Thermoregulation of Pseudomonas aeruginosa Biofilm Formation

Influence of slope, material, and temperature on Listeria monocytogenes and Pseudomonas aeruginosa mono- and dual-species biofilms

Understanding factors influencing Listeria monocytogenes biofilms aid in developing more effective elimination/prevention strategies. This study examined the effect of temperature (4 °C, 21 °C, 30 °C), materials (stainless steel 316 L with 2B and 2 R finishes, glass, and polypropylene), and slope (0°/horizontal or 90°/vertical) on mono- and dual-species biofilms using two L. monocytogenes strains and one Pseudomonas aeruginosa strain. All biofilms were grown in 10% TSB for 24 h and analyzed using culture-based methods. Additionally, the architecture of monospecies biofilms was studied using fluorescence microscopy. Overall, P. aeruginosa showed higher biofilm formation potential (6.2 log CFU/cm2) than L. monocytogenes (4.0 log CFU/cm2). Temperature greatly influenced P. aeruginosa and varied for L. monocytogenes. The slope predominantly influenced L. monocytogenes monospecies biofilms, with cell counts increasing by up to 2 log CFU/cm2. Surface material had little impact on biofilm formation. The study highlights the varying effects of different parameters on multispecies biofilms and the importance of surface geometry.

Phage against the Machine: The SIE-ence of Superinfection Exclusion

Prophages can alter their bacterial hosts to prevent other phages from infecting the same cell, a mechanism known as superinfection exclusion (SIE). Such alterations are facilitated by phage interactions with critical bacterial components involved in motility, adhesion, biofilm production, conjugation, antimicrobial resistance, and immune evasion. Therefore, the impact of SIE extends beyond the immediate defense against superinfection, influencing the overall fitness and virulence of the bacteria. Evaluating the interactions between phages and their bacterial targets is critical for leading phage therapy candidates like Pseudomonas aeruginosa, a Gram-negative bacterium responsible for persistent and antibiotic-resistant opportunistic infections. However, comprehensive literature on the mechanisms underlying SIE remains scarce. Here, we provide a compilation of well-characterized and potential mechanisms employed by Pseudomonas phages to establish SIE. We hypothesize that the fitness costs imposed by SIE affect bacterial virulence, highlighting the potential role of this mechanism in the management of bacterial infections.

Temperature sensing and virulence regulation in pathogenic bacteria

Pathogenic bacteria can detect a variety of environmental signals, including temperature changes. While sudden and significant temperature variations act as danger signals that trigger a protective heat-shock response, minor temperature fluctuations typically signal to the pathogen that it has moved from one environment to another, such as entering a specific niche within a host during infection. These latter temperature fluctuations are utilized by pathogens to coordinate the expression of crucial virulence factors. Here, we elucidate the critical role of temperature in governing the expression of virulence factors in bacterial pathogens. Moreover, we outline the molecular mechanisms used by pathogens to detect temperature fluctuations, focusing on systems that employ proteins and nucleic acids as sensory devices. We also discuss the potential implications and the extent of the risk that climate change poses to human pathogenic diseases.

Biofilm formation in food industries: Challenges and control strategies for food safety

Various pathogens have the ability to grow on food matrices and instruments. This grow may reach to form biofilms. Bacterial biofilms are community of microorganisms embedded in extracellular polymeric substances (EPSs) containing lipids, DNA, proteins, and polysaccharides. These EPSs provide a tolerance and favorable living condition for microorganisms. Biofilm formations could not only contribute a risk for food safety but also have negative impacts on healthcare sector. Once biofilms form, they reveal resistances to traditional detergents and disinfectants, leading to cross-contamination. Inhibition of biofilms formation and abolition of mature biofilms is the main target for controlling of biofilm hazards in the food industry. Some novel eco-friendly technologies such as ultrasound, ultraviolet, cold plasma, magnetic nanoparticles, different chemicals additives as vitamins, D-amino acids, enzymes, antimicrobial peptides, and many other inhibitors provide a significant value on biofilm inhibition. These anti-biofilm agents represent promising tools for food industries and researchers to interfere with different phases of biofilms including adherence, quorum sensing molecules, and cell-to-cell communication. This perspective review highlights the biofilm formation mechanisms, issues associated with biofilms, environmental factors influencing bacterial biofilm development, and recent strategies employed to control biofilm-forming bacteria in the food industry. Further studies are still needed to explore the effects of biofilm regulation in food industries and exploit more regulation strategies for improving the quality and decreasing economic losses.

Characterization of Pseudomonas spp. contamination and in situ spoilage potential in pasteurized milk production process

To investigate the prevalence of Pseudomonas in the pasteurized milk production process and its effect on milk quality, 106 strains of Pseudomonas were isolated from the pasteurized milk production process of a milk production plant in Shaanxi Province, China. The protease, lipase and biofilm-producing capacities of the 106 Pseudomonas strains were evaluated, and the spoilage enzyme activities of their metabolites were assessed by simulating temperature incubation in the refrigerated (7 °C) and transport environment (25 °C) segments and thermal treatments of pasteurization (75 °C, 5 min) and ultra-high temperature sterilization (121 °C, 15 s). A phylogenetic tree was drawn based on 16S rDNA gene sequencing and the top 5 strains were selected as representative strains to identify their in situ spoilage potential by examining their growth potential and ability to hydrolyze proteins and lipids in milk using growth curves, pH, whiteness, Zeta-potential, lipid oxidation, SDS-PAGE and volatile flavor compounds. The results showed that half and more of the isolated Pseudomonas had spoilage enzyme production and biofilm capacity, and the spoilage enzyme activity of metabolites was affected by the culture temperature and sterilization method, but ultra-high temperature sterilization could not completely eliminate the enzyme activity. The growth of Pseudomonas lundensis and Pseudomonas qingdaonensis was less affected by temperature and time, and the hydrolytic capacity of extracellular protease and lipase secreted by Pseudomonas lurida was the strongest, which had the greatest effect on milk quality. Therefore, it is crucial to identify the key contamination links of Pseudomonas, the main bacteria responsible for milk spoilage, and the influence of environmental factors on its deterioration.

Decoding the influence of low temperature on biofilm development: The hidden roles of c-di-GMP

Biofilms are widely used and play important roles in biological processes. Low temperature of wastewater inhibits the development of biofilms derived from wastewater activated sludge. However, the specific mechanism of temperature on biofilm development is still unclear. This study explored the mechanism of temperature on biofilm development and found a feasible method to enhance biofilm development at low temperature. The amount of biofilm development decreased by approximately 66 % and 55 % at 4 °C and 15 °C, respectively, as compared to 28 °C. The cyclic dimeric guanosine monophosphate (c-di-GMP) concentration also decreased at low temperature and was positively correlated with extracellular polymeric substance (EPS) content, formation, and adhesion strength. Microbial community results showed that low temperature inhibited the normal survival of most microorganisms, but promoted the growth of some psychrophile bacteria like Sporosarcina, Caldilineaceae, Gemmataceae, Anaerolineaceae and Acidobacteriota. Further analysis of functional genes demonstrated that the abundance of functional genes related to the synthesis of c-di-GMP (K18968, K18967 and K13590) decreased at low temperature. Subsequently, the addition of exogenous spermidine increased the level of intracellular c-di-GMP and alleviated the inhibition effect of low temperature on biofilm development. Therefore, the possible mechanism of low temperature on biofilm development could be the inhibition of the microorganism activity and reduction of the communication level between cells, which is the closely related to the EPS content, formation, and adhesion strength. The enhancement of c-di-GMP level through the exogenous addition of spermidine provides an alternative strategy to enhance biofilm development at low temperatures. The results of this study enhance the understanding of the influence of temperature on biofilm development and provide possible strategies for enhancing biofilm development at low temperatures.

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.

Combined effects of cold and acid on dual-species biofilms of Pseudomonas fluorescens and Listeria monocytogenes under simulated chilled beef processing conditions

Interactions across bacterial species boundaries are usually influenced by environmental stresses, yet little has been evaluated regarding multifactorial stresses on the fate of dual-species biofilm formation in food industry. In this study, the processing conditions of chilled beef were established as a combination of cold and acid stresses (4 °C and pH 5.4), with pH 7.0 or 25 °C serving as the controls, to investigate the interaction of dual-species biofilm between Pseudomonas fluorescens and Listeria monocytogenes. Dual-species biofilms significantly increased biofilm formation at 72 h under the condition of 25°C-pH7.0 and 25°C-pH5.4 (P < 0.05). Compared with mono-species biofilms, the cell numbers of L. monocytogenes in dual-species biofilms were lower at 25 °C (P < 0.05), however, the adherent cells of L. monocytogenes was higher in dual-species biofilms at 4 °C (P < 0.05). Furthermore, the amount of extracellular polysaccharides and proteins secreted by single P. fluorescens biofilms at 4 °C was more than three times than those at 25 °C. The surface-enhanced Raman spectroscopy further profiled the variability of extracellular polymeric substances (EPS) composition. Additionally, RT-qPCR results revealed an upregulation of biofilm-related and genes in co-culture species. It provides valuable insights into the strategies for removing mixed biofilms under diverse stressful conditions in practical food processing.

Ixodes ricinus tick bacteriome alterations based on a climatically representative survey in Hungary

IMPORTANCE

Climate-sensitive disease vectors, such as ticks, respond to the environment with changes in their microbiome. These changes can affect the emergence or re-emergence of various vector-borne pathogens, such as the causative agent of Lyme borreliosis (LB) or tick-borne encephalitis. This aspect is particularly emphasized in light of climate change. The climatically representative assessment of microbiome differences in various developmental stages of the most common Central European tick species, Ixodes ricinus, deepens our understanding of the potential climatic factors behind microbial relative abundance and interaction changes. This knowledge can support the development of novel disease vector control strategies.

A novel rspA gene regulates biofilm formation and virulence of Salmonella Typhimurium

Salmonella spp. are facultative anaerobic, Gram-negative, rod-shaped bacteria and belongs to the Enterobacteriaceae family. Although much has been known about Salmonella pathogenesis, the functional characterizations of certain genes are yet to be explored. The rspA (STM14_1818) is one such gene with putative dehydratase function, and its role in pathogenesis is unknown. The background information showed that rspA gene is upregulated in Salmonella when it resides inside macrophages, which led us to investigate its role in Salmonella pathogenesis. We generated the rspA knockout strain and complement strain in S. Typhimurium 14028. Ex-vivo and in-vivo infectivity was looked at macrophage and epithelial cell lines and Caenorhabditis elegans (C. elegans). The mutant strain differentially formed the biofilm at different temperatures by altering the expression of genes involved in the synthesis of cellulose and curli. Besides, the mutant strain is hyperproliferative intracellularly and showed increased bacterial burden in C. elegans. The mutant strain became more infectious and lethal, causing faster death of the worms than the wild type, and also modulates the worm's innate immunity. Thus, we found that the rspA deletion mutant was more pathogenic. In this study, we concluded that the rspA gene differentially regulates the biofilm formation in a temperature dependent manner by modulating the genes involved in the synthesis of cellulose and curli and negatively regulates the Salmonella virulence for longer persistence inside the host.

In vitro Activity of Cefepime/Avibactam Against Carbapenem Resistant Klebsiella pneumoniae and Integrative Metabolomics-Proteomics Approach for Resistance Mechanism: A Single-Center Study

Purpose

We aimed to evaluate the in vitro antibacterial effects of combination of cefepime/avibactam against carbapenem-resistant Klebsiella pneumonia (CRKP) and explore the resistance mechanism of FEP/AVI.

Patients and Methods

This study explored the in vitro antibacterial activities of ceftazidime/avibactam (CAZ/AVI) and cefepime/avibactam (FEP/AVI) against 40 and 76 CRKP clinical isolates. Proteomics and metabolomics were employed to investigate the resistance mechanisms of CRKP to FEP/AVI.

Results

FEP/AVI (MIC50/MIC90 0.5/4-64/4 μg/mL, resistance rate 17.1%) showed better antibacterial activity against CRKP than CAZ/AVI (MIC50/MIC90 4/4-128/4 μg/mL, resistance rate 20%) in vitro. Bioinformatics analysis showed that the differentially expressed proteins (DEPs) were enriched in alanine, aspartate and glutamate metabolism, and ribosome. Remarkably, transcriptional and translational activity-related pathways were inhibited in FEP/AVI resistant CRKP. Overlap analysis suggested that H-NS might play an important role in resistance to FEP/AVI in CRKP. The mRNA levels of DEPs-related genes (adhE, gltB, purA, ftsI and hns) showed the same trends as DEPs in FEP/AVI susceptible and resistant strains. FEP/AVI resistant isolates demonstrated stronger biofilm formation capacity than susceptible isolates. Metabolomics results showed that disturbed metabolites were mainly lipids, and adenine was decreased in FEP/AVI resistant CRKP.

Conclusion

These results indicated that H-NS, GltB and SpoT may directly or indirectly promote biofilm formation of CRKP and led to FEP/AVI resistance, but inhibited ribosomal function. Our study provides a mechanistic insight into the acquisition of resistance to FEP/AVI in Klebsiella pneumoniae.

Psychrotrophic Bacteria Equipped with Virulence and Colonization Traits Populate the Ice Cream Manufacturing Environment

Several microbial taxa have been associated with food processing facilities, and they might resist by attaching on tools and equipment even after sanitation procedures, producing biofilms that adhere to the surfaces and might embed other microorganisms, including spoilers and pathogens. There is increasing evidence that these communities can be transferred to the final product. To explore the microbial contamination routes in a facility producing ice creams, we collected foods and environmental swabs from industrial surfaces of equipment and tools and performed taxonomic and functional analyses of the microbial DNA extracted from the environmental samples. Our results suggest that complex communities dominated by psychrotrophic bacteria (e.g., Pseudomonas and Acinetobacter spp.) inhabit the food processing environment, and we demonstrate that these communities might be transferred from the surfaces to the products. Functional analysis performed on environmental samples highlighted the presence of several genes linked to antimicrobial resistance and adherence on abiotic surfaces; such genes were more abundant on food contact (FC) than on other surfaces. Metagenome-assembled genomes (MAGs) of Pseudomonas stutzeri showed genes linked with biofilm formation and motility, which are surely linked to colonizing capabilities in the processing lines. The study highlights clear potential advantages of applying microbiome mapping in the food industry for source tracking of microbial contamination and for planning appropriate ad hoc sanitization strategies. IMPORTANCE Several microbial species might permanently establish in food processing facilities, thus contributing to food loss. In fact, food contact surfaces might transfer microorganisms to intermediates and products, potentially representing a hazard to human health. In this work, we provide evidence of the existence of complex microbial communities overcoming sanitation in an ice cream-producing facility. These communities harbored several genes that could potentially lead to attachment to surfaces and antimicrobial resistance. Also, prediction of routes of contamination showed that several potential spoilage taxa might end up in the final product. Importantly, in this work, we show that mapping the environmental microbiome is a high-resolution technique that might help food business operators ensure food quality and safety through detection of potentially hazardous microorganisms.

Anti-bacterial mechanism of baicalin-tobramycin combination on carbapenem-resistant Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa (P. aeruginosa) is an important cause of nosocomial infections, and contributes to high morbidity and mortality, especially in intensive care units. P. aeruginosa is considered a 'critical' category bacterial pathogen by the World Health Organization to encourage an urgent need for research and development of new antibiotics against its infections.

AIM

To investigate the effectiveness of baicalin combined with tobramycin therapy as a potential treatment method for carbapenem-resistant P. aeruginosa (CRPA) infections.

METHODS

Polymerase chain reaction (PCR) and RT-PCR were used to detect the expression levels of drug-resistant genes (including VIM, IMP and OprD2) and biofilm-related genes (including algD, pslA and lasR) in CRPA that confer resistance to tobramycin, baicalin and tobramycin combined with baicalin (0, 1/8, 1/4, 1/2 and 1MIC).

RESULTS

There was a correlation between biofilm formation and the expression of biofilm-related genes. In addition, VIM, IMP, OprD2, algD, pslA and lasR that confer biofilm production under different concentrations in CRPA were significantly correlated. The synergistic effect of baicalin combined with tobramycin was a significant down-regulation of VIM, IMP, algD, pslA and lasR.

CONCLUSION

Baicalin combined with tobramycin therapy can be an effective treatment method for patients with CRPA infection.

Extracellular matrix affects mature biofilm and stress resistance of psychrotrophic spoilage Pseudomonas at cold temperature

Psychrotrophic Pseudomonas as the dominant spoilage bacteria, have biofilm forming ability, increasing persistence and contamination in the chilled food. Biofilm formation of spoilage Pseudomonas at cold temperature was documented, however, role of extracellular matrix in mature biofilm and stress resistance of psychrotrophic Pseudomonas are much less abundant. The aim of this study was to investigate the biofilm forming characteristics of three spoilers P. fluorescens PF07, P. lundensis PL28, and P. psychrophile PP26 at 25 °C, 15 °C and 4 °C, and to explore their stress resistance to chemical and thermal treatments of mature biofilms. The results showed that biofilm biomass of three Pseudomonas at 4 °C was significantly higher than that at 15 °C and 25 °C. The secretion of extracellular polymeric substances (EPS) greatly increased in those Pseudomonas under low temperature, of which extracellular protein constituted about 71.03%-77.44%. Compared to 25 °C, the mature biofilms were observed to more aggregation and thicker spatial structure at 4 °C ranging from 42.7 to 54.6 μm, in contrast to 25.0-29.8 μm at 25 °C, especially strain PF07. These Pseudomonas biofilms switched into moderate hydrophobicity, and their swarming and swimming were significantly inhibited at low temperature. Furthermore, the resistance to NaClO and heating at 65 °C apparently enhanced for mature biofilm formed at 4 °C, indicating the difference in EPS matrix production influenced the stress resistance of biofilm. In addition, three strains contained alg and psl operons for exopolysaccharide biosynthesis, and biofilm related genes of algK, pslA, rpoS, and luxR were significantly up-regulated, while flgA gene was down-regulated at 4 °C compared to 25 °C, consistent with the above phenotype changes. Thus, the dramatic increase of mature biofilm and their stress resistance in psychrotrophic Pseudomonas were associated with large secretion and protection of extracellular matrix under low temperature, which provide a theoretical basis for subsequent biofilm control during cold chain.

Metal-Resistant PGPR Strain Azospirillum brasilense EMCC1454 Enhances Growth and Chromium Stress Tolerance of Chickpea (Cicer arietinum L.) by Modulating Redox Potential, Osmolytes, Antioxidants, and Stress-Related Gene Expression

Heavy metal stress, including from chromium, has detrimental effects on crop growth and yields worldwide. Plant growth-promoting rhizobacteria (PGPR) have demonstrated great efficiency in mitigating these adverse effects. The present study investigated the potential of the PGPR strain Azospirillum brasilense EMCC1454 as a useful bio-inoculant for boosting the growth, performance and chromium stress tolerance of chickpea (Cicer arietinum L.) plants exposed to varying levels of chromium stress (0, 130 and 260 µM K₂Cr₂O₇). The results revealed that A. brasilense EMCC1454 could tolerate chromium stress up to 260 µM and exhibited various plant growth-promoting (PGP) activities, including nitrogen fixation, phosphate solubilization, and generation of siderophore, trehalose, exopolysaccharide, ACC deaminase, indole acetic acid, and hydrolytic enzymes. Chromium stress doses induced the formation of PGP substances and antioxidants in A. brasilense EMCC1454. In addition, plant growth experiments showed that chromium stress significantly inhibited the growth, minerals acquisition, leaf relative water content, biosynthesis of photosynthetic pigments, gas exchange traits, and levels of phenolics and flavonoids of chickpea plants. Contrarily, it increased the concentrations of proline, glycine betaine, soluble sugars, proteins, oxidative stress markers, and enzymatic (CAT, APX, SOD, and POD) and non-enzymatic (ascorbic acid and glutathione) antioxidants in plants. On the other hand, A. brasilense EMCC1454 application alleviated oxidative stress markers and significantly boosted the growth traits, gas exchange characteristics, nutrient acquisition, osmolyte formation, and enzymatic and non-enzymatic antioxidants in chromium-stressed plants. Moreover, this bacterial inoculation upregulated the expression of genes related to stress tolerance (CAT, SOD, APX, CHS, DREB2A, CHI, and PAL). Overall, the current study demonstrated the effectiveness of A. brasilense EMCC1454 in enhancing plant growth and mitigating chromium toxicity impacts on chickpea plants grown under chromium stress circumstances by modulating the antioxidant machinery, photosynthesis, osmolyte production, and stress-related gene expression.

Bacterial second messenger c-di-GMP: Emerging functions in stress resistance

In natural environments, bacteria constantly encounter various stressful conditions, including nutrient starvation, toxic chemicals, and oxidative stress. The ability to adapt to these adverse conditions is crucial for bacterial survival. Frequently, bacteria utilize nucleotide signaling molecules such as cyclic diguanylate (c-di-GMP) to regulate their behaviors when encounter stress conditions. c-di-GMP is a ubiquitous bacterial second messenger regulating the transition between the planktonic state and biofilm state. An essential feature of biofilms is the production of extracellular matrix that covers bacterial cells and offers a physical barrier protecting the cells from environmental assaults. Beyond that, accumulating evidences have demonstrated that changes in the environment, including stress stimuli, cause the alteration of intracellular levels of c-di-GMP in bacterial cells, which is immediately sensed by a variety of downstream effectors that induce an appropriate stress response. In this review, we summarize recent research on the role of c-di-GMP signaling in bacterial responses to diverse stress conditions.

A Library of Promoter-gfp Fusion Reporters for Studying Systematic Expression Pattern of Cyclic-di-GMP Metabolism-Related Genes in Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa is an environmental microorganism and is a model organism for biofilm research. Cyclic dimeric GMP (c-di-GMP) is a bacterial second messenger that plays critical roles in biofilm formation. P. aeruginosa contains approximately 40 genes that encode enzymes that participate in the metabolism of c-di-GMP (biosynthesis or degradation), yet it lacks tools that aid investigation of the systematic expression pattern of those genes. In this study, we constructed a promoter-gfp fusion reporter library that consists of 41 reporter plasmids. Each plasmid contains a promoter of corresponding c-di-GMP metabolism-related (CMR) genes from P. aeruginosa reference strain PAO1; thus, each promoter-gfp fusion reporter can be used to detect the promoter activity as well as the transcription of corresponding gene. The promoter activity was tested in P. aeruginosa and Escherichia coli. Among the 41 genes, the promoters of 26 genes showed activity in both P. aeruginosa and E. coli. The library was applied to determine the influence of different temperatures, growth media, and subinhibitory concentrations of antibiotics on the transcriptional profile of the 41 CMR genes in P. aeruginosa. The results showed that different growth conditions did affect the transcription of different genes, while the promoter activity of a few genes was kept at the same level under several different growth conditions. In summary, we provide a promoter-gfp fusion reporter library for systematic monitoring or study of the regulation of CMR genes in P. aeruginosa. In addition, the functional promoters can also be used as a biobrick for synthetic biology studies. IMPORTANCE The opportunistic pathogen P. aeruginosa can cause acute and chronic infections in humans, and it is one of the main pathogens in nosocomial infections. Biofilm formation is one of the most important causes for P. aeruginosa persistence in hosts and evasion of immune and antibiotic attacks. c-di-GMP is a critical second messenger to control biofilm formation. In P. aeruginosa reference strain PAO1, 41 genes are predicted to participate in the making and breaking of this dinucleotide. A major missing piece of information in this field is the systematic expression profile of those genes in response to changing environment. Toward this goal, we constructed a promoter-gfp transcriptional fusion reporter library that consists of 41 reporter plasmids, each of which contains a promoter of corresponding c-di-GMP metabolism-related genes in P. aeruginosa. This library provides a helpful tool to understand the complex regulation network related to c-di-GMP and to discover potential therapeutic targets.

The effects of temperature, salt, and phosphate on biofilm and exopolysaccharide production by Azotobacter spp

Inoculation of agriculturally important biofilms to plants under stress conditions has been of great interest in recent years. Therefore, in this study, biofilm- and exopolysaccharide (EPS)-forming ability of Azotobacter spp. was examined under different temperatures, NaCl concentrations, and phosphate levels. Azotobacter strains formed varying levels of biofilm and EPS depending on the tested factors. The pattern of biofilm formation was similar to that of EPS production under the conditions tested. Biofilm and EPS production at 28 °C was consistently higher than at either 18 or 37 °C. Biofilm production significantly increased in A. chroococcum strains (SBS2, SBS4, and SBS12) and A. vinelandii SBS6 with increasing salinity. Furthermore, a strong negative correlation was observed between biofilm or EPS production and increasing phosphate concentrations. Higher phosphate concentrations decreased biofilm and EPS production. In conclusion, contrary to temperature and phosphate effect, salinity differently affected biofilm and EPS production by Azotobacter strains.

Temperature-specific adaptations and genetic requirements in a biofilm formed by Pseudomonas aeruginosa

Pseudomonas aeruginosa is a gram-negative opportunistic pathogen often associated with nosocomial infections that are made more severe by this bacterium's ability to form robust biofilms. A biofilm is a microbial community encompassing cells embedded within an extracellular polymeric substrate (EPS) matrix that is typically secreted by the encased microbial cells. Biofilm formation is influenced by several environmental cues, and temperature fluctuations are likely to be an important stimulus in the lifecycle of P. aeruginosa as it transitions between life in aquatic or soil environments to sites of infection in the human host. Previous work has demonstrated that human body temperature can induce a shift in the biofilm EPS relative to room temperature growth, resulting in an incorporation of a filamentous phage coat protein into the biofilm EPS. In this study, we sought to identify adaptations enabling biofilm formation at room temperature or temperatures mimicking the natural environment of P. aeruginosa (23°C and 30°C) relative to temperatures mimicking life in the human host (37°C and 40°C). We identified higher biofilm: biomass ratios at lower temperatures on certain substrates, which correlated with a higher relative abundance of apparent polysaccharide EPS content. However, the known genes for EPS polysaccharide production in P. aeruginosa PA14 did not appear to be specifically important for temperature-dependent biofilm adaptation, with the pelB gene appearing to be generally important and the algD gene being generally expendable in all conditions tested. Instead, we were able to identify two previously uncharacterized hypothetical proteins (PA14_50070 and PA14_67550) specifically required for biofilm formation at 23°C and/or 30°C relative to temperatures associated with the human host. These unstudied contributors to biofilm integrity may have been previously overlooked since most P. aeruginosa biofilm studies tend to use 37°C growth temperatures. Overall, our study demonstrates that temperature shifts can have dramatic impacts on biofilm structure and highlights the importance of studying environment-specific adaptations in biofilm physiology.

H3-T6SS of Pseudomonas aeruginosa PA14 contributes to environmental adaptation via secretion of a biofilm-promoting effector

Microbial species often occur in complex communities and exhibit intricate synergistic and antagonistic interactions. To avoid predation and compete for favorable niches, bacteria have evolved specialized protein secretion systems. The type VI secretion system (T6SS) is a versatile secretion system widely distributed among Gram-negative bacteria that translocates effectors into target cells or the extracellular milieu via various physiological processes. Pseudomonas aeruginosa is an opportunistic pathogen responsible for many diseases, and it has three independent T6SSs (H1-, H2-, and H3-T6SS). In this study, we found that the H3-T6SS of highly virulent P. aeruginosa PA14 is negatively regulated by OxyR and OmpR, which are global regulatory proteins of bacterial oxidative and acid stress. In addition, we identified a H3-T6SS effector PA14_33970, which is located upstream of VgrG3. PA14_33970 interacted directly with VgrG3 and translocated into host cells. Moreover, we found that H3-T6SS and PA14_33970 play crucial roles in oxidative, acid, and osmotic stress resistance, as well as in motility and biofilm formation. PA14_33970 was identified as a new T6SS effector promoting biofilm formation and thus named TepB. Furthermore, we found that TepB contributes to the virulence of P. aeruginosa PA14 toward Caenorhabditis elegans. Overall, our study indicates that H3-T6SS and its biofilm-promoting effector TepB are regulated by OxyR and OmpR, both of which are important for adaptation of P. aeruginosa PA14 to multiple stressors, providing insights into the regulatory mechanisms and roles of T6SSs in P. aeruginosa.

Yersinia enterocolitica-Derived Outer Membrane Vesicles Inhibit Initial Stage of Biofilm Formation

Yersinia enterocolitica (Y. enterocolitica) is an important food-borne and zoonotic pathogen. It can form biofilm on the surface of food, increasing the risk to food safety. Generally, outer membrane vesicles (OMVs) are spherical nanostructures secreted by Gram-negative bacteria during growth. They play a role in biological processes because they contain biologically active molecules. Several studies have reported that OMVs secreted by various bacteria are associated with the formation of biofilms. However, the interactions between Y. enterocolitica OMVs and biofilm are unknown. This study aims to investigate the effect of Y. enterocolitica OMVs on biofilm formation. Firstly, OMVs were extracted from Y. enterocolitica Y1083, which has a strong biofilm-forming ability, at 15 °C, 28 °C and 37 °C and then characterized. The characterization results showed differences in the yield and protein content of three types of OMVs. Next, by co-culturing the OMVs with Y. enterocolitica, it was observed that the OMVs inhibited the initial stage of Y. enterocolitica biofilm formation but did not affect the growth of Y. enterocolitica. Furthermore, biofilm formation by Salmonella enteritidis and Staphylococcus aureus were also inhibited by OMVs. Subsequently, it was proved that lipopolysaccharides (LPS) in OMVs inhibited biofilm formation., The proteins, DNA or RNA in OMVs could not inhibit biofilm formation. Bacterial motility and the expression of the biofilm-related genes pgaABC, motB and flhBD were inhibited by LPS. LPS demonstrated good anti-biofilm activity against various bacteria. This study provides a new approach to the prevention and control of pathogenic bacterial biofilm.

Early biofilm and streamer formation is mediated by wall shear stress and surface wettability: A multifactorial microfluidic study

Biofilms are intricate communities of microorganisms encapsulated within a self-produced matrix of extra-polymeric substances (EPS), creating complex three-dimensional structures allowing for liquid and nutrient transport through them. These aggregations offer constituent microorganisms enhanced protection from environmental stimuli-like fluid flow-and are also associated with higher resistance to antimicrobial compounds, providing a persistent cause of concern in numerous sectors like the marine (biofouling and aquaculture), medical (infections and antimicrobial resistance), dentistry (plaque on teeth), food safety, as well as causing energy loss and corrosion. Recent studies have demonstrated that biofilms interact with microplastics, often influencing their pathway to higher trophic levels. Previous research has shown that initial bacterial attachment is affected by surface properties. Using a microfluidic flow cell, we have investigated the relationship between both wall shear stress (τw ) and surface properties (surface wettability) upon biofilm formation of two species (Cobetia marina and Pseudomonas aeruginosa). We investigated biofilm development on low-density polyethylene (LDPE) membranes, Permanox® slides, and glass slides, using nucleic acid staining and end-point confocal laser scanning microscopy. The results show that flow conditions affect biomass, maximum thickness, and surface area of biofilms, with higher τw (5.6 Pa) resulting in thinner biofilms than lower τw (0.2 Pa). In addition, we observed differences in biofilm development across the surfaces tested, with LDPE typically demonstrating more overall biofilm in comparison to Permanox® and glass. Moreover, we demonstrate the formation of biofilm streamers under laminar flow conditions within straight micro-channels.

Optimization of a food industry-waste-based medium for the production of the plant growth promoting microorganism Pseudomonas oryzihabitans PGP01 based on agro-food industries by-products

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Several agro-food industry wastes based on potato peels and pulp (FPP), tomato seeds (TS) and cereals (WB) industries were tested for their feasibility in producing P. oryzihabitans PGP01.

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The production of P. oryzihabitans PGP01 in a medium based on FPP supplemented with 10 g L⁻¹ of tryptone, 10 g L⁻¹ of sugar cane molasses, 5 g L⁻¹ nacl and 2.5 g L⁻¹ of K₂HPO₄ allowed to reach similar growth than the commercial medium.

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In 2 L bioreactors, a maximum of 4.4 × 10⁹ CFU mL⁻¹ of P. oryzihabitans PGP01 was obtained after 24 h of growth in the optimized medium, similar than laboratory medium.

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P. oryzihabitans PGP01 grown on the optimized medium preserved its biological activity, maintaining the same effect on roots of in vitro cultured plantlets than when it was grown in the commercial medium.

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This study shows how to re-use food-industry wastes for microbial production, reducing the amount of generated wastes.

In this study, three wastes based on potato peels and pulps, tomato seeds and wheat bran were used as basis for the preparation of a cheap medium to produce the bacterium P. oryzihabitans PGP01. In flasks experiments, P. oryzihabitans PGP01 growth at 25 °C in a medium based on frozen potato peels and pulp (FPP) with tryptone as a nitrogen source resulted in the maximum production compared to the commercial TSB medium. In the scale-up to 2 L bioreactors, FPP supplemented with tryptone, molasses, NaCl and K₂HPO₄ allowed to reach similar biomass production than in the TSB medium. A maximum growth of 4.4 × 10⁹ CFU mL⁻¹ after setting the agitation and the air flux conditions at 400 rpm and 0.75 vvm. Finally, P. oryzihabitans PGP01 growing in this optimized medium conserved its biological activity showing the expected effect in root development previously reported for this microorganism.

Antipathogenic Compounds That Are Effective at Very Low Concentrations and Have Both Antibiofilm and Antivirulence Effects against Pseudomonas aeruginosa

Pseudomonas aeruginosa, a human pathogen, causes both acute and chronic infections that are mediated by virulence factor production and biofilm formation. Since both characteristics of P. aeruginosa are regulated by quorum sensing (QS), we screened 126 synthetic chemicals for anti-QS activity and finally selected the compounds that have both antivirulence and antibiofilm activities. To efficiently screen the chemical library, the following reporter-based bioassay systems were used: the QS- or biofilm-specific promoter-lacZ fusions (lasI_p- or PA1897_p-lacZ for the QS activity and cdrA_p-lacZ for measuring the intracellular c-di-GMP levels). We also measured the production of virulence factors and biofilm formation in P. aeruginosa. A small-animal infection model using mealworms was also used for virulence analysis. From this screening, MHY1383 and MHY1387 were found to have both antivirulence and antibiofilm activities in P. aeruginosa. Most importantly, MHY1383 and MHY1387 exhibited these activities at very low concentrations, showing a significant anti-QS effect at 100 pM and an antibiofilm effect at 1 to 10 pM. By treating P. aeruginosa with these compounds, the virulence factor production and biofilm formation of P. aeruginosa were significantly reduced. These compounds can be developed as promising antipathogenic and antibiofilm drugs that can be applied in situations where such compounds must be used in an extremely low concentration. Our findings also offer a significant advantage for developing therapeutic agents with few adverse side effects.

IMPORTANCE Many antibiotics are increasingly losing their efficacy due to antibiotic resistance mediated by biofilm formation. In this study, we screened a synthetic chemical library and discovered several compounds that have both antivirulence and antibiofilm effects against Pseudomonas aeruginosa, a notorious human pathogen. Two of them had these effects at extremely low concentrations and are expected not to develop resistance, unlike conventional antibiotics, because they have no effect on the growth of bacteria. Our results strongly suggest that these compounds act on the target in a noncompetitive manner, indicating that they are distinct from other previously known quorum sensing inhibitors or biofilm inhibitors. Our findings offer a significant advantage for developing therapeutic agents with few adverse side effects.

Sensory perception in bacterial cyclic diguanylate signal transduction

Cyclic diguanylate (c-di-GMP) signal transduction systems provide bacteria with the ability to sense changing cell status or environmental conditions and then execute suitable physiological and social behaviors in response. In this review, we provide a comprehensive census of the stimuli and receptors that are linked to the modulation of intracellular c-di-GMP. Emerging evidence indicates that c-di-GMP networks sense light, surfaces, energy, redox potential, respiratory electron acceptors, temperature, and structurally diverse biotic and abiotic chemicals. Bioinformatic analysis of sensory domains in diguanylate cyclases and c-di-GMP-specific phosphodiesterases as well as the receptor complexes associated with them reveals that these functions are linked to a diverse repertoire of protein domain families. We describe the principles of stimulus perception learned from studying these modular sensory devices, illustrate how they are assembled in varied combinations with output domains, and summarize a system for classifying these sensor proteins based on their complexity. Biological information processing via c-di-GMP signal transduction not only is fundamental to bacterial survival in dynamic environments but also is being used to engineer gene expression circuitry and synthetic proteins with à la carte biochemical functionalities.

Heterogeneity in biofilm formation and identification of biomarkers of strong biofilm formation among field isolates of Pseudomonas spp

The biofilm formation ability of a collection of thirty-three Pseudomonas spp. isolates from food processing facilities was investigated in order to find biomarkers of strong biofilm production, a characteristic that can determine persistence in food processing environments. The strains were classified according to the colony pigmentation on solid media as green, brown or not pigmented. The biofilm production on stainless steel and polystyrene was assessed by spectrometric determination of the fixed crystal violet, and the biofilm formed on glass, through confocal laser scanning microscopy. Besides, pyoverdine production, catalase activity, RpoS status and cellular hydrophobicity were also monitored. A significantly higher biofilm production level on stainless steel and polystyrene was observed for green-pigmented strains as compared to brown or not pigmented strains. The influence of iron availability on biofilm formation on stainless steel was studied through the addition of the iron scavenger 2,2-bipyridine resulting in a decrease of 40 % in biofilm formation for the not pigmented strains. For most of the potential biomarkers studied (i.e., pyoverdine production, catalase activity, cellular hydrophobicity), the phenotypic heterogeneity observed among strains was mainly dependent on the Pseudomonas species and no strong associations with the biofilm formation capacity were detected. However, the green colony pigmentation on solid media showed good potential as a biomarker of strong biofilm formation on stainless steel and polystyrene both in P. aeruginosa and Pseudomonas spp.

Impact of temperature-dependent phage expression on Pseudomonas aeruginosa biofilm formation

Pseudomonas aeruginosa is a ubiquitous opportunistic pathogen that forms robust biofilms in the different niches it occupies. Numerous physiological adaptations are required as this organism shifts from soil or aquatic environments to a host-associated lifestyle. While many conditions differ between these niches, temperature shifts are a factor that can contribute to physiological stress during this transition. To understand how temperature impacts biofilm formation in this pathogen, we used proteomic and transcriptomic tools to elucidate physiological responses in environment-relevant vs. host-relevant temperatures. These studies uncovered differential expression of various proteins including a phage protein that is associated with the EPS matrix in P. aeruginosa. This filamentous phage was induced at host temperatures and was required for full biofilm-forming capacity specifically at human body temperature. These data highlight the importance of temperature shift in biofilm formation and suggest bacteriophage proteins could be a possible therapeutic target in biofilm-associated infections.

Beyond the Wall: Exopolysaccharides in the Biofilm Lifestyle of Pathogenic and Beneficial Plant-Associated Pseudomonas

The formation of biofilms results from a multicellular mode of growth, in which bacteria remain enwrapped by an extracellular matrix of their own production. Many different bacteria form biofilms, but among the most studied species are those that belong to the Pseudomonas genus due to the metabolic versatility, ubiquity, and ecological significance of members of this group of microorganisms. Within the Pseudomonas genus, biofilm studies have mainly focused on the opportunistic human pathogen Pseudomonas aeruginosa due to its clinical importance. The extracellular matrix of P. aeruginosa is mainly composed of exopolysaccharides, which have been shown to be important for the biofilm architecture and pathogenic features of this bacterium. Notably, some of the exopolysaccharides recurrently used by P. aeruginosa during biofilm formation, such as the alginate and polysaccharide synthesis loci (Psl) polysaccharides, are also used by pathogenic and beneficial plant-associated Pseudomonas during their interaction with plants. Interestingly, their functions are multifaceted and seem to be highly dependent on the bacterial lifestyle and genetic context of production. This paper reviews the functions and significance of the exopolysaccharides produced by plant-associated Pseudomonas, particularly the alginate, Psl, and cellulose polysaccharides, focusing on their equivalents produced in P. aeruginosa within the context of pathogenic and beneficial interactions.