Earthworms are important members of the soil macrofauna that play a significant role in soil structure and fertility. However, there is scanty information on the earthworm gut microbial flora and their metabolic potential. In the present study, the diversity of the microbial community and their metabolic potential from the gut content of four different earthworm species from Indo-Myanmar Biodiversity Hotspot were collected and identified by standard methods. The microbial diversity and their metabolic potential were assessed by high throughput sequencing of V3-V4 region of 16S rRNA using Illumina technology. Analysis of microbial diversity was performed by QIIME software package v.1.8.0 with their metabolic potential by PICRUSt (v1.1) software package. A total of 3,36,047 processed sequences were obtained that generated 3686 operational taxonomic units (OTUs). Major bacterial phyla identified were Proteobacteria (47.1%), Firmicutes (38.9%), Actinobacteria (6.3%), Bacteroidetes (3.6%) and Cyanobacteria (1.1%). The abundant genera were Lysinibacillus (26.9%), Acinetobacter (21.2%), Pseudomonas (4.7%), Bacillus (3.8%), Staphylococcus (3.5%), Stenotrophomonas (1.1%) and Ralstonia (1%). The functional annotation of the metagenome revealed abundance of bacterial community associated with amino acid, carbohydrate as well as energy metabolism. Furthermore, the presence of enzymes involved in the process of denitrification and methanogenesis were also identified. This study gives insight into the gut microbial composition and their putative functional roles in the gut of tropical hilly earthworms. The study on forest and garden soil earthworm gut microbiomes might help us understand the role of these organisms in their respective ecosystems.

Oligochaeta is a class of segmented worms under the phylum Annelida that are characterised by the presence of tiny setae in each body segment. Earthworms are the main members, consisting of approximately 6200 species. Their ecological importance is well known as they are the major soil macro-fauna; Aristotle had named them as “the intestines of soil”. Classification of earthworms is a controversial issue since the introduction of modern taxonomical system on earthworm by Michaelsen in 1921. This is mainly because conventional identification using morphological and anatomical characters are complicated and confusing. The key diagnostic features such as the position and structure of the reproductive organs, clitellum and the associated tubercular pubertatis are not always reliable, particularly in different developmental stages, especially when the available specimens are the juveniles. DNA barcoding has offered a potential solution, even at the levels of identifying the juveniles or cocoons. Several genes including mitochondrial cytochrome-c oxidase I, 16S, 18S and 28S ribosomal RNAs, and protein-coding histone H3 genes have been introduced in the taxonomy and phylogeny of earthworm. It is anticipated that DNA barcoding will help conflicting taxonomy and further exploration of species diversity in India.