Diversity of Ruminococcus strains: a survey of genetic polymorphisms and plant digestibility


Dr D.O. Krause, CSIRO Tropical Agriculture, Long Pocket Laboratories, Private Bag 3, Indooroopilly, Queensland 4068, Australia (e-mail: denis.krause@tag.csiro.au).


Twenty-three strains of Ruminococcus isolated from ruminants were assessed for digestive ability on different plants and purified cellulose. Genetic diversity was assessed by ERIC, REP and 16–23S rDNA spacer polymorphisms. All ruminococci could be typed by ERIC, REP or 16–23S rDNA spacer, but all three typing methods had to be used in concert to differentiate closely related strains. Digestibility of lucerne (Medicago sativa), rhodes grass (Chloris gayana) and spear grass (Heteropogon contortus) were assessed. Dry matter (DM) digestibility was highly correlated (> 0·93) with neutral detergent fibre (NDF) digestibility, but cellulose disc digestibility was a poor indicator of DM and NDF digestibility. Studies demonstrate the wide variation in ability of ruminococci to digest forages, and some recently isolated strains (Y1, LP-9155, AR67, AR71 and AR72) were superior to reference strains (FD-1 and Ra8). Multivariate analysis showed that groupings derived from genotyping data closely resembled those determined by digestibility data. This study indicated that ruminococci are diverse in digestive ability and genotype, and this diversity suggests that there may be highly fibrolytic strains in nature that could be utilized for animal production.