Nitric Oxide Levels regulate the immune response of Drosophila melanogaster reference laboratory strains to bacterial infections. Infect Immun

Studies on the innate immune response against microbial infections inDrosophila melanogaster involve mutant strains and their reference strains that act as experimental controls. We used five standardD. melanogaster laboratory reference strains (Or-egon R, w1118, Canton-S, Cinnabar Brown, and YellowWhite [YW]) and investigated their response against two pathogenic bacteria (Photorhabdus luminescens and Enterococcus faecalis) and two nonpathogenic bacteria (Escherichia coli andMicrococ-cus luteus). We detected high sensitivity among YW flies to bacterial infections and increased bacterial growth compared to the other strains. We also found variation in the transcription of certain antimicrobial peptide genes among strains, with Oregon and YW infected flies showing the highest and lowest gene transcription levels in most cases. We show that Oregon and w1118 flies possess more circulating hemocytes and higher levels of phenoloxidase activity than the other strains upon infection with the nonpathogenic bacteria. We further observed reduced fat accumulation in YW flies infected with the pathogenic bacteria, which suggests a possible decline in physiological condition. Finally, we found that nitrite levels are significantly lower in in-fected and uninfected YW flies compared to w1118 flies and that nitric oxide synthase mutant flies in YW background are more susceptible to bacterial infection compared to mutants in w1118 background. Therefore, increased sensitivity of YW flies to bac-terial infections can be partly attributed to lower levels of nitric oxide. Such studies will significantly contribute toward a better understanding of the genetic variation betweenD. melanogaster reference strains. Genetic variation in the immune response of animals tomicro-bial infections is an important factor in host resistance t