Random Genetic Drift and Selective Pressures Shaping the Blattabacterium Genome

Area of Science:

• Microbial genomics
• Evolutionary biology
• Insect symbiosis

Background:

• Obligate bacterial endosymbionts are common in insects, providing benefits like nutrition.
• Intracellular life profoundly impacts bacterial genomes, balancing host-dependent gene maintenance with genome erosion.
• The cockroach endosymbiont Blattabacterium offers amino acid synthesis to its host.

Purpose of the Study:

• To investigate the selective forces acting on the Blattabacterium genome.
• To compare the genome evolution of Blattabacterium to its free-living relatives.
• To understand the potential for future genome reduction in bacterial endosymbionts.

Main Methods:

• Comparative genomics of eight published Blattabacterium genomes.
• Analysis of selection rates and directionality across the Blattabacterium genome.
• Comparison of genomic data with the free-living relative Flavobacterium.

Main Results:

• The Blattabacterium genome exhibits a 10-fold increase in selection rate compared to Flavobacteria.
• The majority of selection events in Blattabacterium are negative, indicating gene loss.
• Only a few genomic loci show signatures of positive selection.

Conclusions:

• The Blattabacterium genome is undergoing significant erosion due to negative selection and genetic drift.
• Continued genome reduction is predicted for Blattabacterium, mirroring trends in other insect endosymbionts.
• Understanding these evolutionary dynamics is crucial for insect-microbe interactions.