Effect of calcium on Staphylococcus aureus biofilm architecture: A confocal laser scanning microscopic study

Potential of the plant growth-promoting rhizobacterium Rhodococcus qingshengii LMR356 in mitigating lead stress impact on Sulla spinosissima L

Mining-related lead (Pb) pollution of the soil poses serious hazards to ecosystems and living organisms, including humans. Improved heavy metal phytoremediation efficacy, achieved by using phytostabilizing plants assisted by plant-growth-promoting (PGP) microorganisms, has been presented as an effective strategy for remediating polluted soils. The objective of this research was to examine the response and potential of the plant-growth-promoting bacterium LMR356, a Rhodococcus qingshengii strain isolated from an abandoned mining soil, under lead stress conditions. Compared to non-contaminated culture media, the presence of lead induced a significant decrease in auxin production (from 21.17 to 2.65 μg mL-1) and phosphate solubilization (from 33.60 to 8.22 mg L-1), whereas other PGP traits increased drastically, such as 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity (from 38.17 to 71.37 nmol mg-1 h-1 α-ketobutyrate), siderophore production (from 69 to 83%), exopolysaccharide production (from 1952.28 to 3637.72 mg mL-1), biofilm formation, and motility. We, therefore, investigated the behavior of Sulla spinosissima L. in the presence or absence of this strain under a variety of experimental conditions. Under hydroponic conditions, Sulla plants showed endurance to varying lead concentrations (500-1000 μM). Inoculation of plants with Rhodococcus qingshengii strain LMR356 enhanced plant tolerance, as demonstrated by the increase in plant biomass (ranging from 14.41 to 79.12%) compared to non-inoculated Pb-stressed and non-stressed control plants. Antioxidant enzyme activities (increasing by -42.71 to 126.8%) and chlorophyll (383.33%) and carotenoid (613.04%) content were also augmented. In addition to its impact on plant lead tolerance, strain LMR356 showed a growth-promoting effect on Sulla plants when cultivated in sterilized non-contaminated sand. Parameters such as plant biomass (16.57%), chlorophyll (24.14%), and carotenoid (30%) contents, as well as ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT) activities, were all elevated compared to non-inoculated plants. Furthermore, when the same plant species was cultivated in highly polluted soil, inoculation increased plant biomass and improved its physiological properties. These findings demonstrate that LMR356 is a phytobeneficial bacterial strain capable of enhancing Sulla growth under normal conditions and improving its heavy metal tolerance in multi-polluted soils. Thus, it can be considered a promising biofertilizer candidate for growing Sulla spinosissima L. or other selected plants intended for application in restoration and stabilization initiatives aimed at reviving and safeguarding environmentally compromised and polluted soils after mining activities.

Calcium-mediated modulation of Pseudomonas fluorescens biofilm formation

Biofilm formation is usually affected by many environmental factors, including divalent cations. The purpose of the current work was to analyze how calcium (Ca2+) affects the biofilm formation of dairy Pseudomonas fluorescens isolates by investigating their growth, swarming motility, biofilm-forming capacity, extracellular polymeric substance production, and biofilm structures. Moreover, the regulation mechanism of Ca2+ involved in its biofilm formation was explored through RNA-sequencing analysis. This work revealed that supplementation of 5, 10, 15, and 20 mM Ca2+ significantly reduced the swarming motility of P. fluorescens strains (P.F2, P.F4, and P.F17), but the biofilm-forming ability and polysaccharide production were increased after the supplementation of 5 and 10 mM Ca2+. By the supplementation of Ca2+, complex structures with more cell clusters glued together in P. fluorescens P.F4 biofilms were confirmed by scanning electron microscopy, and increased biomass and coverage of P. fluorescens P.F4 biofilms were observed by confocal laser scanning microscopy. In addition, RNA-sequencing results showed that P. fluorescens P.F4 showed a transcriptional response to the supplementation of 10 mM Ca2+, and a total of 137 genes were significantly expressed. The differential genes were represented in 4 upregulated Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways (nonribosomal peptide structures, quorum sensing, biosynthesis of siderophore group nonribosomal peptides, and phenylalanine metabolism), and 4 downregulated KEGG pathways (flagellar assembly, amino sugar and nucleotide sugar metabolism, nitrotoluene degradation, and cationic antimicrobial peptide resistance). The results indicate that Ca2+ might serve as an enhancer to substantially trigger the biofilm formation of dairy P. fluorescens isolates in the dairy industry.

Unraveling the significance of calcium as a biofilm promotion signal for Bacillus licheniformis strains isolated from dairy products

Bacillus licheniformis, a quick and strong biofilm former, is served as a persistent microbial contamination in the dairy industry. Its biofilm formation process is usually regulated by environmental factors including the divalent cation Ca2+. This work aims to investigate how different concentrations of Ca2+ change biofilm-related phenotypes (bacterial motility, biofilm-forming capacity, biofilm structures, and EPS production) of dairy B. licheniformis strains. The Ca2+ ions dependent regulation mechanism for B. licheniformis biofilm formation was further investigated by RNA-sequencing analysis. Results revealed that supplementation of Ca2+ increased B. licheniformis biofilm formation in a dose-dependent way, and enhanced average coverage and thickness of biofilms with complex structures were observed by confocal laser scanning microscopy. Bacterial mobility of B. licheniformis was increased by the supplementation of Ca2+ except the swarming ability at 20 mM of Ca2+. The addition of Ca2+ decreased the contents of polysaccharides but promoted proteins production in EPS, and the ratio of proteins/polysaccharides content was significantly enhanced with increasing Ca2+ concentrations. RNA-sequencing results clearly indicated the variation in regulating biofilm formation under different Ca2+ concentrations, as 939 (671 upregulated and 268 downregulated) and 951 genes (581 upregulated and 370 downregulated) in B. licheniformis BL2-11 were induced by 10 and 20 mM of Ca2+, respectively. Differential genes were annotated in various KEGG pathways, including flagellar assembly, two-component system, quorum sensing, ABC transporters, and related carbohydrate and amino acid metabolism pathways. Collectively, the results unravel the significance of Ca2+ as a biofilm-promoting signal for B. licheniformis in the dairy industry.

Synthesis and Characterization of Durable Antibiofilm and Antiviral Silane-Phosphonium Thin Coatings for Medical and Agricultural Applications

Pathogens such as bacteria and viruses cause disease in a range of hosts, from humans to plants. Bacterial biofilms, communities of bacteria, e.g., Staphylococcus aureusand Escherichia coli, attached to the surface, create a protective layer that enhances their survival in harsh environments and resistance to antibiotics and the host's immune system. Biofilms are commonly associated with food spoilage and chronic infections, posing challenges for treatment and prevention. Tomato brown rugose fruit virus (ToBRFV), a newly discovered tobamovirus, infects tomato plants, causing unique symptoms on the fruit, posing a risk for tomato production. The present study focuses on the effectiveness of silane-phosphonium thin coatings on polymeric films, e.g., polypropylene. Phosphonium has significant antibacterial activity and is less susceptible to antibacterial resistance, making it a safer alternative with a reduced environmental impact. We successfully synthesized silane-phosphonium monomers as confirmed by 31P NMR and mass spectrometry. The chemical composition, thickness, morphology, and wetting properties of the coatings were tested by Fourier-transform infrared spectroscopy with attenuated total reflectance, focused ion beam, atomic force microscopy, environmental scanning electron microscope, and contact angle (CA) measurements. The antibiofilm and antibacterial activities of the coatings were tested against S. aureus and E. coli, while the antiviral activity was evaluated against ToBRFV. The significant antibiofilm and antiviral activity suggests applications in various fields including medicine, agriculture, and the food industry.

Sequestration of cobalt and nickel by biofilm forming bacteria isolated from spent nuclear fuel pool water

In the current study, six bacterial types, isolated from spent nuclear fuel (SNF) pool facility, were investigated for their ability to sequester heavy metals (cobalt and nickel). Biofilm formation by the six bacterial isolates, viz., Bacillus subtilis, Staphylococcus species, Staphylococcus arlettae, Staphylococcus epidermidis, Staphylococcus auricularis, and Chryseobacterium gleum, were assayed, and they were found to have significant biofilm forming property. Their biofilms were characterised using confocal scanning laser microscopy, and their potential to accumulate Co²⁺ and Ni²⁺ from bulk solutions was analysed with respect to time. A comparative assessment of bioaccumulation capacity was done using biofilms, planktonic cells, and live vs dead cells. The strains accumulated Co²⁺ and Ni²⁺ in the range of 4 × 10^-4 to 1 × 10^-5 g/mg of cell biomass. It is interesting to note that dead biomass also showed significant removal of the two metal ions, suggesting an alternative process for metal removal. This study suggests that hostile environments can be a repertoire of putative bacterial species with potential heavy metals and other contaminants remediation properties.

Quinones as an Efficient Molecular Scaffold in the Antibacterial/Antifungal or Antitumoral Arsenal

Quinone-based compounds constitute several general classes of antibiotics that have long shown unwavering efficiency against both Gram-positive and Gram-negative microbial infections. These quinone-based antibiotics are increasingly popular due to their natural origins and are used in natural beverages from herbs or plants in African, Chinese and Indian traditional medicines to treat and prevent various diseases. Quinone-based antibiotics display different bioactive profiles depending on their structures and exert specific biocidal and anti-biofilm properties, and based on recent literature, will be discussed herein.

The Medium Composition Impacts Staphylococcus aureus Biofilm Formation and Susceptibility to Antibiotics Applied in the Treatment of Bone Infections

The biofilm-associated infections of bones are life-threatening diseases, requiring application of dedicated antibiotics in order to counteract the tissue damage and spread of microorganisms. The in vitro analyses on biofilm formation and susceptibility to antibiotics are frequently carried out using methods that do not reflect conditions at the site of infection. To evaluate the influence of nutrient accessibility on Staphylococcus aureus biofilm development in vitro, a cohesive set of analyses in three different compositional media was performed. Next, the efficacy of four antibiotics used in bone infection treatment, including gentamycin, ciprofloxacin, levofloxacin, and vancomycin, against staphylococcal biofilm, was also assessed. The results show a significant reduction in the ability of biofilm to grow in a medium containing elements occurring in the serum, which also translated into the diversified changes in the efficacy of used antibiotics, compared to the setting in which conventional media were applied. The differences indicate the need for implementation of adequate in vitro models that closely mimic the infection site. The results of the present research may be considered an essential step toward the development of in vitro analyses aiming to accurately indicate the most suitable antibiotic to be applied against biofilm-related infections of bones.

Quantitative Analyses of Biofilm by Using Crystal Violet Staining and Optical Reflection

Biofilms have caused many problems, not only in the industrial fields, but also in our daily lives. Therefore, it is important for us to control them by evaluating them properly. There are many instrumental analytical methods available for evaluating formed biofilm qualitatively. These methods include the use of Raman spectroscopy and various microscopes (optical microscopes, confocal laser microscopes, scanning electron microscopes, transmission electron microscopes, atomic force microscopes, etc.). On the other hand, there are some biological methods, such as staining, gene analyses, etc. From the practical viewpoint, staining methods seem to be the best due to various reasons. Therefore, we focused on the staining method that used a crystal violet solution. In the previous study, we devised an evaluation process for biofilms using a color meter to analyze the various staining situations. However, this method was complicated and expensive for practical engineers. For this experiment, we investigated the process of using regular photos that were quantified without any instruments except for digitized cameras. Digitized cameras were used to compare the results. As a result, we confirmed that the absolute values were different for both cases, respectively. However, the tendency of changes was the same. Therefore, we plan to utilize the changes before and after biofilm formation as indicators for the future.

Proposal for Some Affordable Laboratory Biofilm Reactors and Their Critical Evaluations from Practical Viewpoints

Biofilms are a result of bacterial activities and are found everywhere. They often form on metal surfaces and on the surfaces of polymeric compounds. Biofilms are sticky and mostly consist of water. They have a strong resistance to antimicrobial agents and can cause serious problems for modern medicine and industry. Biofilms are composed of extracellular polymeric substances (EPS) such as polysaccharides produced from bacterial cells and are dominated by water at the initial stage. In a series of experiments, using Escherichia coli, we developed three types of laboratory biofilm reactors (LBR) to simulate biofilm formation. For the first trial, we used a rotary type of biofilm reactor for stirring. For the next trial, we tried another rotary type of reactor where the circular plate holding specimens was rotated. Finally, a circular laboratory biofilm reactor was used. Biofilms were evaluated by using a crystal violet staining method and by using Raman spectroscopy. Additionally, they were compared to each other from the practical (industrial) viewpoints. The third type was the best to form biofilms in a short period. However, the first and second were better from the viewpoint of "ease of use". All of these have their own advantages and disadvantages, respectively. Therefore, they should be properly selected and used for specific and appropriate purposes in the future.

Seasonal airway microbiome and transcriptome interactions promote childhood asthma exacerbations

BACKGROUND

Seasonal variation in respiratory illnesses and exacerbations in pediatric populations with asthma is well described, though whether upper airway microbes play season-specific roles in these events is unknown.

OBJECTIVE

We hypothesized that nasal microbiota composition is seasonally dynamic and that discrete microbe-host interactions modify risk of asthma exacerbation in a season-specific manner.

METHODS

Repeated nasal samples from children with exacerbation-prone asthma collected during periods of respiratory health (baseline; n = 181 samples) or first captured respiratory illness (n = 97) across all seasons, underwent bacterial (16S ribosomal RNA gene) and fungal (internal transcribed spacer region 2) biomarker sequencing. Virus detection was performed by multiplex PCR. Paired nasal transcriptome data were examined for seasonal dynamics and integrative analyses.

RESULTS

Upper airway bacterial and fungal microbiota and rhinovirus detection exhibited significant seasonal dynamics. In seasonally adjusted analysis, variation in both baseline and respiratory illness microbiota related to subsequent exacerbation. Specifically, in the fall, when respiratory illness and exacerbation events were most frequent, several Moraxella and Haemophilus members were enriched both in virus-positive respiratory illnesses and those that progressed to exacerbations. The abundance of 2 discrete bacterial networks, characteristically comprising either Streptococcus or Staphylococcus, exhibited opposing interactions with an exacerbation-associated SMAD3 nasal epithelial transcriptional module to significantly increase the odds of subsequent exacerbation (odds ratio = 14.7, 95% confidence interval = 1.50-144, P = .02; odds ratio = 39.17, 95% confidence interval = 2.44-626, P = .008, respectively).

CONCLUSIONS

Upper airway microbiomes covary with season and with seasonal trends in respiratory illnesses and asthma exacerbations. Seasonally adjusted analyses reveal specific bacteria-host interactions that significantly increase risk of asthma exacerbation in these children.

Effect of calcium hydroxide on morphology and physicochemical properties of Enterococcus faecalis biofilm

Calcium hydroxide Ca(OH)2 has been used as an intracanal medicament to targets microbial biofilms and avert secondary infection in the root canal system. This study evaluated the effects of this material on the morphology and physicochemical properties of an established in-vitro biofilm of Enterococcus faecalis. A biofilm of E. faecalis was grown in multichannel plates. The chemicals including Ca2+, OH-, and saturated Ca(OH)2 (ie 21.6 mM) were prepared in order to evaluate which component eradicated or amplified biofilm structure. Various biochemical and microscopic methods were used to investigate the properties of the biofilm. Biofilms treated with Ca(OH)2 absorbed more Ca2+ because of the alkaline pH of the environment and the ions affected the physicochemical properties of the E. faecalis biofilm. A denser biofilm with more cavities and a granular surface was observed in the presence of Ca2+ ions. This resulted in a decrease in the surface-to-biofilm ratio with increases in its biomass, thickness, colony size, and volume. Calcium hydroxide did not destroy E. faecalis biofilms but rather contributed to the biofilm structure. This in-vitro study sheds light on a missing link in the formation of E. faecalis biofilm in which the Ca2+ in Ca(OH)2.

Impedance Characteristics of Monolayer and Bilayer Graphene Films with Biofilm Formation and Growth

Biofilms are the result of bacterial activity. When the number of bacteria (attached to materials’ surfaces) reaches a certain threshold value, then the bacteria simultaneously excrete organic polymers (EPS: extracellular polymeric substances). These sticky polymers encase and protect the bacteria. They are called biofilms and contain about 80% water. Other components of biofilm include polymeric carbon compounds such as polysaccharides and bacteria. It is well-known that biofilms cause various medical and hygiene problems. Therefore, it is important to have a sensor that can detect biofilms to solve such problems. Graphene is a single-atom-thick sheet in which carbon atoms are connected in a hexagonal shape like a honeycomb. Carbon compounds generally bond easily to graphene. Therefore, it is highly possible that graphene could serve as a sensor to monitor biofilm formation and growth. In our previous study, monolayer graphene was prepared on a glass substrate by the chemical vapor deposition (CVD) method. Its biofilm forming ability was compared with that of graphite. As a result, the CVD graphene film had the higher sensitivity for biofilm formation. However, the monolayer graphene has a mechanical disadvantage when used as a biofilm sensor. Therefore, for this new research project, we prepared bilayer graphene with high mechanical strength by using the CVD process on copper substrates. For these specimens, we measured the capacitance component of the specimens’ impedance. In addition, we have included a discussion about the possibility of applying them as future sensors for monitoring biofilm formation and growth.

The role of S-layer Protein (SlpA) in biofilm-formation of Deinococcus radiodurans

AIMS

To investigate the molecular basis of biofilm formation in a recombinant lab strain of Deinococcus radiodurans with a plasmid harbouring gfp and kan^R that acquired the biofilm-forming ability.

METHODS AND RESULTS

D. radiodurans R1 is known as a non-biofilm former bacterium and so far there are no reports on its biofilm-producing capabilities. In this study, we investigated the molecular basis of biofilm formation in a recombinant strain of D. radiodurans using classical biofilm assays, confocal laser scanning microscopy, and real-time PCR. Biochemical analysis of D. radiodurans biofilm matrix revealed that it consisted predominantly of protein and carbohydrate complexes with a little amount of extracellular DNA (eDNA). Further, studies showed that D. radiodurans biofilm formation was enhanced in the presence of 25 mM Ca²⁺ , which enhanced the exopolysaccharide and protein content in the biofilm matrix. Enzymatic treatments with proteinase K, alginate lyase, and DNase I indicated the involvement of some proteinaceous components to be critical in the biofilm formation. RT-PCR studies showed that enhanced expression of a surface layer protein SlpA conferred the biofilm ability to D. radiodurans.

CONCLUSION

Overexpression of SlpA in D. radiodurans conferred the biofilm formation ability to the bacterium, in which a partial role was also played by the recombinant plasmid pKG. It was also shown that the presence of Ca²⁺ in the growth medium enhanced SlpA production, thus improving biofilm stability and biofilm maturation of D. radiodurans.

SIGNIFICANCE AND IMPACT

This study shows how biofilm formation can be augmented in D. radiodurans. The finding has implications for the development of D. radiodurans biofilm-based biotechnological applications.

Exploring the role of microbial biofilm for industrial effluents treatment

Biofilm formation on biotic or abiotic surfaces is caused by microbial cells of a single or heterogeneous species. Biofilm protects microbes from stressful environmental conditions, toxic action of chemicals, and antimicrobial substances. Quorum sensing (QS) is the generation of autoinducers (AIs) by bacteria in a biofilm to communicate with one other. QS is responsible for the growth of biofilm, synthesis of exopolysaccharides (EPS), and bioremediation of environmental pollutants. EPS is used for wastewater treatment due to its three-dimensional matrix which is composed of proteins, polysaccharides, humic-like substances, and nucleic acids. Autoinducers mediate significantly the degradation of environmental pollutants. Acyl-homoserine lactone (AHL) producing bacteria as well as quorum quenching enzyme or bacteria can effectively improve the performance of wastewater treatment. Biofilms-based reactors due to their economic and ecofriendly nature are used for the treatment of industrial wastewaters. Electrodes coated with electro-active biofilm (EAB) which are obtained from sewage sludge, activated sludge, or industrial and domestic effluents are getting popularity in bioremediation. Microbial fuel cells are involved in wastewater treatment and production of energy from wastewater. Synthetic biological systems such as genome editing by CRISPR-Cas can be used for the advanced bioremediation process through modification of metabolic pathways in quorum sensing within microbial communities. This narrative review discusses the impacts of QS regulatory approaches on biofilm formation, extracellular polymeric substance synthesis, and role of microbial community in bioremediation of pollutants from industrial effluents.

Chemical Components of Aqueous Extracts of Melia azedarach Fruits and Their Effects on The Transcriptome of Staphylococcus aureus

Staphylococcus aureus is the causative agent of numerous and varied clinical infections. Crude aqueous extracts of Melia azedarach fruits inhibit the planktonic growth and initial biofilm formation of S. aureus in a dose-dependent manner. Moreover, the biofilm topologies became sparse and decreased as the concentration of the aqueous extracts increased. RNA-Seq analyses revealed 532 differentially expressed genes (DEGs) after S. aureus exposure to 0.25 g/ml extracts; 319 of them were upregulated, and 213 were downregulated. The majority of DEGs were categorized into abundant sub-groups in the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Finally, untargeted UHPLC-MS/MS analyses of the aqueous extracts of M. azedarach fruits demonstrated a highly complex profile in positive and negative electrospray ionization modes. The extracts primarily consisted of lipids and lipid-like molecules, organic acids and their derivatives, phenylpropanoids, polyketides, organoheterocyclic compounds, and benzenoids annotated by abundant lipid maps and KEGG pathways. Overall, this study provides evidences that the aqueous extracts of M. azedarach fruits can control S. aureus infections and sought to understand the mode of action of these extracts on S. aureus.

The High Impact of Staphylococcus aureus Biofilm Culture Medium on In Vitro Outcomes of Antimicrobial Activity of Wound Antiseptics and Antibiotic

The staphylococcal biofilm-based infections of wounds still pose a significant therapeutical challenge. Treated improperly, they increase the risk of limb amputation or even death of the patient. The present algorithms of infected wound treatment include, among others, the application of antiseptic substances. In vitro wound biofilm models are applied in order to scrutinize their activity. In the present work, using a spectrum of techniques, we showed how the change of a single variable (medium composition) in the standard in vitro model translates not only to shift in staphylococcal biofilm features but also to the change of efficacy of clinically applied wound antimicrobials such as octenidine, polyhexamethylene biguanide, chlorhexidine, hypochlorite solutions, and locally applied gentamycin. The data presented in this study may be of a pivotal nature, taking into consideration the fact that results of in vitro analyses are frequently used to propagate application of specific antimicrobials in hospitals and ambulatory care units.

Staphylococcus aureus: biofilm formation and strategies against it

The formation of Staphylococcus aureus biofilm causes significant infections in the human body. Biofilm forms through the aggregation of bacterial species and brings about many complications. It mediates drug resistance and persistence and facilitates the recurrence of infection at the end of antimicrobial therapy. Biofilm formation goes through a series of steps to complete, and any interference in these steps can disrupt its formation. Such interference may occur at any stage of biofilm production, including attachment, monolayer formation, and accumulation. Interfering agents can act as quorum sensing inhibitors and interfere in the functionality of quorum sensing receptors, attachment inhibitors and affect the cell hydrophobicity. Among these inhibiting strategies, attachment inhibitors could serve as the best agents against biofilm formation. If pathogens abort the attachment, the following stages of biofilm formation, e.g., accumulation and dispersion, will fail to materialize. Inhibition at this stage leads to suppression of virulence factors and invasion. One of the best-known inhibitors is a chelator that collects metal, Fe+, Zn+, and magnesium critical for biofilm formation. These influential factors in the binding and formation of biofilm are investigated, and the coping strategy is discussed. This review examines the stages of biofilm formation and determines what factors interfere in the continuity of these steps. Finally, the inhibition strategies are investigated, reviewed, and discussed. Keywords: Biofilm, Staphylococcus, Biofilm inhibitor, Dispersion, Antibiofilm agent, EPS, PIA.

A Spectrofluorophotometrical Method Based on Fura-2-AM Probe to Determine Cytosolic Ca2+ Level in Pseudomonas syringae Complex Bacterial Cells

Calcium signaling is an emerging mechanism by which bacteria respond to environmental cues. To measure the intracellular free-calcium concentration in bacterial cells, [Ca²⁺]_i, a simple spectrofluorometric method based on the chemical probe Fura 2-acetoxy methyl ester (Fura 2-AM) is here presented using Pseudomonad bacterial cells. This is an alternative and quantitative method that can be completed in a short period of time with low costs, and it does not require the induction of heterologously expressed protein-based probes like Aequorin. Furthermore, it is possible to verify the properties of membrane channels involved in Ca²⁺ entry from the extracellular matrix. This method is in particular valuable for measuring [Ca²⁺]_i in the range of 0.1-39.8 µM in small cells like those of prokaryotes.

Destruction of Staphylococcus aureus biofilms by combining an antibiotic with subtilisin A or calcium gluconate

In S. aureus biofilms, bacteria are embedded in a matrix of extracellular polymeric substances (EPS) and are highly tolerant to antimicrobial drugs. We thus sought to identify non-antibiotic substances with broad-spectrum activity able to destroy the EPS matrix and enhance the effect of antibiotics on embedded biofilm bacteria. Among eight substances tested, subtilisin A (0.01 U/mL) and calcium gluconate (CaG, Ca²⁺ 1.25 mmol/L) significantly reduced the biomass of biofilms formed by at least 21/24 S. aureus isolates. Confocal laser scanning microscopy confirmed that they both eliminated nearly all the proteins and PNAG from the matrix. By contrast, antibiotics alone had nearly no effect on biofilm biomass and the selected one (oxytetracycline-OTC) could only slightly reduce biofilm bacteria. The combination of OTC with CaG or subtilisin A led to an additive reduction (average of 2 log₁₀ CFU/mL) of embedded biofilm bacteria on the isolates susceptible to OTC (MBC < 10 μg/mL, 11/24). Moreover, these two combinations led to a reduction of the embedded biofilm bacteria higher than 3 log₁₀ CFU/mL for 20–25% of the isolates. Further studies are now required to better understand the factors that cause the biofilm produced by specific isolates (20–25%) to be susceptible to the combinations.

The Association of Calcium and Vitamin D Use With Implant Survival of Total Knee Arthroplasty: A Nationwide Population-Based Cohort Study

BACKGROUND

Calcium and vitamin D have been regarded as beneficial nutrients for bone metabolism that may affect survival of arthroplasties. However, the relationship between their use and revision rate of knee arthroplasty has not been evaluated. Thus, we investigated an association between calcium and vitamin D use and the revision rate after primary total knee arthroplasty.

METHODS

A nationwide population-based cohort study was conducted using the Korean National Health Insurance database. We included patients diagnosed with knee osteoarthritis and underwent primary total knee arthroplasty between 2009 and 2018. Risk for arthroplasty revision was estimated using a Cox proportional hazards model with time-dependent covariates. Log-rank test was used to assess survival of knee arthroplasty.

RESULTS

Out of 142,147 subjects, 28,403 were calcium and vitamin D users and 113,744 were never users. Calcium and vitamin D significantly reduced the revision risk with a 6-month drug use lag period (adjusted hazard ratio [aHR] 0.56, 95% confidence interval [CI] 0.45-0.70). Calcium and vitamin D combination use for more than 1 year was associated with reduced revision risks in both patients with periprosthetic joint infection (aHR 0.63, 95% CI 0.42-0.95) and patients without infection (aHR 0.70, 95% CI 0.54-0.91). Implant survival was significantly improved in calcium and vitamin D combination users for more than 1 year compared with never users (log-rank P < .001).

CONCLUSION

Combination use of calcium and vitamin D with a dose of 800 IU or greater for more than 1 year was associated with the greatest reduction in the risks for revision surgery after total knee arthroplasty.

Analyzing microalgal biofilm structures formed under different light conditions by evaluating cell-cell interactions

Biofilm structure plays an important role in microalgae biofilm-based culture. This work aims to understand microalgal biofilm structures formed under different light conditions. Here, Scenedesmus obliquus was biofilm cultured under the light spectra of white, blue, green, and red, and the photoperiods of 5:5 s, 30:30 min, and 12:12 h (light : dark period). Biofilms were observed with confocal laser scanning microscopes and profilometry, then the porosity and roughness of biofilm were determined. We found that cells under white light formed a heterogeneous biofilm with many voids, high porosity, and roughness. While under red and blue lights, cells formed homogeneous biofilms with low porosity. Biofilm structures formed under different photoperiods were different. The mechanism of forming different biofilm structures under different light conditions was interpreted from the aspect of cell-cell interactions. Moreover, the results revealed that biomass accumulation increased with the increasing biofilm porosity due to the high effective diffusion coefficient.

Characterization of Actinobacillus seminis biofilm formation

Actinobacillus seminis is an autochthonous gram-negative bacterium that affects reproductive organs, causing epididymitis, low fertility, and occasional abortions in ovine and goats. The virulence factors and the pathogenicity mechanisms of A. seminis have not been clearly elucidated yet. In this work, biofilm production by A. seminis in in vitro assays is described and characterized. After 48-h incubation at 37 °C in trypticase soy broth, A. seminis formed biofilms containing an extracellular matrix comprised mainly of fibrillar material. Microaerophilia or the presence of calcium diminished biofilm formation in approximately 50% and 70%, respectively, but low iron concentrations increased it 40%. Through enzymatic digestion, it was found that proteins were the main component of these biofilms. Structural observations through scanning electron microscopy indicated the presence of a high amount of fibrillar material in which bacteria were immersed. Antibodies against different bacterial surface proteins, such as anti-biofilm matrix and anti-adhesin, diminished biofilm formation in 70% and 25%, respectively; whereas furanone C-30 and LED-209, compounds described as quorum-sensing inhibitors, completely inhibited biofilm formation. In conclusion, environmental conditions can influence strongly biofilm formation in A. seminis, and this could be an advantageous strategy that allows bacteria to persist inside a host.

Calcineurin signaling pathway influences Aspergillus niger biofilm formation by affecting hydrophobicity and cell wall integrity

BACKGROUND

Biofilms, as a kind of fixed-cell community, can greatly improve industrial fermentation efficiency in immobilized fermentation, but the regulation process is still unclear, which restricts their application. Ca2+ was reported to be a key factor affecting biofilm formation. However, the effect of Ca2+ on biofilm structure and microbiology was yet only studied in bacteria. How Ca2+-mediated calcineurin signaling pathway (CSP) alters biofilm formation in bacteria and fungi has rarely been reported. On this basis, we investigated the regulation of CSP on the formation of biofilm in Aspergillus niger.

RESULTS

Deletion of the key genes MidA, CchA, CrzA or CnaA in the CSP lowered the Ca2+ concentration in the mycelium to a different extent, inhibited the formation of A. niger biofilm, reduced the hydrophobicity and adhesion of spores, destroyed the cell wall integrity of hyphae, and reduced the flocculation ability of hyphae. qRT-PCR results showed that the expression of spore hydrophobic protein RodA, galactosaminogalactan (GAG) biosynthesis genes (uge3, uge5, agd3, gtb3), and α-1,3-glucan biosynthesis genes (ags1, ags3) in the ∆MidA, ∆CchA, ∆CrzA, ∆CnaA strains were significantly down-regulated compared with those of the wild type (WT). In addition, the transcription levels of the chitin synthesis gene (chsB, chsD) and β-1,3-glucan synthesis gene (FksA) were consistent with the change in chitin and β-1,3-glucan contents in mutant strains.

CONCLUSION

These results indicated that CSP affected the hydrophobicity and adhesion of spores, the integrity of mycelial cell walls and flocculation by affecting Ca2+ levels in mycelium, which in turn affected biofilm formation. This work provides a possible explanation for how CSP changes the formation of A. niger biofilm, and reveals a pathway for controlling biofilm formation in industrial immobilized fermentation.

Uranium bioremediation by acid phosphatase activity of Staphylococcus aureus biofilms: Can a foe turn a friend?

In this study, Staphylococcus aureus biofilms, which are considered a foe for being pathogenic, were tested for their uranium bioremediation capacity to find out if they can turn out to be a friend. Acid phosphatase activity, which is speculated to aid in bio-precipitation of U(VI) from uranyl nitrate solution, was assayed in biofilms of seven different S. aureus strains. The presence of acid phosphatase enzyme was detected in the biofilms of all S. aureus strains (in the range of 3.1 ± 0.21 to 26.90 ± 2.32 μi.u./g), and found to be higher when compared to that of their planktonic phenotypes. Among all, S. aureus V329 biofilm showed highest biofilm formation ability along with maximum phosphatase activity (26.9 ± 2.32 μi.u./g of biomass). Addition of phosphate enhanced the U(VI) remediation when treated with uranyl nitrate solution. S. aureus V329 biofilm showed significant U tolerance with only a 3-log reduction when exposed to 10 ppm U(VI) for 1 h. When treated in batch mode, V329 biofilm successfully remediated up to 47% of the 10 ppm U(VI). This new approach using the acid phosphatase from the S. aureus V329 biofilm presents an alternative method for the remediation of uranium contamination.

Environmental factors modulate biofilm formation by Staphylococcus aureus

Biofilm formation on indwelling medical devices represents an exclusive evasion mechanism for many pathogenic bacteria to establish chronic infections. Staphylococcus aureus is one of the major bacterial pathogens that are able to induce both animal and human infections. The continued emergence of multiple drug-resistant S. aureus, especially methicillin-resistant S. aureus, is problematic due to limited treatment options. Biofilm formation by S. aureus complicates the treatment of methicillin-resistant S. aureus infections. Therefore, elucidating the mechanisms of biofilm formation in this pathogen is important for the development of alternative therapeutic strategies. Various environmental and genetic factors contribute to biofilm formation. In this review, we address the environmental factors and discuss how they affect biofilm formation by S. aureus.

Enhanced synergistic effects of xylitol and isothiazolones for inhibition of initial biofilm formation by Pseudomonas aeruginosa ATCC 9027 and Staphylococcus aureus ATCC 6538

Bacterial biofilms, formed on biotic or abiotic surfaces, can lead to serious environmental or medical problems. Therefore, it is necessary to find novel antimicrobial agents to combat biofilms, or more effective combinations of existing biocides. In this study, initial biofilms of Pseudomonas aeruginosa ATCC 9027 and Staphylococcus aureus ATCC 6538 in the presence of xylitol or xylitol and isothiazolones were determined using crystal violet staining in 96-well microplates and confocal laser scanning microscopy. Xylitol and isothiazolones exhibited enhanced synergistic inhibition of initial biofilm formation, and also the structure and production of extracellular polymeric substances by P. aeruginosa ATCC 9027 and S. aureus ATCC 6538 in a dose-dependent manner. In addition, xylitol and isothiazolones inhibited and restored the swimming motility of P. aeruginosa ATCC 9027, respectively. These findings show that a combination of xylitol and isothiazolones exerts pronounced antimicrobial activity against P. aeruginosa and S. aureus biofilms and may be applicable for preventing or reducing bacterial biofilms in vitro.

Characterization of Biofilm Formed by Phenanthrene-Degrading Bacteria on Rice Root Surfaces for Reduction of PAH Contamination in Rice

One effective method in to reduce the uptake of organic contaminants by plants is the development of a root barrier. In this study, the characterization of biofilm structure and function by phenanthrene-degrading Pseudomonas sp. JM2-gfp on rice root surfaces were carried out. Our results showed that root surfaces from three rice species, namely Liaojing401, Koshihikari, and Zhenzhuhong all present hydrophobicity and a high initial adhesion of strain JM2-gfp. Matured robust biofilm formation occurred at 48 h on the root surfaces. The biofilm exhibited cell dense aggregates and biomass embedded in the extracellular polymeric substance (EPS) matrix. EPS composition results showed that the proteins, carbohydrates, lipids and nucleic acids are produced in the biofilm, while the content varied with rice species. Under the initial concentration of phenanthrene 50 mg·L-1, the residual phenanthrene in plant roots from 'Zhengzhuhong', 'Koshihikari' and 'Liaojing401' with biofilm mediated were significantly decreased by 71.9%, 69.3% and 58.7%, respectively, compared to those without biofilm groups after 10 days of exposure. Thus, the biofilm colonized on roots plays an important role of degradation in order to reduce the level of phenanthrene uptake of plants. Thereby, the present work provides significant new insights into lowering the environmental risks of polycyclic aromatic hydrocarbons (PAHs) in crop products from contaminated agriculture soils.

A Na+ /Ca2+ exchanger of the olive pathogen Pseudomonas savastanoi pv. savastanoi is critical for its virulence

In a number of compatible plant-bacterium interactions, a rise in apoplastic Ca2+ levels is observed, suggesting that Ca2+ represents an important environmental clue, as reported for bacteria infecting mammalians. We demonstrate that Ca2+ entry in Pseudomonas savastanoi pv. savastanoi (Psav) strain DAPP-PG 722 is mediated by a Na+ /Ca2+ exchanger critical for virulence. Using the fluorescent Ca2+ probe Fura 2-AM, we demonstrate that Ca2+ enters Psav cells foremost when they experience low levels of energy, a situation mimicking the apoplastic fluid. In fact, Ca2+ entry was suppressed in the presence of high concentrations of glucose, fructose, sucrose or adenosine triphosphate (ATP). Since Ca2+ entry was inhibited by nifedipine and LiCl, we conclude that the channel for Ca2+ entry is a Na+ /Ca2+ exchanger. In silico analysis of the Psav DAPP-PG 722 genome revealed the presence of a single gene coding for a Na+ /Ca2+ exchanger (cneA), which is a widely conserved and ancestral gene within the P. syringae complex based on gene phylogeny. Mutation of cneA compromised not only Ca2+ entry, but also compromised the Hypersensitive response (HR) in tobacco leaves and blocked the ability to induce knots in olive stems. The expression of both pathogenicity (hrpL, hrpA and iaaM) and virulence (ptz) genes was reduced in this Psav-cneA mutant. Complementation of the Psav-cneA mutation restored both Ca2+ entry and pathogenicity in olive plants, but failed to restore the HR in tobacco leaves. In conclusion, Ca2+ entry acts as a 'host signal' that allows and promotes Psav pathogenicity on olive plants.

Introducing BAIT (Biofilm Architecture Inference Tool): a software program to evaluate the architecture of oral multi-species biofilms

Biofilm model systems are used to study biofilm growth and predict the effects of anti-biofilm interventions within the human oral cavity. Many in vitro biofilm model systems use a confocal laser scanning microscope (CLSM) in conjunction with image analysis tools to study biofilms. The aim of this study was to evaluate an in-house developed image analysis software program that we call BAIT (Biofilm Architecture Inference Tool) to quantify the architecture of oral multi-species biofilms following anti-biofilm interventions using a microfluidic biofilm system. Differences in architecture were compared between untreated biofilms and those treated with water (negative control), sodium gluconate ('placebo') or stannous fluoride (SnF2). The microfluidic system was inoculated with pooled human saliva and biofilms were developed over 22 h in filter-sterilized 25 % pooled human saliva. During this period, biofilms were treated with water, sodium gluconate, or SnF2 (1000, 3439 or 10 000 p.p.m. Sn2+) 8 and 18 h post-inoculation. After 22 h of growth, biofilms were stained with LIVE/DEAD stain, and imaged by CLSM. BAIT was used to calculate biofilm biovolume, total number of objects, surface area, fluffiness, connectivity, convex hull porosity and viability. Image analysis showed oral biofilm architecture was significantly altered by 3439 and 10 000 p.p.m. Sn2+ treatment regimens, resulting in decreased biovolume, surface area, number of objects and connectivity, while fluffiness increased (P<0.01). In conclusion, BAIT was shown to be able to measure the changes in biofilm architecture and detects possible antimicrobial and anti-biofilm effects of candidate agents.

Effects of arsenic on the biofilm formations of arsenite-oxidizing bacteria

Arsenite-oxidizing bacteria (AOB) play a key role in the biogeochemical cycle of arsenic in the environment, and are used for the bioremediation of As contaminated groundwater; however, it is not yet known about how arsenic affects biofilm formations of AOB, and how biofilm formations affect bacterial arsenite-oxidizing activities. To address these issues, we isolated seven novel AOB strains from the arsenic-contaminated soils. They can completely oxidize 1.0 mM As(III) in 22-60 h. Their arsenite oxidase sequences show 43-99% identities to those of other known AOB. Strains Cug1, Cug2, Cug3, Cug4, and Cug6 are able to form biofilms with thickness of 15-95 µm, whereas Cug8 and Cug9 cannot form biofilms. It is interesting to see that arsenite inhibited the biofilm formations of heterotrophic AOB strains, but promoted the biofilm formations of autotrophic strains in a concentration-dependent manner. The arsenite-oxidizing rates of Cug1 and Cug4 biofilms are 31.6% and 27.6% lower than those of their suspension cultures, whereas the biofilm activities of other strains are similar to those of their suspension cultures. The biofilm formation significantly promoted the bacterial resistance to arsenic. This work is the first report on the complex correlations among environmental arsenic, bacterial biofilm formations and bacterial arsenite-oxidizing activities. The data highlight the diverse lifestyle of different AOB under arsenic stress, and provide essential knowledge for the screening of efficient AOB strains used for constructions of bioreactors.

Role of Ttca of Citrobacter Werkmanii in Bacterial Growth, Biocides Resistance, Biofilm Formation and Swimming Motility

To screen, identify and study the genes involved in isothiazolone resistance and biofilm formation in Citrobacter werkmanii strain BF-6. A Tn5 transposon library of approximately 900 mutants of C. werkmanii strain BF-6 was generated and screened to isolate 1,2-benzisothiazolin-3-one (BIT) resistant strains. In addition, the tRNA 2-thiocytidine (32) synthetase gene (ttcA) was deleted through homologous recombination and the resulting phenotypic changes of the ΔttcA mutant were studied. A total of 3 genes were successfully identified, among which ΔttcA mutant exhibited a reduction in growth rate and swimming motility. On the other hand, an increase in biofilms formation in ΔttcA were observed but not with a significant resistance enhancement to BIT. This work, for the first time, highlights the role of ttcA gene of C. werkmanii strain BF-6 in BIT resistance and biofilm formation.

Staphylococcus aureus biofilm removal by targeting biofilm-associated extracellular proteins

Background & objectives:

Among cell surface proteins, biofilm-associated protein (Bap) promotes biofilm development in Staphylococcus aureus strains. The aim of this study was to investigate proteinase-mediated biofilm dispersion in different isolates of S. aureus.

Methods:

Biofilm assay was done in 96-well microtitre plate to evaluate the effect of proteinase K on biofilms of bovine mastitis S. Aureus isolates. Extracellular polymeric substances were extracted and evaluated for their composition (protein, polysaccharides and extracellular DNA), before and after the proteinase K treatment.

Results:

Biofilm assay showed that 2 µg/ml proteinase K significantly inhibited biofilm development in bap-positive S. aureus V329 as well as other S. aureus isolates (SA7, SA10, SA33, SA352), but not in bap-mutant M556 and SA392 (a weak biofilm-producing strain). Proteinase K treatment on S. aureus planktonic cells showed that there was no inhibition of planktonic growth up to 32 µg/ml of proteinase K. Proteinase K treatment on 24 h old preformed biofilms showed an enhanced dispersion of bap-positive V329 and SA7, SA10, SA33 and SA352 biofilms; however, proteinase K did not affect the bap-mutant S. aureus M556 and SA392 biofilms. Biofilm compositions study before and after proteinase K treatment indicated that Bap might also be involved in eDNA retention in the biofilm matrix that aids in biofilm stability. When proteinase K was used in combination with antibiotics, a synergistic effect in antibiotic efficacy was observed against all biofilm-forming S. aureus isolates.

Interpretation & conclusions:

Proteinase K inhibited biofilms growth in S. aureus bovine mastitis isolates but did not affect their planktonic growth. An enhanced dispersion of preformed S. aureus biofilms was observed on proteinase K treatment. Proteinase K treatment with antibiotics showed a synergistic effect against S. aureus biofilms. The study suggests that dispersing S. aureus by protease can be of use while devising strategies against S. aureus biofilms.

A preliminary investigation of metal element profiles in the serum of patients with bloodstream infections using inductively-coupled plasma mass spectrometry (ICP-MS)

BACKGROUND

We determined metal element profiles (MEPs) by inductively-coupled plasma mass spectrometry (ICP-MS) in the serum of patients with blood stream infection (BSI) and find out very important (VIP) metal elements in specific infections.

METHODS

Sixty-eight metal elements were identified in both serum and the bacteria isolated from 14 BSI patients with Staphylococcus infection, 39 with Enterobacteriaceae infection, 5 with Enterococcus infection and 58 healthy subjects without infection by ICP-MS methods. Statistical analysis, Principal Component Analysis (PCA) and Partial Least Squares Discriminant Analysis (PLS-DA) were performed to process data among different groups, select differential metal elements and operate correlation analysis.

RESULTS

The MEPs in the serum of BSI patients with 4 types of bacteria (Staphylococcus aureus, Escherichia coli, Enterococcus faecium, and Klebsiella pneumonia), and the corresponding MEPs of the bacteria were established. VIP metal elements were screened out in different BSI patients. Correlation analysis showed that there were some correlations between serum concentrations of metal elements and bacterial infection.

CONCLUSION

We found differential metal elements in the serum of BSI patients compared with controls, thus providing a basis for the diagnosis, prevention and treatment of BSI from the perspective of metallomics.

Plasma, serum, albumin, and divalent metal ions inhibit the adhesion and the biofilm formation of Cutibacterium (Propionibacterium) acnes

Adhesion and biofilm formation of human skin bacteria C. acnes on plasma, serum and albumin-coated polystyrene or in the presence of these blood components were studied. The proteins which were pre-adsorbed to polystyrene surface or added to the medium simultaneously with bacterial cells reduced C. acnes adhesion and biofilm formation by 2-5 times to compare to the control. The role of calcium, magnesium and zinc on C. acnes attachment was also assessed. Calcium (1 and 10 mM) had the inhibitory effect on C. acnes adhesion, whereas zinc (1 and 10 mM) diminished the biofilm formation of C. acnes. We also observed that C. acnes cells did not bind to erythrocytes. Thus, we suggest that bacteria C. acnes preferably colonize the plasma-poor environment due to the inhibitory effect of blood components, in particular, albumin, calcium, and zinc.

Hygrocin C from marine-derived Streptomyces sp. SCSGAA 0027 inhibits biofilm formation in Bacillus amyloliquefaciens SCSGAB0082 isolated from South China Sea gorgonian

Several ansamycins have been reported to inhibit bacterial biofilm formation and accelerate the eradication of developed biofilms, but little is known about the effect of hygrocin C, an ansamycin, on bacterial biofilm formation. Here, hygrocin C was isolated from the marine-derived Streptomyces sp. SCSGAA 0027 and reported for the first time to be capable of inhibiting the biofilm formation of Staphylococcus aureus and Bacillus amyloliquefaciens SCSGAB0082 with the production of anti-microbial lipopeptides from South China Sea gorgonian Subergorgia suberosa at concentrations of less than minimum inhibitory concentrations. Moreover, hygrocin C also promoted the eradication of developed biofilms, affected the biofilm architecture, and lowered the extracellular polymeric matrix formation, cell motility, and surface hydrophobicity in B. amyloliquefaciens, which was in accordance with the inhibition of biofilm formation. Furthermore, transcriptome analysis revealed that hygrocin C altered the transcripts of several genes associated with bacterial chemotaxis and flagellar, two-component system and the synthesis of arginine and histidine, which are important for bacterial biofilm formation. In conclusion, hygrocin C could be used as a potential biofilm inhibitor against S. aureus and B. amyloliquefaciens. But further genetic investigations are needed to provide more details for elucidation of the molecular mechanisms responsible for the effects of hygrocin C on B. amyloliquefaciens biofilm formation.

Complete genome sequence of Citrobacter werkmanii strain BF-6 isolated from industrial putrefaction

Background

In our previous study, Citrobacter werkmanii BF-6 was isolated from an industrial spoilage sample and demonstrated an excellent ability to form biofilms, which could be affected by various environmental factors. However, the genome sequence of this organism has not been reported so far.

Results

We report the complete genome sequence of C. werkmanii BF-6 together with the description of the genome features and its annotation. The size of the complete chromosome is 4,929,789 bp with an average coverage of 137×. The chromosome exhibits an average G + C content of 52.0%, and encodes 4570 protein coding genes, 84 tRNA genes, 25 rRNA operons, 3 microsatellite sequences and 34 minisatellite sequences. A previously unknown circular plasmid designated as pCW001 was also found with a length of 212,549 bp and a G + C content of 48.2%. 73.5%, 75.6% and 92.6% of the protein coding genes could be assigned to GO Ontology, KEGG Pathway, and COG (Clusters of Orthologous Groups) categories respectively. C. werkmanii BF-6 and C. werkmanii NRBC 105721 exhibited the closest evolutionary relationships based on 16S ribosomal RNA and core-pan genome assay. Furthermore, C. werkmanii BF-6 exhibits typical bacterial biofilm formation and development. In the RT-PCR experiments, we found that a great number of biofilm related genes, such as bsmA, bssR, bssS, hmsP, tabA, csgA, csgB, csgC, csgD, csgE, and csgG, were involved in C. werkmanii BF-6 biofilm formation.

Conclusions

This is the first complete genome of C. werkmanii. Our work highlights the potential genetic mechanisms involved in biofilm formation and paves a way for further application of C. werkmanii in biofilms research.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4157-9) contains supplementary material, which is available to authorized users.

Biofilms formed within the acidic and the neutral biotrickling filters for treating H2S-containing waste gases

Microbial cell in the innermost biofilm have higher viability, and produce polysaccharide as the main component of EPS in acidic environment.

Graft polymerization of styryl bisphosphonate monomer onto polypropylene films for inhibition of biofilm formation

There has been increased concern during the past few decades over the role bacterial biofilms play in causing a variety of health problems, especially since they exhibit a high degree of resistance to antibiotics and are able to survive in hostile environments. Biofilms consist of bacterial aggregates enveloped by a self-produced matrix attached to the surface. Ca(2+) ions promote the formation of biofilms, and enhance their stability, viscosity, and strength. Bisphosphonates exhibit a high affinity for Ca(2+) ions, and may inhibit the formation of biofilms by acting as sequestering agents for Ca(2+) ions. Although the antibacterial activity of bisphosphonates is well known, research into their anti-biofilm behavior is still in its early stages. In this study, we describe the synthesis of a new thin coating composed of poly(styryl bisphosphonate) grafted onto oxidized polypropylene films for anti-biofilm applications. This grafting process was performed by graft polymerization of styryl bisphosphonate vinylic monomer onto O2 plasma-treated polypropylene films. The surface modification of the polypropylene films was confirmed using surface measurements, including X-ray photoelectron spectroscopy, atomic force microscopy, and water contact angle goniometry. Significant inhibition of biofilm formation was achieved for both Gram-negative and Gram-positive bacteria.

Calcium transcriptionally regulates the biofilm machinery of Xylella fastidiosa to promote continued biofilm development in batch cultures

The functions of calcium (Ca) in bacteria are less characterized than in eukaryotes, where its role has been studied extensively. The plant-pathogenic bacterium Xylella fastidiosa has several virulence features that are enhanced by increased Ca concentrations, including biofilm formation. However, the specific mechanisms driving modulation of this feature are unclear. Characterization of biofilm formation over time showed that 4 mM Ca supplementation produced denser biofilms that were still developing at 96 h, while biofilm in non-supplemented media had reached the dispersal stage by 72 h. To identify changes in global gene expression in X. fastidiosa grown in supplemental Ca, RNA-Seq of batch culture biofilm cells was conducted at three 24-h time intervals. Results indicate that a variety of genes are differentially expressed in response to Ca, including genes related to attachment, motility, exopolysaccharide synthesis, biofilm formation, peptidoglycan synthesis, regulatory functions, iron homeostasis, and phages. Collectively, results demonstrate that Ca supplementation induces a transcriptional response that promotes continued biofilm development, while biofilm cells in nonsupplemented media are driven towards dispersion of cells from the biofilm structure. These results have important implications for disease progression in planta, where xylem sap is the source of Ca and other nutrients for X. fastidiosa.

Biofilm Matrix Proteins

Proteinaceous components of the biofilm matrix include secreted extracellular proteins, cell surface adhesins, and protein subunits of cell appendages such as flagella and pili. Biofilm matrix proteins play diverse roles in biofilm formation and dissolution. They are involved in attaching cells to surfaces, stabilizing the biofilm matrix via interactions with exopolysaccharide and nucleic acid components, developing three-dimensional biofilm architectures, and dissolving biofilm matrix via enzymatic degradation of polysaccharides, proteins, and nucleic acids. In this article, we will review functions of matrix proteins in a selected set of microorganisms, studies of the matrix proteomes of Vibrio cholerae and Pseudomonas aeruginosa, and roles of outer membrane vesicles and of nucleoid-binding proteins in biofilm formation.

Calcium-chelating alizarin and other anthraquinones inhibit biofilm formation and the hemolytic activity of Staphylococcus aureus

Staphylococcal biofilms are problematic and play a critical role in the persistence of chronic infections because of their abilities to tolerate antimicrobial agents. Thus, the inhibitions of biofilm formation and/or toxin production are viewed as alternative means of controlling Staphylococcus aureus infections. Here, the antibiofilm activities of 560 purified phytochemicals were examined. Alizarin at 10 μg/ml was found to efficiently inhibit biofilm formation by three S. aureus strains and a Staphylococcus epidermidis strain. In addition, two other anthraquinones purpurin and quinalizarin were found to have antibiofilm activity. Binding of Ca²⁺ by alizarin decreased S. aureus biofilm formation and a calcium-specific chelating agent suppressed the effect of calcium. These three anthraquinones also markedly inhibited the hemolytic activity of S. aureus, and in-line with their antibiofilm activities, increased cell aggregation. A chemical structure-activity relationship study revealed that two hydroxyl units at the C-1 and C-2 positions of anthraquinone play important roles in antibiofilm and anti-hemolytic activities. Transcriptional analyses showed that alizarin repressed the α-hemolysin hla gene, biofilm-related genes (psmα, rbf, and spa), and modulated the expressions of cid/lrg genes (the holin/antiholin system). These findings suggest anthraquinones, especially alizarin, are potentially useful for controlling biofilm formation and the virulence of S. aureus.

Effect of biofilm parameters and extracellular polymeric substance composition on polycyclic aromatic hydrocarbon degradation

This study with ten marine isolates demonstrates that the attached phenotypes of the marine bacteria showed significant variation in biofilm architecture and, in turn, biodegradation of PAHs.