Bacteria Are a Major Determinant of Orsay Virus Transmission and Infection inCaenorhabditis elegans

The microbiota is a key determinant of the physiology and immunity of animal hosts. The factors governing the transmissibility of viruses between susceptible hosts are incompletely understood. Bacteria serve as food forCaenorhabditis elegansand represent an integral part of the natural environment ofC. elegans.We determined the effects of bacteria isolated withC. elegansfrom its natural environment on the transmission of Orsay virus inC. elegansusing quantitative virus transmission and host susceptibility assays. We observed thatOchrobactrumspecies promoted Orsay virus transmission, whereasPseudomonas luridaMYb11 attenuated virus transmission relative to the standard laboratory bacterial foodEscherichia coliOP50. We found that pathogenicPseudomonas aeruginosastrains PA01 and PA14 further attenuated virus transmission. We determined that the amount of Orsay virus required to infect 50% of aC. eleganspopulation onP. luridaMYb11 compared withOchrobactrum vermisMYb71 was dramatically increased, over three orders of magnitude. Host susceptibility was attenuated even further in presence ofP. aeruginosaPA14. Genetic analysis of the determinants ofP. aeruginosarequired for attenuation ofC. eleganssusceptibility to Orsay virus infection revealed a role for regulators of quorum sensing. Our data suggest that distinct constituents of theC. elegansmicrobiota and potential pathogens can have widely divergent effects on Orsay virus transmission, such that associated bacteria can effectively determine host susceptibility versus resistance to viral infection. Our study provides quantitative evidence for a critical role for tripartite host-virus-bacteria interactions in determining the transmissibility of viruses among susceptible hosts.