Growth characteristics on cellobiose of three different anaerobic fungi isolated from the ovine rumen

Abstract

Three morphologically different anaerobic fungi, a Neocallimastix sp. strain (LM-1), a Piromonas sp. strain (SM-1), and a Sphaeromonas sp. strain (NM-1), were isolated from the rumens of sheep. Growth studies were conducted with each isolate in batch cultures by using an anaerobic semidefined medium that lacked ruminal fluid and contained 0.5% cellobiose. Cultures were incubated for periods of up to 10 days, and fungal growth was assessed at regular intervals by dry weight measurements. Samples of fungal biomass were also analyzed for cell-associated protein and, after acid hydrolysis, for chitin as hexosamine. The isolates produced similar yields of dry weight and contained similar amounts of protein. However, strain LM-1 grew at a higher rate and contained less than half the level of chitin compared with the other two isolates. There were high positive correlations between chitin and protein for all three fungi, but comparisons of these parameters with dry weights were affected by the presence of variable amounts of storage carbohydrate. The amount of storage carbohydrate reached maximum levels in strain LM-1 during mid-growth phase and then quickly declined thereafter. When dry weight yields for strain LM-1 were adjusted for changes in storage carbohydrate, high positive correlations were obtained between dry weight and protein or chitin. The storage carbohydrate was probably an alpha-1,4-glucan with alpha-1,6 branches.