Use of 16S-rRNA based techniques to investigate the ecological succession of microbial populations in the immature lamb rumen: Tracking of a specificstrain of inoculated Ruminococcus and interactions with other microbial populations in vivo

The establishment of microorganisms in the rumen is a critical step if rume n manipulation is to be accomplished by use of microbial inoculants. Microb ial populations in the maturing rumen undergo successional changes and, whi le in a state of flux, provide a possible opportunity for the introduction of specific strains of bacteria. While the rumen of the young lamb was matu ring, we measured changes in several microbial populations with 16S-rRNA sp ecific oligonucleotides: Rumincoccus, Fibrobacter, eukaryotes, Gram-positiv e bacteria, the Bacteroides-Porphromonas-Prevotella group, and anaerobic ru men fungi. In this study we repeatedly dosed 15 lambs with approximately 3. 4 x 10(8) to 0.8 x 10(9) Ruminococcus cells dose(-1), twice a week, for 7 w k from 23 d to 63 d of age. Of the five Ruminococcus strains dosed (R. albu s SY3 and AR67, and R. flavefaciens Y1, LP9155, and AR72) the most specific primers (based on 16S rDNA) were obtained for strain SY3. There was an inc rease in the eukaryotic population during dosing, and it was hypothesized t hat protozoal predation contributed to the disappearance of strain SY3. At the end of dosing PCR amplification showed that SY3 were approximately 10(9 ) cells ml(-1), but decreased to below the detection limit of the PCR syste m (8.6 x 10(4) ml(-1)) within 28 d postdosing. These experiments showed tha t fibrolytic populations increased significantly (P < 0.1) above the contro ls during the dosing period and were elevated for several days postdosing. This suggests that dosing of highly fibrolytic bacteria makes more of the f iber available to other organisms able to degrade fiber, and in so doing in creases the overall fibrolytic activity of the rumen. Examination of the su ccession of gram-positive bacteria and the Bacteroides-Porphromonas-Prevote lla group showed a decline in relative abundance as the lambs matured.