Deciphering primordial cyanobacterial genome functions from protein network analysis

Area of Science:

• Evolutionary biology
• Microbial genomics
• Biochemistry

Background:

• Cyanobacteria ancestors caused the Great Oxidation Event (GOE) ~2.4 billion years ago.
• Cyanobacteria remain vital for primary production and global nitrogen cycles.
• Limited knowledge exists on primordial cyanobacteria's evolutionary history and gene content.

Purpose of the Study:

• To investigate the evolutionary history and gene content of primordial cyanobacteria.
• To reconstruct ancestral functions of early cyanobacteria.
• To understand cyanobacteria's position in prokaryotic evolution.

Main Methods:

• Utilized protein similarity networks with 48 cyanobacteria proteomes.
• Included 84 reference proteomes from methanogens, obligate anaerobes, facultative aerobes, and obligate aerobes.
• Analyzed network metric degree to infer evolutionary relationships and ancestral functions.

Main Results:

• Cyanobacteria show strong relationships with obligate anaerobes for core functions, suggesting their origin.
• Reconstructed primordial functions include photosynthesis, hydrogenases, and stress defense genes.
• 60% of these genes are found in both reaction center I (RC-I) and RC-II bacteria, possibly due to selective loss.
• Cyanobacteria act as a hub connecting anaerobes and obligate aerobes.

Conclusions:

• Cyanobacteria evolved from anaerobic ancestors, retaining core functions while developing new ones.
• Primordial cyanobacteria possessed key genes for photosynthesis, hydrogen metabolism, and environmental resilience.
• The study positions cyanobacteria as a pivotal evolutionary link between anaerobic and aerobic life forms.