Chlamydial contribution to anaerobic metabolism during eukaryotic evolution

Area of Science:

• Evolutionary Biology
• Microbial Ecology

Background:

• The origin of eukaryotes is a central question in evolutionary biology.
• Current hypotheses suggest a syntrophic relationship between archaea and alphaproteobacteria involving hydrogen (H2) exchange.
• However, evidence for H2 metabolism gene origins in eukaryotes from these groups is lacking.

Purpose of the Study:

• To investigate the origin of hydrogen (H2) metabolism genes in eukaryotes.
• To explore alternative sources for eukaryotic H2 metabolism beyond archaea and alphaproteobacteria.

Main Methods:

• Phylogenetic analyses of H2 metabolism gene components.
• Comparative genomics of anaerobic chlamydiae from marine sediments.
• Description of a newly identified bacterial group, Anoxychlamydiales.

Main Results:

• Anoxychlamydiales, a novel group of anaerobic chlamydiae, uniquely possess genes for H2 metabolism.
• Phylogenetic analyses indicate Anoxychlamydiales homologs are the closest relatives to eukaryotic H2 metabolism sequences.
• This challenges previous hypotheses on the origin of eukaryotic H2 metabolism.

Conclusions:

• An ancestor of Anoxychlamydiales likely contributed key H2 metabolism genes to the early eukaryotic lineage.
• This supports a mosaic model for the evolutionary origin of eukaryotic metabolism.
• The findings highlight the importance of exploring diverse microbial lineages for understanding eukaryotic evolution.