Functional Metagenomics from the Rumen Environment—A Review

The rumen microbiome plays an essential role in ruminant physiology, nutrition and pathology as well as host immunity. A better understanding of rumen microbial processes and identification of which populations are responsible for specific functions within the rumen microbiome will lead to better management and sustainable utilization of the available feed base while maintaining a low environmental impact. Recent advance in the culture independent method of microbiology such as metagenomics, unravels potentially the rumen microbial process. There are two basic types of metagenomics studies: Sequence-based and function-based metagenomics. Sequence-based metagenomics involves sequencing and analysis of DNA from environmental samples. Its purpose is to assemble genomes, identify genes, find complete metabolic pathways, and compare organisms of different communities. Whereas functional metagenomics is the study of the collective genome of a microbial community by expressing it in a foreign host usually Escherichia coli (E. coli). It is a promising approach unearthing novel enzymes even from yet to culture rumen microbiota. Further advances in the screening techniques promise vast opportunities to rumen microbiologists, and animal nutritionist. The identification of novel enzyme through functional metagenomics consists of three parts: rumen sample collection; DNA library construction and screening of individual clone. Functional metagenomics was successfully applied to identify different antibiotics, hydrolytic enzymes, antibiotic resistance genes, and many other functions; moreover, it allowed characterization of genes encoding enzymes with a particular activity, which represents completely novel sequence. There are a number of outputs from functionally screened rumen product such as carbohydrate active enzymes (CAZymes) that can break down plant cell walls. Company involved commercialization of metagenomics research such as Syngenta, Genencor International, BRAIN etc., has produced many biological molecules of commercial interest. The aim of this paper is to elucidate functional metagenomics, from rumen environment and its potential for commercial purpose.