The utilization and digestion of cellulose by the rumen ciliate Diploplastron affine

Abstract

Rumen protozoa are known to contribute to fibre digestion, but the fibrolytic enzymes of the majority of ciliate species have been poorly recognised to date. The aims of the study were, first, to determine the influence of crystalline cellulose on the survival and population density of the ciliate Diploplastron affine when cultured in vitro, and second to identify and characterise the protozoal enzymes catalysing the hydrolysis of cellulose. It was found that crystalline cellulose, when added to a culture medium, increased the number of protozoa maintained in vitro. We observed that the bacteria-free ciliates fermented microcrystalline cellulose and produced 43.3 nmol volatile fatty acids/protozoon/h. A cell extract prepared from the bacteria-free ciliates degraded crystalline cellulose in the rate of 11.5 nmol released glucose/mg protein/min, whereas the degradation rates of carboxymethyl-cellulose (CMC), avicel and cellobiose were 343, 6.8 and 145 nmol released glucose/mg protein/min respectively. Two distinct peaks in the activity of relevant enzymes were identified following ion exchange chromatography of the protozoal cell extract and the presence of two different CMC-ases were confirmed by zymographic studies. CMC was mainly degraded to mono- and disaccharides but that some other oligosaccharides were also present. Cellobiose was the only product of avicel digestion.