Ancient balancing selection on heterocyst function in a cosmopolitan cyanobacterium.

Area of Science:

• Microbial evolution
• Bacterial genetics
• Cyanobacteria adaptation

Background:

• Bacterial adaptation traditionally emphasizes rapid, repeatable changes.
• Genetic variation is not expected to persist long-term in microbes without selection.
• Multicellular cyanobacteria like Fischerella thermalis offer unique models for studying evolution.

Purpose of the Study:

• Investigate the long-term maintenance of genetic variation in Fischerella thermalis.
• Determine the role of gene content polymorphism in bacterial adaptation.
• Explore the impact of environmental factors on genetic diversity over evolutionary timescales.

Main Methods:

• Phylogenetic analysis of Fischerella thermalis populations.
• Gene content analysis to identify polymorphisms.
• Experimental assessment of heterocyst function under varying temperatures.

Main Results:

• A widespread gene content polymorphism has been maintained for tens of millions of years.
• This polymorphism affects gas permeability of heterocysts.
• Spatial temperature variation favors alternative alleles, influencing heterocyst function and fitness.

Conclusions:

• Ancient balancing selection may play a significant role in maintaining microbial diversity.
• Environmental factors like temperature can drive the long-term persistence of genetic variation.
• This challenges the conventional view of rapid, transient adaptation in bacteria.