Embryo-like features in developing Bacillus subtilis biofilms
Correspondence between evolution and development has been discussed for more than two centuries1. Recent work reveals that phylogeny-ontogeny correlations are indeed present in developmental transcriptomes of eukaryotic clades with complex multicellularity2-10. Nevertheless, it has been largely ignored that the pervasive presence of phylogeny-ontogeny correlations is a hallmark of development in eukaryotes6, 10-12. This perspective opens a possibility to look for similar parallelisms in biological settings where developmental logic and multicellular complexity are more obscure13-16. For instance, it has been increasingly recognized that multicellular behaviour underlies biofilm formation in bacteria13, 14, 17-19. However, it remains unclear whether bacterial biofilm growth shares some basic principles with development in complex eukaryotes14-16, 18, 20. Here we show that the ontogeny of growing Bacillus subtilis biofilms recapitulates phylogeny at the expression level. Using time-resolved transcriptome and proteome profiles, we found that biofilm ontogeny correlates with the evolutionary measures, in a way that evolutionary younger and more diverged genes were increasingly expressed towards later timepoints of biofilm growth. Molecular and morphological signatures also revealed that biofilm growth is highly regulated and organized into discrete ontogenetic stages, analogous to those of eukaryotic embryos11, 21. Together, this suggests that biofilm formation in Bacillus is a bona fide developmental process comparable to organismal development in animals, plants and fungi. Given that most cells on Earth reside in the form of biofilms22 and that biofilms represent the oldest known fossils23, we anticipate that the widely-adopted vision of the first life as a single-cell and free-living organism needs rethinking.