#  Pathogen bacteria modulates host pheromone response in order to promote mating 

 





January 05, 2023

 

 

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 Exposure to pathogens and parasites often changes social behavior of the host animals, including humans. These changes immediately affect the resistance of the hosts and contribute to the long-term adaptation to the pathogens. However, the conduit from pathogen exposure to host social behavior is largely unknown. In a new study in *[Nature ](https://www.nature.com/articles/s41586-022-05561-9)*researchers in Professor Yun Zhang's lab discover a biological pathway through which *Caenorhabditis elegans* hermaphrodites respond to bacterial infection by suppressing their response to a dispersing pheromone, which cues an increase in the rate of outcrossing with males, enhancing their ability to generate genetic diversity in the progeny.

 Pathogens live among extreme environmental conditions that negatively impact the fitness and survival of the host animals. Host animals have evolved to develop adaptive strategies that have acute and long-term effects on resistance. When hosts encounter pathogens their social behavior rapidly changes (such as aggregation and sexual behavior) to reduce exposure risk and enhance survival. In the long run, pathogen-host interactions also shape the evolution of the host species by favoring outcrossing that increases genetic diversity through recombination. However, how outcrossing and mating are regulated in response to pathogen infection is not understood. In this study researchers, led by postdoctural researcher Taihong Wu, use *Caenorhabditis elegans* to address this long-standing question.

 There are two sexes in *C. elegans*, hermaphrodites (which produce both eggs and sperms) and males. While the hermaphrodites reproduce mainly through self-fertilization, they maintain the ability to outcross with males. Under normal conditions, adult hermaphrodites avoid a mixture of pheromones that serves as a dispersing cue. Surprisingly, the researchers found that infection by a virulent *Pseudomonas aeruginosa* bacterial strain PA14 suppresses the avoidance. This social behavioral change depends on the chemosensory neurons AWA, which are known to be activated by attractive odorants to elicit attraction. AWA, which do not normally respond to the pheromones, generate a robust activation in response to the pheromones when the animals are infected by the pathogenic bacteria. By sequencing the transcripts in AWA neurons in PA14-infected hermaphrodite worms and in uninfected worms, the team identified a single chemoreceptor STR-44 that is highly induced in AWA by PA14 infection. They also showed that STR-44 functions as a pheromone receptor and its activity in AWA is required for pathogen-induced suppression of pheromone avoidance and AWA’s response to the pheromones.

 Interestingly, they found that exposure to PA14 increases the rate of mating in hermaphrodites and this increase requires the function of STR-44 in AWA. Because the avoidance of the pheromones disperses the hermaphrodites, the researchers think that suppressing the avoidance increases the effective density of the host hermaphrodites and facilitates the encounter of the hermaphrodites with males to promote mating. The results demonstrate that interaction between the worm and the pathogen regulates pheromone response in the host to promote mating by activating the expression of a pheromone receptor that is not normally in use. The study's findings identify a mechanism that can facilitate the adaptation of the host under pathogen stress.

 [Harvard Gazette](https://news.harvard.edu/gazette/story/2023/03/scientists-explain-how-an-infection-can-produce-genetic-diversity/) coverage.

#####  *Image: C. elegan hermaphrodite. Credit: Bob Goldstein, UNC Chapel Hill*



 

 

 



 

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