Ecophysiology of cellulolytic bacteria in the rumen
The rumen microbial populations involved in the degradation of barley straw and clover/ryegrass forage during incubation in sacco were studied by the analysis of microbial phospholipids. The results suggested that the adherent populations differed from those in the liquid phase of the rumen contents, and that the microorganisms attached to barley straw differed from those attched to clover/ryegrass. In addition, the population adherent to barley straw appeared to change during the degradative process. The latter point was supported by observations using the electron microscope. When barley straw was incubated in vitro with Ruminococcus flavefaciens prior to incubation in the rumen, phospholipid analysis suggested that R.flavefaciens persisted during 72 h incubation in the rumen, although as a declining component of the mixed population. Ruminococcus flavefaciens was possibly displaced or other 'free' sites of attachment were occupied by different species. The in vitro incubation of Ruminococcus flavefaciens and Fibrobacter succinogenes on clover/ryegrass and barley straw showed that the presence of F.succinogenes reduced the population size of R.flavefaciens and the degradability of clover/ryegrass suggesting a competitive or antagonist interaction betweeen these species. The analysis of phospholipid marker components and viable counts showed that R.flavefaciens rapidly outgrew F.succinogenes. Ruminococcus flavefaciens and Fibrobacter succinogenes differed in the quantity and nature of the soluble plant components that accumulated in the culture liquids. After training Ruminococcus flavefaciens strain 17 to grow on different forages, adaptation through enhanced substrate degradation was detected when cultures were grown repeatedly on ryegrass. Significant increases in specific xylanase and beta-xylosidase activities were detected. It is concluded that the increase in dry matter solubilization and enzyme activities during prolonged subculture on ryegrass probably resulted from forward mutations.