Taxonomic and functional annotation of gut bacterial communities of Eisenia foetida and Perionyx excavatus.

Epigeic earthworms can significantly hasten the decomposition of organic matter, which is known to be mediated by gut associated microflora. However, there is scanty information on the abundance and diversity of the gut bacterial flora in different earthworm genera fed with a similar diet, particularly Eisenia foetida and Perionyx excavatus. In this context, 16S rDNA based clonal survey of gut metagenomic DNA was assessed after growth of these two earthworms on lignocellulosic biomass. A set of 67 clonal sequences belonging to E. foetida and 75 to P. excavatus were taxonomically annotated using MG-RAST and RDP pipeline servers. Highest number of sequences were annotated to Proteobacteria (38-44%), followed by unclassified bacteria (14-18%) and Firmicutes (9.3-11%). Comparative analyses revealed significantly higher abundance of Actinobacteria and Firmicutes in the gut of P. excavatus. The functional annotation for the 16S rDNA clonal libraries of both the metagenomes revealed a high abundance of xylan degraders (12.1-24.1%). However, chitin degraders (16.7%), ammonia oxidizers (24.1%) and nitrogen fixers (7.4%) were relatively higher in E. foetida, while in P. excavatus; sulphate reducers and sulphate oxidizers (12.1-29.6%) were more abundant. Lignin degradation was detected in 3.7% clones of E. foetida, while cellulose degraders represented 1.7%. The gut microbiomes showed relative abundance of dehalogenators (17.2-22.2%) and aromatic hydrocarbon degraders (1.7-5.6%), illustrating their role in bioremediation. This study highlights the significance of differences in the inherent microbiome of these two earthworms in shaping the metagenome for effective degradation of different types of biomass under tropical conditions.