Turgor pressure responses of a gram-negative bacterium to antibiotic treatment, measured by collapse of gas vesicles

Abstract

The internal hydrostatic pressure of Ancylobacter aquaticus was measured by collapsing the gas vesicles with an externally applied pressure. Turgor pressure was measured in conjunction with various antibiotic treatments to elucidate some aspects of the biophysics of gram-negative cell wall function. Differences in the effects of these drugs either alone or in combination with other treatments were related to known biochemical activities of these drugs. Our previous work, demonstrating a heterogeneous cellular response to beta-lactam antibodies, was confirmed and extended. Most of the cell wall growth-inhibiting antibiotics resulted in some cells (those in component I) developing a higher pressure, while the remainder (those in component II) lost turgor. Although the fraction of the cells in each component varied a little from subculture to subculture, it did not vary with time or choice of antibiotic treatment. Mecillinam gave a nearly monophasic response. All antibiotics blocking macromolecular synthesis gave monophasic curves. The 50% collapse pressure in some cases, however, was lower higher, or the same as the control.

Osmosensing by Bacteria: Signals and Membrane-Based Sensors

“…The available techniques for the detection and monitoring of turgor pressure include (i) direct monitoring of individual cells with a microscopic pressure probe (102), (ii) cytoplasmic freezing-point analysis of whole cells (187), (iii) analysis of the relationship between extracellular osmolality and the pressure-induced collapse of cytoplasmic gas vesicles (154,215,216,290), (iv) comparison of the osmolalities of extracellular media and corresponding cell extracts (260), and (v) analysis of the relationship between cell volume and extracellular osmolality (the plasmolysis titration) (200,294).…”

Autolysis Control Hypotheses for Tolerance to Wall Antibiotics

“…While there are no good routine ways to measure the turgor pressure of bacteria, the best available one is that described by Walsby (58). His technique was further improved so that measurements could be carried out quickly and more accurately (30,44,45). However, this approach has the inherent disadvantage that it can work only with cells that possess gas vacuoles (sometimes called vesicles).…”

“…A special apparatus was constructed to obtain measurements (30,44,45). One part served to allow a sample of cells placed in the pressure system to be exposed to hydrostatic pressure in a programmed way.…”

Bacterial Wall as Target for Attack

“…However, methods to measure turgor pressure are lacking. Because of the importance of turgor pressure, a light-scattering apparatus and method were developed and used to study turgor pressure and the effect of wall antibiotics on it (41,47,62,64). Only a short summary can be given here; reference 43 gives a more detailed review.…”