Electron microscopic examination of uncultured soil-dwelling bacteria.
Bacteria living in soil collected from a rice paddy in Fukuoka, Japan, were examined by electron microscopy using a freeze-substitution fixation method. Most of the observed bacteria could be categorized, based on the structure of the cell envelope and overall morphology, into one of five groups: (i) bacterial spore; (ii) Gram-positive type; (iii) Gram-negative type; (iv) Mycobacterium like; and (v) Archaea like. However, a few of the bacteria could not be readily categorized into one of these groups because they had unique cell wall structures, basically resembling those of Gram-negative bacteria, but with the layer corresponding to the peptidoglycan layer in Gram-negative bacteria being extremely thick, like that of the cortex of a bacterial spore. The characteristic morphological features found in many of these uncultured, soil-dwelling cells were the nucleoid being in a condensed state and the cytoplasm being shrunken. We were able to produce similar morphologies in vitro using a Salmonella sp. by culturing under low-temperature, low-nutrient conditions, similar to those found in some natural environments. These unusual morphologies are therefore hypothesized to be characteristic of bacteria in resting or dormant stages.
Department of Bacteriology, Faculty of Medical Science, Kyushu University, Fukuoka, Japan. amako@jcom.home.ne.jp
Kazunobu
K
Amako
Akemi
A
Takade
Hiroaki
H
Taniai
Shin-ichi
S
Yoshida
D001105:Archaea / Q000302:isolation & purification* / Q000648:ultrastructure*; D001419:Bacteria / Q000302:isolation & purification* / Q000648:ultrastructure*; D002473:Cell Wall / Q000648:ultrastructure; D003593:Cytoplasm / Q000648:ultrastructure; D007564:Japan; D046529:Microscopy, Electron, Transmission; D012988:Soil Microbiology; D013171:Spores, Bacterial / Q000648:ultrastructure