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.
Amako
Kazunobu
K
Department of Bacteriology, Faculty of Medical Science, Kyushu University, Fukuoka, Japan. amako@jcom.home.ne.jp
Takade
Akemi
A
Taniai
Hiroaki
H
Yoshida
Shin-ichi
S
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