Tryptophan biosynthesis and production of other related compounds from indole and L-serine by mixed ruminal bacteria, protozoa, and their mixture in vitro

(T)ryptophan (Trp) biosynthesis and production of other related compounds f rom 1 mM each of indole (IND), L-serine (Ser), and IND plus Ser by mixed ru minal bacteria (B), protozoa (P), and their mixture (BP) in an in vitro sys tem were quantitatively investigated. Ruminal microorganisms were anaerobic ally incubated at 39 degrees C for 12 h. Trp and other related compounds pr oduced in both the supernatants and microbial hydrolyzates of the incubatio n were analyzed by HPLC. B, P, and BP suspensions were not able to produce Trp when incubated with only IND or Ser. Appreciable amounts of Trp (9.8, 3 .1, and 6.6% of substrate) were produced from IND plus Ser after 12 h by B, P, and BP suspensions, respectively. Trp produced from IND + Ser in B was found only in the hydrolyzate, whereas it was found in the medium as a free form in P. after a 12-h incubation period. Rumen bacteria and protozoa wer e separately demonstrated for the first time to produce Trp from IND plus S er, and the ability of P to produce Trp from IND plus Ser was about one-thi rd that of B in 12 h. Trp produced from IND plus Ser by B, P, and BP suspen sions was simultaneously degraded into its related compounds, and, among th em, indoleacetic acid (IAA) was a major product found in B. Production of I AA was 4.3, 0.3, and 3.2% of IND in 12 h by B, P, and BP suspensions, respe ctively. A small amount of skatole (SKT) (1.1 and 2.5% in B and BP, respect ively) and p-cresol (CRL) (2.4 and 3.4% in B and BP, respectively) were als o produced from IND plus Ser during 12-h incubation. P suspension produced no SKT or CRL from IND plus Ser in 12-h incubation. These results suggested , for the Gst time that both rumen bacteria and protozoa have an ability to produce Trp, from IND plus Ser, and the ability was higher in B than in P. The ratios of Trp produced From IND plus Ser to that from indolepyruvic ac id by B, P, and BP were 1:3.4, 1:14.2, and 1:6.6 during 12-h incubation per iod. From these results, the degree of importance of producing Trp from IND plus Ser in the rumen was indicated.