Lateral and Perpendicular Interaction Forces Involved in Mobile and Immobile Adhesion of Microorganisms on Model Solid Surfaces

Gliding and near-surface swimming of microorganisms are described as a mobile form of microbial adhesion that need not necessarily be reversible. It is argued that the reversibility of microbial adhesion depends on the depth of the secondary interaction minimum, calculated from the forces between an organism and a substratum acting in a direction perpendicular to the substratum surface. The mobility of adhering microorganisms depends on lateral interactions between the organisms. On ideally homogeneous and smooth model surfaces, only mobile adhesion occurs because the multibody, lateral interactions are weak compared with the thermal or Brownian motion energy of the organisms. Minor chemical or structural heterogeneities, which exist on all real-life surfaces, yield a lateral interaction on adhering microorganisms. This causes their immobilization, which helps to explain the physicochemical nature of microbial gliding or near-surface swimming. Moreover, these lateral interaction energies are one order of magnitude smaller than the Lifshitz-Van der Waals, electrostatic, and acid-base forces acting perpendicular to substratum surfaces that are responsible for adhesion. Received: 2 April 1998 / Accepted: 26 May 1998     

Influence of calcium and other cations on surface adhesion of bacteria and diatoms: A review

Association with a surface is an important aspect of survival for microorganisms in natural and manmade environments/Both bacteria and diatoms are involved in such associations. In many cases, this leads to surface fouling, which often results in surface deterioration and mechanical failure in industrial systems. We now know that microorganisms exploit many strategies to establish associations with surfaces. As in the case of other cellular processes, calcium ions seem to play an important role in adhesion of cells to surfaces. Calcium is involved in non-specific interactions such as neutralization of the electrical double layer between cell and substratum surface as well as specific adhesive interactions that cannot be replaced by other cations. The unique properties of calcium ions promote both specific and non-specific interactions with protein and polysaccha-ride adhesin molecules at the cell surface. As important, but less well understood, calcium ions also influence the way microbial cells interact with different substrata.     

Mycoplasma biofilms ex vivo and in vivo

Biofilms are communities of microorganisms that are encased in polymeric matrixes and grow attached to biotic or abiotic surfaces. Despite their enhanced ability to resist antimicrobials and components of the immune system in vitro , few studies have addressed the interactions of biofilms with the host at the organ level. Although mycoplasmas have been shown to form biofilms on glass and plastic surfaces, it has not been determined whether they form biofilms on the tracheal epithelium. We developed a tracheal organ-mounting system that allowed the entire surface of the tracheal lumen to be scanned using fluorescence microscopy. We observed the biofilms formed by the murine respiratory pathogen Mycoplasma pulmonis on the epithelium of trachea in tracheal organ culture and in experimentally infected mice and found similar structure and biological characteristics as biofilms formed in vitro . This tracheal organ-mounting system can be used to study interactions between biofilms formed by respiratory pathogens and the host epithelium and to identify the factors that contribute to biofilm formation in vivo .     

Natural roles of biosurfactants

Microorganisms produce a variety of surface-active agents (or surfactants). These can be divided into low-molecular-weight molecules that lower surface and interfacial tensions efficiently and high-molecular-weight polymers that bind tightly to surfaces. These surfactants, produced by a wide variety of microorganisms, have very different chemical structures and surface properties. It is therefore reasonable to assume that different groups of biosurfactants have different natural roles in the growth of the producing microorganisms. Moreover, as their chemical structures and surface properties are so different, each emulsifier probably provides advantages in a particular ecological niche. Several bioemulsifiers have antibacterial or antifungal activities. Other bioemulsifiers enhance the growth of bacteria on hydrophobic water-insoluble substrates by increasing their bioavailability, presumably by increasing their surface area, desorbing them from surfaces and increasing their apparent solubility. Bioemulsifiers also play an important role in regulating the attachment–detachment of microorganisms to and from surfaces. In addition, emulsifiers are involved in bacterial pathogenesis, quorum sensing and biofilm formation. Recent experiments indicate that a high-molecular-weight bioemulsifier that coats the bacterial surface can be transferred horizontally to other bacteria, thereby changing their surface properties and interactions with the environment.     

Effects of polymicrobial communities on host immunity and response

Microorganisms grow as members of microbial communities in unique niches, such as the mucosal surfaces of the human body. These microbial communities, containing both commensals and opportunistic pathogens, serve to keep individual pathogens 'in check' through a variety of mechanisms and complex interactions, both between the microorganisms themselves and the microorganisms and the host. Recent studies shed new light on the diversity of microorganisms that form the human microbial communities and the interactions these microbial communities have with the host to stimulate immune responses. This occurs through their recognition by dendritic cells or their ability to induce differential cytokine and defensin profiles. The differential induction of defensins by commensals and pathogens and the ability of the induced defensins to interact with the antigens from these microorganisms may attenuate proinflammatory signaling and trigger adaptive immune responses to microbial antigens in a multistep process. Such an activity may be a mechanism that the host uses to sense what is on its mucosal surfaces, as well as to differentiate among commensals and pathogens.     

Causes and consequences of plant-associated biofilms

The rhizosphere is the critical interface between plant roots and soil where beneficial and harmful interactions between plants and microorganisms occur. Although microorganisms have historically been studied as planktonic (or free-swimming) cells, most are found attached to surfaces, in multicellular assemblies known as biofilms. When found in association with plants, certain bacteria such as plant growth promoting rhizobacteria not only induce plant growth but also protect plants from soil-borne pathogens in a process known as biocontrol. Contrastingly, other rhizobacteria in a biofilm matrix may cause pathogenesis in plants. Although research suggests that biofilm formation on plants is associated with biological control and pathogenic response, little is known about how plants regulate this association. Here, we assess the biological importance of biofilm association on plants.     

The impact of perinatal immune development on mucosal homeostasis and chronic inflammation

The mucosal surfaces of the gut and airways have important barrier functions and regulate the induction of immunological tolerance. The rapidly increasing incidence of chronic inflammatory disorders of these surfaces, such as inflammatory bowel disease and asthma, indicates that the immune functions of these mucosae are becoming disrupted in humans. Recent data indicate that events in prenatal and neonatal life orchestrate mucosal homeostasis. Several environmental factors promote the perinatal programming of the immune system, including colonization of the gut and airways by commensal microorganisms. These complex microbial-host interactions operate in a delicate temporal and spatial manner and have an important role in the induction of homeostatic mechanisms.     

Factors affecting the attachment of rhizospheric bacteria to bean and soybean roots

The plant rhizosphere is an important soil ecological environment for plant-microorganism interactions, which include colonization by a variety of microorganisms in and around the roots that may result in symbiotic, endophytic, associative, or parasitic relationships within the plant, depending on the type of microorganisms, soil nutrient status, and soil environment. Rhizosphere competence may be attributable to the differences in the extent of bacterial attachment to the root surface. We present results of the effect of various factors on the attachment to bean (Phaseolus vulgaris) and soybean (Glycine max) roots of some bacterial species of agronomic importance, such as Rhizobium tropici, Rhizobium etli, Ensifer fredii (homotypic synonym Sinorhizobium fredii), and Azospirillum brasilense; as well as the attachment capability of the plant growth promoting rhizobacteria Pseudomonas fluorescens and Chryseobacterium balustinum. Additionally, we have studied various bacterial traits, such as autoaggregation and flagella movements, which have been postulated to be important properties for bacterial adhesion to surfaces. The lack of mutual incompatibility between rhizobial strains and C. balustinum has been demonstrated in coinoculation assays.     

Bioremediation of weathered-building stone surfaces

Atmospheric pollution and weathering of stone surfaces in urban historic buildings frequently results in disfigurement or damage by salt crust formation (often gypsum), presenting opportunities for bioremediation using microorganisms. Conventional techniques for the removal of these salt crusts from stone have several disadvantages: they can cause colour changes; adversely affect the movement of salts within the stone structure; or remove excessive amounts of the original surface. Although microorganisms are commonly associated with detrimental effects to the integrity of stone structures, there is growing evidence that they can be used to treat this type of stone deterioration in objects of historical and cultural significance. In particular, the ability and potential of different microorganisms to either remove sulfate crusts or form sacrificial layers of calcite that consolidate mineral surfaces have been demonstrated. Current research suggests that bioremediation has the potential to offer an additional technology to conservators working to restore stone surfaces in heritage buildings.     

Screening for lectin-like protein-producing microorganisms based on cell surface proteins

A method for screening lectin-producing microorganisms was developed. The presence of lectin on microbial cell surfaces was used as an index for their selective isolation. The lectin-producing microorganisms adhered to sugar-modified agarose beads and were selectively eluted with specific saccharide solutions. Spin columns were an effective tool for excluding non-lectin producers. Eighty-seven percent of the microorganisms that were eluted from the beads showed hemagglutination. The results of sequence analysis indicated that some of the eluted microorganisms have not been previously identified as lectin-producing microorganisms.     

An assessment of the dynamic stability of microorganisms on patterned surfaces in relation to biofouling control

Microstructure-based patterned surfaces with antifouling capabilities against a wide range of organisms are yet to be optimised. Several studies have shown that microtopographic features affect the settlement and the early stages of biofilm formation of microorganisms. It is speculated that the fluctuating stress–strain rates developed on patterned surfaces disrupt the stability of microorganisms. This study investigated the dynamic interactions of a motile bacterium (Escherichia coli) with microtopographies in relation to initial settlement. The trajectories of E. coli across a patterned surface of a microwell array within a microchannel-based flow cell system were assessed experimentally with a time-lapse imaging module. The microwell array was composed of 256 circular wells, each with diameter 10?μm, spacing 7?μm and depth 5?μm. The dynamics of E. coli over microwell-based patterned surfaces were compared with those over plain surfaces and an increased velocity of cell bodies was observed in the case of patterned surfaces. The experimental results were further verified and supported by computational fluid dynamic simulations. Finally, it was stated that the nature of solid boundaries and the associated microfluidic conditions play key roles in determining the dynamic stability of motile bacteria in the close vicinity over surfaces.     

Capsular polysaccharides secreted by building façade colonisers: characterisation and adsorption to surfaces

Exopolymers secreted by algal and cyanobacterial strains isolated from building fa?ades were imaged by microscopy techniques. They were extracted and characterised to investigate their possible contribution to interactions with solid surfaces. The polymers were polysaccharides, with anionic and hydrophobic properties varying between the various strains. Capsular polysaccharides extracted from a strain of Klebsormidium flaccidum adsorbed in higher amounts on hydrophobic than on hydrophilic surfaces. These results tend to confirm the hypothesis that exopolymers are important in the colonisation process of microorganisms to surfaces.     

Unlocking the diversity and biotechnological potential of marine surface associated microbial communities

Marine sessile eukaryotic hosts provide a unique surface for microbial colonisation. Chemically mediated interactions between the host and colonising microorganisms, interactions between microorganisms in the biofilm community and surface-specific physical and chemical conditions impact differently on the diversity and function of surface-associated microbial assemblages compared with those in planktonic systems. Understanding the diversity and ecology of surface-associated microbial communities will greatly contribute to the discovery of next-generation, bioactive compounds. On the basis of recent conceptual and technological advances insights into the microbiology of marine living surfaces are improving and novel bioactives, including those previously ascribed as host derived, are now revealed to be produced by members of the surface-associated microbial community.     

Commensal bacteria make a difference

Nowhere is the relationship between microorganisms and eukaryotes as diverse, intimate and clinically relevant as in the gastrointestinal tract. An estimated 500-1000 mostly anaerobic species reside in the intestine, approaching enormous densities of 10(11)-10(12) organisms per gram colon content. The commensal interactions between intestinal microorganisms and animal hosts have been difficult to study in the past because of the diversity of microorganisms involved and because of the lack of culturability that accompanies many microbial consortia. However, recent work has provided new insights into these interactions.     

Analysis of bacterial communities on historical glass by denaturing gradient gel electrophoresis of PCR-amplified gene fragments coding for 16S rRNA.

The present study describes the analysis of bacterial communities on historical window glass by denaturing gradient gel electrophoresis of PCR-amplified 16S rDNA fragments. So far, only a few studies have been published in which the microflora and the corrosion mechanisms of glass surfaces have been investigated. Some microorganisms, especially fungi, have been isolated from different glass samples in the past. However, our results demonstrate that bacterial communities on biodeteriorated glass surfaces are much more complex than previously believed. In addition, bacteria were identified, which have never been isolated from glass samples before.     

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

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.     

微生物耐铝机制的研究进展

铝毒是酸性土壤中限制作物生产最主要的因素。微生物与铝作用逐渐受到关注,一些微生物特别是模式微生物的耐铝机制已被提出。主要综述了酵母,假单胞菌及其它微生物耐铝机制的研究进展,并展望了微生物耐铝机制研究发展的方向。     

Effect of surface potential on consumption of charged substrates

Due to the surface charge inherent on all microorganism cell surfaces, the consumption of charged molecules by these microorganisms will be affected by the electrostatic interactions between the substrate and the cell surface. This article derives an equation that shows that these electrostatic interactions result in a change in the Monod half-velocity constant. The resulting rate of consumption is affected and can be either higher or lower than the rate of consumption of an uncharged substrate molecule.     

A review of non-DLVO interactions in environmental colloidal systems

The interaction and behavior of surfaces orcolloids is of quantitative significance inunderstanding the transport and fate ofcompounds and microorganisms in environmentalsystems. Historically, the DLVO model ofcolloid stability has described theseinteractions. This model finds its basis in aforce (energy) balance that comprisesattractive van der Waals and repulsiveelectrostatic interactions. Recently, the DLVOmodel has been found unable to fully describebiotic and abiotic colloidal behavior inaqueous media. The suspending phase (commonlywater) is often treated as a force (energy)transmitting or propagating medium. It isreasonable to believe that the structure ofwater may participate in a more significantfashion. Moreover, other moieties (sorbed anddissolved) may also have non-DLVO effects. Significant work has been focused on extendingthe precepts of the traditional DLVO model toaccommodate these non-DLVO forces (energies). This paper reviews many of the interactionsthat play a role in environmental systems andare not commonly subsumed by the traditionalDLVO model: e.g., hydrogen bonding and thehydrophobic effect, hydration pressure,non-charge transfer Lewis acid baseinteractions, and steric interactions.     

Pathogenomics of non-pathogens

Analysing the genomes of non-pathogenic microorganisms, in addition to its basic and applied scientific interest, can also shed considerable light on the study of pathogenic microorganisms. Two of the three microorganisms described here are rarely pathogenic, but carry genetic determinants that have previously been identified as being important for the pathogenicity of other microorganisms. This underlines the growing understanding that many so-called 'virulence genes' are probably involved in more general interactions between the microorganism and the host or the environment.