The effects of high-power microwaves on the ultrastructure of Bacillus subtilis.
OBJECTIVE
To investigate the microbicidal mechanisms of high-power microwave (2.0 kW) irradiation on Bacillus subtilis and to determine the effect of this procedure on the ultrastructure of the cell wall.


RESULTS
We performed viability test, examined cells using transmission electron microscopy (TEM), and measured the release of intracellular proteins and nucleic acids. The inactivation rate of B. subtilis by 2.0-kW microwave irradiation was higher than that of a domestic microwave (0.5 kW). Few proteins were released from either microwaved or boiled cells. However, the leakage of nucleic acids from 2.0-kW-microwaved cells was significantly higher than that of 0.5-kW-microwaved or boiled cells. Therefore, we examined ultrastructural alterations of microwaved or boiled cells to analyse the pattern of release of cytoplasmic contents. Although boiled cells did not show any ultrastructural changes on TEM, 2.0-kW-microwaved cells showed disruption of the cell wall.


CONCLUSIONS
The microbicidal mechanisms of 2.0-kW microwave irradiation include damage to the microbial cell wall, breakage of the genomic DNA, and thermal coagulation of cytoplasmic proteins.


CONCLUSIONS
TEM images showed that the cytoplasmic protein aggregation and cell envelope damage by microwave irradiation were different from the ultrastructural changes observed after boiling.
Department of Microbiology and Cancer Research Institute, College of Medicine, Chungnam National University, Daejeon, Korea.
S-Y
SY
Kim
E-K
EK
Jo
H-J
HJ
Kim
K
K
Bai
J-K
JK
Park
D001412:Bacillus subtilis / Q000528:radiation effects* / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000528:radiation effects*; D002473:Cell Wall / Q000528:radiation effects* / Q000648:ultrastructure; D006358:Hot Temperature; D046529:Microscopy, Electron, Transmission; D008872:Microwaves; D012329:RNA, Bacterial / Q000528:radiation effects*
D001426:Bacterial Proteins; D012329:RNA, Bacterial