killing the tested strains, therefore, could be developed as an anti-virulent drug to overcome biofilm and antimicrobial resistance problems.

Determination of key factors affecting biofilm formation on the aged Poly(ethylene terephthalate) during anaerobic digestion

Biofilm formation on plastic surface is a growing concern because it can alter the plastic surface properties and exacerbate the ecological risk. Identifying key factors that affecting biofilm formation is critical for effective pollution control. In this study, the poly (ethylene terephthalate) (PET) was aged in water and air conditions with UV irradiation, then incubated in the digestate of food waste anaerobic digestion to allow biofilm formation. Surface analysis techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier-transform infrared spectroscopy with attenuated total reflection (FTIR-ATR), were utilized to investigated the changes in the topography, roughness, hydrophily, and functional groups change of the PET surface during the aging process. Confocal laser scanning microscopy (CLSM) was used to determine the distribution of microorganisms on the PET surface after incubation in the digestate. This study focused on understanding the interactions between the PET surface and biofilm to identify critical surface factors that affect biofilm formation. Results showed that the four months aging process decreased the contact angle of the PET surface from 96.92° to 76.08° and 68.97° in water and air conditions, respectively, corresponding to an increase of 44% and 70% in the surface energy. Additionally, aging in air conditions led to a rougher surface compared to water conditions. The arithmetic roughness average (Ra) of the PET-Water was 11.0 nm, comparable to that of the pristine PET, while the value of PET-Air was much higher (43.9 nm). The results further indicated that biofilm formation during anaerobic digestion was more sensitive to roughness than hydrophily. The PET surface aged in air conditions provided a more suitable environment for microbial reproduction, leading to the aggradation of living cells.

Advances in the Application of Quorum Sensing to Regulate Electrode Biofilms in Bioelectrochemical Systems

Bioelectrochemical systems (BESs) are an emerging technology for wastewater treatment and resource recovery. These systems facilitate electron transfer between microorganisms and electrodes, enabling their application in various fields, such as electricity production, bioremediation, biosensors, and biocatalysis. However, electrode biofilms, which play a critical role in BESs, face several challenges (e.g., a long acclimation period, low attached biomass, high electron transfer resistance, and poor tolerance and stability) that limit the development of this technology. Quorum sensing (QS) is a communication method among microorganisms that can enhance the performance of BESs by regulating electrode biofilms. QS regulation can positively impact electrode biofilms by enhancing extracellular electron transfer (EET), biofilm formation, cellular activity, the secretion of extracellular polymeric substances (EPS), and the construction of microbial community. In this paper, the characteristics of anode electrogenic biofilms and cathode electrotrophic biofilms in BESs, EET mechanisms, and the main factors affecting biofilm formation were summarized. Additionally, QS regulation mechanisms for biofilm formation, strategies for enhancing and inhibiting QS, and the application of QS regulation for electrode biofilms in BESs were systematically reviewed and discussed. This paper provides valuable background information and insights for future research and development of BES platforms based on QS regulation of electrode biofilms.

Characterization of functional amyloid curli in biofilm formation of an environmental isolate Enterobacter cloacae SBP-8.

The biofilm formation by bacteria is a complex process that is strongly mediated by various genetic and environmental factors. Biofilms contribute to disease infestation, especially in chronic infections. It is, therefore important to understand the factors affecting biofilm formation. This study reports the role of a functional amyloid curli in biofilm formation at various abiotic surfaces, including medical devices, by an environmental isolate of Enterobacter cloacae (SBP-8) which has been known for its pathogenic potential. A knockout mutant of csgA, the gene encoding the major structural unit of curli, was created to study the effect of curli on biofilm formation by E. cloacae SBP-8. Our findings confirm the production of curli at 25°C and 37°C in the wild-type strain. We further investigated the role of curli in the attachment of E. cloacae SBP-8 to glass, enteral feeding tube, and foley latex catheter. Contrary to the previous studies reporting the curli production below 30°C in the majority of biofilm-forming bacterial species, we observed its production in E. cloacae SBP-8 at 37°C. The formation of more intense biofilm in wild-type strain on various surfaces compared to curli-deficient strain (ΔcsgA) at both 25°C and 37°C suggested a prominent role of curli in biofilm formation. Further, electron and confocal microscopy studies demonstrated the formation of diffused monolayers of microbial cells on the abiotic surfaces by ΔcsgA strain as compared to the thick biofilm by respective wild-type strain, indicating the involvement of curli in biofilm formation by E. cloacae SBP-8. Overall, our findings provide insight into biofilm formation mediated by curli in E. cloacae SBP-8. Further, we show that it can be expressed at a physiological temperature on all surfaces, thereby indicating the potential role of curli in pathogenesis.

Deletion of pbpC Enhances Bacterial Pathogenicity on Tomato by Affecting Biofilm Formation, Exopolysaccharides Production, and Exoenzyme Activities in Clavibacter michiganensis.

Penicillin-binding proteins (PBPs) are considered essential for bacterial peptidoglycan biosynthesis and cell wall assembly. Clavibacter michiganensis is a representative Gram-positive bacterial species that causes bacterial canker in tomato. pbpC plays a significant role in maintaining cell morphological characteristics and stress responses in C. michiganensis. The current study demonstrated that the deletion of pbpC commonly enhances bacterial pathogenicity in C. michiganensis and revealed the mechanisms through which this occurs. The expression of interrelated virulence genes, including celA, xysA, xysB, and pelA, were significantly upregulated in △pbpC mutants. Compared with those in wild-type strains, exoenzyme activities, the formation of biofilm, and the production of exopolysaccharides (EPS) were significantly increased in △pbpC mutants. It is noteworthy that EPS were responsible for the enhancement in bacterial pathogenicity, with the degree of necrotic tomato stem cankers intensifying with the injection of a gradient of EPS from C. michiganensis. These findings highlight new insights into the role of pbpC affecting bacterial pathogenicity, with an emphasis on EPS, advancing the current understanding of phytopathogenic infection strategies for Gram-positive bacteria.

P092 Punica Granatum affects gut biofilm-forming bacteria and promotes intestinal mucosal healing regulating the crosstalk between epithelial cells and intestinal fibroblasts

Abstract Background Punica Granatum (PG), is a bioactive compound of Pomegranate exerting anti-inflammatory activities. Clinical studies have demonstrated an improvement of clinical response in inflammatory bowel diseases (IBD) patients when PG was taken as a complement to standard medications. However, the molecular mechanisms underlying its beneficial effects are still scarcely investigated. In this study, we assessed the effects of PG on bacterial biofilm formation, and we investigated the properties of the PG to promote mucosal wound healing. Methods Bacterial biofilm formation was assessed using microfluidic devices for 24 or 48 hours. Acute colitis model was induced in C57BL/6N mice by 3% dextran sodium sulfate administration in their drinking water for 5 days. During the recovery phase of colitis, mice received saline or PG (200 mg/kg body weight) oral gavage for 11 days. . Colitis was scored daily evaluating the body weight loss, bleeding and consistency of stool. In vivo intestinal permeability was performed by fluorescein isothiocyanate-conjugated dextran assay, bacterial translocation by Fluorescence in situ hybridization on tissues, whereas epithelial and mucus integrity by immunostaining for JAM-A and MUC-2 markers. Primary fibroblasts, isolated from healthy and inflamed area of 6 IBD patients, and Caco-2 cells were stimulated with or without PG (15 ug/ml). Inflammatory mediators were measured at mRNA and protein levels by RT-PCR, WB or by Bio-plex multiplex immunoassay respectively. Results Microfluidic experiments revealed beneficial effects of PG to inhibit biofilm formation of GRAM- bacteria and to promote the expansion of some intestinal commensal Gram+ bacteria. In vivo, PG boosted the recovery phase of colitis promoting a complete restoration of intestinal barrier with the regeneration of the mucus layer compared to saline group as also demonstrated by no traces of bacteria spread into the mucosa. The PG enriched crypt-associated fibroblasts. In vitro, inflamed fibroblasts responded to PG by down-regulating the release of metalloproteinases, IL-6, IL-8 and up-regulating the levels of HGF. Caco-2 cells cultured in medium supplemented with PG increased the expression of Sox-9 and CD44, whereas in the presence of HGF or when plated with fibroblast-conditioned medium displayed a decrease expression of Sox-9 and CD44 and increase of AXIN2, a negative regulator of Wnt signaling. Conclusion These data provide new insight of the multiple effects of PG on promoting mucosal homeostasis in IBD by affecting biofilm formation of pathogens, promoting expansion of commensals and favoring the regeneration of intestinal barrier by regulating the crosstalk between epithelial cells and stromal cells.

Rcs phosphorelay affects the sensitivity of Escherichia coli to plantaricin BM-1 by regulating biofilm formation.

Introduction: Plantaricin BM-1 is a class IIa bacteriocin produced by Lactobacillus plantarum BM-1 that exerts significant antibacterial activity against many foodborne bacteria. Studies have shown that class IIa bacteriocins inhibit Gram-positive bacteria via the mannose phosphotransferase system; however, their mechanism of action against Gram-negative bacteria remains unknown. In this study, we explored the mechanism through which the Rcs phosphorelay affects the sensitivity of Escherichia coli K12 cells to plantaricin BM-1. Methods and Results: The minimum inhibitory concentrations of plantaricin BM-1 against E. coli K12, E. coli JW5917 (rcsC mutant), E. coli JW2204 (rcsD mutant), and E. coli JW2205 (rcsB mutant) were 1.25, 0.59, 1.31, and 1.22 mg/ml, respectively. Growth curves showed that E. coli JW5917 sensitivity to plantaricin BM-1 increased to the same level as that of E. coli K12 after complementation. Meanwhile, scanning electron microscopy and transmission electron microscopy revealed that, under the action of plantaricin BM-1, the appearance of E. coli JW5917 cells did not significantly differ from that of E. coli K12 cells; however, cell contents were significantly reduced and plasmolysis and shrinkage were observed at both ends. Crystal violet staining and laser scanning confocal microscopy showed that biofilm formation was significantly reduced after rcsC mutation, while proteomic analysis identified 382 upregulated and 260 downregulated proteins in E. coli JW5917. In particular, rcsC mutation was found to affect the expression of proteins related to biofilm formation, with growth curve assays showing that the deletion of these proteins increased E. coli sensitivity to plantaricin BM-1. Discussion: Consequently, we speculated that the Rcs phosphorelay may regulate the sensitivity of E. coli to plantaricin BM-1 by affecting biofilm formation. This finding of class IIa bacteriocin against Gram-negative bacteria mechanism provides new insights.

Quantifying biofilm propagation on chemically modified surfaces

Conditions affecting biofilm formation differ among bacterial species and this presents a challenge to studying biofilms in the lab. This work leverages functionalized silanes to control surface chemistry in the study of early biofilm propagation, quantified with a semi-automated image processing algorithm. These methods support the study of Pantoea sp. YR343, a gram-negative bacterium isolated from the poplar rhizosphere. We found that Pantoea sp. YR343 does not readily attach to hydrophilic surfaces but will form biofilms with a “honeycomb” morphology on hydrophobic surfaces. Our image processing algorithm described here quantified the evolution of the honeycomb morphology over time, and found the propagation to display a logarithmic behavior. This methodology was repeated with a flagella-deficient fliR mutant of Pantoea sp. YR343 which resulted in reduced surface attachment. Quantifiable differences between Pantoea WT and ΔfliR biofilm morphologies were captured by the image processing algorithm, further demonstrating the insight gained from these methods.

Prevalence of microplastics, antibiotic resistant genes and microplastic associated biofilms in estuary - A review

The estuarine ecosystem is under threat due to the addition of different anthropogenic pollutants. Among the various pollutants, microplastics(MPs), and antibiotics play a significant role in affecting estuarine organisms and human health by transport through the food chain. In the estuaries, microorganisms, including pathogens, colonise microplastics by the development of biofilms. Estuaries have long been home to MPs, served as novel hubs for the transmission of Antibiotic Resistance Genes (ARGs). As a result of their continual interactions with a variety of aquatic creatures, MP-associated bacterial communities will eventually present a transfer opportunity to organisms that consume MPs. To comprehend the presence of microplastics and ARGs in the estuaries, a thorough review is necessary. This review discusses the various sources of MPs and antibiotic pollution, as well as the transport of ARGs via biofilm formed on MPs. Furthermore, the factors affecting biofilm formation in estuaries are reviewed. In addition, the transport of ARGs by microbial populations within biofilm is discussed. The ARGs are transported into the food chain, which will be a threat to human health. Hence, the occurrence of antibiotic-resistant genes in fish is discussed.

The temperature-dependent expression of type II secretion system controls extracellular product secretion and virulence in mesophilic Aeromonas salmonida SRW-OG1.

Aeromonas salmonicida is a typical cold water bacterial pathogen that causes furunculosis in many freshwater and marine fish species worldwide. In our previous study, the pathogenic A. salmonicida (SRW-OG1) was isolated from a warm water fish, Epinephelus coioides was genomics and transcriptomics analyzed. Type II secretion system was found in the genome of A. salmonicida SRW-OG1, while the expressions of tatA, tatB, and tatC were significantly affected by temperature stress. Also, sequence alignment analysis, homology analysis and protein secondary structure function analysis showed that tatA, tatB, and tatC were highly conservative, indicating their biological significance. In this study, by constructing the mutants of tatA, tatB, and tatC, we investigated the mechanisms underlying temperature-dependent virulence regulation in mesophilic A. salmonida SRW-OG1. According to our results, tatA, tatB, and tatC mutants presented a distinct reduction in adhesion, hemolysis, biofilm formation and motility. Compared to wild-type strain, inhibition of the expression of tatA, tatB, and tatC resulted in a decrease in biofilm formation by about 23.66%, 19.63% and 40.13%, and a decrease in adhesion ability by approximately 77.69%, 80.41% and 62.14% compared with that of the wild-type strain. Furthermore, tatA, tatB, and tatC mutants also showed evidently reduced extracellular enzymatic activities, including amylase, protease, lipase, hemolysis and lecithinase. The genes affecting amylase, protease, lipase, hemolysis, and lecithinase of A. salmonicida SRW-OG1 were identified as cyoE, ahhh1, lipA, lipB, pulA, HED66_RS01350, HED66_RS19960, aspA, fabD, and gpsA, which were notably affected by temperature stress and mutant of tatA, tatB, and tatC. All above, tatA, tatB and tatC regulate the virulence of A. salmonicida SRW-OG1 by affecting biofilm formation, adhesion, and enzymatic activity of extracellular products, and are simultaneously engaged in temperature-dependent pathogenicity.

Deletion of luxS gene mediated by λRed gene recombination technology reduces biofilm formation and stress resistance of Lactobacillus fermentum

This study investigated the effects of the luxS gene on the biofilm formation of Lactobacillus fermentum and its stress resistance. Deletion of the luxS gene was related to the physiological characteristics of biofilm development, strain resistance, bacterial morphology, biofilm morphology, functional group types, the main components of the biofilm, and the expression of related genes. Therefore, a luxS gene-deficient strain was constructed using λRed gene recombination technology, and the biofilm production and stress resistance of the WT and ΔluxS strains were compared. Deletion of the gene reduced the biofilm formation of L. fermentum and its resistance to acid, bile salt, high temperatures, and a hypertonic environment. Further, this work found that its deletion affects the types of functional groups in biofilms, and at the same time downregulate the expressions of the fabI, cysE, argR, and purD genes, thus reducing the levels of fatty acids, exopolysaccharide, protein, and eDNA in biofilms. A correlation analysis found that protein in biofilms was the most important factor affecting biofilm formation. In conclusion, the luxS gene in L. fermentum is involved in the regulation of biofilm formation and stress resistance. These findings provide a theoretical basis for the study of the mechanism of biofilm formation in beneficial bacteria.

Structural basis for environmental sensing in Pseudomonas fluorescens

Over the past decades, it has become clear that bacteria often prefer a sessile over a free‐swimming lifestyle. The transition from a mobile to an immobile, social lifestyle, called a biofilm, is induced in response to a variety of environmental stimuli, such as carbon or phosphate sources, linked to signaling via the second messenger cyclic‐di‐GMP (c‐di‐GMP). In gammaproteobacteria, c‐di‐GMP regulates cell adhesion to biotic and abiotic surfaces through the transmembrane Lap system that controls the surface presentation of large adhesin proteins. Signaling specificity is achieved through direct physical interaction between a c‐di‐GMP‐producing diguanylate cyclases (DGCs) and LapD, the c‐di‐GMP receptor central to the Lap system. To date, ten DGCs have been identified as regulators of LapD, affecting biofilm formation. However, how they differ functionally and the stimuli to which they respond are often not well understood. To shed light on the environmental sensing mechanism for DGC activation, we have determined the structure of the periplasmic domain of two DGCs in P. fluorescens, a model organism for biofilm research. These domains, belonging to the CACHE family of protein domains, protrude into the periplasm where they encounter their respective ligands, which correlates with their activation. By comparing the structures of CACHE domains and their ligand binding profiles, we identify molecular signatures that contribute to c‐di‐GMP signaling specificity, environmental sensing, and biofilm formation.

Biofilm formation and its implications on the properties and fate of microplastics in aquatic environments: A review

Particulate plastic fragments (micro and nano-plastics) in aquatic environments provide abundant solid substrates, which serve as an important habitat for a variety of microorganisms. Surfaces of microplastics (MPs) exhibit hydrophobicity that facilitate the adsorption of dissolved organic carbon (DOC) in the aquatic environment. Furthermore, MPs act as substrata, as well as a carbon source including the readily bioavailable DOC, which promote the formation of microbial biofilms. These biofilms have varied metabolic actions that govern the subsequent succession of micro- and meso-organisms habitation of MPs. The assemblage of ecosystems colonising the plastic environment is often referred to as the “plastisphere”. Polymer type, environmental conditions, including nutrient status, salinity, and season, affect the microbial composition of the biofilm. Microbial habitation accelerated by biofilm formation on particulate plastics enables the movement of microorganisms, especially in the aquatic environment, and impacts the transport and toxicity of contaminants associated with these particulate plastic fragments. This review paper describes the processes of microbial habitation and subsequent biofilm formation, the factors affecting biofilm formation, and the implications of biofilm formation on the mobility of microorganisms, degradation of MPs, and the bioavailability of contaminants associated with MPs.

Fluidic bacterial diodes rectify magnetotactic cell motility in porous environments

Directed motility enables swimming microbes to navigate their environment for resources via chemo-, photo-, and magneto-taxis. However, directed motility competes with fluid flow in porous microbial habitats, affecting biofilm formation and disease transmission. Despite this broad importance, a microscopic understanding of how directed motility impacts the transport of microswimmers in flows through constricted pores remains unknown. Through microfluidic experiments, we show that individual magnetotactic bacteria directed upstream through pores display three distinct regimes, whereby cells swim upstream, become trapped within a pore, or are advected downstream. These transport regimes are reminiscent of the electrical conductivity of a diode and are accurately predicted by a comprehensive Langevin model. The diode-like behavior persists at the pore scale in geometries of higher dimension, where disorder impacts conductivity at the sample scale by extending the trapping regime over a broader range of flow speeds. This work has implications for our understanding of the survival strategies of magnetotactic bacteria in sediments and for developing their use in drug delivery applications in vascular networks.

Biofilm Formation by Marine Cobetia marina alex and Pseudoalteromonas spp: Development and Detection of Quorum Sensing N-Acyl Homoserine Lactones (AHLs) Molecules

Surfaces submerged in seawater are colonized by various microorganisms, resulting in the formation of heterogenic marine biofilms. This work aims to evaluate the biofilm formation by Cobetia marina alex and doing a comparative study between this promising strain with the two bacterial strains isolated previously from the Mediterranean seawater, Alexandria, Egypt. Three strains; Cobetia marina alex, Pseudoalteromonas sp. alex, and Pseudoalteromonas prydzensis alex were screened for biofilm formation using the crystal violet (CV) quantification method in a single culture. The values of biofilm formed were OD600= 3.0, 2.7, and 2.6, respectively leading to their selection for further evaluation. However, factors affecting biofilm formation by C. marina alex were investigated. Biofilm formation was evaluated in single and multispecies consortia. Synergistic and antagonistic interactions proved in this work lead to the belief that these bacteria have the capability to produce some interesting signal molecules N-acyl Homoserine Lactones (AHLs)