In vitro metabolism of phenylalanine by ruminal bacteria, protozoa, and their mixture.

Abstract

An in vitro study was conducted to examine the metabolism of phenylalanine (Phe) by mixed rumen bacteria (B), mixed rumen protozoa (P), and a combination of the two (BP). Rumen microorganisms were collected from fistulated goats fed lucerne cubes (Medicago sativa) and a concentrated mixture twice a day. Microbial suspensions were anaerobically incubated at 39°C for 12 h. Phe and some other related compounds in both supernatants and microbial hydrolysates of the incubations were analysed by HPLC. The net degradation rate (µmollg microbial nitrogen) of Phe in B was about 1.5-fold higher than that in P. Phe was converted mainly into phenylacetic acid (PAA) and unknown compound(s) that presumably involved tyrosine in B, P, and BP during the 12h incubation period. Small amounts of benzoic acid (BZA), and traces of phenylpropionic acid (PPR) and phenyllactic acid (PLA) were also produced from Phe. PAA production in B was found to be higher than that in P, whereas it was significantly higher in BP. Although BZA production was less than one-tenth that of PAA production, it was higher in P than in B and BP. PPR was detected in both B and BP, but not in P. PLA was detected only in B. The production of unknown compound(s) was higher in B than in P and BP.

Effects of salinomycin and vitamin B6 on in vitro metabolism of phenylalanine and its related compounds by ruminal bacteria, protozoa and their mixture.

“…In tryptophan metabolism by rumen B, the production of skatole from indoleacetic acid was completely inhibited by SL, and no tryptophan was found to be produced from indoleacetic acid in the supernatants of the P suspensions with or without SL as reported by Okuuchi et al (1993). The observations of Allison (1965) and Kristensen (1974) reporting the production of Phe from PAA by rumen bacteria were again confirmed in this experiment, though it was also confirmed in our previous study (Amin and Onodera, 1997a). On the other hand, the production of Phe from PAA was shown to be enhanced by B 6 in all the microbial suspensions.…”

“…Phe was converted mainly to PAA, and the production of PAA in B, P and BP suspensions with and without SL and B 6 is shown in Table 3. PAA production from Phe was almost similar to results reported previously (Amin and Onodera, 1997a). In B suspensions without additives, 187 and 284 µmol/g MN (163 and 254 µM) of Phe were converted to PAA, while the production of PAA in the suspensions with SL was inhibited (pϽ0.05) by 70.0 and 72.5% during the 6 and 12 h incubation periods, respectively.…”

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

“…Thus, it is necessary to clarify whether Tyr or its precursor (HPA) can be produced from Phe by rumen microorganisms. Phe has been shown to be deaminated and converted to PAA by rumen bacteria (Van Den Hende et al, 1964;Amin and Onodera, 1997a), rumen protozoa (Coleman, 1967;Amin and Onodera, 1997a) and mixed rumen microorganisms (Patton and Kesler, 1967;Martin, 1973;Amin and Onodera, 1997a). During the studies with [U-14C]L-Phe, Scott et al (1964) observed that most of the radioactivity was present in PAA and slight activity was found in phenylpropionic acid (PPA) and benzoic acid (BZA).…”

“…There is few information about the production of Tyr from Phe by rumen microorganisms. In the study of Phe metabolism by rumen bacteria and protozoa, a relatively large amount of an unknown compound was detected at the same retention time as Tyr on the chromatograms of HPLC (Amin and Onodera, 1997a). However, the compound was not identified as Tyr because the peak of Tyr overlapped with p-hydroxyphenylacetic acid (HPA) by the HPLC method (Amin et al, 1995).…”

“…However, no quantitative data for the production of PAA, PPA or BZA were presented by them. In a recent study, Amin and Onodera (1997a) reported the quantitative productions of PAA and PPA from Phe. They first reported that BZA was produced from Phe by rumen bacteria and also by rumen protozoa, but PPA and phenyllactic acid (PLA) were produced from Phe not by rumen protozoa but by only mixed tureen bacteria.…”