Ruminal-ciliated protozoa

Rumen protozoa were first reported by Gruby in 1843. Since then efforts in understanding the function of these organisms have increased, albeit at a slower rate than efforts applied to understand the rumen bacteria, due to the increased complexity of working with rumen protozoa. Rumen protozoa belong mainly within the phylum Ciliophora and belong to one of the two orders, Vestibuliferida and Entodiniomorphida (often referred to as the holotrich and entodiniomorphids, respectively). Although they are less enumerate than rumen bacteria they are larger in size and account for anywhere between 5 and 50% of microbial biomass in the rumen. It is also known that ruminants possess defined populations of rumen protozoa (types A, B, O and K), the exact reason being unknown, although host genomics and/or predatory behaviour (i.e. protozoa feeding on other protozoa) have been implicated. The rumen protozoa possess two types of nuclei, the micronuclei and the macronuclei, with the micronuclei behaving as a germline nucleus which is not involved in RNA transcription, whereas the macronuclei undergo RNA transcription for vegetative growth.