A novel approach combining the Calgary Biofilm Device and Phenotype MicroArray for the characterization of the chemical sensitivity of bacterial biofilms

Streptomyces virginiae XDS1-5, an antagonistic actinomycete, as a biocontrol to peach brown rot caused by Monilinia fructicola

BACKGROUND

Peach brown rot, caused by the pathogen Monilinia fructicola, represents a significant postharvest infectious disease affecting peach fruit. This disease is responsible for a substantial increase in fruit decay rates, leading to significant economic losses, often exceeding 50%. Currently, there is a growing interest in identifying biocontrol agents to mitigate peach brown rot, with a predominant interest in Bacillus species.

RESULTS

In this investigation, we isolated 410 isolates of actinomycetes from non-farmland ecosystem soil samples. Subsequently, 27 isolates exhibiting superior inhibitory capabilities were selected. Among these, strain XDS1-5 demonstrated the most robust fungistatic effect against brown rot disease, achieving an 80% inhibition rate in vitro and a 66% inhibition rate in vivo. XDS1-5 was identified as belonging to the Streptomyces virginiae species. Furthermore, a fermentation filtrate of XDS1-5 exhibited the ability to metabolize 34.21% of the tested carbon sources and 7.37% of the tested nitrogen sources. Particularly noteworthy was its capacity to disrupt the cell membrane structure directly, leading to increased cell membrane permeability and cytoplasmic leakage. Additionally, our investigation indicated that indoline, a metabolite produced by XDS1-5, played a pivotal role in inhibiting the growth of M. fructicola.

CONCLUSION

In summary, our study has identified a biocontrol actinomycete, XDS1-5, with the potential to effectively inhibit postharvest brown rot disease in peaches. This finding holds great significance for the biological control of peach brown rot, offering promising prospects for mitigating the economic losses associated with this devastating disease. © 2024 Society of Chemical Industry.

Use of Quorum Sensing Inhibition Strategies to Control Microfouling

Interfering with the quorum sensing bacterial communication systems has been proposed as a promising strategy to control bacterial biofilm formation, a key process in biofouling development. Appropriate in vitro biofilm-forming bacteria models are needed to establish screening methods for innovative anti-biofilm and anti-microfouling compounds. Four marine strains, two Pseudoalteromonas spp. and two Vibrio spp., were selected and studied with regard to their biofilm-forming capacity and sensitivity to quorum sensing (QS) inhibitors. Biofilm experiments were performed using two biofilm cultivation and quantification methods: the xCELLigence^® system, which allows online monitoring of biofilm formation, and the active attachment model, which allows refreshment of the culture medium to obtain a strong biofilm that can be quantified with standard staining methods. Although all selected strains produced acyl-homoserine-lactone (AHL) QS signals, only the P. flavipulchra biofilm, measured with both quantification systems, was significantly reduced with the addition of the AHL-lactonase Aii20J without a significant effect on planktonic growth. Two-species biofilms containing P. flavipulchra were also affected by the addition of Aii20J, indicating an influence on the target bacterial strain as well as an indirect effect on the co-cultured bacterium. The use of xCELLigence^® is proposed as a time-saving method to quantify biofilm formation and search for eco-friendly anti-microfouling compounds based on quorum sensing inhibition (QSI) strategies. The results obtained from these two in vitro biofilm formation methods revealed important differences in the response of biosensor bacteria to culture medium and conditions, indicating that several strains should be used simultaneously for screening purposes and the cultivation conditions should be carefully optimized for each specific purpose.

Analysis of biosorption and biotransformation mechanism of Pseudomonas chengduensis strain MBR under Cd(II) stress from genomic perspective

Microbial treatment of heavy metal-polluted sites is considered an environmentally friendly bioremediation technology with high potential. This study shows that Pseudomonas chengduensis strain MBR, a bacterium that can potentially be applied in the treatment of heavy metal pollution, is most affected by Cd(II) stress at the beginning of its growth. Up to 100% of total Cd(II) adsorption occurs in the first 48 h after treatment of stationary phase cells with Cd(II). A biofilm forms on the cell surface, Cd(II) adsorbs, and is reduced to Cd (0) in the form of nanoscale particles. The genome of strain MBR was sequenced, annotated and analyzed. We identified various genes potentially related to cadmium resistance, transport and metabolism. Analysis of the strain MBR genome is helpful to explore the mechanism of Cd(II) resistance, and can provide new ideas for cadmium pollution control.

Time-Dependent Changes in Morphostructural Properties and Relative Abundances of Contributors in Pleurotus ostreatus/Pseudomonas alcaliphila Mixed Biofilms

Pleurotus ostreatus dual biofilms with bacteria are known to be involved in rock phosphate solubilization, endophytic colonization, and even in nitrogen fixation. Despite these relevant implications, no information is currently available on the architecture of P. ostreatus-based dual biofilms. In addition to this, there is a limited amount of information regarding the estimation of the temporal changes in the relative abundances of the partners in such binary systems. To address these issues, a dual biofilm model system with this fungus was prepared by using Pseudomonas alcaliphila 34 as the bacterial partner due to its very fast biofilm-forming ability. The application of the bacterial inoculum to already settled fungal biofilm on a polystyrene surface coated with hydroxyapatite was the most efficient approach to the production of the mixed system the ultrastructure of which was investigated by a multi-microscopy approach. Transmission electron microscopy analysis showed that the adhesion of bacterial cells onto the mycelial cell wall appeared to be mediated by the presence of an abundant layer of extracellular matrix (ECM). Scanning electron microscopy analysis showed that ECM filaments of bacterial origin formed initially a reticular structure that assumed a tabular semblance after 72 h, thus overshadowing the underlying mycelial network. Across the thickness of the mixed biofilms, the presence of an extensive network of channels with large aggregates of viable bacteria located on the edges of their lumina was found by confocal laser scanning microscopy; on the outermost biofilm layer, a significant fraction of dead bacterial cells was evident. Albeit with tangible differences, similar results regarding the estimation of the temporal shifts in the relative abundances of the two partners were obtained by two independent methods, the former relying on qPCR targeting of 16S and 18S rRNA genes and the latter on ester-linked fatty acid methyl esters analysis.

Molecular biological tools in concrete biodeterioration - a mini review

Concrete structures develop biofilms when exposed to various environments. At a certain stage, the microbial films destroy the concrete structures leading to significant deterioration. Culture-dependent techniques give an incomplete picture of the microbial communities on the concrete surface. Culture-independent techniques or molecular biological tools pave a new way to analyse microbial communities involved in concrete biodeterioration. This study highlights the need to 'build' a database, for Microbiologically Influenced Concrete Corrosion (MICC) involving microbial groups that are being identified using culture-dependent and independent techniques. The role of molecular tools such as 16S rRNA sequencing, denaturing gradient gel electrophoresis (DGGE), Fluorescent in situ hybridization (FISH), Real-time Polymerase Chain Reaction (RT-PCR), microarray analysis, 2-Dimensional gel electrophoresis (2-DE) in analysing microbial communities on the concrete structures have been reviewed in this paper.

Sweetening Inhaled Antibiotic Treatment for Eradication of Chronic Respiratory Biofilm Infection

PURPOSE

The failure of chronic therapy with antibiotics to clear persistent respiratory infection is the key morbidity and mortality factor for patients with chronic lung diseases, primarily due to the presence of biofilm in the lungs. It is hypothesised that carbon sources, such as mannitol, could stimulate the metabolic activity of persister cells within biofilms and restore their susceptibility to antibiotics. The aims of the current study are to: (1) establish a representative in vitro model of Pseudomonas aeruginosa biofilm lung infection, and (2) investigate the effects of nebulised mannitol on antibiotic efficacy, focusing on ciprofloxacin, in the eradication of biofilm.

METHOD

Air interface biofilm was cultured onto Snapwell inserts incorporated into a modified pharmacopeia deposition apparatus, the Anderson Cascade Impactor (ACI). Three different formulations including mannitol only, ciprofloxacin only and combined ciprofloxacin and mannitol were nebulised onto the P. aeruginosa biofilm using the modified ACI. Antibacterial effectiveness was evaluated using colony-forming units counts, biofilm penetration and scanning electron microscopy.

RESULTS

Nebulised mannitol promotes the dispersion of bacteria from the biofilm and demonstrated a synergistic enhancement of the antibacterial efficacy of ciprofloxacin compared to delivery of antibiotic alone.

CONCLUSIONS

The combination of ciprofloxacin and mannitol may provide an important new strategy to improve antibiotic therapy for the treatment of chronic lung infections. Furthermore, the development of a representative lung model of bacterial biofilm could potentially be used as a platform for future new antimicrobial pre-clinical screening.

In Vitro Evaluation of Biofilm Dispersal as a Therapeutic Strategy To Restore Antimicrobial Efficacy

As a proof-of-concept study, the direct impact of biofilm dispersal on the in vitro efficacy of imipenem and tobramycin was evaluated against 3-day-old biofilms of Pseudomonas aeruginosa Arabinose induction of biofilm dispersal via activation of the phosphodiesterase YhjH in the P. aeruginosa engineered strain PAO1/p _BAD -yhjH resulted in increased antimicrobial efficacy and synergy of the imipenem-tobramycin combination. These results support the use of biofilm dispersal to enhance antimicrobial efficacy in the treatment of biofilm-associated infections, representing a promising therapeutic strategy.

Chronic Wound Biofilms: Pathogenesis and Potential Therapies

Chronic wounds are a growing medical problem that cause high rates of morbidity and mortality, costing the healthcare industry in the United States millions of dollars annually. Chronic wound healing is hampered by the presence of bacterial infections that form biofilms, in which the bacteria are encased in exopolysaccharide (EPS) and are less metabolically active than their free-living counterparts. Bacterial biofilms make chronic wounds more refractory to treatment and slow tissue repair by stimulating chronic inflammation at the wound site. Bacterial species communicate through a mechanism known as quorum sensing (QS) to regulate and coordinate the gene expression that is important for virulence-factor production, including biofilm formation. This review focuses on the relationships between chronic wounds, biofilms, and QS in the virulence of chronic-wound pathogens.

Electrical spiking in bacterial biofilms

In nature, biofilms are the most common form of bacterial growth. In biofilms, bacteria display coordinated behaviour to perform specific functions. Here, we investigated electrical signalling as a possible driver in biofilm sociobiology. Using a multi-electrode array system that enables high spatio-temporal resolution, we studied the electrical activity in two biofilm-forming strains and one non-biofilm-forming strain. The action potential rates monitored during biofilm-forming bacterial growth exhibited a one-peak maximum with a long tail, corresponding to the highest biofilm development. This peak was not observed for the non-biofilm-forming strain, demonstrating that the intensity of the electrical activity was not linearly related to the bacterial density, but was instead correlated with biofilm formation. Results obtained indicate that the analysis of the spatio-temporal electrical activity of bacteria during biofilm formation can open a new frontier in the study of the emergence of collective microbial behaviour.

Variable Responses to Carbon Utilization between Planktonic and Biofilm Cells of a Human Carrier Strain of Salmonella enterica Serovar Typhi

Salmonella enterica serovar Typhi (S. Typhi) is a foodborne pathogen that causes typhoid fever and infects only humans. The ability of S. Typhi to survive outside the human host remains unclear, particularly in human carrier strains. In this study, we have investigated the catabolic activity of a human carrier S. Typhi strain in both planktonic and biofilm cells using the high-throughput Biolog Phenotype MicroArray, Minimum Biofilm Eradication Concentration (MBEC) biofilm inoculator (96-well peg lid) and whole genome sequence data. Additional strains of S. Typhi were tested to further validate the variation of catabolism in selected carbon substrates in the different bacterial growth phases. The analyzes of the carbon utilization data indicated that planktonic cells of the carrier strain, S. Typhi CR0044 could utilize a broader range of carbon substrates compared to biofilm cells. Pyruvic acid and succinic acid which are related to energy metabolism were actively catabolised in the planktonic stage compared to biofilm stage. On the other hand, glycerol, L-fucose, L-rhamnose (carbohydrates) and D-threonine (amino acid) were more actively catabolised by biofilm cells compared to planktonic cells. Notably, dextrin and pectin could induce strong biofilm formation in the human carrier strain of S. Typhi. However, pectin could not induce formation of biofilm in the other S. Typhi strains. Phenome data showed the utilization of certain carbon substrates which was supported by the presence of the catabolism-associated genes in S. Typhi CR0044. In conclusion, the findings showed the differential carbon utilization between planktonic and biofilm cells of a S. Typhi human carrier strain. The differences found in the carbon utilization profiles suggested that S. Typhi uses substrates mainly found in the human biliary mucus glycoprotein, gallbladder, liver and cortex of the kidney of the human host. The observed diversity in the carbon catabolism profiles among different S. Typhi strains has suggested the possible involvement of various metabolic pathways that might be related to the virulence and pathogenesis of this host-restricted human pathogen. The data serve as a caveat for future in-vivo studies to investigate the carbon metabolic activity to the pathogenesis of S. Typhi.

Mixed-species biofilms cultured from an oil sand tailings pond can biomineralize metals

Here, we used an in vitro biofilm approach to study metal resistance and/or tolerance of mixed-species biofilms grown from an oil sand tailings pond in northern Alberta, Canada. Metals can be inhibitory to microbial hydrocarbon degradation. If microorganisms are exposed to metal concentrations above their resistance levels, metabolic activities and hydrocarbon degradation can be slowed significantly, if not inhibited completely. For this reason, bioremediation strategies may be most effective if metal-resistant microorganisms are used. Viability was measured after exposure to a range of concentrations of ions of Cu, Ag, Pb, Ni, Zn, V, Cr, and Sr. Mixed-species biofilms were found to be extremely metal resistant; up to 20 mg/L of Pb, 16 mg/L of Zn, 1,000 mg/L of Sr, and 3.2 mg/L of Ni. Metal mineralization was observed by visualization with scanning electron microscopy with metal crystals of Cu, Ag, Pb, and Sr exuding from the biofilms. Following metal exposure, the mixed-species biofilms were analyzed by molecular methods and were found to maintain high levels of species complexity. A single species isolated from the community (Rhodococcus erythropolis) was used as a comparison against the mixed-community biofilm and was seen to be much less tolerant to metal stress than the community and did not biomineralize the metals.

A simple and inexpensive device for biofilm analysis

The Calgary Biofilm Device (CBD) has been described as a technology for the rapid and reproducible assay of biofilm susceptibilities to antibiotics. In this study a simple and inexpensive alternative to the CBD was developed from polypropylene (PP) microcentrifuge tubes and pipette tip boxes. The utility of the device was demonstrated using Candida glabrata, a yeast that can develop antimicrobial-resistant biofilm communities. Biofilms of C. glabrata were formed on the outside surface of microcentrifuge tubes and examined by quantitative analysis and scanning electron microscopy. Growth of three C. glabrata strains, including a clinical isolate, demonstrated that biofilms could be formed on the microcentrifuge tubes. After 24 h incubation the three C. glabrata strains produced biofilms that were recovered into cell suspension and quantified. The method was found to produce uniform and reproducible results with no significant differences between biofilms formed on PP tubes incubated in various compartments of the device. In addition, the difference between maximum and minimum counts for each strain was comparable to those which have been reported for the CBD device.

Draft Genome Sequence of Chromate-Resistant and Biofilm-Producing Strain Pseudomonas alcaliphila 34

We report the draft genome sequence of Pseudomonas alcaliphila 34, a Cr(VI)-hyperresistant and biofilm-producing bacterium that might be used for the bioremediation of chromate-polluted soils. The genome sequence might be helpful in exploring the mechanisms involved in chromium resistance and biofilm formation.