Esterase activity of pure cultures of rumen bacteria as expressed by the hydrolysis of p-nitrophenylpalmitate.

Seventy-four strains of rumen bacteria comprising 20 genera were tested for the ability to hydrolyze p-nitrophenylpalmitate (PNPP-C16). This ability was detectable in all cultures tested, but the level of activity was quite variable. Known lipolytic strains of these bacteria showed generally low levels of activity in this assay, which suggests that the hydrolysis of this artificial substrate indicates a general esterase activity and not a lipase activity, as reported in the literature. The highest activity was found to occur in strains known to be feed-particle-associated digesters of starch, pectin and cellulose. In fractionated rumen contents, p-nitrophenylpalmitase activity was largely associated with feed particles. Although the in vivo role of the enzymes that hydrolyze PNPP-C16 remains obscure, it appears that they are primarily of microbial origin, and may be important in hydrolyzing ester bond-containing compounds from plant material.