The Journal of Medical Microbiology, Vol 35, Issue 6 338-344, Copyright © 1991 by Society for General Microbiology
Surface layers of Eubacterium yurii subsp. yurii and their possible role in test-tube brush formation and iron acquisition
G. N. Krywolap, W. Fischlschweiger, C. L. Dabirsiaghi and B. S. Margaret
Department of Microbiology, University of Maryland School of Dentistry, Baltimore 21201.
Eubacterium yurii subsp. yurii is an anaerobic, gram-positive rod. On
isolation E. yurii forms cellular arrangements resembling test-tube brushes
(TTB). Although TTB decreased in size and number on repeated laboratory
subculture in enriched media, media poor in available iron enhanced
formation of these. Plasmids were not demonstrated, even after
chloramphenicol enhancement. To characterise the nature and possible
physiological roles of the structures of the TTB, they were examined by
transmission electronmicroscopy (TEM) with thin-section, negative-staining,
shadow-casting, freeze-etching and freeze-fracturing techniques, and by
scanning electronmicroscopy (SEM). Previous studies by phase-contrast
microscopy revealed an amorphous core, the size of which varied in direct
proportion to the number of associated bacterial cells. Thin sections of
the TTB showed a gram-positive cell wall with additional surface layers.
Negative staining, shadow casting and freeze etching revealed a surface
layer comprising subunits in tetragonal array (P4 symmetry). Shadow casting
showed also that the outermost layer of the cells was composed of fibrillar
structures closely associated with but distinct from, the tetragonal layer.
The fibrils extended from the cell surface in clumps or strands. The
presence of these fibrils was confirmed by the freeze-fracture technique
and SEM. Chemical analysis of the core material of the TTB showed it to be
low in carbohydrate (0.06%) and protein (0.2%). Energy-dispersive X-ray
spectrometry showed that the core was composed mostly of iron.(ABSTRACT
TRUNCATED AT 250 WORDS)
