General Microbiology - Schlegel, H. 1987

Prokaryotes: A Systematic Review
Gram-negative anaerobic bacteria (Group 9)

Gram-negative anaerobic rods and vibrio-shaped Bacteria are widespread in anaerobic ecosystems. The Study of these bacteria began relatively late; it turned out that they numerically dominate the intestinal tract, the rumen of ruminants, and putrid sludge. This is primarily due to their sensitivity to oxygen and requirement for СО₂. The rods are either non-motile or motile, possessing peritrichous flagella.

Species of the genus Bacteroides (B. fragilis, B. succinogenes) rank among the dominant Gram-negative bacteria in human feces. Fecal matter can consist of up to 30% (by dry weight) bacteria. A 1 g sample of wet mass contains 10¹⁰ Representatives of the genus Bacteroides, 10⁶–10⁸ coliform bacteria, and approximately the same number of streptococci and lactobacilli. The numerical ratio of strictly anaerobic bacteria to facultative anaerobes is roughly 40:1. All species of the genus Bacteroides rely exclusively on Fermentation, converting glucose into succinate, acetate, formate, lactate, and other acids.

The genus Fusobacterium derives its name from the spindle-like shape of its Cells; these are relatively long rods. A characteristic feature of the genus is that butyrate is the primary fermentation product. Various species are found in the intestine and feces, as well as in the Oral Cavity.

Leptotrichia forms filaments up to 200 µm in length that lack flagella. L. buccalis occurs in the oral cavity. DL-lactate is the principal product of glucose fermentation.

Vibrio-shaped bacteria closely related to these three genera will be discussed in Section 3.13 (Selenomonas, Butyrivibrio, Succinivibrio) or, depending on their ecological and metabolic characteristics, in other sections (Desulfovibrio in Section 9.2, Selenomonas in Section 8.3, Butyrivibrio in Section 8.5).