Production of tyrosine and other aromatic compounds from phenylalanine by rumen microorganisms

Rumen contents from three fistulated Japanese native goats fed Lucerne hay cubes (Medicago sativa)and concentrate mixture were collected to prepare th e suspensions of mixed rumen bacteria (B), mixed protozoa (P) and a combina tion of the two (BP). Microbial suspensions were anaerobically incubated at 39 degrees C for 12h with or without 1 mM of L-phenylalanine (Phe). Phe, t yrosine (Tyr) and other related compounds in both supernatant and microbial hydrolysates of the incubations were analyzed by HPLC. Tyr can be produced from Phe not only by rumen bacteria but also by rumen protozoa. The produc tion of Tyr during 12h incubation in B (183.6 mu mol/g MN) was 4.3 times hi gher than that in P. One of the intermediate products between Phe and Tyr s eems to be p-hydroxyphenylacetic acid. The rate of the net degradation of P he incubation in B (76.0 mu mol/g MN/h) was 2.4 times higher than in P. In the case of all rumen microorganisms, degraded Phe was mainly (>53%) conver ted into phenylacetic acid. The production of benzoic acid was higher in P than in B suspensions. Small amount of phenylpyruvic acid was produced from Phe by both rumen bacteria and protozoa, but phenylpropionic acid and phen yllactic acid were produced only by rumen bacteria.