Thornhill, P. | bioRxiv Science

bioRxiv2024

Genetic variation in trophic avoidance shows fruit flies are generally attracted to bacterial pathogens

Pathogen avoidance behaviours are often assumed to be an adaptive host defence from infection. However, there is limited experimental data on the prerequisite for this assumption: heritable, intrapopulation phenotypic variation for avoidance. We investigated trophic pathogen avoidance in 122 inbred Drosophila melanogaster lines, and in a derived outbred population. Using the FlyPAD system, we tracked the feeding choice that flies made between substrates that were either clean or contained a bacterial pathogen. We uncovered significant, but weakly heritable variation in the preference index among fly lines. However, instead of avoidance, most lines demonstrated a preference for several bacterial pathogens, showing avoidance only for extremely high bacterial concentrations. Bacterial preference was not associated with susceptibility to infection and was retained in flies with disrupted immune signalling. Phenotype-genotype association analysis indicated several novel genes (CG2321, CG2006, ptp99A) associated with increased preference for the bacterial substrate, while the amino-acid transporter sobremesa was associated with greater aversion. Together with previous work showing fitness benefits of consuming high-protein diets, our results suggest that bacterial attraction may instead reflect a dietary preference for protein over carbohydrate. More work quantifying intrapopulation variation in avoidance behaviours is needed to fully assess its importance in host-pathogen evolutionary ecology.

ecology↗

bioRxiv2020

Deep sequencing reveals Campylobacter in commercial meat chickens less than 8 days old.

Campylobacter from contaminated poultry meat is a major source of human gastroenteritis worldwide. To date, attempts to control this zoonotic infection with on-farm biosecurity measures have been inconsistent. A cornerstone of these efforts has been the detection of chicken infection with microbiological culture, which typically does not occur until birds are at least 21 days old. Using molecular methods for detecting Campylobacter presence, 16S microbiome analysis and deep sequencing of the Campylobacter porA gene, Campylobacter can be identified at very low levels in most or all flocks fewer than 8 days old. These young chicks exhibit a much greater diversity of porA types than older birds testing positive for Campylobacter by culture or qPCR. This suggests that, as the bacteria multiply sufficiently to be detected by culture methods, one or two strains, as indicated by porA type, dominate the infection. The findings that (i) most young chicks carry some Campylobacter and (ii) not all flocks become Campylobacter positive by culture, suggests that efforts to control infection should concentrate on how to maintain Campylobacter at low levels by the prevention of the overgrowth of single strains, which ultimately leads to the contamination of food.

microbiology↗