Symbiotic interactions at the origin of eukaryotes

Introduction

Recent advances in environmental microbiology, metagenomics, and phylogenomics strongly suggest that the eukaryotic cell evolved from symbiotic consortia involving an Asgard archaeon and, at least, the alphaproteobacterial ancestor of the mitochondrion.

Background

However, many genes of prokaryotic origin in the last eukaryotic common ancestor (LECA) appear to originate neither from archaea nor alphaproteobacteria. This suggests that other bacteria (e.g., Deltaproteobacteria) may have contributed to eukaryogenesis as additional symbionts or gene donors.

Objectives

To ascertain the origin of these genes, it is essential to better understand the ecology of symbiotic microbial consortia involving Asgard archaea (AA). In particular, the project aims to identify the partners with which they interact in natural ecosystems.

Methodology

In this project, I will combine several advanced techniques:

1. Metagenomics
2. Phylogenomics
3. Fluorescence-activated single-cell/consortium sorting
4. High-throughput microfluidics
5. State-of-the-art fluorescence and electron microscopy techniques
6. Cultivation approaches

These methods will be used to identify and characterize members of AA syntrophic consortia and their associated viruses in a broad variety of microbial mats and oxygen-poor environments.

Expected Outcomes

With this information, I aim to:

i) Identify the partners of AA syntrophic consortia across ecosystems, determine whether they co-evolve, and unravel their ecological preferences.

ii) Characterize the metabolic interactions and phenotypic properties of AA symbiotic consortia in culture and/or from sorted consortia populations.

iii) Characterize the cell ultrastructure and potential presence of endomembranes in members of AA consortia, their three-dimensional organization, and their spatial distribution in microbial mats.

iv) Identify potential bacterial symbiotic partners involved in eukaryogenesis, in addition to the mitochondrial alphaproteobacterial ancestor, and/or gene donors to the LECA or its Asgard archaeal ancestor.

Conclusion

Our results should substantially advance understanding of eukaryogenesis.