Comparative Gene Essentiality across the Bacterial Domain

Comparative genomics among bacteria has been used to gain insight into the minimal number of conserved genes in biological pathways. Essentiality studies have provided information regarding which genes are non-dispensable (essential, E) for cell growth. Here, we integrated studies of gene conservation, essentiality and function, performed in 47 diverse bacterial species. We showed there is a modest positive correlation between genome size and number of essential genes. Interestingly, we observed a clear shift in the functions assigned to these essential genes as genome size increases. For instance, essential genes related to transcription and translation dominate small genomes. In contrast, in large genomes functions of essential genes are related with cellular processing and metabolism. Finally, and most intriguing, we found a group of genes that while being highly conserved are also typically non-essential. This suggests that some housekeeping genes confer a significant survival benefit in nature while being non-essential in vitro.