Microorganisms attach to surfaces and develop biofilms. Biofilm-associated cells can be differentiated from their suspended counterparts by generation of an extracellular polymeric substance (EPS) matrix, reduced growth rates, and the up- and down- regulation of specific genes. Attachment is a complex process regulated by diverse characteristics of the growth medium, substratum, and cell surface. An established biofilm structure comprises microbial cells and EPS, has a defined architecture, and provides an optimal environment for the exchange of genetic material between cells. Cells may also communicate via quorum sensing, which may in turn affect biofilm processes such as detachment. Biofilms have great importance for public health because of their role in certain infectious diseases and importance in a variety of device-related infections. A greater understanding of biofilm processes should lead to novel, effective control strategies for biofilm control and a resulting improvement in patient management.

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Biofilms: microbial life on surfaces.

Principles of microbial PAH-degradation in soil.

In this review, initial microbial adhesive interactions are divided into adhesion to substratum surfaces, coaggregation between microbial pairs and co-adhesion between sessile and planktonic microorganisms of different strains or species. The physico-chemical mechanisms underlying the adhesive interactions are described and a critical review is given of currently employed methods to study microbial adhesive interactions, with an emphasis on the use of the parallel plate flow chamber. Subsequently, for each of the three microbial adhesive interactions distinguished, the role of Lifshitz-van der Waals, acid-base and electrostatic interactions is described based on existing literature.

Physico-chemistry of initial microbial adhesive interactions – its mechanisms and methods for study

Microscopic entities, microorganisms that drastically affect human health need to be thoroughly investigated. A biofilm is an architectural colony of microorganisms, within a matrix of extracellular polymeric substance that they produce. Biofilm contains microbial cells adherent to one-another and to a static surface (living or non-living). Bacterial biofilms are usually pathogenic in nature and can cause nosocomial infections. The National Institutes of Health (NIH) revealed that among all microbial and chronic infections, 65% and 80%, respectively, are associated with biofilm formation. The process of biofilm formation consists of many steps, starting with attachment to a living or non-living surface that will lead to formation of micro-colony, giving rise to three-dimensional structures and ending up, after maturation, with detachment. During formation of biofilm several species of bacteria communicate with one another, employing quorum sensing. In general, bacterial biofilms show resistance against human immune system, as well as against antibiotics. Health related concerns speak loud due to the biofilm potential to cause diseases, utilizing both device-related and non-device-related infections. In summary, the understanding of bacterial biofilm is important to manage and/or to eradicate biofilm-related diseases. The current review is, therefore, an effort to encompass the current concepts in biofilm formation and its implications in human health and disease.

Bacterial biofilm and associated infections

Publisher Summary It is noted that colloidal particles can be effectively transported through subsurface porous media under certain hydrogeochemical conditions. If present in large concentrations, mobile colloids can act as carriers for strongly sorbing contaminants and thereby provide an unretarded transport pathway for contaminants that are otherwise strongly retarded. This potential transport pathway can be considered in risk assessments of sites heavily contaminated with toxic chemicals, such as certain radionuclides, heavy metals, and hydrophobic organic compounds. The chapter reviews the current state of knowledge about the behavior of colloids in porous media and their role in contaminant transport. The chapter also identifies some important future research needs. Colloids are commonly defined as small particles or other entities with dimensions roughly between 1 nm and 1 μm. These size limits to dissolved molecules on one side and to larger suspended particles on the other side. Colloidal particles remain stable in suspension over long time periods, unless they coagulate to form larger aggregates or deposit onto surfaces of larger grains.

Mobile Subsurface Colloids and Their Role in Contaminant Transport

The presence and chain length of mycolic acids of bacteria of the genera Corynebacterium, Rhodococcus, Gordona, Mycobacterium, and Arthrobacter and of coryneform bacteria containing a type B peptidoglycan were related to the cell surface hydrophobicity of the bacteria, which in turn was related to adhesion of the cells to defined surfaces such as Teflon and glass. The origin of the overall negative charge of these bacteria is discussed.

Physicochemical Cell Surface and Adhesive Properties of Coryneform Bacteria Related to the Presence and Chain Length of Mycolic Acids

Deposition of Pseudomonas putida mt2 and Rhodococcus strain C125 during transport through columns packed with Teflon grains was investigated. Deposition was analyzed in terms of the clean bed collision efficiency α0 (the probability of a cell to attach upon reaching a cell-free substratum) and the surface area blocked by attached cells. Blocking was quantified by a blocking factor B, the ratio of the blocked area per cell to the geometric area of a cell. At an average interstitial fluid velocity of 200 μm s-1, α0 is close to unity (0.83 ± 0.01) for both strains, indicating that cell−solid interactions are almost completely favorable for deposi tion. Values for B of 1.6 ± 0.1 and 12.0 ± 0.8 were obtained for Ps. putida and Rhodococcus strain C125, respectively. This difference is consistent with differences in cell size and cell−cell repulsion, which were both smaller for Ps. putida than for Rhodococcus strain C125. At coverages close to saturation, multilayer adhesion and/or pore clogging occurs for the w...

Bacterial Deposition in Porous Media Related to the Clean Bed Collision Efficiency and to Substratum Blocking by Attached Cells

The factors identified to be important for the aerobic biodegradation of alpha-hexachlorocyclohexane (alpha-HCH) in a soil slurry are temperature, auxiliary carbon source, substrate concentration, and soil inhomogeneities. Temperatures in the range of 20 to 30 degrees C were determined to be most favorable for biodegradation of alpha-HCH. No alpha-HCH biodegradation was detected at temperatures below 4 degrees C and above 40 degrees C. The addition of auxiliary organic carbon compounds showed repressive effects on alpha-HCH biomineralization. Increased oxygen partial pressures reduced the repressive effects of added auxiliary organic carbon compounds. A linear relationship between alpha-HCH concentration and its conversion rate was found in a Lineweaver-Burk plot. Inhomogeneities such as clumping of alpha-HCH significantly affected its biodegradation. Inhomogeneity as an influence on biodegradation has not drawn sufficient attention in the past, even though it certainly has affected both laboratory studies and the application of biotechnological methods to clean up contaminated sites. On the basis of metabolites detected during degradation experiments, the initial steps of aerobic alpha-HCH bioconversion in a soil slurry are proposed.

Aerobic biomineralization of alpha-hexachlorocyclohexane in contaminated soil

Deposition of seven bacterial strains on spherical glass and Teflon collectors was studied in vertical down-flow columns at an ionic strength (I) of 0.1 M. The various bacteria had either one of the following types of major cell−surface constituents:  nonpolysac charide (NP), amphiphilic (AMPH), or anionic polysaccharide (AP) macromolecules. Deposition was analyzed in terms of the clean bed collision efficiency α0 (the probability of a cell to attach upon reaching a substratum free of cells) and a blocking factor B (the ratio of the area blocked by an attached cell to the geometric area of a cell). The value of α0 decreased from 1.0 to about 0.01 in the following order of cell−surface constituents/collector combina tions:  NP/Teflon and AMPH/Teflon > NP/glass > AMPH/glass, AP/Teflon, and AP/glass. The value for B, at a Peclet number of 1 × 105, increased from about 3 to 18 in the order NP/low cell charge < NP or AMPH/high cell charge < AP/high cell charge. This indicates that cell−cell repulsion enhances ...

A.J.B. Zehnder

Papers

Physicochemical Cell Surface and Adhesive Properties of Coryneform Bacteria Related to the Presence and Chain Length of Mycolic Acids

Bacterial Deposition in Porous Media Related to the Clean Bed Collision Efficiency and to Substratum Blocking by Attached Cells

Aerobic biomineralization of alpha-hexachlorocyclohexane in contaminated soil

Bacterial deposition in porous media : Effects of cell-coating, substratum hydrophobicity, and electrolyte concentration

Effect of substrate adsorption and microbial adhesion on bacterial growth and activity.