Development of method for evaluating cell hardness and correlation between bacterial spore hardness and durability.
BACKGROUND
Despite the availability of conventional devices for making single-cell manipulations, determining the hardness of a single cell remains difficult. Here, we consider the cell to be a linear elastic body and apply Young's modulus (modulus of elasticity), which is defined as the ratio of the repulsive force (stress) in response to the applied strain. In this new method, a scanning probe microscope (SPM) is operated with a cantilever in the "contact-and-push" mode, and the cantilever is applied to the cell surface over a set distance (applied strain).


RESULTS
We determined the hardness of the following bacterial cells: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and five Bacillus spp. In log phase, these strains had a similar Young's modulus, but Bacillus spp. spores were significantly harder than the corresponding vegetative cells. There was a positive, linear correlation between the hardness of bacterial spores and heat or ultraviolet (UV) resistance.


CONCLUSIONS
Using this technique, the hardness of a single vegetative bacterial cell or spore could be determined based on Young's modulus. As an application of this technique, we demonstrated that the hardness of individual bacterial spores was directly proportional to heat and UV resistance, which are the conventional measures of physical durability. This technique allows the rapid and direct determination of spore durability and provides a valuable and innovative method for the evaluation of physical properties in the field of microbiology.
Laboratory for Core Technology, Development Kirin Beverage Co, Ltd,, Technovillage 3F, 1-17-1 Namamugi, Yokohama 230-8628, Japan. kouichi_nakanishi@kirin.co.jp
Koichi
K
Nakanishi
Akinori
A
Kogure
Takenao
T
Fujii
Ryohei
R
Kokawa
Keiji
K
Deuchi
D001419:Bacteria / Q000166:cytology* / Q000528:radiation effects; D001709:Biotechnology / Q000379:methods*; D055119:Elastic Modulus; D006244:Hardness; D006358:Hot Temperature; D020527:Microscopy, Scanning Probe; D013171:Spores, Bacterial / Q000166:cytology / Q000528:radiation effects; D014466:Ultraviolet Rays