Biomedical Research 2012 Volume 23 Issue 1 Biomedical Research 2012; 23 (1): 9-21 Review article Host-microbial interaction in the mammalian intestine and their metabolic role inside Dipendra Raj Pandeya 1,2 , Roshan D’Souza 1 , Md. Mashiar Rahman 1 , Shahina Akhter 1 , Hyeon-Jin Kim 3 , Seong-Tshool Hong 1* 1 Laboratory of Genetics, Department of Microbiology and Immunology, Institute of Medical Science, Chonbuk National University Medical School, Chonju, Chonbuk 561-712, South Korea 2 Department of Biochemistry, Nepal Army Institute of Health Sciences, Sanobharayng, Kathmandu, Nepal 3 JINIS BDRD Institute, JINIS Biopharmaceuticals Co, 3700 Wilshire Blvd, Los Angeles, California, USA Abstract The mammalian gut has coevolved over millions of years with a vast consortium of mi- crobes, which were physically, intimately and densely associated with our body. From birth, this population is in continuous and intimate contact with intestinal tissues. Recent results indicate that indigenous bacteria play a crucial inductive role in gut development during early postnatal life. These findings have revealed that the mammalian intestine is poised for interaction with its prokaryotic partners, which are essential for its normal development. During their coevolution, the bacterial microbiota has established multiple mechanisms to influence the eukaryotic host, generally in a beneficial fashion, and maintain their stable niche. The prokaryotic genomes of the human microbiota encode a spectrum of metabolic capabilities beyond that of the host genome, making the microbiota an integral component of human physiology. Gaining a fuller understanding of both partners in the normal gut- microbiota interaction may shed light on how the relationship can go awry and contribute to a spectrum of immune, inflammatory, and metabolic disorders and may reveal mechanisms by which this relationship could be manipulated toward therapeutic ends. This review pro- vides a brief overview of this exciting, emerging field. Keywords: Microbiota, postnatal, coevolution, eukaryotic, prokaryotic, metabolic Accepted November 16 2011 Introduction Prokaryotic organisms can exist in intimate and continu- ous contact with members of the eukaryotic kingdom. The implications of this statement reflect an emerging theme in the life sciences that has recently come to the forefront of our general view of multicellular plants and animals – that microbes may affect our biology in profound and perhaps previously unsuspected ways. It may be surpris- ing to learn that the human gastrointestinal tract is home to 10 14 bacterial organisms [1]. In fact, there are more bacteria in the gut than there are somatic cells in the body. These resident bacteria are referred to as commensal mi- crobiota and their arrival during the first few postnatal days’ sets up a symbiotic association that is necessary and crucial to normal physiology. The complex and dynamic ecosystem of indigenous microbes residing in the intes- tine may collectively be referred to as the intestinal mi- crobiota. This lifelong association is essential to host pathogen defence and plays an important role in nutrient uptake and metabolism [2]. All mammals are born sterile and immediately after birth, they are initiated into a life- long process of colonization by foreign microorganisms that inhabit most environmentally exposed surfaces (such as the skin, mouth, gut and vagina) [3]. From that moment on, humans become and remain colonised by microbes. Nearly every surface of mammals that is exposed to the environment is inhabited by commensal bacteria. There is no better example of such a surface than the colon, which contains an astounding number of bacteria, whereas less has been reported from upper gastro-intestinal tract habi- tats [4]. The thousands of bacteria, fungi and other mi-