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Biofilm formation in the life cycle of the cellulolytic actinomycete Thermobifida fusca
- A. N. Alonso, P. J. Pomposiello, S. B. Leschine
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- Published online by Cambridge University Press:
- 19 November 2008, pp. 1-11
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Actinomycetes have been used with enormous success in industrial processes; however, little is known about biofilm formation by these filamentous microbes, or community development on insoluble substrates such as cellulose. We hypothesized that biofilm formation is a general strategy used by actinomycetes in the degradation of cellulose, and that it may serve as a means for these microbes to secure nutrients and persist in their environments. The objective of this study was to examine biofilm production by Thermobifida fusca, an actinomycete that rapidly degrades cellulose by means of a well-characterized extracellular cellulase system. Thermobifida fusca cells grew as biofilms attached to both nutritive (e.g. dialysis tubing membrane) and non-nutritive surfaces. Dialysis tubing was colonized by T. fusca aleuriospores but not by mycelial pellets, except when mycelial pellets were disrupted by sonication. Microscopic examination of surface-attached growth revealed structures characteristic of biofilms, with cells embedded in fibrous material suggestive of an extracellular polymeric matrix. Concanavalin A bound to the extracellular polymeric substance of biofilms and mycelial pellets, indicating alpha-linked d-mannosyl and/or alpha-linked d-glucosyl residues. The carbohydrate content of both biofilms and mycelial pellets increased during growth. Also, DNase I inhibited biofilm production, suggesting a role for extracellular DNA in T. fusca biofilm development. Cellulose degradation and expression of celE (encoding endoglucanase E5) was similar for T. fusca biofilms and mycelial pellets. Results of this study indicate that, in the life cycle of this actinomycete, cellulose is specifically colonized by aleuriospores, which germinate, grow and degrade cellulose, ultimately developing into biofilms encased in a carbohydrate-containing exopolymeric matrix, a hallmark of biofilm production.
EDTA treatment diminishes the antibacterial and anti-adherence effect of calcium hydroxide on Enterococcus faecalis: an in vitro study
- S. George, A. Kishen
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- Published online by Cambridge University Press:
- 10 November 2008, pp. 1-10
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This study sought to understand the cell surface characteristics, viability and biofilm-forming potential of Enterococcus faecalis cells sequentially exposed to EDTA and calcium hydroxide, as in endodontic treatment. Bacterial cells exposed to EDTA and calcium hydroxide were assayed for cell viability, membrane integrity, cell surface hydrophobicity and surface charge, while alteration in the surface topography of E. faecalis cells was examined using atomic force microscopy (AFM). The bacterial adherence potential to type I collagen was also examined to assess the biofilm-forming capacity of E. faecalis cells exposed to EDTA and calcium hydroxide. It was found that calcium hydroxide treatment reduced the viability of E. faecalis. However, prior exposure to EDTA significantly reduced the antibacterial effect of calcium hydroxide (P < 0.05). Calcium hydroxide treatment resulted in impaired cell wall morphology, observed as increased surface roughness and pore formation under AFM. However, these topographical changes induced by calcium hydroxide were significantly reduced in EDTA pretreated cells (P < 0.05). Calcium hydroxide treatment caused reduction in hydrophobicity and adherence of E. faecalis to type I collagen. These effects due to calcium hydroxide were also significantly altered in EDTA-pretreated cells (P < 0.001). The findings from this study showed that the antibacterial and anti-adherence effect of calcium hydroxide was diminished by prior exposure of E. faecalis cells to EDTA.
Effect of gravitational deposition on biofilm formation and development
- Y. Yang
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- Published online by Cambridge University Press:
- 10 November 2008, pp. 1-9
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Although gravitational deposition is generally regarded to be important during biofilm development because it provides a mechanism by which bacteria can come into contact with a surface, this process is usually neglected in most biofilm studies. The purpose of this study was to develop a better understanding of the effect of gravitational deposition by comparing the development of biofilms on the upper and lower surfaces of a capillary glass tube biofilm reactor under various hydrodynamic conditions. Pure cultures of Pseudomonas fluorescens and Shewanella oneidensis MR-1 were used for the test. Results demonstrated that gravitational deposition significantly influences biofilm development under slow laminar flow conditions, which may be attributable to the effect of gravity on both attachment and detachment during the initial reversible attachment phase and the later development phase. Additionally, it was shown that hydrodynamic conditions have the potential to reduce the impact of gravitational deposition on biofilm development, and that this became less significant with an increase in flow rate. These results will be useful for comparing biofilm development in different biofilm systems.
Studies on enhancement of biofilm formation and adherence due to mechanical treatment of titanium surfaces in cooling-water systems
- R. P. George, J. Gopal, P. Muraleedharan, B. Anandkumar, R. Baskaran, S. Maruthamuthu, R. K. Dayal
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- Published online by Cambridge University Press:
- 10 November 2008, pp. 1-7
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Titanium has proven to be the heat exchanger material of choice for sea-water-cooled power plants owing to its outstanding resistance to pitting and crevice corrosion in a wide range of aggressive media. However, the inertness of the titanium surface makes it highly susceptible to biofilm formation and subsequent biofouling. This can hinder the heat transfer properties and flow of water. Fouling control strategies in condensers include a combination of mechanical, chemical and thermal treatments. However, reports from various industrial situations suggest that mechanical treatment may not have long-term effects. This study aimed to find out whether mechanical cleaning eventually enhances biofilm formation and increases the adherence of biofilm. In our studies epifluorescence micrographs of biofilms on control and mechanically treated titanium surfaces clearly showed accelerated biofilm formation as well as increased adherence on the mechanically cleaned surface. Total counts of viable bacteria acquired by culturing technique, and biofilm thickness measurements made using microscopic techniques, confirmed this observation. Surface profilometry showed increased roughness of the titanium surface, facilitating adherence of biofilm. The number of microbial species was higher on mechanically cleaned and re-exposed surfaces than on fresh titanium. Thus we concluded that mechanical cleaning can increase biofilm formation and adherence of biofilm, thereby increasing the potential of biofouling in the long term.
Susceptibility of microcosm subgingival dental plaques to lethal photosensitization
- I. U. Allan, J. F. O'Neill, C. K. Hope
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- Published online by Cambridge University Press:
- 17 December 2007, pp. 1-7
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Photodynamic therapy (PDT) offers potential as a non-invasive treatment of periodontal disease. In this study, microcosm biofilms were grown in vitro under conditions designed to mimic subgingival plaques typically found in patients with periodontitis. To investigate potential PDT modalities, biofilms were exposed to light from a helium/neon laser in conjunction with a photosensitizer, toluidine blue O (TBO), at varying output and concentration, respectively. To determine cytotoxic effects, viability profiling was undertaken on whole biofilms using standard plating methods, and on horizontal cross-sections of biofilms using confocal laser-scanning microscopy (CLSM) in conjunction with a differential viability stain. A light energy dose of 94.5 J in combination with 81.7 μM TBO was found to be optimal, achieving significant kills of over 97%. CLSM enabled visualization of the effects of PDT in three dimensions. Viability profiling of the CLSM images revealed that lethal photosensitization was most effective in the upper layers of biofilm. PDT was found to reduce the viability of subgingivally modelled plaques in vitro by a magnitude similar to that of chlorhexidine digluconate, which is commonly used to treat periodontal disease. The findings of this study indicate that PDT may be an effective alternative to conventional modalities in the treatment of periodontal disease.