A rumen strain of Megasphaera elsdenii was grown on glucose and lactat
e in monensin-free and monensin-supplemented medium (10 mg/L). Monensi
n had no effect on growth rate, growth yields, metabolic pattern and c
omposition of cells. Growth yields of dry matter and protein were high
er in cultures supplied with glucose than in cultures supplied with la
ctate. The bacterium compensated the lower gain of energy from ferment
ation of lactate by rapid utilization of this substrate. Cells grown o
n glucose contained more saccharide and less protein than lactate-grow
n cells.