Motility in Procaryotic Organisms: Problems, Points of View, and Perspectives

Abstract

Summary 1. Procaryotic motility mechanisms are more difficult to investigate than those of the generally larger, hence more easily observable, eucaryotic forms. Furthermore, although the function—namely translational locomotion—is the same, the biomechanisms by which this end is accomplished may be, in fact, quite distinct in the two forms. 2. Observational techniques for studying procaryotic motility are relatively crude and qualitative. Progress toward a greater understanding of motility phenomena will be made correlative with advances derived from devising specific techniques involving approaches adapted from electrical engineering, biophysics and cybernetics. 3. There is a great amount of information at hand concerning the qualitative and quantitative chemical composition of procaryotic flagella, but there is no assurance that preparatory techniques include either the entire organelle on the one hand, or do not introduce subtle errors on the other hand. Similarly, the structural features of flagella as derived from electron‐microscope studies of fixed preparations may be themselves influenced by the techniques employed to reveal them. 4. Chemotactic responses of bacteria have been noted almost since the beginning of bacteriology as a formal scientific endeavour, yet the study of transduction of environmental stimuli, using motile bacteria as experimental subjects, is a relatively recent development. We have proposed that the cytoplasmic membrane may act as a non‐specific receptor‐transmitter of such signals in motile bacteria. If this is found to be the case, perhaps a sensory code may be more amenable to discovery here than with more complex forms of organisms. 5. Knowledge of the physical aspects in procaryotic flagellar movement is extremely fragmentary. There is some information on the movements of living functional flagellar fascicles, but this form of movement of an individual flagellum is purely speculative. We have proposed that the procaryotic flagellum is a rigid or semi‐rigid helix, which does not transmit helical waves of contraction, and that its movements are governed by a specialized area of the cytoplasmic membrane. The flagellum may rotate or wobble within the flagellar basal bulb to produce the motion necessary for propulsion. This view ‘explains’ many of the known properties of procaryotic flagella. 6. The basis of gliding motility remains unknown even after a great deal of experimental work. In our view, the secretion of slime is necessary for adhesion to a solid surface, and movement is believed to be mediated by a mechanism involving contractile waves. 7. Studies on procaryotic motility may yield valuable information on certain areas of general biological interest. Among these are: (a) the transduction of environmental stimuli and the sensory code; (b) the development of reproducible observational techniques for quantitative data on the hydrodynamic and biophysical parameters of cell motion in procaryotic forms; (c) the phenomenon of unicellular ‘behaviour’ and the survival value and evo...

Studies on Negative Chemotaxis and the Survival Value of Motility in Pseudomonas Fluorescens

“…A gap, synapse, or an equivalent thereof, and a primitive 'muscle-membrane' or contractile element, may be coupled with, and activate, a rigid or semirigid non-contractile flagellum. The chemical events may be similar to those found in higher animals, based upon acetylcholine (Doetsch & Hageage, 1968).…”

“…A theory developed by us, in the course of laboratory experiences with various flagellated bacteria (Doetsch, 1966 b; Doetsch, Cook & Vaituzis, 1967) suggested that the flagellum or flagellar fascicle is part of an excito-motor system developed for spacial accommodation. Stimuli are considered to be ' sensed ' by the cytoplasmic membrane acting as a 'monitor' or signal receptor.…”

“…Tactic responses involve not only mechanisms by which bacteria move, but imply the (possible) existence of sensing and transducing devices which direct bacteria towards conditions most suitable for survival and multiplication (Doetsch & Hageage, 1968).…”

“…The energy of such stimuli is transduced into a signal causing a reversal in direction of flagellar motion. A mechanism whereby this might be accomplished has been suggested by Doetsch & Hageage (1968). All chemotactic responses by bacteria may thus be considered movements away from environmental conditions which induce a critical change in membrane potential.…”

Defects in contact-stimulated gliding during aggregation by Myxococcus xanthus

“…Gliding involves the slow smooth movement of cells in the direction of their long axis without the use of flagella (2,12,14). Although models for gliding motility have been proposed (3,4,6,23,24,28,31), the mechanism of gliding is not understood, and the components of the motility apparatus have not been identified. Highly ordered strands have been observed by electron microscopy in Myxococcusfulvus (24).…”