Introduction
The high-altitude (HA) area in the Karakoram range has typical environmental challenges, such as low oxygen pressure, temperature, humidity, high radiation and dry weather etc., leading to series of physiological and metabolic disorders1,2 . In addition, change in the diet includes high fiber and low protein products as major portion of diet, while consumption of vegetables and fruits is significantly reduced. Such places are mainly populated with natives, personnel on duties and researchers. Several associations between chronic human diseases including inflammatory bowel disease (IBD) like Crohn’s disease, some extra-intestinal disorders including asthma, metabolic syndrome, allergies, cardiovascular disease, and obesity 3,4,5, , altered gut microbiota constitution and its functions have been reported in last few years6,7 . At least 30% of sojourners from low land report adverse effects at HA including cardiac, respiratory & neurological symptoms, joint pains, headache, nausea, vomiting, bloating and IBD. Little work has been done on the effect of HA hypoxia on digestive system in either patients with altitude illness or in healthy individuals. In fact, symptoms of digestive system such as anorexia, loss of appetite, stomach/abdominal pain, constipation, epigastralgia, heart burn, dyspepsia, vomiting, diarrhea, hematemesis, piles and peptic ulcers are frequently reported in mountaineers and altitude sojourners8,9,10,11,12 . Moreover, epidemiological and clinical studies suggest that gastro Intestinal bleeding (GIB) is not uncommon at HA, and is often life-threatening13,14 . The problems could be due to the release of host metabolites causing inflammation or the interaction between the host and gut microflora14,15,16 .
Exciting time to study the body associated microbes and the human microbiota, consisting of 100 trillion bacteria along its 400m2 surface area, encoding 100fold more genes than our own genome17 . The in-depth analysis of the microbes make it to realize their influence on human physiology in different areas to characterize the global presence of microbial diversity under different environments and dietary habits. It is reported that the microbial diversity in the gastrointestinal tract plays a crucial role in host physiology, including involvement in nutrient metabolism and gut barrier18 . However microbiome composition driving factors are not fully understood yet, due to several factors including limited sample size, inconsistent DNA extraction and varied sequencing methods19,20,21 . Various reports support the involvement of environment, genetics, antibiotic usage22 and lifestyle factors including diet23,24,25 . Even short exposure to HA can alter the composition of gut microbiota26,27 . Li and Zhao28 and Li et al29 , have reported contribution of HA, genetics and dietary factors in Tibetan and Chinese Han groups in shaping gut microbiota. Overall gut microbiome has been investigated in some Indian tribal populations irrespective of their ethnicity and dietary habits20 . Das et al30 compared Indian urban and rural population at 228m with HA population at 3500m, with respect to their dietary habits and geographies. Study performed on western Indian population at 153m compared to other geographies revealed a distinct taxonomic and functional niche31 .
To the best of our knowledge there has been no study so far on genome wide changes on human response at extreme altitude and that ours is the first attempt as a comparative analysis on Indian sojourners belonging to the same ethnicity ascending to extreme altitude, to compass the complete meta genomic map and networks involved in extreme altitude (3500 – 5800m) responses. We used 16s rRNA associations with Whole genome sequencing (WGS) applying the same metagenomics DNA extraction & sequencing platform and bioinformatics pipeline to yield not only profiles of bacterial composition and diversity, but also estimate the functional potential of the microbiome32 . For quantifying bacterial species abundance and intra-species genomic variation we used MIDAS, a computational pipeline, followed by novel strain level analysis by METABET2 approach to quantify gene content of prevalent bacterial species and identified significant intra species population composition associated with environmental factors at extreme altitudes. The findings revealed striking microbial dysbiosis proving important to shed light on human acclimated processes and prevention of the physiological changes associated with it at HA. It is expected that besides classifying the gut microbial repertoire, particularly going down to strain variation at nucleotide level and differences in gene content, may provide crucial information in deciphering important insights in correlating the structure of gut microbiome, microbial pathogenicity, various metabolic disorders and host adaptation of pathogens33 or other related microbial conversions and outbreaks34,35 at high and extreme altitudes.