[PhD Thesis Public Presentation_Zoom] ‐ Jigyasa Arora– “Functional metagenomics and evolution of termite gut microbiome.”
Presenter: Jigyasa Arora
Supervisor: Prof. Thomas Bourguignon
Unit: Evolutionary Genomics Unit
Zoom URL: to be available 48 hours prior to the examination
Title: Functional metagenomics and evolution of termite gut microbiome.
Termites are amongst the most abundant terrestrial animals on earth, largely due to their ability to digest lignocellulose, the most abundant organic molecule on earth. Lignocellulose is broken down in the termite gut with the help of symbiotic bacteria. Studies using the 16S rRNA marker have shown that termites and their gut bacteria have had a complex coevolutionary history. Although many gut microbes are found nowhere else than in termite guts, bacterial communities do vary with termite diet. Up to now, studies have been focusing on termite species easy to sample or having a pest status. This sampling bias against early-evolving termite lineages and lineages feeding on substrates different than wood preclude a global understanding of the evolutionary history of termites and their gut microbes. To fill this gap, I sequenced whole gut metagenomes of 201 termite samples and Cryptocercus kyebangensis, a species of the genus sister to termites, sampled across the termite tree of life to represent termite phylogenetic and dietary diversity. Applying a combination of phylogenetic comparative methods and phylogenetic reconstructions, my thesis showcases that (i) the gut microbiome of all termites possess similar genes for carbohydrate breakdown and other metabolic pathways involved in the digestion of cellulose. The proportion of these genes vary with termite phylogeny and diet but the acquisition of a diet of soil from a wood-feeding ancestor was accompanied by changes in gene abundance rather than by the acquisition of new genes and pathways. Using ten single-copy protein-coding marker gene sequences, (ii) I studied the pattern of coevolution between termites and each of their gut bacterial phyla. I found significant cophylogenetic signals between termites and a dozen of gut bacterial lineages that were acquired by the common ancestor of all termites or by specific termite lineages. Finally, (iii) I investigated horizontal gene transfers among termite gut bacteria for genes involved in lignocellulose digestion. I found numerous horizontal transfers among microbial phyla. Overall, my Ph.D. thesis sheds new light on how gut microbiome has coevolved with their termite hosts since the inception of this nutritional symbiosis, some 150 million years.