Biofilm

About: Biofilm is a research topic. Over the lifetime, 23010 publications have been published within this topic receiving 906812 citations. The topic is also known as: biofilms.

Staphylococcus aureus biofilms: recent developments in biofilm dispersal.

Abstract: Staphylococcus aureus is a major cause of nosocomial and community-acquired infections and represents a significant burden on the healthcare system. S. aureus attachment to medical implants and host tissue, and the establishment of a mature biofilm, play an important role in the persistence of chronic infections. The formation of a biofilm, and encasement of cells in a polymer-based matrix, decreases the susceptibility to antimicrobials and immune defenses, making these infections difficult to eradicate. During infection, dispersal of cells from the biofilm can result in spread to secondary sites and worsening of the infection. In this review, we discuss the current understanding of the pathways behind biofilm dispersal in S. aureus, with a focus on enzymatic and newly described broad-spectrum dispersal mechanisms. Additionally, we explore potential applications of dispersal in the treatment of biofilm-mediated infections.

Biofilm formation mechanisms and targets for developing antibiofilm agents

Abstract: Biofilms are communities of microorganisms that are attached to a surface and play a significant role in the persistence of bacterial infections. Bacteria within a biofilm are several orders of magnitude more resistant to antibiotics, compared with planktonic bacteria. Thus far, no drugs are in clinical use that specifically target bacterial biofilms. This is probably because until recently the molecular details of biofilm formation were poorly understood. Bacteria integrate information from the environment, such as quorum-sensing autoinducers and nutrients, into appropriate biofilm-related gene expression, and the identity of the key players, such as cyclic dinucleotide second messengers and regulatory RNAs are beginning to be uncovered. Herein, we highlight the current understanding of the processes that lead to biofilm formation in many bacteria.

Cyclic voltammetry of biofilms of wild type and mutant Geobacter sulfurreducens on fuel cell anodes indicates possible roles of OmcB, OmcZ, type IV pili, and protons in extracellular electron transfer

Abstract: Geobacteracea are distinct for their ability to reduce insoluble oxidants including minerals and electrodes without apparent reliance on soluble extracellular electron transfer (ET) mediators. This property makes them important anode catalysts in new generation microbial fuel cells (MFCs) because it obviates the need to replenish ET mediators otherwise necessary to sustain power. Here we report cyclic voltammetry (CV) of biofilms of wild type (WT) and mutant G. sulfurreducens strains grown on graphite cloth anodes acting as electron acceptors with acetate as the electron donor. Our analysis indicates that WT biofilms contain a conductive network of bound ET mediators in which OmcZ (outer membranec-type cytochrome Z) participates in homogeneous ET (through the biofilm bulk) while OmcB mediates heterogeneous ET (across the biofilm/electrode interface); that type IV pili are important in both reactions; that OmcS plays a secondary role in homogenous ET; that OmcE, important in Fe(III) oxide reduction, is not involved in either reaction; that catalytic current is limited overall by the rate of microbial uptake of acetate; that protons generated from acetate oxidation act as charge compensating ions in homogenous ET; and that homogenous ET, when accelerated by fast voltammetric scan rates, is limited by diffusion of protons within the biofilm. These results provide the first direct electrochemical evidence substantiating utilization of bound ET mediators by Geobacter biofilms and the distinct roles of OmcB and OmcZ in the extracellular ET properties of anode-reducing G. sulfurreducens.

Conduction-based modeling of the biofilm anode of a microbial fuel cell

Abstract: The biofilm of a microbial fuel cell (MFC) experiences biofilm-related (growth and mass transport) and electrochemical (electron conduction and charger-transfer) processes. We developed a dynamic, one-dimensional, multi-species model for the biofilm in three steps. First, we formulated the biofilm on the anode as a "biofilm anode" with the following two properties: (1) The biofilm has a conductive solid matrix characterized by the biofilm conductivity (kappa(bio)). (2) The biofilm matrix accepts electrons from biofilm bacteria and conducts the electrons to the anode. Second, we derived the Nernst-Monod expression to describe the rate of electron-donor (ED) oxidation. Third, we linked these components using the principles of mass balance and Ohm's law. We then solved the model to study dual limitation in biofilm by the ED concentration and local potential. Our model illustrates that kappa(bio) strongly influences the ED and current fluxes, the type of limitation in biofilm, and the biomass distribution. A larger kappa(bio) increases the ED and current fluxes, and, consequently, the ED mass-transfer resistance becomes significant. A significant gradient in ED concentration, local potential, or both can develop in the biofilm anode, and the biomass actively respires only where ED concentration and local potential are high. When kappa(bio) is relatively large (i.e., > or =10(-3) mS cm(-1)), active biomass can persist up to tens of micrometers away from the anode. Increases in biofilm thickness and accumulation of inert biomass accentuate dual limitation and reduce the current density. These limitations can be alleviated with increases in the specific detachment rate and biofilm density.

Transition from reversible to irreversible attachment during biofilm formation by Pseudomonas fluorescens WCS365 requires an ABC transporter and a large secreted protein.

Abstract: We report the identification of an ATP-binding cassette (ABC) transporter and an associated large cell-surface protein that are required for biofilm formation by Pseudomonas fluorescens WCS365. The genes coding for these proteins are designated lap for large adhesion protein. The LapA protein, with a predicted molecular weight of approximately 900 kDa, is found to be loosely associated with the cell surface and present in the culture supernatant. The LapB, LapC and LapE proteins are predicted to be the cytoplasmic membrane-localized ATPase, membrane fusion protein and outer membrane protein component, respectively, of an ABC transporter. Consistent with this prediction, LapE, like other members of this family, is localized to the outer membrane. We propose that the lapEBC-encoded ABC transporter participates in the secretion of LapA, as strains with mutations in the lapEBC genes do not have detectable LapA associated with the cell surface or in the supernatant. The lap genes are conserved among environmental pseudomonads such as P. putida KT2440, P. fluorescens PfO1 and P. fluorescens WCS365, but are absent from pathogenic pseudomonads such as P. aeruginosa and P. syringae. The wild-type strain of P. fluorescens WCS365 and its lap mutant derivatives were assessed for their biofilm forming ability in static and flow systems. The lap mutant strains are impaired in an early step in biofilm formation and are unable to develop the mature biofilm structure seen for the wild-type bacterium. Time-lapse microscopy studies determined that the lap mutants are unable to progress from reversible (or transient) attachment to the irreversible attachment stage of biofilm development. The lap mutants were also found to be defective in attachment to quartz sand, an abiotic surface these organisms likely encounter in the environment.