Hallgren, J.; Dharamshi, J. E.; Rodriguez-Gijon, A.; Nuy, J.; Garcia, S. L.; Jonas, K.

Model bacteria are fundamental for research, but knowledge about their ecology and evolution is often limited. Here we establish evolutionary and ecological context for the model organism Caulobacter crescentus, an alphaproteobacterium intensively studied for its dimorphic lifecycle. By analyzing the species relationships and genetic potential of hundreds of Caulobacterales species, we reveal striking diversity regarding their environmental distribution, morphology, cell development, and metabolism. Our work provides insights into the evolutionary history of morphological features such as the cell curvature determinant crescentin and uncovers a striking case of convergent loss of traits for cellular dimorphism among close relatives of C. crescentus. Moreover, we find that genes for phototrophy are widespread across Caulobacterales and that the new genus Acaudatibacter, described here, includes the first reported Caulobacterales lineage with photoautotrophic potential. Our study advances our understanding of an environmentally widespread bacterial order and sheds light onto the evolution of fundamental prokaryotic features.