Do. Krause et Jb. Russell, AN RIBOSOMAL-RNA APPROACH FOR ASSESSING THE ROLE OF OBLIGATE AMINO ACID-FERMENTING BACTERIA IN RUMINAL AMINO-ACID DEAMINATION, Applied and environmental microbiology, 62(3), 1996, pp. 815-821
Ruminal amino acid degradation is a nutritionally wasteful process tha
t produces excess ruminal ammonia. Monensin inhibited the growth of mo
nensin-sensitive, obligate amino acid-fermenting bacteria and decrease
d the ruminal ammonia concentrations of cattle, 16S rRNA probes indica
ted that monensin inhibited the growth of Peptostreptococcus anaerobiu
s and Clostridium sticklandii in the rumen, Clostridium aminophilum wa
s monensin sensitive in vitro, but C. aminophilum persisted in the rum
en after monensin was added to the diet. An in vitro culture system wa
s developed to assess the competition of C. aminophilum, P. anaerobius
, and C. sticklandii with predominant ruminal bacteria (PRE), PRE were
isolated from a 10(8) dilution of ruminal fluid and maintained as a m
ixed population with a mixture of carbohydrates, PRE did not hybridize
with the probes to C. aminophilum, P. anaerobius, or C. sticklandii.
PRB deaminated Trypticase in continuous culture, but the addition of C
. aminophilum, P. anaerobius, and C. sticklandii caused a more-than-tw
ofold increase in the steady-state concentration of ammonia, C. aminop
hilum, P. anaerobius, and C. sticklandii accounted for less than 5% of
the total 16S rRNA and microbial protein. Monensin eliminated P. anae
robius and C. sticklandii from continuous cultures, but it could not i
nhibit C. aminophilum. The monensin resistance of C. aminophilum was a
growth rate-dependent, inoculum size-independent phenomenon that coul
d not be maintained in batch culture, On the basis of these results, w
e concluded that the feed additive monensin cannot entirely counteract
the wasteful amino acid deamination of obligate amino acid-fermenting
ruminal bacteria.