Selenomonas ruminantium

The bacterium has a rod-shaped structure.

Selenomonas ruminantium was originally placed with the Gram-positive Firmicutes phylum based on its 16S rRNA gene. It was believed to be correct until the flagellar basal test was performed.

The observation of flagella under electron microscope revealed the presence of four rings, a typical sign of gram negative species. Observation of the flagellar basal structure confirms that S. ruminantium has an outer membrane, a characteristic of Gram-negative bacteria . Gram-positive outer membranes or mycomembranes were recently reported for the Gram-positive general Corynebacterium and Mycobacterium, but none of them have flagella.

The tuft of flagella is seen arising from the concave of basal body of S.ruminantium. The movement is achieved by self rotation about the axis of the body by the rotational force exerted by the tuft at the centre. If the polar region to midpoint distance is considered as 50% the tuft is located at the midpoint represented as 50% of the organism.

The bacteria also exhibits polar or lateral flagellar structures depending upon the medium in which they are developed.

Their flagella exhibits polymorphic properties depending upon the environment of the bacteria. Generally the flagellae protruding from all points are clustered around the midpoint. Flagellin is glycosylated.

The bacterial flagella's existence depends upon the pH. The rumen pH is about 5.5 to 7.