Ba. Cummings et al., IDENTITY AND INTERACTIONS OF RUMEN MICROBES ASSOCIATED WITH DIETARY SULFATE-INDUCED POLIOENCEPHALOMALACIA IN CATTLE, American journal of veterinary research, 56(10), 1995, pp. 1384-1389
To study their role in sulfate reduction, anaerobic bacteria were cult
ured from numen fluid samples of cattle fed high-carbohydrate, short-f
iber diets with and without added sulfate. The steers fed the diet wit
h added sulfate developed polioencephalomalacia. Microbiological metho
ds included colony-type profiles, molybdate sensitivity, presence of d
esulfoviridin, sulfate reduction rates of pure and mixed cultures, and
incubation time effects on sulfate reduction. Colony-type profiles in
dicated decreased diversity, but no relative change in numbers of sulf
ate-reducing bacteria in rumen fluid from cattle fed diets with and wi
thout added sulfate. Thirteen bacterial isolates were selected for fur
ther study on the basis of colony type, sulfate-reducing activity, and
growth in lactate, sulfate, and yeast extract media. Seven of the iso
lates had Desulfovibrio-like characteristics (ie, they were gram-negat
ive, motile rods that reduced sulfate, were inhibited by molybdate, an
d contained the pigment desulfoviridin). The remaining 6 isolates were
gram-negative, nonmotile rods. Four of these released sulfide from cy
steine, and 2 generated only limited amounts of sulfide from sulfate o
r cysteine. The 7 sulfate-reducing isolates generated sulfide in rumen
fluid broth medium at greater rates than those observed in fresh nume
n fluid. Sulfate reduction could be sustained in cultures for prolonge
d incubation times if the gas phase containing hydrogen sulfide was re
placed at frequent intervals. Variations in the amount of sulfate redu
ced by the pure cultures were most pronounced at short incubation time
s. Sulfate reduction was not inhibited in mixed cultures of sulfate-re
ducing and nonsulfate-reducing bacteria.