[ESAC Student Seminar] Maddie Paoletti

“The phylogenetic history of rTCA-based autotrophy in the metabolically diverse phylum, Campylobacterota”

Molecular phylogenomics reconstructs the microbial natural history of life using the evolutionary history preserved within the genetics of lineages and their metabolisms, which are informative for reconstructing palaeoecological or biogeochemical shifts over geologic time. A key target for this approach is the reductive tricarboxylic acid (rTCA) cycle, a bacterial carbon fixation pathway widely hypothesized as a prebiotic or primitive metabolism within early life. However, this assumption is not necessarily consistent with the extant diversity of the metabolism. Previous efforts to constrain its origins within the order Chlorobiales found each enzyme possessed an independent history of horizontal gene transfer (HGT), demonstrating a patchwise “chimeric” acquisition of rTCA through the lineage’s diversification. Yet a composite understanding of rTCA inheritance across the tree of life remains unexplored, which this work aims to elucidate. Campylobacterota, previously known as Epsilonproteobacteria, is a metabolically diverse microbial phylum with close homology to Aquificota, a separate rTCA autotrophic phylum, which has been hypothesized to share a stem rTCA autotrophic ancestor with one another. Using a phylogenomic approach to reconstruct the history of each step, results show enzymes were both acquired and/or replaced across the phylum over time via HGT, with independent histories of extant rTCA pathways within Campylobacteria and Aquificota. These findings of chimeric rTCA assembly are a novel observation for an autotrophic metabolism; while it suggests it is not a remnant of a conserved primordial pathway, this ability to independently evolve may be evidence of the ubiquity of rTCA in biotic and prebiotic systems.

ESAC Student Seminar Series

A forum for students and postdocs to share recent research, hone presentation skills, and build community among peers, sponsored by the EAPS Student Advisory Committee. Open to current EAPS graduate and undergraduate students and postdocs. Typically hosted on Thursdays during the semester, including pizza lunch.

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