Noteworthy
 

Bacterial genomes are not a laundry list of genes, but dynamic structures intimately connected with cellular function. As a result, natural selection has a heavy hand in shaping chromosomal architecture – the position of genes within chromosomes – into configurations that best coordinate gene expression.

 

One influence on genome architecture is the phenomenon of replication-associated gene dosage effects. Replication of a bacterium's circular chromosome begins at a single point (oriC), then proceeds in both directions, until the two forks meet at the opposite end (ter). In fast-growing cells, new rounds of replication begin before the previous one is completed. This results in 2- to 8-fold more copies of the genes near oriC than those near ter. Since gene expression still occurs during replication, growth rate-dependent gene copy number changes can have profound impacts of gene expression.

 

It had been known that the position of a few bacterial gene families – particularly those related to transcription, translation, and sporulation – are biased towards oriC or ter. However, new research shows that natural selection broadly favors specific chromosomal positions for most gene families. Analyzing the position of over 4400 gene families from 910 bacterial species, the authors found that nearly two-thirds are nonrandomly distributed around the chromosome. The effect was strongest among fast-growing species which are the most impacted by replication-associated gene dosage effects.

 

These findings reveal the broad importance of gene position within bacterial chromosomes, and fundamentally link growth, genome organization, and resource allocation. They emphasize that while bacterial chromosomes are incredibly flexible in terms of gene content, they are highly conservative in terms of chromosome organization. In addition to elucidating basic evolutionary principles, these results could have important implications for artificial genome design and annotation of uncharacterized genes.

 

(This Noteworthy entry was contributed by Kevin Blake.)

 

 

 

 

Do you want to comment on this post? We would be delighted to hear from you! Please send us an email, or comment on Mastodon or Bluesky. We'll be posting comment threads that arise below (with your permission). Feel free to subscribe if you'd like to get regular notifications about new blog posts.