Evolutionary relationships among photosynthetic bacteria

Area of Science:

• Microbiology
• Evolutionary Biology
• Genomics

Background:

• Understanding the evolutionary history of bacteria, particularly photosynthetic groups, from a common ancestor has been a persistent challenge in microbiology.
• Previous attempts to resolve bacterial phylogeny have faced limitations in clearly defining major bacterial groups and their relationships.

Purpose of the Study:

• To elucidate the evolutionary pathways and branching order of major bacterial groups, with a focus on photosynthetic lineages.
• To establish a robust molecular framework for bacterial classification using conserved protein sequence alterations.

Main Methods:

• Analysis of 25 conserved inserts or deletions (indels) in highly conserved and widely distributed bacterial proteins.
• Application of the indel model to 82 completed bacterial genomes to predict and verify the presence or absence of these molecular signatures.
• Deduction of relative branching orders based on the identified indel patterns.

Main Results:

• A clear molecular definition and deduced branching order for all major bacterial groups were established using the indel model.
• The indel model demonstrated high accuracy, with only 11 exceptions observed across 1842 observations in 82 bacterial genomes.
• Heliobacterium species (monoderm, RC 1) were identified as the most ancestral photosynthetic lineage, followed by green nonsulfur bacteria (diderm, RC 2) among Gram-negatives.

Conclusions:

• Conserved indels provide a powerful and reliable method for resolving long-standing questions in bacterial evolution and phylogeny.
• The study outlines a detailed evolutionary tree of bacterial groups, highlighting the early divergence of photosynthetic lineages.
• Later photosynthetic groups likely acquired reaction center genes through descent or lateral gene transfer from earlier branching lineages.