Kevin C. Marshall

Adhesion: A tactic in the survival strategy of a marine vibrio during starvation

The mesophilic marineVibrio DW1 increases in number and decreases rapidly in size within 5 h of exposure to starvation conditions. The decrease in cell size continues with further starvation, but is accompanied by a rapid decline in viability. Starvation-induced dwarfs show an enhanced rate of adhesion to siliconized glass surfaces, an effect that is related to the appearance of bridging polymer at the cell surface. It is suggested that the adhesive properties of dwarf forms may enhance their chance of survival in oligotrophic marine conditions.

Mechanisms of Bacterial Adhesion at Solid-Water Interfaces

Any consideration of the mechanisms whereby bacteria adhere to solid surfaces must take account of the surface properties of the bacteria as well as those of the substrata concerned. Properties of bacterial surfaces have been dealt with by Wicken (Chapter 2) and those of apparently inert substratum surfaces by Loeb (Chapter 5). Bacteria can be considered as living colloidal particles (Marshall, 1973, 1976). They range in size from about 0.2 µm to several micrometers in length, and the majority of bacteria are about 1.0 µm in length or diameter. The density of a bacterial cell is only slightly greater than that of water. Stable suspensions of bacteria in dilute electrolytes (e.g., nutrient media) result, in part, from a mutual electrostatic repulsion between like charges on the bacterial surfaces. As revealed by electrophoretic measurements (Fig. 1), bacteria possess a net negative surface charge at pH values found in most natural habitats. A charge reversal at low pH values is indicative of the presence of some charged basic (amino) groups, which are revealed when dissociation of acidic (carboxyl, phosphate) groups is suppressed at the low pH values (Plummer and James, 1961). The positively charged groups appear to be evenly distributed over the surface of Flexibacter aurantiacus CW7 (Marshall and Cruickshank, 1973). Bacteria also exhibit variations in overall surface free energy of the cells, with some bacteria possessing relatively hydrophilic surfaces and others relatively hydrophobic surfaces (Mudd and Mudd, 1924; Magnusson et al., 1977; Dahlback et al., 1981). The distribution of hydrophobic sites on bacterial cells is not necessarily uniform and may result in a preferred orientation of certain bacteria at interfaces (Marshall and Cruickshank, 1973).

Physicochemical and in situ observations on the adhesion of gliding bacteria to surfaces

The ability of Flexibacter BH3 to adhere to solid surfaces and to overcome the horizontal drag involved in gliding across the surfaces was considered in terms of the Stefan adhesion principle. The extracellular slime produced by Flexibacter BH3 was suitable as a Stefan adhesive because it exhibited viscous properties characteristic of a linear colloid, increasing the adhesiveness of the bacterium but allowing translational motion across the surface. The water-soluble slime was a glycoprotein, containing glucose, fucose, galactose and some uronic acid. Vesicles and tubules on the outer surface of Flexibacter BH3 possessed trilaminar membranes, contained 2-keto-3-deoxyoctonate (KDO), and showed identity with phenol-extracted lipopolysaccharide (LPS) in gel-diffusion tests.Sections of Flexibacter BH3 gliding on a gold film overlaying an agar medium reveraled a highly convuluted cell envelope outer membrane, portions of which closely conformed to the microcontours of the gold surface. Possible mechanisms of gliding are discussed in relation to this close association with solid surface features, to the finding that flexibility and spiral motion are not essential for gliding, and to evidence revealing the extrusion of slime in advance of “pathfinder” bacteria.

Bacterial Polymers: Physicochemical Aspects of Their Interactions at Interfaces

How do bacteria stick to a surface? There is still not enough information about to answer this question especially at the molecular level. This question only gives rise to more questions. What is the structure of the true adhesive bacterial polymer? Is only one bacterial polymer or several polymers involved in the adhesion process? What is the role of proteins associated with the bacterial polysaccharides? What type of polymer is produced for the adhesion to hydrophobic surfaces? Is the polymer produced as a response to the surface ? This review is an attempt to summarize the physicochemical aspects of bacterial polymers and their interaction with surfaces. It was tried to give an overview of the literature published in this field. The article is divided into the following sections: first, the forces involved in bacterial adhesion are described. Second, the theoretical approaches to bacterial adhesion are discussed. Third, different fluid conditions are investigated. Fourth, the nature of different bacterial polymers which are important for the interaction with a surface is elaborated. Fifth, the current knowledge about biological polymers at interfaces is shown. And sixth, the role of polymers in the adhesion of bacteria available to date is highlighted.

Bacterial scavenging: Utilization of fatty acids localized at a solid-liquid interface

A model oligotrophic aquatic system involving localization of fatty acids on a solid surface was used to quantitate scavenging by three bacteria; Leptospira biflexa patoc 1 which adheres reversibly, pigmented Serratia marcescens EF190 which adheres irreversibly, and a non-pigmented hydrophilic mutant of EF190. The Leptospira and pigmented Serratia displayed two distinct scavenging strategies which are related to their different methods of adhesion. The Leptospira efficiently scavenged [1-14C] stearic acid from the surface in 24 h, whereas the pigmented hydrophobic Serratia initially showed a faster rate of removal but the overall rate was considerably slower than that of the Leptospira. The hydrophilic, non-pigmented Serratia required 50h incubation to remove significant amounts of the labelled fatty acid. The greater scavenging ability of the hydrophobic pigmented Serratia strain compared to the hydrophilic non-pigmented mutant could not be attributed to differences in viability of fatty acid metabolism. The hydrophobicity of the pigmented Serratia allows for firmer adhesion and greater interaction with the surface localized nutrients.

Microbial footprints : a new approach to adhesive polymers

Extracellular polymers are responsible for attachment of bacteria to inert surfaces. To date, adhesive polymers have been isolated from the culture supernatant or from the bacterial cell surface. The true adhesive polymer may be synthesised during the early adhesion process resulting in irreversible adhesion. In this study, marine bacteria were allowed to adhere to hydrophobic surfaces, then cells were detached using an ultrasonic water bath with adjustable energy input and degassing periods. The remaining “footprints”; were demonstrated by the use of various chemical staining techniques for light microscopy. In addition they were examined by transmission electron microscopy and by scanning electron microscopy. Finally, with a new method using lectins in combination with a fluorescent protein stain, it was possible to clearly demonstrate the “footprint”; material remaining on the surface. With this new approach it should be possible to develop a method for harvesting enough material to investigate the che...

Utilization of surface localized substrate by non-adhesive marine bacteria

Thirty-four marine bacteria were isolated from the eluate of seawater passed through a column of glass beads coated with stearic acid. Irreversible attachment of these isolates to stearic acid-coated glass surfaces ranged from 7.6–100% of the total attached population, with 7 isolates exhibiting less than 10% irreversible adhesion. All 14 isolates tested were able to utilize surface bound14C-stearic acid, even though some showed mostly reversible adhesion to the surface. More detailed studies were made comparing the reversibly adheringVibrio MH3 with the irreversibly adheringPseudomonas NCMB2021. MH3 cells were readily removed from the surface by a gentle shear force, and a significant degree of14C-labeling of MH3 cells, but not of NCMB2021 cells, in the bulk phase was observed. The ecological significance of nutrient scavenging at solid surfaces by reversibly attached bacteria is considered.

Retention of the Gramnegative marine bacterium SW8 on surfaces — effects of microbial physiology, substratum nature and conditioning films

Abstract The effect of films of organic compounds, the conditioning films (CF), adsorbed to the inanimate substrata stainless steel, germanium, polypropylene and perspex on retention of either the carbon (acetate)- or nitrogen (ammonia)-limited nonmotile Gram-negative marine bacterium SW8 was investigated. CF were deposited from marine or freshwater aquatic samples and from solutions containing bovine serum albumin, myoglobin, lactoglobulin or humic acids. SW8 was exposed to both “clean” and CF-coated test substrata in laminar fluid flow chambers for 10 min. CF modified attachment of SW8 relative to clean substrata in 70% of the cases. The following categories of CF were observed: (i) CF that appeared to control retention of SW8 irrespective of the type of substratum; (ii) CF that either increased or decreased the retention of SW8 on all substrata without altering the relative order of retention on the substrata and (iii) CF that affected retention of SW8 in an apparently substratum-specific manner. When retention of the two phenotypes differed, carbon-limited SW8 attached in higher numbers than nitrogen-limited SW8. No correlation was found between water contact angles on either “clean” or CF-coated substrata and retention of cells. In some experiments, SW8 was retained in aggregates. Such aggregation predominated on hydrophobic substrata, with nitrogen-limited organisms and on materials coated with CF from environmental waters. No difference in hydrophobicity or surface charge was found between the two physiologically different states of the organism. The ecological implications of these results and possible mechanisms of interactions of organisms with CF-coated substrata are discussed.

Effects of a clay mineral on microbial predation and parasitism ofEscherichia coli.

Montmorillonitic clay influences the biological control ofEscherichia coli in aquatic systems, the magnitude of the effects being dependent on the state of the clay and the type of host-antagonist interaction. The interaction ofBdellovibrio andE. coli was partially inhibited by the presence of montmorillonite. Because it is highly motile,Bdellovibrio apparently could penetrate any colloidal clay barrier aroundE. coli if the clay envelope was thin enough. Colloidal clay had little effect on predation ofE. coli by the myxobacteriumPolyangium, and had no effect on the activity of the amoebaVexillifera. Crude clay, on the other hand, resulted in a physical separation of predator and prey, and this completely inhibited theE. coli-Polyangium interaction and slowed the rate of engulfment ofE. coli byVexillifera.The interference of natural biological control by clays may alter the microbial balance favoring survival of fecal microorganisms and resulting in their accumulation in saline sediments. This could constitute a health hazard if these organisms were released by upwelling of bottom waters or were desorbed in estuarine systems by dilution during heavy rains.

Continuous observations of bacterial gliding motility in a dialysis microchamber: The effects of inhibitors

Use of a dialysis microchamber has allowed continuous observations on the same set of gliding bacteria during changes in the composition of the perfused medium. This procedure has revealed the presence of an adaptive, cyanide-insensitive metabolic pathway, which allows cyanide-treated Flexibacter BH3 to begin gliding again at a reduced rate when glucose is the substrate. In addition, it has revealed that individual flexibacter cells can maintain their gliding motility for up to 20 h in the absence of exogenous substrate.Gliding in Flexibacter BH3 was prevented by those inhibitors blocking the electron transport process. Inhibitors of glucose metabolism did not prevent motility, since the flexibacters obviously metabolize endogenous substrate under such circumstances. Proton ionophores, which induce membrane depolarization, rapidly inhibited gliding in Flexibacter BH3. This inhibition was irreversible in the case of gramicidin S. Gliding was not inhibited by cytochalasin B or antiactin antibody. High concentrations of Ca2+ were particularly inhibitory to the gliding process. The significance of these results is discussed in relation to a possible mechanism of gliding involving the generation of rhythmical contractions in the outer cell membrane of Flexibacter BH3.