Faculty Opinions recommendation of Is there a role for quorum sensing signals in bacterial biofilms?
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Bacteria form multicellular biofilm communities on most surfaces. Genetic analysis of biofilm formation has led to the proposal that extracellular signals and quorum-sensing regulatory systems are essential for differentiated biofilms. Although such a model fits the concept of density-driven cell-cell communication and appear to describe biofilm development in several bacterial species and conditions, biofilm formation is multifactorial and complex. Hydrodynamics, nutrient load and intracellular carbon flux have major impacts, presumably by altering the expression of cellular traits essential for bacterial adaptation during the different stages of biofilm formation. Hence, differentiated biofilms may also be the net result of many independent interactions, rather than being determined by a particular global quorum sensing system. PMID: 12057678Keywords:
Multicellular organism
This paper presented the influence of Al(III) on biodegradability, micromorphology, composition and functional groups characteristics of the biofilm extracellular polymeric substances (EPS) during different growth phases. The sequencing batch biofilm reactors were developed to cultivate biofilms under different Al(III) dosages. The results elucidated that Al(III) affected biofilm development adversely at the beginning of biofilm growth, but promoted the biofilm mass and improved the biofilm activity with the growth of the biofilm. The micromorphological observation indicated that Al(III) led to a reduction of the filaments and promotion of the EPS secretion in growth phases of the biofilm, also Al(III) could promote microorganisms to form larger colonies for mature biofilm. Then, the analysis of EPS contents and components suggested that Al(III) could increase the protein (PN) of tightly bound EPS (TB-EPS) which alleviated the metal toxicity inhibition on the biofilm during the initial phases of biofilm growth. The biofilm could gradually adapt to the inhibition caused by Al(III) at the biofilm maturation moment. Finally, through the Fourier transform infrared spectroscopy, it was found that Al(III) was beneficial for the proliferation and secretion of TB-EPS functional groups, especially the functional groups of protein and polysaccharides.
Extracellular polymeric substance
Bacterial growth
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Biofilms are matrix-enclosed microbial aggregations that adhere to biological or non-biological surfaces. They represent a significant and incompletely understood mode of growth for bacteria and fungi. Biofilm infections cause many deaths and high health costs worldwide. Biofilm infections on indwelling devices or implants are difficult to eradicate because of their much better protection against macrophages and antibiotics, compared to free living cells, leading to severe clinical complications often with lethal outcome. One promising approach to combat biofilm infections independent from the conventional control by antibiotics is the generation of functional surfaces preventing the attachment of bacteria. Another aim is the communication machinery used by bacteria to establish a biofilm, the so called quorum-sensing. Here, small diffusible compounds are produced and sensed by the producing cells to measure their concentration and hence cell density. Natural compounds and synthetic analogues have been used successfully to prevent biofilm formation by quorum- quenching. These compounds are still in the preclinical phase, often struggling with toxicity. A principal problem of quorum-quenchers is their high species specificity, resulting in the control of only some pathogenic strains leaving other pathogens untouched. A field still in its infancy is the control of virulence factors expression not preventing the biofilm but suppressing its virulence. This review will give an overview over the pros and cons of the individual targets and an outlook of future developments. Keywords: Biofilm, quorum-sensing, quorum-quenching, microbial community, antivirulence therapy
Quorum Quenching
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Homoserine
Extracellular polymeric substance
Autoinducer
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Faculty Opinions recommendation of Is there a role for quorum sensing signals in bacterial biofilms?
Bacteria form multicellular biofilm communities on most surfaces. Genetic analysis of biofilm formation has led to the proposal that extracellular signals and quorum-sensing regulatory systems are essential for differentiated biofilms. Although such a model fits the concept of density-driven cell-cell communication and appear to describe biofilm development in several bacterial species and conditions, biofilm formation is multifactorial and complex. Hydrodynamics, nutrient load and intracellular carbon flux have major impacts, presumably by altering the expression of cellular traits essential for bacterial adaptation during the different stages of biofilm formation. Hence, differentiated biofilms may also be the net result of many independent interactions, rather than being determined by a particular global quorum sensing system. PMID: 12057678
Multicellular organism
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Objective:To understand the effects of quorum sensing system on P. aeruginosa biofilm formation. Methods:Examination of the biofilm developments of PAO1,lasIrhlI and lasRrhlR mutants in vitro by means of scanning electronic microscopy (SEM) after three days' incubation.Results:After three days' incubation,well developed biofilm was observed in PAO1 group,whereas poor biofilm formation was seen in lasIrhlI and lasRrhlR mutant groups.Conclusion:Quorum sensing system is important in the formation of P.aeruginosa biofilm.
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Multicellular organism
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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.
Biofouling
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In this study,the correlation between quorum sensing and biofilm forming of 43 marine bacterial strains was evaluated by quantitatively detecting the activity of acyl-homoserine lactones(AHLs) and AI-2 signals,as well as the biofilm formation in the 43 bacterial strains.The results revealed that 9 of the 10(90%) AHL activity strains displayed definite biofilm-forming capacity,7 of these 10 strains exhibited highly structured architecture in biofilm.67% of AI-2 activity strains have strong biofilm-forming capacity.The results also indicated that the strains with AHL activity usually presented strong biofilm-forming capacity.However,other bacteria which cannot produce quorum sensing signal still exhibit strong biofilm-forming capacity.Therefore,it could be indicated that for environmental bacteria,the existing of quorum sensing signal molecule(especially the AHL) in bacterial strains,usually tends to be a sufficient condition other than a necessary one for forming biofilms
Homoserine
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