Metagenomic analysis of the microbiomes in ruminants and other herbivores

Many conceptual breakthroughs in the life sciences would not have been possible without first developing techniques and instrumentation to investigate biological processes and molecules. In 1995, The Institute for Genomic Research (TIGR) completely sequenced, assembled and published the fist genome of a free-living organism, that of Haemophilus influenzae Rd. This milestone in scientific achievement has allowed microbiologists to progress from a reductionist approach of studying one gene at a time to the examination of microbial biology from an organismal perspective, using a combination of existing and newly developed (bio)chemical and computational (in silico) approaches. These fields of investigation are often defined with an 'omics' suffix. Hence, genomics refers to the holistic examination of the genetic blueprint that a microbe has acquired, at that point in evolutionary time, to support its lifestyle. Transcriptomics, proteomics and metabolomics refer to a similar level of analysis at the RNA, protein and metabolite levels, respectively. Furthermore, the latest advances in sequencing technologies and cloning vectors better enable a detailed examination of the structure and function of microbial communities, including those organisms that cannot readily be cultured, and we refer to the integrative use of the following methods as the basis of an emerging scientific discipline referred to as metagenomics: 1. Bacterial artificial chromosome and fosmid cloning technologies: Community genomic DNA is cloned in large fragments (>50-150 kilobases [kb]) to create libraries of bacterial artificial chromosomes (BACs), or smaller fragments (∼40 kb) are cloned into fosmid vectors. These libraries can then be screened by DNA- and activity-based screens for genes encoding any number of particular functions including hydrolytic and other enzymes central to schemes of carbon sequestration. 2. High throughput DNA sequencing and bioinformatics: Both BAC and fosmid libraries and whole genomes of select bacteria can be sequenced, and function inferred, in relatively short periods of time by using high throughput sequencing systems and bioinformatics. 3. Use of small subunit ribosomal RNA as a measure of biodiversity: An extensive database of RNA sequences supports both PCR- and hybridization-based methods of assessing microbial diversity and population dynamics. Through cloncal frequencies, the relative population sizes can be estimated