Beverley A. Humphrey

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.

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.

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.

The triggering effect of surfaces and surfactants on heat output, oxygen consumption and size reduction of a starving marine Vibrio.

The marine Vibrio DW1 exhibited a positive response in heat output to a dialysis membrane surface in the presence of substrate (100 mM sodium glutamate) and, more particularly, in the absence of exogenous substrate (starvation conditions). The latter result paralleled the previously reported decrease in cell volume and increase in oxygen consumption by starving bacteria at a similar surface. Modified Moritas salts (MMS) did not extract nutrients from the dialysis membrane, but an artificial seawater containing tris buffer (ASW-tris) did extract surface active and nutrient materials from the membrane. The ASW-tris membrane extract and a commercial surfactant, Tween 85, were found to mimic the effects of the dialysis membrane surface by inducing a decrease in cell volume, and an increasing oxygen consumption and heat output of Vibrio DW1 even in the bulk liquid. The significance of the adsorption of naturally occurring surfactants at surfaces in relation to the behaviour of bacteria at the surfaces is discussed.

Adhesion: a possible survival strategy for leptospires under starvation conditions

The saprophyticLeptospira biflexa serovarpatoc 1 did not undergo a major reduction in size upon starvation, but starvation did result in greater adhesiveness of the leptospires. Adhesion may provide a strategy for survival of leptospires in oligotrophic habitats because these bacteria can scavenge fatty acids adsorbed at surfaces. Provision of an energy substrate (fetal calf serum) to starved cells resulted in an increase in cell size and motility and a decrease in adhesion of the leptospires. Glucose was not utilized as an energy source.

Group antigens in slow-growing rhizobia

SummaryInternal group antigens of several slow-growing and fast-growing Rhizobium strains were tested by gel-diffusion against antisera to three strains of Rhizobium japonicum. At least one, generally two common antigens were found in 13 strains of R. japonicum, 4 strains of R. lupini, 4 strains isolated from cowpea and two slow-growing strains isolated from Lotus. Forty-six fast-growing rhizobia (including two from Lotus and 4 from Leucaena leucocephala) were clearly distinguished from the slow-growing strains in tests with the same antisera. They were wholly negative (9) or gave a much weaker non-identical line with one antiserum (24 strains), two antisera (8) or three antisera (5). The 5 strains of agrobacteria grouped with the fast-growing rhizobia.

Modification of the Antigenic Surface of Rhizobium trifolii by a Deficiency of Calcium

SUMMARY: Quantitative absorption of antisera was used to study the effect of calcium on the antigenic surface of Rhizobium trifolii. Antisera to Ca-deficient and Ca-adequate rhizobia (whole or broken) revealed two parts in the absorption curve: range I in which there was ready removal of most of the agglutinating antibody with a very small absorbing dose; range 2 in which the remaining agglutinating antibody resisted absorption. When Ca-adequate bacteria were used for absorption, range I consisted of about 87% of the total titre. The corresponding figure with Ca-deficient bacteria was 95%. These values have been attributed to three types of antibody; avid I (readily absorbed by either kind of bacterium), avid 2 (readily absorbed by Ca-deficient bacteria), non-avid (difficult to absorb with either bacterium). The fact that avid antibody 2 was absorbed readily by Ca-deficient bacteria but with difficulty by Ca-adequate bacteria may be due to a quantitative deficiency of a particular antigen on the surface of the Ca-adequate bacterium, or to a structural condition which gives the antigen lower affinity for its homologous antibody. Absorption characteristic of Ca-deficient rhizobia was obtained with the Ca-adequate bacteria treated with EDTA under conditions known to remove 90% of Ca from the cell. Broken bacteria to some extent simulated the absorption curve found with Ca-deficient bacteria. It is suggested that Ca located in the surface lipopolysaccharide layer of the wall of rhizobium grown with a sufficiency of this element obscures or modifies an antigenic group. Glucuronic acid found in the somatic antigen fraction of this bacterium is suggested as a possible site of Ca action.

Loss of agglutinating specificity in stock cultures of Rhizobium meliloti.

Several strains of Rhizobium meliloti which have been subcultured for 23–33 years have changed from being markedly specific in their somatic agglutination reactions to become widely cross-reactive. On the other hand a fresh collection of the same species obtained from naturally nodulated, field-grown plants revealed the high degree of agglutinating specificity which had previously characterised the old-cultures. Attempts to reselect a specific substrain from old cross-agglutinating cultures by six plant passages, or to detect change to cross reactivity by ten successive subcultures of recent isolates were unsuccessful. However, one strain, isolated in 1939, was recently found to contain both specific and cross-reactive substrains.Practically all the cultures, both old and recent, showed considerable mutability in colony characteristics but none of these was consistently correlated with cross agglutinability. Instability in 6.4% (w/v) NaCl was characteristic of the cross-agglutinating cultures. Cross reactivity was associated with a shared lipopolysaccharide antigen (LPS) which appeared to be obscured by an outer antigen in most strains still showing specific agglutinability. In the exceptional case of strain SU27, agglutination could be attributed to its specific LPS.