Tryptophan biosynthesis and production of other related compounds from indolepyruvic acid by mixed ruminal bacteria, protozoa, and their mixture in vitro

Tryptophan (Trp) biosynthesis and the production of other related compounds by mixed ruminal bacteria (B), protozoa (P), and their mixture (BP) in an in vitro system were quantitatively investigated by using 1 mw of indole-3- pyruvic acid (IPA) as substrate. Ruminal microorganisms were anaerobically incubated at 39 degrees C for 12 h, Trp and other related compounds in both the supernatants and the microbial hydrolyzates of the incubation were ana lyzed by HPLC. As a whole, about 334, 440, and 436 mu m of Trp were produce d from IPA in 12 h by B, P and BP suspensions, respectively. In the B suspe nsion, a greater portion of synthesized Trp (242 mu m) from IPA was accumul ated as free form in the medium, whereas a large amount of Trp (92 mu m) wa s incorporated into cell protein in a 12-h incubation. On the other hand, i n the P suspension, a large amount of Trp (475 mu m) from IPA was also foun d as free form in the supernatant in a 12-h incubation. Protozoa did not in corporate Trp into cell protein, but they liberated endogenous Trp (34 mu m ) into the medium. The net productions of Trp from IPA were 344.3 and 447.7 mu mol/g of microbial nitrogen in 12 h by 6 and P suspensions, respectivel y. The ability of P to synthesize Trp from IPA was about 30% higher than th at of 6 in 12 h, Trp produced from IPA by B, P, and BP suspensions were sim ultaneously degraded into its related compounds, and among them, indoleacet ic acid (IAA) was a major product found in all microbial suspensions. Produ ctions of IAA were 124, 25, and 99 mu m from IPA in 12 h by B, P, and BP su spensions, respectively. The formation of indolelactic acid (ILA) from IPA was observed for the first time in all microbial suspensions, and it was ab out 84, 24, and 54 mu m in 12 h by B, P, and BP respectively. Higher IAA an d ILA productions were observed in B when compared with P A small amount of skatole (SKT) (26 mu m) was produced from IPA in B, whereas a sizable amou nt of SKT (38 mu m) was found in BP after a 12-h incubation, p-Cresol (CRL) was also produced from IPA by both B (43 mu m) and BP (65 mu m) suspension s in 12 h, and this is also the first discovery to show the formation of CR L from IPA by B and BP suspensions. BP suspension was more active to produc e both SKT and CRL from IPA, though P suspension has no ability to produce either SKT or CRL from IPA during a 12-h incubation.