Origin and evolution of a bacterial developmental programme
Bacterial spores are the most resilient cells known in this planet. They are formed by some bacteria as the result of a developmental programme through which vegetative cells, capable of growth and division, undergo a metamorphosis into a dormant highly resilient spore. Spore differentiation mobilizes hundreds of genes, representing over 10% of the genome. Many of these genes have sporulation-specific functions, i.e., they are not required for the usual cycle of bacterial growth and division.
Understanding the molecular mechanisms of spore formation in bacteria has been the focus of Adriano Henriques Lab (previous articles are available here, here and here). The group works with both the model organism Bacillus subtilis, an aerobic spore-former that is also a bitech industry workhorse, and with Clostridium difficile, a strict anaerobe and a major human intestinal pathogen. Their newly published article, "From root to tips: sporulation evolution and specialization in Bacillus subtilis and the intestinal pathogen Clostridioides difficile", was accepted for publication by the journal Molecular Biology and Evolution.
The work by Paula Ramos-Silva (IGC), Mónica Serrano and Adriano Henriques (ITQB NOVA) shows that the sporulation pathway exists since the emergence of a group of bacteria known as the Firmicutes, some 2.5 to 3 billion years ago. Their common ancestor had already developed the main stages of the sporulation programme, which is very similar to that of contemporary species, raising the question of how more sophisticated regulatory and cell morphogenesis circuits have appeared.
The researchers traced the path of sporulation evolution in several bacterial lineages. They show that sporulation involved the invention of many new genes, especially in B. subtilis and related organisms. In contrast, for C. difficile, several genes important for sporulation where acquired by horizontal gene transfer from other species in the gastro-intestinal tract. Spores, which are oxygen-resistant, are essential for the persistence and spreading of this strict anaerobe.
This is an important finding because it shows that Clostridium difficile uses the repertoire of genes in the gut microbiome to adjust its sporulation program to the needs of a lifestyle in the gut ecosystem. One example are the genes coding for the proteins that form the spore surface and allow for interactions with host cells, important at the early stages of infection. Another example is the acquisition of genes coding for spore-associated receptor proteins that bind bile salts and trigger spore germination, without which colonisation/infection would be impossible. This work shows how key sporulation/germination genes are acquired by C. difficile, and may point to new strategies to fight this pathogen.
Original paper
Molecular Biology and Evolution | doi.org/10.1093/molbev/msz175
From root to tips: sporulation evolution and specialization in Bacillus subtilis and the intestinal pathogen Clostridioides difficile
Paula Ramos-Silva, Mónica Serrano and Adriano O. Henriques
