Culture techniques for ciliate protozoa from the rumen: Recent advances and persistent challenges

Ciliate protozoa are key members of the microbial community of the rumen. Their study is important to the health and productivity of cattle, which are their hosts. However, there have been persistent challenges in culturing this microbial group in the laboratory. This review will sum up recent advances along with these persistent challenges. Protozoa have been maintained in three types of cultures (ex vivo, in vitro batch, in vitro continuous). Ex vivo cultures are prepared readily from rumen contents by washing away contaminating cells (e.g., bacteria). They have been useful in making basic observations of metabolism, such as which types of fermentation products protozoa form. However, these cultures can be maintained for only short periods (minutes or hours). In vitro batch and in vitro continuous cultures can be used in longer experiments (weeks or longer). However, it is not currently possible to maintain protozoa in these cultures unless bacteria are also present. We conclude the review with a protocol for preparing ex vivo cultures of protozoa. Our protocol has been standardized and used successfully across animal diets, users, and institutions. We anticipate this review will prepare others to culture rumen ciliate protozoa and reach new insights into this important microbial group.