Effect on Rumen Bacteria of Methionine Hydroxy Analog and Sulfur-Containing Amino Acids, in Vitro

Abstract

Summary Fermentation of glucose by rumen bacteria utilizing urea as the only source of nitrogen was carried out with or without MHA. The logarithmic growth rate was observed to increase about 2.5 times due to MHA. The lag phase was markedly stimulated in regard to bacterial N synthesis but not to total bacterial dry matter production. Bacterial activity generated a more negative redox potential than MHA making it improbable that MHA functioned as a reducing agent aiding in the anaerobiosis of the medium. The free hydroxyl group or the Ca salt of MHA were not essential for the stimulatory effect of MHA on bacterial growth. Inorganic sources of sulfur or amino acids other than the sulfur-containing amino acids did not have a growth-stimulating effect as measured at 4.5 hr of fermentation. Cystine, cysteine and methionine individually stimulated bacterial growth similar to that of MHA. These observations indicated that any of the sulfur-containing amino acids or MHA can be rapidly converted to the other sulfur-containing amino acids, but the synthesis of the sulfur-containing amino acids from inorganic sulfur is a rate-limiting process for growth of rumen bacteria metabolizing a readily available carbohydrate.