Spiroplasma poulsonii is a vertically transmitted endosymbiont of Drosophila melanogaster that causes male-killing, that is the death of infected male embryos during embryogenesis. Here we report a natural variant of S. poulsonii that is efficiently vertically transmitted yet does not selectively kill males, but kills rather a subset of all embryos regardless of their sex, a phenotype we call “blind-killing”. We show that the natural plasmid of S. poulsonii has an altered structure: Spaid, the gene coding for the male-killing toxin, is deleted in the blind-killing strain, confirming its function as a male-killing factor. We then further investigate several hypotheses that could explain the sex-independent toxicity of this new strain on host embryos. As the second non-male-killing variant isolated from a male-killing original population, this new strain raises questions on how male-killing is maintained or lost in fly populations. As a natural knock-out of Spaid, which is unachievable yet by genetic engineering approaches, this variant also represents a valuable tool for further investigations on the male-killing mechanism. This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.