devI is an evolutionarily young negative regulator of Myxococcus xanthus development.

Area of Science:

• Microbiology
• Bacterial Development
• Evolutionary Biology

Background:

• Myxococcus xanthus undergoes starvation-induced development, forming mounds and differentiating into spores.
• The dev locus, containing a CRISPR-Cas system, is crucial for this process, with mutations in devS or devR impairing sporulation.
• Natural isolates exhibit significant polymorphism in the dev operon's promoter region, with many lacking a functional promoter yet sporulating normally.

Purpose of the Study:

• To investigate the role of the dev promoter and downstream genes in Myxococcus xanthus development and sporulation.
• To elucidate the relationship between the dev CRISPR-Cas system and the observed sporulation defects in natural isolates.
• To understand the evolutionary history of the dev operon, particularly the devI gene and its promoter.

Main Methods:

• Comparative analysis of the dev operon promoter region in natural M. xanthus isolates.
• Genetic manipulation, including deletion of the dev promoter and the devI gene, in a laboratory reference strain.
• Complementation experiments and introduction of premature stop codons to assess gene function.
• Phylogenetic analysis to trace the evolutionary integration of devI and its promoter.

Main Results:

• The dev promoter is non-functional in most natural isolates and dispensable for development in the lab strain.
• Deletion of the dev promoter or devI suppressed the sporulation defect of devS/devR mutants.
• DevRS proteins negatively autoregulate devI expression, and DevI protein inhibits sporulation when overexpressed.
• devI is absent in most natural isolates, indicating recent evolutionary acquisition in some lineages.

Conclusions:

• DevI acts as a cell-autonomous sporulation inhibitor, negatively regulated by the DevRS CRISPR-Cas proteins.
• The dev promoter and devI gene are dispensable for M. xanthus development and appear to have been recently acquired in specific lineages.
• This study reveals novel insights into the mechanistic role and evolutionary trajectory of the dev operon in M. xanthus sporulation.