Multiple toxin-antitoxin (TA) systems are housed in different locations within the bacterial genome and are known to be associated with various cellular processes and stress-related adaptation. In endosymbionts, although, the TA system has scarce occurrence but studies have highlighted its presence in enhancing host-symbiont interactions. Wolbachia, an obligate endosymbiont, has recently been proposed as a biocontrol agent which may be helpful in controlling vector-borne diseases. There are reports suggesting the role of TA system in inducing cytoplasmic incompatibility in case of Wolbachia, however, the underlying mechanism is still not known. The present study, therefore, aims at exploring the diversity of TA system in four novel (sourced from India) and three reference genomes (NCBI) of Wolbachia strains. Interestingly, we found several putative toxins and antitoxins of RelEB family of Type II TA system in these Wolbachia genomes. The results show wMel genome possessed more number of putative TA loci than wRi genome. In addition, searching through the other sequenced Wolbachia genomes in NCBI, a complete absence of TA system was observed in Wolbachia-infected nematodes. The sequence-wide analysis of all the putative RelEB proteins present amongst the Wolbachia endosymbiont and within the free-living bacterial genomes reveal strain-specific similarities and conserved sequences. However, large amount of sequence diversity was observed between Wolbachia and free-living bacteria. Understanding this sequence variation may help shed light on the differences between these two forms of bacteria and could also explain their niche preferences.

The present work aims to identify the microbial diversity associated with six Indian Drosophila species using next generation sequencing (NGS) technology and to discover the nature of their distribution across species and eco-geographic regions. Whole fly gDNA of six Drosophila species were used to generate sequences in an Illumina platform using NGS technology. De novo based assembled raw reads were blasted against the NR database of NCBI using BLASTn for identification of their bacterial loads. We have tried to include Drosophila species from different taxonomical groups and subgroups and from three different eco-climatic regions India; four species belong to Central India, while the rest two, D. melanogaster and D. ananassae, belong to West and South India to determine both their species-wise and region-wide distribution. We detected the presence of 33 bacterial genera across all six study species, predominated by the class Proteobacteria. Amongst all, D. melanogaster was found to be the most diverse by carrying around 85% of the bacterial diversity. Our findings infer both species-specific and environment-specific nature of the bacterial species inhabiting the Drosophila host. Though the present results are consistent with most of the earlier studies, they also remain incoherent with some. The present study outcome on the host-bacteria association and their species specific adaptation may provide some insight to understand the host-microbial interactions and the phenotypic implications of microbes on the host physiology. The knowledge gained may be importantly applied into the recent insect and pest population control strategy going to implement through gut microflora in India and abroad.

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