Natural infections often consist of multiple pathogens of the same or different species. When coinfections occur, pathogens compete for access to host resources and fitness is determined by how well a pathogen can reproduce compared to its competitors. Yet not all hosts provide the same resource pool. Males and females, in particular, commonly vary in both their acquisition of resources and investment in immunity, but their ability to modify any competition between different pathogens remains unknown. Using the Daphnia magna–Pasteuria ramosa model system, we exposed male and female hosts to either a single genotype infection or coinfections consisting of two pathogen genotypes of varying levels of virulence. We found that coinfections within females favored the transmission of the more virulent pathogen genotype, whereas coinfections within male hosts resulted in equal transmission of competing pathogen genotypes. This contrast became less pronounced when the least virulent pathogen was able to establish an infection first, suggesting that the influence of host sex is shaped by priority effects. We suggest that sex is a form of host heterogeneity that may influence the evolution of virulence within coinfection contexts and that one sex may be a reservoir for pathogen genetic diversity in nature.
11Natural infections often consist multiple pathogens of the same or different species. In multiple 12 infections, pathogens compete for access to host resources and fitness is determined by how well 13 a pathogen can reproduce compared to its competitors. Given the propensity for males and 14 females to exhibit variation in pathogen-induced reduction in lifespan or fecundity, we explore 15 how host sex may modulate the competitive ability of pathogens, potentially favouring the 16 transmission of different pathogen genotypes. Using the Daphnia magna -Pasteuria ramosa 17 model system, we exposed male and female hosts to either a single genotype infection or co-18 infections consisting of two pathogen genotypes of varying levels of virulence, measured as 19 pathogen-induced reduction in host lifespan. We found that co-infections within females generally 20 favoured the transmission of the more virulent pathogen genotype. Conversely, co-infections 21 within male hosts resulted in equal transmission of competing genotypes, or favoured the 22 transmission of the less virulent pathogen genotype in treatments where it established prior to 23 the more virulent competitor. These results suggest that sex is a form of host heterogeneity which 24 may influence the evolution of virulence within co-infection contexts and that one sex may be a 25 reservoir for pathogen genetic diversity in nature. 26 27
Diverse aerobic bacteria use atmospheric hydrogen (H2) and carbon monoxide (CO) as energy sources to support growth and survival. Though recently discovered, trace gas oxidation is now recognised as a globally significant process that serves as the main sink in the biogeochemical H2 cycle and sustains microbial biodiversity in oligotrophic ecosystems. While trace gas oxidation has been reported in nine phyla of bacteria, it was not known whether archaea also use atmospheric H2. Here we show that a thermoacidophilic archaeon, Acidianus brierleyi (Thermoproteota), constitutively consumes H2 and CO to sub-atmospheric levels. Oxidation occurred during both growth and survival across a wide range of temperatures (10 to 70 C). Genomic analysis demonstrated that A. brierleyi encodes a canonical carbon monoxide dehydrogenase and, unexpectedly, four distinct [NiFe]-hydrogenases from subgroups not known to mediate aerobic H2 uptake. Quantitative proteomic analyses showed that A. brierleyi differentially produced these enzymes in response to electron donor and acceptor availability. A previously unidentified group 1 [NiFe]-hydrogenase, with a unique genetic arrangement, is constitutively expressed and upregulated during stationary phase and aerobic hydrogenotrophic growth. Another archaeon, Metallosphaera sedula, was also found to oxidize atmospheric H2. These results suggest that trace gas oxidation is a common trait of aerobic archaea, which likely plays a role in their survival and niche expansion, including during dispersal through temperate environments. These findings also demonstrate that atmospheric H2 consumption is a cross-domain phenomenon, suggesting an ancient origin of this trait, and identify previously unknown microbial and enzymatic sinks of atmospheric H2 and CO.
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