Lawrence Berkeley National Laboratory

Bacterial endospore formation is a complex developmental pathway involving differential and staged expression of hundreds of genes in response to overcrowding or nutrititional stress. Most of the insights into the genetics and molecular biology of this pathway have come from studies of Bacillus subtilis. However, as new genomic and expression data for other spore-formers becomes available, one may ask to what extent this pathway is conserved phylogenetically, over evolutionary time, as well as transcriptionally, over physiological time. Methods: Here, we collect and compare genomic and expression data from four spore-formers (B. subtilis, B. anthracis, C. acetobutylicum, B. cereus) using a combination of statistical and phylogenetic methods. Results: Preliminary results show that genes sharing expression patterns are not always evolutionarily conserved, but that genes sharing phylogenetic patterns are typically co-expressed. Furthermore, the sporulation pathway shows clear evidence of niche modifications in that the free-living but phylogenetically divergent bacteria (B. subtilis and C. acetobutylicum) have significantly different expression patterns in conserved genes as compared to the more closely related pathogenic bacteria (B. cereus and B. anthracis). Conclusion: These results shed light on the conservation of spore-formation in terms of its temporal and ecological roles, and provide an early insight into the evolution of pathway dynamics.