The effect of different centrifugation conditions in the isolation of mixed rumen bacteria on their content of nitrogen and diaminopimelic acid: use of duodenal content as raw material

The objective of the present study was, to investigate the effect of varying conditions of differential centrifugation of duodenal content on the isolation of bacteria (B-fraction) and feed particles + protozoa (FP-fraction). The treatments at low-speed centrifugation were as follows: 100 x g/5 min, 400 x g/10 min, 1000 x g/10 min and 2000 x g/10 min, high speed conditions were 30,000 x g/30 min/4 degrees C. The results of three experiments are given. Analytical examination gave similar results for N-contents for all treatments, the mean values being 7.90 +/- 0.27% (n = 12) for B-fractions and 6.53 +/- 0.73% (n = 12) for FP-fractions. Increasing the low-speed from 100 x g to 2000 x g lead to increasing DAP-contents and decreasing N:DAP-ratios of the bacterial isolates, the values being 2.43, 3.02, 3.22 and 3.39 mg DAP/g DM and 32.0, 27.4, 25.0 and 23.0 N:DAP-ratio. Decreased isolation of bacterial material in the B-fraction in conjunction with increased incorporation in the FP-fraction resulted in rising the speed of the low speed centrifugation. The rates of loss of DAP, measured by comparison with the total amount were 10, 32, 48 and 70% respectively. It was concluded to prefer the isolation of bacteria from rumen fluid.