Biofilms are widespread in nature and constitute an important strategy implemented by microorganisms to survive in sometimes harsh environmental conditions. They can be beneficial or have a negative ...impact particularly when formed in industrial settings or on medical devices. As such, research into the formation and elimination of biofilms is important for many disciplines. Several new methodologies have been recently developed for, or adapted to, biofilm studies that have contributed to deeper knowledge on biofilm physiology, structure and composition. In this review, traditional and cutting-edge methods to study biofilm biomass, viability, structure, composition and physiology are addressed. Moreover, as there is a lack of consensus among the diversity of techniques used to grow and study biofilms. This review intends to remedy this, by giving a critical perspective, highlighting the advantages and limitations of several methods. Accordingly, this review aims at helping scientists in finding the most appropriate and up-to-date methods to study their biofilms.
Bacterial biofilms are complex surface attached communities of bacteria held together by self-produced polymer matrixs mainly composed of polysaccharides, secreted proteins, and extracellular DNAs. ...Bacterial biofilm formation is a complex process and can be described in five main phases: (i) reversible attachment phase, where bacteria non-specifically attach to surfaces; (ii) irreversible attachment phase, which involves interaction between bacterial cells and a surface using bacterial adhesins such as fimbriae and lipopolysaccharide (LPS); (iii) production of extracellular polymeric substances (EPS) by the resident bacterial cells; (iv) biofilm maturation phase, in which bacterial cells synthesize and release signaling molecules to sense the presence of each other, conducing to the formation of microcolony and maturation of biofilms; and (v) dispersal/detachment phase, where the bacterial cells depart biofilms and comeback to independent planktonic lifestyle. Biofilm formation is detrimental in healthcare, drinking water distribution systems, food, and marine industries, etc. As a result, current studies have been focused toward control and prevention of biofilms. In an effort to get rid of harmful biofilms, various techniques and approaches have been employed that interfere with bacterial attachment, bacterial communication systems (quorum sensing, QS), and biofilm matrixs. Biofilms, however, also offer beneficial roles in a variety of fields including applications in plant protection, bioremediation, wastewater treatment, and corrosion inhibition amongst others. Development of beneficial biofilms can be promoted through manipulation of adhesion surfaces, QS and environmental conditions. This review describes the events involved in bacterial biofilm formation, lists the negative and positive aspects associated with bacterial biofilms, elaborates the main strategies currently used to regulate establishment of harmful bacterial biofilms as well as certain strategies employed to encourage formation of beneficial bacterial biofilms, and highlights the future perspectives of bacterial biofilms.
Type IV pili are involved in adhesion, twitching motility, aggregation, biofilm formation and virulence in a variety of Gram-negative bacteria.
the causative agent of melioidosis and a Tier 1 ...biological select agent, is a Gram-negative bacterium with eight type IV pili-associated loci (TFP1 to TFP8). Most have not been fully characterized. In this study, we investigated
, an uncharacterized TFP8 gene that encodes a type IVB pilus protein subunit. Using genetic deletion and complementation analysis in
JW270, we demonstrate that
plays an important role in twitching motility and adhesion to A549 human alveolar epithelial cells. Compared to JW270, the JW270
mutant failed to display twitching motility and did not adhere to the epithelial cells. These phenotypes were partially reversed by the complementation of
in the mutant strain. The study also shows that
is expressed only during the onset of mature biofilm formation and at the dispersal of a biofilm, suggesting that the motility characteristic is required to form a biofilm. Our study is the first to suggest that the
gene in TFP8 contributes to twitching motility, adhesion and biofilm formation, indicating that the gene may contribute to
virulence.
Biofilm refers to the complex, sessile communities of microbes found either attached to a surface or buried firmly in an extracellular matrix as aggregates. The biofilm matrix surrounding bacteria ...makes them tolerant to harsh conditions and resistant to antibacterial treatments. Moreover, the biofilms are responsible for causing a broad range of chronic diseases and due to the emergence of antibiotic resistance in bacteria it has really become difficult to treat them with efficacy. Furthermore, the antibiotics available till date are ineffective for treating these biofilm related infections due to their higher values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), which may result in in-vivo toxicity. Hence, it is critically important to design or screen anti-biofilm molecules that can effectively minimize and eradicate biofilm related infections. In the present article, we have highlighted the mechanism of biofilm formation with reference to different models and various methods used for biofilm detection. A major focus has been put on various anti-biofilm molecules discovered or tested till date which may include herbal active compounds, chelating agents, peptide antibiotics, lantibiotics and synthetic chemical compounds along with their structures, mechanism of action and their respective MICs, MBCs, minimum biofilm inhibitory concentrations (MBICs) as well as the half maximal inhibitory concentration (IC
50
) values available in the literature so far. Different mode of action of anti biofilm molecules addressed here are inhibition via interference in the quorum sensing pathways, adhesion mechanism, disruption of extracellular DNA, protein, lipopolysaccharides, exopolysaccharides and secondary messengers involved in various signaling pathways. From this study, we conclude that the molecules considered here might be used to treat biofilm-associated infections after significant structural modifications, thereby investigating its effective delivery in the host. It should also be ensured that minimum effective concentration of these molecules must be capable of eradicating biofilm infections with maximum potency without posing any adverse side effects on the host.
Biofouling, caused by microbial biofilm formation on the membrane surface and in pores, is a major operational problem in membrane bioreactors (MBR). Many quorum quenching (QQ) bacteria have been ...isolated and applied to MBR to reduce biofouling. However, for more effective MBR biofouling control, novel approaches for isolating QQ bacteria and applying them in MBR are needed. Therefore, Listeria grayi (HEMM-2) was isolated using a mixture of different N-acyl homoserine lactones (AHLs). HEMM-2 degraded various AHLs, regardless of the length and oxo group in the carbon chain, with quorum sensing (QS) inhibition ratios of 47–61%. This QQ activity was attributed to extracellular substances in HEMM-2 cell-free supernatant (CFS). Furthermore, the HEMM-2 CFS negatively regulated QS-related gene expression, inhibiting Pseudomonas aeruginosa and activated sludge-biofilm formation by 53–75%. Surprisingly, when the HEMM-2 CFS was directly injected into a laboratory-scale MBR system, biofouling was not significantly affected. Biofouling was only controlled by cell suspension (CS) of HEMM-2, indicating the importance of QQ bacteria in MBR. The HEMM-2 CS increased operation time to reach 0.4 bar, a threshold transmembrane pressure for complete biofouling, from 315 h to 371 h. Taken together, HEMM-2, which is effective in the degradation of various AHLs, and its applicable method to MBR may be considered a potent approach for controlling biofouling and understanding the behavior of QQ bacteria in MBR systems.
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•A quorum quenching bacterium was isolated with acyl-homoserine lactone mixtures.•HEMM-2 degraded various acyl-homoserine lactones by extracellular substances.•Quorum quenching of P. aeruginosa occurred at transcription levels by HEMM-2.•HEMM-2 effectively inhibited bacterial and activated sludge-biofilm formation.•Direct injection of HEMM-2 to a lab-scale membrane bioreactor reduced biofouling.
Phytoremediation is an economic way to attenuate soil heavy metal pollution, but is frequently limited by its low pollutant-removing efficiency. Recently, we revealed the close relation between ...polysaccharide-based biofilm formation and cadmium removal. In this study, for improving the phytoremediation efficiency, an artificial polysaccharide-binding protein was designed by synthetic biology techniques to regulate biofilm formation. The artificial protein Syn contained two polysaccharide-binding domains from the Ruminococcus flavefaciens CttA and the Clostridium cellulolyticum CipC, preferentially binding polysaccharides exposed on both cadmium-treated bacteria and plant roots. Under cadmium stress, Syn remarkably promoted bacterial polysaccharide production from 99 mg/L to 237 mg/L, leading to 1.23-fold higher biofilm biomass. During treatment of the remediation plants with exogenous cadmium-capturing bacteria, Syn improved root biofilm formation, with the root surface polysaccharide contents increasing by 79%, and the Log10 CFU/g root increasing from 7.01 to 7.80. Meanwhile, Syn remodeled the rhizosphere microbiome, especially increasing the abundance of the bacterial groups involved in biofilm formation and stress tolerance, e.g., Pseudomonas, Enterobacter, etc. Consequently, Syn promoted plant cadmium adsorption, with the cadmium-removing efficiency increasing from 17.2% to 33.8%. This study sheds light on synthetic biology-based regulation of biofilm formation for enhanced phytoremediation.
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•Cadmium gently induces biofilm formation of cadmium-capturing bacteria.•The artificial protein Syn exhibits high capacity to bind polysaccharides.•Syn strongly promotes functional biofilm formation on roots of remediation plants.•Syn increases the rhizosphere abundance of biofilm-related bacterial groups.•Syn strongly enhances soil cadmium removal by the remediation plants.
The effects of microbial colonization and biofilm formation on microplastics in the marine and coastal environments have aroused global concern recently. However, the simultaneous influences of ...exposure time and depth on biofilm formation, and subsequently on the properties variations of microplastics is less studied. In this study, polyethylene (PE) film was exposed at three depths (2 m, 6 m, and 12 m) for three time periods (30 days, 75 days, and 135 days) in the coastal seawater of Yellow Sea, China. The results show that the total amount of biofilms markedly increased with exposure time, but decreased with water depth. Typical morphologies and compositions of biofilms such as coccus-, rod-, disc-shaped bacteria and filaments, as well as a dense layer of extracellular polymeric substances were observed on the surfaces of the PE microplastics. Biofilm formation could decrease the hydrophobicity of PE microplastics, and increase the abundances of hydrophilic C−O and CO groups on the surface of PE. Alphaproteobacteria, Gammaproteobacteria and Bacteroidia were identified as the core microbiome of the PE associated biofilms, while the dominant bacteria families vary from the early to the late phases of the biofilm formation. Our results indicate that microplastics associated biofilms could affect the environmental processes and fates of microplastics in the marine and coastal environment.
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•Biofilm formation and its influences on PE properties were investigated.•The thickness of biofilms on PE increases with exposure time but decreases with depth.•Biofilms could decrease the hydrophobicity and change the functional groups of PE.•The dominant PE colonizing microbial community varies during the biofilm formation.
A biofilm is an assemblage of microbial cells attached to a surface and encapsulated in an extracellular polymeric substance (EPS) matrix. The formation of a biofilm is one of the important ...mechanisms of bacterial resistance, which not only leads to hard-to-control bacterial infections in humans and animals but also enables bacteria to be a major problem in various fields, such as food processing, wastewater treatment and metalworking. Quorum sensing (QS) is a bacterial cell-to-cell communication process that depends on the bacterial population density and is mediated by small diffusible signaling molecules called autoinducers (AIs). Bacteria use QS to regulate diverse arrays of functions, including virulence and biofilm formation. Therefore, the interference with QS by using QS inhibiting agents, including QS inhibitors (QSIs) and quorum quenching (QQ) enzymes, to reduce or even completely repress the biofilm formation of pathogenic bacteria appears to be a promising approach to control bacterial infections. In this review, we summarize the mechanisms of QS-regulating biofilm formation and QS-inhibiting agents that control bacterial biofilm formation, strategies for the discovery of new QS inhibiting agents, and the current applications of QS-inhibiting agents in several fields to provide insight into the development of effective drugs to control pathogenic bacteria.
•A series of 26 lactones and lactams inhibited biofilm formation (>60 %) of S. oralis.•A set of lactams act as inhibitors of single-species biofilms of oral pathogenic bacteria.•Single-species ...biofilms of oral commensal bacteria can be inhibited by rubrolides analogues.•The use of lactones and lactams can be an alternative approach to control bacterial single-species biofilms.•Non-cytotoxic lactones can control single-biofilm of several oral bacteria.
In this study, a series of 26 lactones and lactams have been investigated for their effect against 14 single-species biofilm of oral commensal and pathogenic species (Streptococcus oralis, S. mitis, S. sanguinis, S. gordonii, Actinomyces naeslundii, A. viscosus, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, Porphyromonas gingivalis, Prevotella intermedia, Streptococcus mutans, S. sobrinus, S. salivarius, Veillonella parvula). At the dose of 128 mg/mL, all substances inhibited biofilm formation of S. oralis by more than 60 %, and 19 caused >60 % reduction in the biofilm production by S. sanguinis and A. naeslundi. In addition, 16 compounds showed better results against P. intermedia and F. nucleatum, inhibiting biofilm formation by > 50 %, while 8 compounds caused >40 % reduction in the biofilm formation of A. actinomycetemcomitans. Compounds 5b, 5c, 5d, 5f, and 7 g were the only ones active against S. mutans, and 6d was the only one active against S. sobrinus biofilm formation. Amongst all compounds tested, 24 maintained cell viability above 50 % after 24 h of exposure. In summary, a set of lactones and lactams capable of inhibiting single-species biofilms of oral commensal and pathogenic bacteria without showing significant cytotoxicity against oral epithelial cells were identified. These results highlight the potential of using such antibiofilm compounds as an alternative approach to control oral biofilms.
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One of the emerging conundrums of Campylobacter food-borne illness is the bacterial ability to survive stressful environmental conditions. We evaluated the heterogeneity among 90 C. jejuni and 21 C. ...coli isolates from different sources in Egypt with respect to biofilm formation capabilities (under microaerobic and aerobic atmosphere) and resistance to a range of stressors encountered along the food chain (aerobic stress, refrigeration, freeze-thaw, heat, peracetic acid, and osmotic stress). High prevalence (63%) of hyper-aerotolerant (HAT) isolates was observed, exhibiting also a significantly high tolerance to heat, osmotic stress, refrigeration, and freeze-thaw stress, coupled with high biofilm formation ability which was clearly enhanced under aerobic conditions, suggesting a potential link between stress adaptation and biofilm formation. Most HAT multi-stress resistant and strong biofilm producing C. jejuni isolates belonged to host generalist clonal complexes (ST-21, ST-45, ST-48 and ST-206). These findings highlight the potential role of oxidative stress response systems in providing cross-protection (resistance to other multiple stress conditions) and enhancing biofilm formation in Campylobacter and suggest that selective pressures encountered in hostile environments have shaped the epidemiology of C. jejuni in Egypt by selecting the transmission of highly adapted isolates, thus promoting the colonization of multiple host species by important disease-causing lineages.
•Oxidative stress defense responses in Campylobacter are associated with enhanced biofilm formation capabilities.•Host generalist lineages are better equipped to withstand hostile environmental conditions favoring zoonotic transmission.•Multi-stress adapted Campylobacter isolates challenges efforts made to eliminate this foodborne pathogen from the food chain.
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