First genomic insights into prokaryotic endosymbioses from the archaeal domain of life

Published: 2018-08-17


By studying the genomes of two endosymbiotic interactions between ciliates and methanogenic archaea, Thijs Ettema (Uppsala University/SciLifeLab) and colleagues have got the first insights into prokaryotic endosymbioses from the archaeal domain of life. Sequencing was performed by the National Genomics Infrastructure, NGI, at SciLifeLab.

Endosymbiosis is the phenomenon of one organism living within the body or cells of another organism in a symbiotic relationship with the host body or cell, and is widespread in the microbial world. Bacteria that have invaded eukaryotic host cells constitute the major part of known endosymbiotic interactions, but methanogenic archaea have also been found to thrive in anaerobic protists.

Thijs Ettema and his team have investigated the genomes of two distantly related methanogenic endosymbionts that have been acquired in two independent events by closely related anaerobic ciliate hosts Nyctotherus ovalis and Metopus contortus, respectively.

The results, presented in The ISME Journal, reveal that the genomes of both endosymbionts are in an early stage of adaptation towards endosymbiosis. This was evidenced by the large number of genes becoming pseudogenes – genes that have lost some functionality in cellular gene expression or protein-coding ability. The researchers observed loss of genes involved in amino acid biosynthesis in both endosymbiont genomes, indicating that the endosymbionts rely on their hosts for obtaining several essential nutrients.

Read full scientific paper in The ISME Journal