Preliminary Characterization of Phage-like Particles from the Male-Killing Mollicute Spiroplasma poulsonii (an Endosymbiont of Drosophila)

Abstract

AbstractViruses are vastly abundant and influential in all ecosystems, and are generally regarded as pathogens. Viruses of prokaryotes (themselves highly diverse and abundant) are known as bacteriophages or phages. Phages engage in diverse associations with their hosts, and contribute to regulation of biogeochemical processes, horizontal movement of genes, and control of bacterial populations. Recent studies have revealed the influential role of phage in the association of arthropods and their heritable endosymbiotic bacteria (e.g. the Proteobacteria genera Wolbachia and Hamiltonella). Despite prior studies (∼30 years ago) documenting presence of phage in the mollicute Spiroplasma infecting Drosophila, genomic sequences of such phage are lacking, and their effects on the Spiroplasma-Drosophila interaction have not been comprehensively characterized. The present work isolated phage-like particles from the male-killing Spiroplasma poulsonii (strains NSRO and MSRO-Br) harbored by Drosophila melanogaster. Isolated particles were subjected to DNA sequencing, assembly, and annotation. Our results recovered three ∼19 kb phage-like contigs (two in NSRO and one in MSRO-Br), and two smaller non-phage-like contigs encoding a known Spiroplasma toxin and an insertion element. Whole or parts of the particle-derived contigs were found in the genome assemblies of members of the Spiroplasma poulsonii clade. Although our results do not allow us to distinguish whether the contigs obtained represent infective phage-like particles capable of transmitting their DNA to new hosts, their encoding of several typical phage genes suggests that they are at least remnants of functional phage. We discuss potential implications of our findings and suggest future directions.