Decomposition of Soluble Casein by Rumen Ciliate Protozoa

Abstract

Rumen ciliate protozoa are roughly grouped into holotrichs and entodiniomorphs, and it has been assumed that the formar decompose both soluble and insoluble casein but that the latter decompose only insoluble casein.However, it was recently shown that entodiniomorphid protozoa produce extra-cellular proteolytic enzymes and that soluble casein is decomposed by these enzymes.This experiment was conducted in order to re-examine the decomposition of soluble casein by entodiniomorphid and holotrich protozoa.One Holstein cow (5 years-old and weighing about 600 kg) fitted with a rumen fistula was fed daily with a ration consisting of 3 kg of rice straw and 4 kg of concentrate (commercial formula feed, CP 13.5%) and given water adlibitum.Rumen ciliate protozoa were separated into two groups of holotrichs and entodiniomorphs by settling and centrifugation of rumen liquid which was taken through the fistula 1 hour after feeding. Both ciliate groups were suspended in a salt buffer solution. These protozoa suspensions and their sonicated solutions were incubated with or without soluble casein at 39°C, and non protein nitrogen (NPN) in the incubation mediums was measured.The results obtained are summarized as follows: 1) When holotrich protozoa suspension was in cubated with soluble casein, NPN in the medium increased very little within 2 hours. 2) The entodiniomorphid protozoa suspension decomposed soluble casein immedi ately after the start of incubation. 3) The decomposition of soluble casein by holotrich protozoa was evidently detected after 5 hours of incubation. 4) Sonicated preparations of both entodiniomorphid and holotrich protozoa decomposed soluble casein. 5) Decomposition of soluble casein by entodiniomorphid protozoa decreased markedly via starvation for 20 hours, but there was little change in the case of holotrich protozoa. 6) These results suggest that holotrich protozoa would store temporarily soluble casein within their bodies and then decompose it slowly.