Formation Of Biofilm Structures Research Articles

Examining the Frequency of Selected Genes Involved in Biofilm Formation in Clinical Isolates of Acinetobacter Baumannii

Introduction: Acinetobacter baumannii, a non-fermenting Gram-negative coccobacillus, exhibits high resistance to antimicrobial compounds. Biofilm formation is a crucial feature in many Acinetobacter species, contributing to their antibiotic resistance. The present study aimed to investigate the prevalence of ompA, csuA, bap and pgaB genes in clinical isolates of Acinetobacter baumannii with biofilm formation ability. Methods: In this cross-sectional study, 49 isolates of Acinetobacter baumannii were collected from patients hospitalized in the health centers of Borujerd City. Acinetobacter baumannii isolates were confirmed by biochemical tests. In these isolates, the biofilm production ability was investigated by microtitreplate method. Then, using PCR method and specific primers, ompA, csuA, bap and pgaB genes were identified.The collected data were analyzed descriptively and analytically using SPSS version 16 software. Data analysis was done with Chi-square test, Fisher's exact test, and P<0.05 was considered as the basis of significance. Results: The presence of ompA, csuA, bap, and pgaB genes was detected in 87%, 92%, 98%, and 100% of the isolates, respectively. Additionally, the microtitreplate method revealed that biofilm formation was strong in 3 isolates (6%), moderate in 17 isolates (35%), and weak in 29 isolates (59%). Conclusion: The prevalence of genes associated with biofilm formation in Acinetobacter baumannii isolates was high. This suggests that the studied isolates possess a significant ability to form biofilm structures.

Examination of the Structure and Formation Streptococcus mutans Biofilm Induced by Glucose, Lactose, Soy Protein, and Iron.

Streptococcus mutans, the main causative agent of caries, have the ability to form biofilms on the surface of teeth. The availability of nutrients such as glucose, lactose, soy protein, and iron can influence S. mutans in biofilm formation. All four sources of nutrients have been shown to increase the formation of S. mutans biofilms. The purpose of this study was to determine the structure and thickness of S. mutans biofilms induced by glucose, lactose, soy protein, and iron. This experimental laboratory study aimed to examine the formation of biofilm structures (chemical elements) and determine the thickness of S. mutans biofilms induced by glucose, lactose, soy protein, and iron. The structures (chemical elements) were examined using scanning electron microscopy-energy-dispersive X-ray (SEM-EDX) analysis. Confocal laser scanning microscopy (CLSM) was used to determine the thickness of S. mutans biofilms with an Olympus FV1000 microscope, and the findings were analyzed using Olympus Fluoview Ver. 4.2a software. It was established that the results of SEM-EDX examination of the structure of S. mutans biofilms induced by glucose had oxygen (O) as the dominant chemical element (30.24 w%); lactose reported oxygen (O) as the dominant element (29.65 w%); soy protein had carbon (C) as the dominant element (34.31 w%); and iron showed oxygen (O) as the dominant element (32.51 w%). The thickness (measured by the CLSM examination) of biofilms induced by glucose, lactose, soy protein, and iron were 17,666, 12,666, 18,000, and 15,666 nm, respectively. The structure of S. mutans biofilms induced by glucose, lactose, and iron contain the following elements in amounts from the highest to lowest: O, C, N, P, and S; the biofilm produced by S. mutans induced by soy protein in amounts from the highest to lowest comprised the elements: C, O, N, S, and P. The S. mutans biofilms induced by soy protein had the maximum thickness, followed by those induced by glucose, iron, and lactose.

Investigating the synergic effects of the extracts of Camellia sinensis, Rosmarinus officinalis and Thymus with ampicillin against resistant Pseudomonas aeruginosa species

Introduction: The most common bacterium linked to the hospital and pneumonia-related infections is Pseudomonas aeroginosa, a known opportunistic pathogen. High mortality rates are brought on by this bacterium in hospitalized patients, immunocompromised individuals, and cystic fibrosis patients. The formation of biofilm structures has also made it more challenging to treat patients. Due to the severe side effects of the antibiotics, the lack of efficacy due to resistance, and the well-documented antibacterial effects of traditional plants, this study investigated the antibacterial properties of the combination of thyme, rosemary, and green tea. Therefore, the main purpose of the current study was to examine the antibacterial and anti-biofilm effects of the extracts of these three plants. Method: Pseudomonas arginosa strains were obtained from patients at Ghaem Hospital, Mashhad, Iran. The efficacy of various antibiotics on different strains was studied, and bacterial strains were classified into sensitive, semi-sensitive, and resistant. The minimum inhibitory concentration (MIC) of the combination of the three extracts, as well as the antibiotic of choice, was determined. The effect of the extract on the biofilm formation was also investigated. Results: The results indicated that the ternary composition has significant antibacterial and anti-biofilm effects; also, the combination of these three extracts has shown significant synergistic properties with each other. Further, the extracts inhibited the formation and growth of the biofilm. Conclusion: Results of this study indicated that the optimum combination of the three extracts possessed a remarkable antibacterial and anti-biofilm activity. Further, we have shown the synergistic antibacterial activity of the three extracts improved in the presence of the antibiotic of choice, resulting in a decrease in the MIC value of the antibiotic.

Unveiling the persistent threat: recent insights into Listeria monocytogenes adaptation, biofilm formation, and pathogenicity in foodborne infections.

Listeriosis is a severe disease caused by the foodborne pathogen Listeria monocytogenes, posing a significant risk to vulnerable populations such as the elderly, pregnant women, and newborns. While relatively uncommon, it has a high global mortality rate of 20-30%. Recent research indicates that smaller outbreaks of the more severe, invasive form of the disease occur more frequently than previously thought, despite the overall stable infection rates of L. monocytogenes over the past 10years. The ability of L. monocytogenes to form biofilm structures on various surfaces in food production environments contributes to its persistence and challenges in eradication, potentially leading to contamination of food and food production facilities. To address these concerns, this review focuses on recent developments in epidemiology, risk evaluations, and molecular mechanisms of L. monocytogenes survival in adverse conditions and environmental adaptation. Additionally, it covers new insights into strain variability, pathogenicity, mutations, and host vulnerability, emphasizing the important events framework that elucidates the biochemical pathways from ingestion to infection. Understanding the adaptation approaches of L. monocytogenes to environmental stress factors is crucial for the development of effective and affordable pathogen control techniques in the food industry, ensuring the safety of food production.

Construction and characterization of stable multi-species biofilms formed by nine core gut bacteria on wheat fiber.

Microbial aggregation mainly occurs on the intestinal epithelium, mucosal layer and undigested food particles in the gastrointestinal tract (GIT). Undigested food particles are usually insoluble dietary fiber (IDF), which can be easily obtained through daily diet, but there are few studies investigating whether the gut bacteria adhering to undigested food particles can form multi-species biofilms. In this study, we prepared mono- and multi-species biofilms using 18 core gut bacteria via a dynamic fermentation method, and it was found that multi-species composed of nine core gut bacteria (M9) showed the best biofilm formation ability. Cell counts of the nine bacteria in multi-species biofilms were 9.36, 11.85, 10.17, 9.93, 12.88, 11.39, 10.089, 9.06, and 13.21 Log10 CFU mL-1. M9 was tightly connected and regularly stacked on wheat fiber and had larger particle sizes than mono-species biofilms. M9 retained biofilm formation ability under pH and bile salt stresses. A human feces invasion experiment demonstrated that M9 can stably adhere to wheat fiber under the interference of complex gut bacteria, and the M9 multi-species biofilm had positions that can be filled by various gut bacteria. Metabolome results indicated that the M9 multi-species biofilm had more metabolic productions and more complex interspecies interactions than mono-species biofilms. This study provides a dynamic fermentation method to prepare multi-species biofilms on wheat fiber in vitro. It will also offer a research basis for clarifying whether gut bacteria can utilize IDF to form biofilm structures in vivo and the possible interspecific interactions and physiological functions of bacteria in biofilms.

Effect of Acetic Acid on Clinical Isolated Pseudomonas aeruginosa Biofilm in Chronic Suppurative Otitis Media: In vitro Study

Background: Forming biofilms on bacteria can inhibit the penetration of antimicrobial agents and avoid the immune defence system. It becomes one of the factors causing therapy failure and chronicity of infection. Pseudomonas aeruginosa is the most common bacteria found in Chronic Suppurative Otitis Media (CSOM), which has the virulence ability to form biofilm structures. Some studies have reported that acetic acid can inhibit and eradicate biofilm complexes and is thought to be an alternative to additional therapy against bacterial infections that form biofilms. Objective: to explain the effect of acetic acid inhibiting and eradicating Pseudomonas aeruginosa biofilm in CSOM. Methods: This study used an experimental in vitro laboratory with a post-test-only control group method. Samples were taken from the secretions of the mastoid cavity of CSOM patients. The inhibitory effect of acetic acid was observed by administering acetic acid to Pseudomonas aeruginosa. In contrast, the effect of eradicating biofilm was observed by administering acetic acid to Pseudomonas aeruginosa which had already formed a biofilm. The observations in this study were using the microtiter plate assay method and were measured with an ELISA reader. Data analysis used the One-Way Anova test and multiple comparisons (Tukey HSD Test). Result: The inhibitory effect of acetic acid on the growth of Pseudomonas aeruginosa biofilm was obtained (p=0.000) with significant results (p <0.05) between the positive control group and the concentration group of 0.16%, 0.31%, 0.63%, 1.25%, 2.5%, and 5%. The Minimum Biofilm Inhibitory Concentration (MIBC) value of acetic acid in forming Pseudomonas aeruginosa biofilms was 0.16%. The effect of acetic acid eradication on Pseudomonas aeruginosa biofilms (p=0.000) with significant results (p<0.05) between the positive control group and the concentration group of 0.08%, 0.16%, 0.31%, 0.63%, 1.25%, 2.5%, and 5%. While the minimum value of acetic acid Biofilm Eradication Concentration (MEBC) for Pseudomonas aeruginosa biofilm eradication was 0.08%. Conclusion: Acetic acid inhibits the formation and eradication of Pseudomonas aeruginosa biofilms in CSOM.

The effectiveness of biofilm formation of daily cultures of clinically significant strains of opportunistic bacteria

Background. The formation of biofilm structures by microorganisms living in the hospital environment is a serious medical problem. To conduct correct experimental studies, it is necessary to know the speed and efficiency of biofilm formation by clinically significant species of opportunistic bacteria. Aim: to study the kinetics of plankton culture growth and the rate of biofilm formation by clinically significant pathogens of infections associated with medical care to substantiate the methodology of further research. Materials and methods. The strains from the working collection of the Laboratory for Microbiome and Microecology of the Scientific Сentre for Family Health and Human Reproduction Problems were used. Experiments were carried out with conditionally pathogenic microorganisms of the Enterobacteriaceae family and non-fermenting gram-negative bacteria. The optical density was measured, the total microbial number of the cell suspension was determined, and the morphological structure of the biofilm was evaluated using a light microscope on sterile cover glasses for thespecies Pseudomonas aeruginosa, Klebsiella pneumoniae and Serratia marcescens. Results. The duration of the lag phase of the kinetic curve of cell growth varied in isolates of S. marcescens, P. aeruginosa and K. pneumoniae from 1 to 4 and 6 hours of cultivation, respectively. Despite this, the exponential growth phase was the same for all tested isolates and amounted to 4 hours. Thus, isolates of clinically significant species entered the stationary growth phase after 5–10 hours of cultivation and were characterized as fast-growing. On abiotic surfaces, after 8 hours of incubation of the tested cultures, the initial stages of the formation of biofilm structures were observed, after 20 hours the formed multilayer biofilm was visualized, after 24 hours succession occurred, new single cells were attached to the place of the detached structures. Conclusion. The data obtained on the duration of the main stages of growth kinetics compared with the visualization of the formation of biofilm structures on abiotic surfaces should be taken into account when studying the effects of disinfectants, antiseptics and antibacterial drugs on planktonic cells and biofilm associations of clinically significant opportunistic microorganisms.

EFFECT OF Mg, Zn, Ca, AND Fe SUPPLEMENTS ON GROWTH, PROBIOTIC POTENTIAL, AND BIOFILM-FORMING CAPACITY OF LACTOBACILLUS BACTERIA

The gut microbiome is a complete set of microorganisms found in the gastrointestinal (GI) tract. Lactobacillus spp. are beneficial bacteria that are normally found in the gut. They are used as a type of probiotic in order to create a homeostasis in the human microflora. One of the challenges for these bacteria is the ability to adapt to different environments in order to survive and function properly. The main research question of this study was to see whether specific dietary supplements (calcium citrate, iron(II)fumarate, zinc, magnesium oxide) change bacterial properties of Lactobacillus reuteri (L. reuteri) (DSM 17938) and Lactobacillus rhamnosus (L. rhamnosus) GG (ATCC 53103). Presence of dietary supplements affected antibiotic sensitivity of tested bacteria. Results of biochemical testing minimally changed. MICs of tested supplements have been determined as well, where L. reuteri tolerated higher concentrations of supplements compared to L. rhamnosus. Probiotic efficiency was also tested through bile and acid tolerance assays. Obtained results showed that presence of dietary supplements did not alter probiotic efficiency. According to other studies L. reuteri and L. rhamnosus form biofilm structures in the human gut, however they showed very low affinity to form biofilms before and after treatment with dietary supplements when tested in vitro. Previous studies showed that L. reuteri could be used in a treatment for autistic-spectrum disorders. According to results from this study, patients with ASD should avoid zinc in the form of capsules (as dietary supplements) from their diets, since it inhibits growth of L. reuteri. In general, tested dietary supplements, except zinc, did not affect bacterial properties on a large scale.

Integrated moving bed biofilm reactor with partial denitrification-anammox for promoted nitrogen removal: Layered biofilm structure formation and symbiotic functional microbes

Partial denitrification/anaerobic ammonia oxidation (anammox) (PD/A) is currently an advanced nitrogen removal process. This study developed a PD/A system in a moving bed biofilm reactor. Results showed that the nitrogen removal efficiency reached 76.60% with a COD/NO3-N of 2.0, and the contribution of anammox was 88.01%. Further analysis showed that the biocarriers could form layered pH and dissolved oxygen structures to promote the aggregation of different functional bacteria at various depths, thus stabilizing the coupled process. Microbial structure analysis showed that the abundance of Saccharimonadales, responsible for denitrification, increased from 0% to 36.27% between day 0 and day 120, while the abundance of Candidatus Jettenia, responsible for anammox, decreased from 10.41% to 2.20%. The synergistic effect of Saccharimonadales and Candidatus Jettenia enabled stable and efficient removal of nitrogen. This study proposed a novel configuration of the PD/A process and provided a theoretical basis for its promotion and application.

Listeria monocytogenes - How This Pathogen Survives in Food-Production Environments?

The foodborne pathogen Listeria monocytogenes is the causative agent of human listeriosis, a severe disease, especially dangerous for the elderly, pregnant women, and newborns. Although this infection is comparatively rare, it is often associated with a significant mortality rate of 20–30% worldwide. Therefore, this microorganism has an important impact on food safety. L. monocytogenes can adapt, survive and even grow over a wide range of food production environmental stress conditions such as temperatures, low and high pH, high salt concentration, ultraviolet lights, presence of biocides and heavy metals. Furthermore, this bacterium is also able to form biofilm structures on a variety of surfaces in food production environments which makes it difficult to remove and allows it to persist for a long time. This increases the risk of contamination of food production facilities and finally foods. The present review focuses on the key issues related to the molecular mechanisms of the pathogen survival and adaptation to adverse environmental conditions. Knowledge and understanding of the L. monocytogenes adaptation approaches to environmental stress factors will have a significant influence on the development of new, efficient, and cost-effective methods of the pathogen control in the food industry, which is critical to ensure food production safety.

The Union Is Strength: The Synergic Action of Long Fatty Acids and a Bacteriophage against Xanthomonas campestris Biofilm.

Xanthomonas campestris pv. campestris is known as the causative agent of black rot disease, which attacks mainly crucifers, severely lowering their global productivity. One of the main virulence factors of this pathogen is its capability to penetrate and form biofilm structures in the xylem vessels. The discovery of novel approaches to crop disease management is urgent and a possible treatment could be aimed at the eradication of biofilm, although anti-biofilm approaches in agricultural microbiology are still rare. Considering the multifactorial nature of biofilm, an effective approach against Xanthomonas campestris implies the use of a multi-targeted or combinatorial strategy. In this paper, an anti-biofilm strategy based on the use of fatty acids and the bacteriophage (Xccφ1)-hydroxyapatite complex was optimized against Xanthomonas campestris mature biofilm. The synergic action of these elements was demonstrated and the efficient removal of Xanthomonas campestris mature biofilm was also proven in a flow cell system, making the proposed approach an effective solution to enhance plant survival in Xanthomonas campestris infections. Moreover, the molecular mechanisms responsible for the efficacy of the proposed treatment were explored.

Ex Vivo Murine Skin Model for B. burgdorferi Biofilm.

Borrelia burgdorferi, the causative agent of Lyme disease, has been recently shown to form biofilm structures in vitro and in vivo. Biofilms are tightly clustered microbes characterized as resistant aggregations that allow bacteria to withstand harsh environmental conditions, including the administration of antibiotics. Novel antibiotic combinations have recently been identified for B. burgdorferi in vitro, however, due to prohibiting costs, those agents have not been tested in an environment that can mimic the host tissue. Therefore, researchers cannot evaluate their true effectiveness against B. burgdorferi, especially its biofilm form. A skin ex vivo model system could be ideal for these types of experiments due to its cost effectiveness, reproducibility, and ability to investigate host–microbial interactions. Therefore, the main goal of this study was the establishment of a novel ex vivo murine skin biopsy model for B. burgdorferi biofilm research. Murine skin biopsies were inoculated with B. burgdorferi at various concentrations and cultured in different culture media. Two weeks post-infection, murine skin biopsies were analyzed utilizing immunohistochemical (IHC), reverse transcription PCR (RT-PCR), and various microscopy methods to determine B. burgdorferi presence and forms adopted as well as whether it remained live in the skin tissue explants. Our results showed that murine skin biopsies inoculated with 1 × 107 cells of B. burgdorferi and cultured in BSK-H + 6% rabbit serum media for two weeks yielded not just significant amounts of live B. burgdorferi spirochetes but biofilm forms as well. IHC combined with confocal and atomic force microscopy techniques identified specific biofilm markers and spatial distribution of B. burgdorferi aggregates in the infected skin tissues, confirming that they are indeed biofilms. In the future, this ex vivo skin model can be used to study development and antibiotic susceptibility of B. burgdorferi biofilms in efforts to treat Lyme disease effectively.

Spatio-temporal formation of biofilms and extracellular matrix analysis in Azospirillum brasilense.

Elucidation of biofilm structure formation in the plant growth-promoting rhizobacterium Azospirillum brasilense is necessary to gain a better understanding of the growth of cells within the extracellular matrix and its role in the colonization of plants of agronomic importance. We used immunofluorescence microscopy and confocal laser scanning microscopy to study spatio-temporal biofilm formation on an abiotic surface. Observations facilitated by fluorescence microscopy revealed the presence of polar flagellin, exopolysaccharides, outer major membrane protein (OmaA) and extracellular DNA in the Azospirillum biofilm matrix. In static culture conditions, the polar flagellum disaggregated after 3 days of biofilm growth, but exopolysaccharides were increasing. These findings suggest that the first step in biofilm formation may be attachment, in which the bacterium first makes contact with a surface through its polar flagellum. After attaching to the surface, the long flagella and OmaA intertwine the cells to form a network. These bacterial aggregates initiate biofilm development. The underlying mechanisms dictating how the biofilm matrix components of A. brasilense direct the overall morphology of the biofilm are not well known. The methods developed here might be useful in further studies that analyze the differential spatial regulation of genes encoding matrix components that drive biofilm construction.

Characterization of biofilm formation and induction of apoptotic DNA fragmentation by nontypeable Haemophilus influenzae on polarized human airway epithelial cells

Nontypeable Haemophilus influenzae (NTHi) is a common airway commensal and opportunistic pathogen that persists within biofilm communities in vivo. Biofilm studies so far are mainly based on assays on plastic surfaces. The aim of this work was to investigate the capacity of clinical NTHi strains to form biofilm structures on polarized Calu-3 human airway epithelial cells and primary normal human bronchial epithelial cells and to characterize the biofilm architecture. Formation of adherent NTHi biofilms post colonization of host cells at multiple time-points was evaluated using confocal laser scanning microscopy and electron microscopy. NTHi biofilms were analyzed in terms of biofilm height and presence of extracellular matrix components, and their apoptotic effects on epithelial cells were measured by TUNEL assay. Strain Fi176 was observed to form robust biofilms on airway epithelia over time, while disrupting the integrity of Calu-3 monolayer by 72 h of co-culture. NTHi biofilms were observed to induce apoptotic DNA fragmentation in host cells at 24 h post infection. Biofilm formation on cell monolayers by Fi176ΔpilA strain was markedly reduced compared to WT strain. Biofilm inhibition and disruption assays by crystal violet staining indicated that DNA and proteins are part of NTHi biofilms in vitro. Our findings highlight critical stages of NTHi pathogenesis following host colonization and provide useful biofilm models for future antimicrobial drug discovery investigations.

The era of 'omics' technologies in the study of microbiologically influenced corrosion.

Efforts to elucidate the relationships between microorganisms and metal corrosion were mainly directed to understanding the formation of biofilm structures grown on corroded surfaces. The emergence of high throughput DNA sequencing techniques has helped in the description of microbial species involved directly and indirectly in the corrosion processes of alloys. Coupled with sequencing from environmental samples, other methodologies such as metatranscriptome, metaproteomics and metabolomics have allowed a new horizon to be opened on the understanding of the role of corrosive microbial biofilm. Several groups of bacteria and archaea were identified, showing the dominance of Proteobacteria in several samples analyzed and members of groups that previously received less attention, such as Firmicutes and Bacteroidetes. Our research also shows that metagenomic studies describe the presence of various Archaea domain thermophilic and methanogenic groups associated with metal corrosion. Thus, opening the prospect of describing new microbial groups as possible participants in this current global concern.

Oxidative stress under low oxygen conditions triggers hyperflagellation and motility in the Antarctic bacterium Pseudomonas extremaustralis.

Reactive oxygen species and nitrogen species (ROS and RNS), produced in a wide range of physiological process even under low oxygen availability, are among the main stressors found in the environment. Strategies developed to combat them constitute key features in bacterial adaptability and survival. Pseudomonas extremaustralis is a metabolic versatile and stress resistant Antarctic bacterium, able to grow under different oxygen conditions. The present work explores the effect of oxidative stress under low oxygen conditions in P. extremaustralis, by combining RNA deep sequencing analysis and physiological studies. Cells grown under microaerobiosis exhibited more oxidative damage in macromolecules and lower survival rates than under aerobiosis. RNA-seq analysis showed an up-regulation of genes related with oxidative stress response, flagella, chemotaxis and biofilm formation while chaperones and cytochromes were down-regulated. Microaerobic cultures exposed to H2O2 also displayed a hyper-flagellated phenotype coupled with a high motility behavior. Moreover, cells that were subjected to oxidative stress presented increased biofilm formation. Altogether, our results suggest that a higher motile behavior and augmented capacity to form biofilm structures could work in addition to well-known antioxidant enzymes and non-enzymatic ROS scavenging mechanisms to cope with oxidative stress at low oxygen tensions.

Time-variable expression levels of mazF, atlE, sdrH, and bap genes during biofilm formation in Staphylococcus epidermidis.

Staphylococcus epidermidis is an opportunistic pathogen causing infections related to the usage of implants and medical devices. Pathogenicity of this microorganism is mainly linked to its capability to form biofilm structures. Biofilm formation vastly depends on several factors including different proteins. We studied the expression levels of three proteins including SdrH, Bap, AtlE, and MazF at different time intervals during the course of biofilm formation. In this study, a catheter-derived S. epidermidis isolate with strong ability of biofilm formation was selected. PCR assay was used to detect sdrH, bap, atlE, and mazF genes in this isolate. Real-time PCR was used to determine the expression levels of these genes after 4, 8, and 20h during the course of biofilm formation. The studied genes showed different expression levels at different time intervals during biofilm formation by real-time PCR method. Expression levels of atlE and sdrH genes were the highest at 4h, whereas bap gene showed the highest expression level at 8h during the course of biofilm formation. In addition, the expression level of mazF gene peaked at 4h and then progressively decreased at 8 and 20h. Our results suggest the importance of AtlE, SdrH, and MazF proteins in the establishment and development of the biofilm structure. In addition, our results showed the important role of protein Bap in the accumulation of biofilm structure. Future studies are required to understand the exact role of MazF in the process of biofilm formation.

The role of biofilms in the corrosion of steel in marine environments.

Metal corrosion is a major global concern in many economic sectors. The degradation of metal surfaces is responsible for losses in values that account for about 3% of gross domestic product (GDP) only in the US. Parts of all corrosion processes described in different environments are present mainly in marine environments. The marine environment is characterized as favoring the corrosion processes of several metallic alloys, damaging structures used in the construction of ships, ports, oil pipelines, and others. Despite chemical corrosion being the most frequently described in these environments, studies show the participation of microorganisms in direct corrosion processes or in the acceleration/influence of the corrosive action, through the formation of complex biofilms. These structures create favorable conditions for microorganisms to degrade metal surfaces, causing damage known as pitting and crevices. Currently, diverse technicians are employed in biocorrosion research, e.g. electronic microscopy, and DNA sequencing. These techniques have clarified the dynamic process of the formation of biofilm structures, allowing understanding of the succession of different species during the evolution of the structure. Improving the understanding of how this interaction between biofilm and metallic surface occurs will enable better evaluation of strategies to avoid or decelerate the degradation of metallic structures in marine environments.

Contact-Dependent Growth Inhibition Proteins in Acinetobacter baylyi ADP1

Bacterial contact-dependent growth inhibition (CDI) systems are two-partner secretion systems in which toxic CdiA proteins are exported on the outer membrane by cognate transporter CdiB proteins. Upon binding to specific receptors, the C-terminal toxic (CT) domain, detached from CdiA, is delivered to neighbouring cells. Contacts inhibit the growth of not-self-bacteria, lacking immunity proteins co-expressed with CdiA, but promote cooperative behaviours in “self” bacteria, favouring the formation of biofilm structures. The Acinetobacter baylyi ADP1 strain features two CdiA, which differ significantly in size and have different CT domains. Homologous proteins sharing the same CT domains have been identified in A. baumannii. The growth inhibition property of the two A. baylyi CdiA proteins was supported by competition assays between wild-type cells and mutants lacking immunity genes. However, neither protein plays a role in biofilm formation or adherence to epithelial cells, as proved by assays carried out with knockout mutants. Inhibitory and stimulatory properties may be similarly uncoupled in A. baumannii proteins.

Mesoscopic Energy Minimization Drives Pseudomonas aeruginosa Biofilm Morphologies and Consequent Stratification of Antibiotic Activity Based on Cell Metabolism.

ABSTRACTSegregation of bacteria based on their metabolic activities in biofilms plays an important role in the development of antibiotic resistance. Mushroom-shaped biofilm structures, which are reported for many bacteria, exhibit topographically varying levels of multiple drug resistance from the cap of the mushroom to its stalk. Understanding the dynamics behind the formation of such structures can aid in design of drug delivery systems, antibiotics, or physical systems for removal of biofilms. We explored the development of metabolically heterogeneous Pseudomonas aeruginosa biofilms using numerical models and laboratory knockout experiments on wild-type and chemotaxis-deficient mutants. We show that chemotactic processes dominate the transformation of slender and hemispherical structures into mushroom structures with a signature cap. Cellular Potts model simulation and experimental data provide evidence that accelerated movement of bacteria along the periphery of the biofilm, due to nutrient cues, results in the formation of mushroom structures and bacterial segregation. Multidrug resistance of bacteria is one of the most threatening dangers to public health. Understanding the mechanisms of the development of mushroom-shaped biofilms helps to identify the multidrug-resistant regions. We decoded the dynamics of the structural evolution of bacterial biofilms and the physics behind the formation of biofilm structures as well as the biological triggers that produce them. Combining in vitro gene knockout experiments with in silico models showed that chemotactic motility is one of the main driving forces for the formation of stalks and caps. Our results provide physicists and biologists with a new perspective on biofilm removal and eradication strategies.