Some factors controlling the attachment of the rumen holotrich protozoa Isotricha intestinalis and I. prostoma to plant particles in vitro.

The rumen holotrich protozoa Isotricha intestinalis and I. prostoma showed chemotaxis to sucrose, glucose and fructose. They attached themselves, by means of an organelle on the anterior cell surface, to particulate sources of these carbohydrates provided soluble protein was present in the medium. The concentration of protein eliciting attachment varied with the species and the state of nutrition of the cell, but was between 20 and 150 microgram ml-1. Attachment occurred only if the concentration of carbohydrate, at its source, exceeded the chemotaxis threshold concentration (50 micrometer for sucrose) and if it was less than 1 mM. At concentrations exceeding 1 mM, indiscriminate attachment to gas-liquid and solid-liquid interfaces occurred, provided the protein concentration was high enough to elicit attachment. In the rumen, soluble carbohydrates diffusing from food particles may attract the protozoa which attach themselves to the particles in the presence of soluble plant protein at less than 20 microgram ml-1; these conditions exist in the host animal soon after feeding when fed infrequently. The attachment mechanism may confer an ecological advantage on the Isotricha spp. over other rumen organisms dependent on soluble carbohydrates as energy and carbon sources.