Rare Biosphere in Human Gut: A Less Explored Component of Human Gut Microbiota and Its Association with Human Health

With the advent of next-generation sequencing technologies, we are able to ascertain the vast microbial diversity of various habitats. These studies have led to the discovery of presence and persistence of microbial communities that are extremely low in the abundance. These rare microbial taxa in soil and marine environments are known to act as seed-bank for the organisms that are waiting for the favorable conditions to make their move. The human body is one of the diverse ecosystems known to us supporting the growth of myriads of microbes in or on our body. Studies in the last decade or so have significantly contributed to our understanding of the involvement of these human-associated microbes with our health and diseases. So far, the studies on human gut microbiota have focused largely on dominated microbial species, and the information about the rare taxa associated with the human body is still lurking. This chapter provides evidence that microbes from the three domains of life (bacteria, archaea, and eukarya) existing in the gut have the rare components relevant to human health. Hence, we advocate the need for more studies concerning the rare taxa present in the human gut and their association with the general well-being.