Molecular methods for studying methanogens of the human gastrointestinal tract: current status and future directions.

Until recently, human gut microbiota was believed to be colonized by few methanogenic archaeal species. Much higher microbial diversity within the human gut was revealed by the use of molecular approaches as compared to routine microbiological techniques, but still, a lot remains unknown. Molecular techniques has the advantage of being rapid, reproducible, and can be highly discriminative as compared to conventional culturing methods. Some of them provide both qualitative and quantitative information. However, the choice of method should be taken with care to avoid biases. The advent of next-generation sequencing gives much deeper information from which functional and ecological hypotheses can be drawn. In this review, molecular techniques that are currently used together with their possible future developments to study gut methanogenic communities are indicated along with their limitations and difficulties that are encountered during their implementation. Moreover, the high amount of metagenomics data from the human gut microbiome indicate that this environment could be a paradigm for new directions in methanogen diversity studies and help to develop new approaches for other environments as well. Concerning humans, this should help us to better understand the possible association of methanogens with some of the diseased conditions and their peculiar distribution among age groups in human.