Preliminary Characterization of Phage-like Particles from the Male-Killing Mollicute Spiroplasma poulsonii (an Endosymbiont of Drosophila)
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abstract
AbstractBacteriophages are vastly abundant, diverse, and influential, but with few exceptions (e.g. the Proteobacteria generaWolbachiaandHamiltonella), the role of phages in heritable bacteria-arthropod interactions, which are ubiquitous and diverse, remains largely unexplored. Despite prior studies documenting phage-like particles in the mollicuteSpiroplasmaassociated withDrosophilaflies, genomic sequences of such phage are lacking, and their effects on theSpiroplasma-Drosophilainteraction have not been comprehensively characterized. We used a density step gradient to isolate phage-like particles from the male-killing bacteriumSpiroplasma poulsonii(strains NSRO and MSRO-Br) harbored byDrosophila melanogaster. Isolated particles were subjected to DNA sequencing, assembly, and annotation. Several lines of evidence suggest that we recovered phage-like particles of similar features (shape, size, DNA content) to those previously reported inDrosophila-associatedSpiroplasmastrains. We recovered three 19 kb phage-like contigs (two in NSRO and one in MSRO-Br) containing 2124 open reading frames, a read-alignment pattern consistent with circular permutation, and terminal redundancy (at least in NSRO). Although our results do not allow us to distinguish whether these phage-like contigs 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 also recovered two smaller non-phage-like contigs encoding a knownSpiroplasmatoxin (Ribosome Inactivating Protein; RIP), and an insertion element, suggesting that they are packaged into particles. Substantial homology of our particle-derived contigs was found in the genome assemblies of members of theSpiroplasma poulsoniiclade.
