The interaction of the direct dye Congo red with intact beta-D-glucans provides the basis for a rapid and sensitive assay system for bacterial strains possessing beta-(1 leads to 4),(1 leads to 3)-D-glucanohydrolase, beta-(1 leads to 4)-D-glucanohydrolase, and beta-(1 leads to 3)-D-glucanohydrolase activities. A close correspondence was observed between cellulolytic activity and beta-(1 leads to 4)-D-glucanohydrolase and beta-(1 leads to 4),(1 leads to 3)-D-glucanohydrolase activities in isolates from the bovine rumen. Many of these isolates also possessed beta-(1 leads to 3)-D-glucanohydrolase activity, and this characteristic may have taxonomic significance.

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The species composition, distribution, and biodiversity of the bacterial communities in the rumen of cows fed alfalfa or triticale were investigated using 16S rRNA gene clone library analyses. The rumen bacterial community was fractionated and analyzed as three separate fractions: populations in the planktonic, loosely attached to rumen digesta particles, and tightly attached to rumen digesta particles. Six hundred and thirteen operational taxonomic units (OTUs) belonging to 32 genera, 19 families, and nine phyla of the domain Bacteria were identified from 1014 sequenced clones. Four hundred and fifty one of the 613 OTUs were identified as new species. These bacterial sequences were distributed differently among the three fractions in the rumen digesta of cows fed alfalfa or triticale. Chao 1 estimation revealed that, in both communities, the populations tightly attached to particulates were more diverse than the planktonic and those loosely attached to particulates. S-Libshuff detected significant differences in the composition between any two fractions in the rumen of cows with the same diet and between the communities fed alfalfa and triticale diets. The species richness estimated for the communities fed alfalfa and triticale is 1027 and 662, respectively. The diversity of the rumen bacterial community examined in this study is greater than previous studies have demonstrated and the differences in the community composition between two high-fiber diets have implications for sample selection for downstream metagenomics applications.

The previously described hybrid plasmid pC7 which carries lacI+ O+Δ(Z)Y+ A+ on a 12.3 × 106‐Mr DNA fragment [Teather et al. (1978) Mol. Gen. Genet. 159, 239–248] was partially digested with the restriction endonuclease EcoRI under conditions reducing the recognition sequence to ↓ d(A‐A‐T‐T) and ligated to the vector pBR322. lacY‐carrying inserts of various sizes (Mr, 1.5–4.7 × 106) were obtained. Hybrid plasmid pTE18 (2300‐base‐pair insert) carries part of the I (repressor) gene, the promotor‐operator region, part of the Z (β‐galactosidase) gene, the Y (lactose carrier) gene and part of the A (transacetylase) gene. Upon induction of pTE18‐harbouring strains the Y‐gene product is expressed at a nearly constant rate for several generations and accumulates to a level of 12–16% of the total cytoplasmic membrane protein. Integration into the membrane leads to active carrier as judged by binding and transport measurements.

McAllister, T. A., Beauchemin, K. A., Alazzeh, A. Y., Baah, J., Teather, R. M. and Stanford, K. 2011. Review: The use of direct fed microbials to mitigate pathogens and enhance production in cattle. Can. J. Anim. Sci. 91: 193–211. Direct-fed microbials (DFM) have been employed in ruminant production for over 30 yr. Originally, DFM were used primarily in young ruminants to accelerate establishment of the intestinal microflora involved in feed digestion and to promote gut health. Further advancements led to more sophisticated mixtures of DFM that are targeted at improving fiber digestion and preventing ruminal acidosis in mature cattle. Through these outcomes on fiber digestion/rumen health, second-generation DFM have also resulted in improvements in milk yield, growth and feed efficiency of cattle, but results have been inconsistent. More recently, there has been an emphasis on the development of DFM that exhibit activity in cattle against potentially zoonotic pathogens such as Escherichia coli O157:H7, Salmonella spp. and Staphylococcus aureus. Regulatory requirements have limited the microbial species within DFM products to organisms that are generally recognized as safe, such as lactic acid-producing bacteria (e.g., Lactobacillus and Enterococcus spp.), fungi (e.g., Aspergillus oryzae), or yeast (e.g., Saccharomyces cerevisiae). Direct-fed microbials of rumen origin, involving lactate-utilizing species (e.g., Megasphaera elsdenii, Selenomonas ruminantium, Propionibacterium spp.) and plant cell wall-degrading isolates of Butyrivibrio fibrisolvens have also been explored, but have not been commercially used. Development of DFM that are efficacious over a wide range of ruminant production systems remains challenging because[0] comprehensive knowledge of microbial ecology is lacking. Few studies have employed molecular techniques to study in detail the interaction of DFM with native microbial communities or the ruminant host. Advancements in the metagenomics of microbial communities and the genomics of microbial–host interactions may enable DFM to be formulated to improve production and promote health, responses that are presently often achieved through the use of antimicrobials in cattle.