Schwiesow, M. | bioRxiv Science

bioRxiv2022

Distinct pathways of adaptive evolution in Cryptococcus neoformans reveal a point mutation in adenylate cyclase with drastic tradeoffs for pathogenicity

Pathogenic fungi populate a wide range of environments and infect a diversity of host species. Despite this substantial biological flexibility, the impact of interactions between fungi and their hosts on the evolution of pathogenicity remains unclear. We studied how repeated interactions between the fungus Cryptococcus neoformans and relevant environmental and mammalian host cells--amoeba and mouse macrophages--shape the evolution of this model fungal pathogen. First, using a collection of clinical and environmental isolates of C. neoformans, we characterized a range of survival phenotypes for these strains when exposed to host cells of different species. We then performed serial passages of an environmentally isolated C. neoformans strain through either amoeba or macrophages for ~75 generations to observe how these interactions select for improved replication within hosts. In an adapted population, we identified a single point mutation in the adenylate cyclase gene, CAC1, that swept to fixation and confers a strong competitive advantage for growth inside of macrophages. Strikingly, this growth advantage in macrophages is inversely correlated with disease severity during mouse infections, suggesting that adaptations to specific host niches can markedly reduce the pathogenicity of these fungi. These results raise intriguing questions about the influence of cAMP signaling on pathogenicity and highlight the role of seemingly small adaptive changes in promoting fundamental shifts in the intracellular behavior and virulence of these important human pathogens.

microbiology↗

bioRxiv2022

Rapid Evolution of Glycan Recognition Receptors Reveals an Axis of Host-Microbe Conflicts at Carbohydrate-Protein Interfaces

Detection of microbial pathogens is a primary function of many mammalian immune proteins. This can be accomplished through the recognition of diverse microbial-produced macromolecules including proteins, nucleic acids and carbohydrates. Many pathogens subvert host defenses by rapidly changing these structures to avoid detection, placing strong selective pressures on host immune proteins that repeatedly adapt to remain effective. Signatures of rapid evolution have been identified in numerous host immunity proteins involved in the detection of pathogenic protein substrates, but whether the same signals can be observed in host proteins engaged in interactions with other pathogen-derived molecules has received much less attention. This focus on protein-protein interfaces has largely obscured the study of fungi as contributors to host-pathogen evolutionary conflicts, despite their importance as a formidable class of vertebrate pathogens. Here, we provide evidence that many mammalian immune receptors involved in the detection of microbial glycans have been subject to recurrent positive selection. Notably, we find that rapidly evolving sites in these genes primarily cluster in key functional domains involved in carbohydrate recognition. Further, we identified convergent patterns of substitution in distinct primate populations at a site in the Melanin Lectin gene that has been associated with increased risk of invasive fungal disease. Our results also highlight the power of evolutionary analyses to reveal uncharacterized interfaces of host-pathogen conflict by identifying genes, such as CLEC12A, with strong signals of positive selection across multiple mammalian lineages. These results suggest that the realm of interfaces shaped by host-microbe conflicts extends beyond the world of host-viral protein-protein interactions and into the world of microbial glycans and fungi.

evolutionary biology↗