Metagenomic study of the Large Intestinal Bacterial Flora in South India

Abstract

In South Indian healthy rural adult population, 6 phyla, 25 families and 58 genera were detected using culture-independent cloning-sanger sequencing approach. The abundant phyla were Firmicutes followed by Proteobacteria. The Firmicutes: Bacteroidetes ration in adult population was 4.0. The abundant genera in South Indian rural adults were Escherichia/Shigella, Faecalibacterium, Oscillibacter and Klebsiella. The number of phyla increased with age in childhood through adolescents (i.e., from post-weaning, pre-school to school going). Firmicutes and Bacteroidetes were equally distributed in the post-weaning children. Phylum Firmicutes followed by Proteobacteria were abundant in preschool and school going groups. Less variability of genera was observed in post-weaning group compared to preschool and school going groups. Firmicutes: Bacteroidetes ratio increased with age with 1.0, 2.4 and 5.1 in post-weaning, preschool and school going groups respectively. The abundant genera in post-weaning group were Prevotella and Bacteroides. Genera Gemmiger, Bacteroides, Dialister and Escherichia/Shigella were abundant in preschool children and Genera Escherichia/Shigella, Prevotella, Acetivibrio, Allobaculum and Klebsiella were more prevalent in school going adolescents. In the South Indian rural elderly population over 65 years of age, 6 phyla, 25 families and 61 genera were detected. The phylum Bacteroidetes was dominant followed by Firmicutes. Archaea belonging to 2 phyla and 5 genera were detected in different age groups. Euryarchaeota and Crenarchaeota were the two genera detected. Euryarchaeota formed the most abundant phylum. Methanobrevibacter was the most prevalent genus among all the age groups accounting for 98% in neonates, 96% in post-weaning, 100% each in preschool, school going and adult population. Interindividual and intergroup variability was observed between rural and tribal adults. Phylogenetic analysis suggested evolution of these two groups from a common ancestor.