Humidity-dependent bacterial cells functional morphometry investigations using atomic force microscope

Abstract

The effect of a relative humidity (RH) in a range of 93-65% on morphological and elastic properties of Bacillus cereus and Escherichia coli cells was evaluated using atomic force microscopy. It is shown that gradual dehumidification of bacteria environment has no significant effect on cell dimensional features and considerably decreases them only at 65% RH. The increasing of the bacteria cell wall roughness and elasticity occurs at the same time. Observed changes indicate that morphological properties of B. cereus are rather stable in wide range of relative humidity, whereas E. coli are more sensitive to drying, significantly increasing roughness and stiffness parameters at RH </= 84% RH. It is discussed the dependence of the response features on differences in cell wall structure of gram-positive and gram-negative bacterial cells.

Figure 1

AFM phase images of B. cereus (a) and E. coli (b) on mica surface at 93% RH. The white bar indicates 1 μm. There are no qualitative changes that can be seen in the pictures at different RH values.

Figure 2

Roughness distribution of B. cereus (a) and E. coli (b).

Figure 3

Diagram of Young's modulus distribution; *−P < .05 (Wilcoxon's signed-rank test).