M. Morrison et Ri. Mackie, NITROGEN-METABOLISM BY RUMINAL MICROORGANISMS - CURRENT UNDERSTANDINGAND FUTURE PERSPECTIVES, Australian Journal of Agricultural Research, 47(2), 1996, pp. 227-246
This review presents an outline of our current understanding of rumina
l nitrogen metabolism from three perspectives: proteolytic microorgani
sms and their enzymes, intraruminal recycling of microbial protein, an
d enzymes of ammonia assimilation. Some of the pending advances and fu
ture research opportunities in these areas are also discussed. The 'sm
ugglin' concept appears to offer the potential to inhibit peptide-util
izing bacteria selectively in the rumen, as demonstrated by initial st
udies with Prevotella ruminicola. The relative contributions of protoz
oa-, bacteriophage-, and self-mediated lysis of bacteria to intrarumin
al recycling of microbial protein are not yet quantified, and further
efforts to understand the biology and dynamics of ruminal bacteriophag
e and protozoa populations are warranted. In Ruminococcus flavefaciens
and Prevotella ruminicola, glutamate dehydrogenase (GDH) appears to b
e the predominant route of ammonia assimilation irrespective of ammoni
a concentration, and peptides modulate GDH activity in P. ruminicola.
The physiological basis behind the difference between optimal ammonia
concentrations for ruminal fibre digestion and microbial protein synth
esis remains unclear. Molecular biology techniques extend beyond their
application in pursuit of the 'superbug' concept, by offering new and
exciting opportunities to understand better microbial physiology, div
ersity, and ecology. Fundamental research in these areas must be conti
nued if further advances in feed utilization and nutrient retention ar
e to be realized.