The effect of interactions between a bacterial strain isolated from drinking water and a pathogen surrogate on biofilms formation diverged under static vs flow conditions

Construction of synthetic anti-fouling consortia: fouling control effects and polysaccharide degradation mechanisms

The physical states and chemical components of bulk sludge determine the occurrence and development of membrane fouling in membrane bioreactors. Thus, regulation of sludge suspensions can provide new strategies for fouling control. In this study, we used "top-down" enrichment to construct a synthetic anti-fouling consortium (SAC) from bio-cake and evaluate its roles in preventing membrane fouling. The SAC was identified as Massilia-dominated and could almost wholly degrade the alginate solution (1,000 mg/L) within 72 h. Two-dimensional Fourier transformation infrared correlation spectroscopy (2D-FTIR-CoS) analysis demonstrated that the SAC induced the breakage of glycosidic bond in alginates. The co-cultivation of sludge with a low dosage of SAC (ranging from 0 to 1%) led to significant fouling mitigation, increased sludge floc size, and decreased unified membrane fouling index value (0.55 ± 0.06 and 0.11 ± 0.05). FTIR spectra and X-ray spectroscopy analyses demonstrated that the addition of SAC decreased the abundance of the O-acetylation of polysaccharides in extracellular polymeric substances. Secondary derivatives analysis of amide I spectra suggested a strong reduction in the α-helix/(β-sheet + random coil) ratio in the presence of SAC, which was expected to enhance cell aggregation. Additionally, the extracellular secretions of SAC could both inhibit biofilm formation and strongly disperse the existing biofilm strongly during the biofilm incubation tests. In summary, this study illustrates the feasibility and benefits of using SAC for fouling control and provides a new strategy for fouling control.

Advances in the Microbiology of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an opportunistic pathogen of significant concern to susceptible patient populations. This pathogen can cause nosocomial and community-acquired respiratory and bloodstream infections and various other infections in humans. Sources include water, plant rhizospheres, animals, and foods. Studies of the genetic heterogeneity of S. maltophilia strains have identified several new genogroups and suggested adaptation of this pathogen to its habitats. The mechanisms used by S. maltophilia during pathogenesis continue to be uncovered and explored. S. maltophilia virulence factors include use of motility, biofilm formation, iron acquisition mechanisms, outer membrane components, protein secretion systems, extracellular enzymes, and antimicrobial resistance mechanisms. S. maltophilia is intrinsically drug resistant to an array of different antibiotics and uses a broad arsenal to protect itself against antimicrobials. Surveillance studies have recorded increases in drug resistance for S. maltophilia, prompting new strategies to be developed against this opportunist. The interactions of this environmental bacterium with other microorganisms are being elucidated. S. maltophilia and its products have applications in biotechnology, including agriculture, biocontrol, and bioremediation.

Pseudomonas putida as a potential biocontrol agent against Salmonella Java biofilm formation in the drinking water system of broiler houses

Background

Environmental biofilms can induce attachment and protection of other microorganisms including pathogens, but can also prevent them from invasion and colonization. This opens the possibility for so-called biocontrol strategies, wherein microorganisms are applied to control the presence of other microbes. The potential for both positive and negative interactions between microbes, however, raises the need for in depth characterization of the sociobiology of candidate biocontrol agents (BCAs). The inside of the drinking water system (DWS) of broiler houses is an interesting niche to apply BCAs, because contamination of these systems with pathogens plays an important role in the infection of broiler chickens and consequently humans. In this study, Pseudomonas putida, which is part of the natural microbiota in the DWS of broiler houses, was evaluated as BCA against the broiler pathogen Salmonella Java.

Results

To study the interaction between these species, an in vitro model was developed simulating biofilm formation in the drinking water system of broilers. Dual-species biofilms of P. putida strains P1, P2, and P3 with S. Java were characterized by competitive interactions, independent of P. putida strain, S. Java inoculum density and application order. When equal inocula of S. Java and P. putida strains P1 or P3 were simultaneously applied, the interaction was characterized by mutual inhibition, whereas P. putida strain P2 showed an exploitation of S. Java. Lowering the inoculum density of S. Java changed the interaction with P. putida strain P3 also into an exploitation of S. Java. A further increase in S. Java inhibition was established by P. putida strain P3 forming a mature biofilm before applying S. Java.

Conclusions

This study provides the first results showing the potential of P. putida as BCA against S. Java in the broiler environment. Future work should include more complex microbial communities residing in the DWS, additional Salmonella strains as well as chemicals typically used to clean and disinfect the system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-020-02046-5.

Ecological insights into the underlying evolutionary patterns of biofilm formation from biological wastewater treatment systems: Red or Black Queen Hypothesis?

Interspecies interactions and phylogenetic distances were studied to reveal the underlying evolutionary adaptations of biofilms sourced from wastewater treatment processes. Based on 380 pairwise cocultures of 40 strains from two microbial aggregates (surface-attached and mobile aggregates [flocs]) at two substrate concentrations (LB broth and 0.1× LB broth), interspecies interactions were explored using biofilm classification schemes. There was a strong source-dependence of biofilm development formed by the monocultures, that is, a higher biofilm formation potential for strains from attached aggregates than for those from sludge flocs at both substrate concentrations. Interestingly, the results showed that total biofilm reduction was dominant in the dual-species biofilm sourced from flocs in both LB broth (67.37%) and 0.1× LB broth (64.21%), indicating high interspecific competition in mobile aggregates and the independence of substrate concentrations. However, biofilm reduction was higher (33.68%) than induction (19.37%) for the biofilms formed by surface-attached aggregates in LB broth, while the opposite trend was apparent in 0.1× LB broth, suggesting the occurrence of indeterministic processes for biofilm formation and important roles of substrate concentrations. In addition, the more closely related phylogenetic relationships of cocultures from mobile aggregates were consistent with higher competition compared with those from surface-attached aggregates. Overall, the underlying evolutionary patterns of biofilms formed from mobile aggregates consistently followed the essence of the "Red Queen Hypothesis," while biofilms developed from surface-attached aggregates were not deterministic. This study advanced our understanding of biofilm-related treatment processes using the principles of microbial ecology.

Biofilm formation potential and chlorine resistance of typical bacteria isolated from drinking water distribution systems

Biofilms are the main carrier of microbial communities throughout drinking water distribution systems (DWDSs), and strongly affect the safety of drinking water. Understanding biofilm formation potential and chlorine resistance is necessary for exploring future disinfection strategies and preventing water-borne diseases. This study investigated biofilm formation of five bacterial strains isolated from a simulated DWDS at different incubation times (24 h, 48 h, and 72 h), then evaluated chlorine resistance of 72 h incubated biofilms under chlorine concentrations of 0.3, 0.6, 1, 2, 4, and 10 mg L⁻¹. All five bacterial strains had biofilm formation potential when incubated for 72 h. The biofilm formation potential of Acinetobacter sp. was stronger than that of Bacillus cereus, Microbacterium sp. and Sphingomonas sp. were moderate, and that of Acidovorax sp. was weak. In contrast, the order of chlorine resistance was Bacillus sp. > Sphingomonas sp. > Microbacterium sp. > Acidovorax sp. > Acinetobacter sp. Thus, the chlorine resistance of a single-species biofilm has little relation with the biofilm formation potential. The biofilm biomass is not a major factor affecting chlorine resistance. Moreover, the chlorine resistance of a single-species biofilm is highly related to the physiological state of bacterial cells, such as their ability to form spores or secrete extracellular polymeric substances, which could reduce the sensitivity of the single-species biofilm to a disinfectant or otherwise protect the biofilm.

Biofilms are the main carrier of microbial communities throughout drinking water distribution systems (DWDSs), and strongly affect the safety of drinking water.

Influence of surface copper content on Stenotrophomonas maltophilia biofilm control using chlorine and mechanical stress

This work aimed to evaluate the action of materials with different copper content (0, 57, 96 and 100%) on biofilm formation and control by chlorination and mechanical stress. Stenotrophomonas maltophilia isolated from drinking water was used as a model microorganism and biofilms were developed in a rotating cylinder reactor using realism-based shear stress conditions. Biofilms were characterized phenotypically and exposed to three control strategies: 10 mg l^-1 of free chlorine for 10 min, an increased shear stress (a fluid velocity of 1.5 m s^-1 for 30s), and a combination of both treatments. These shock treatments were not effective in biofilm control. The benefits from the use of copper surfaces was found essentially in reducing the numbers of non-damaged cells. Copper materials demonstrated better performance in biofilm prevention than chlorine. In general, copper alloys may have a positive public health impact by reducing the number of non-damaged cells in the water delivered after chlorine exposure.

Wide-scale study of 206 buildings in the Netherlands from 2011 to 2015 to determine the effect of drinking water management plans on the presence of Legionella spp

Previous analysis of the Dutch National Legionella Outbreak Detection Program 2002-2012 has shown that buildings required to maintain a Legionella control plan for their drinking water installation are more likely to test positive for Legionella spp. Than buildings without such a plan (38% versus 22% of samples). To clarify this discrepancy, we analysed the results of mandatory water sample testing conducted as part of risk assessments in 206 buildings in the Netherlands from 2011 to 2015. Of the 6171 samples analysed, 16.2% exceeded the Dutch drinking water standard for Legionella spp. of 100 CFU/litre. In buildings with ≤50 tap points, the average percentage of samples containing ≥100 CFU/litre was 28.2%, and from buildings with >50 tap points, it was 12.2%. Analysis of serial samples (taken every 6 months) from each building showed that 33.2% of all buildings tested positive for at least one sample every 6 months. The overall increase was 4.4% per year. Analysis of Legionella subgroups showed that while the majority of positive samples contained L. non-pneumophila (96.9%), some samples did contain L. pneumophila serogroup 1 (1.0%) and serogroups 2-14 (2.1%). Our data suggest that the Dutch mandatory risk assessment and drinking water management plan is not sufficiently effective in preventing the proliferation of Legionella spp. and may even contribute to proliferation. This analysis should now be expanded to include other areas of the Netherlands in order to understand the geographical differences that we observed in our results, and why smaller buildings appear to be more likely to test positive for Legionella spp.