Genomic analyses of < i > Symbiomonas scintillans < /i > show no evidence for endosymbiotic bacteria but does reveal the presence of giant viruses

by Anna Cho, Gordon Lax, Samuel J. Livingston, Yumiko Masukagami, Mariia Naumova, Olivia Millar, Filip Husnik, Patrick J. KeelingSymbiomonas scintillans Guillou et Chr étiennot-Dinet, 1999 is a tiny (1.4 μm) heterotrophic microbial eukaryote. The genus was named based on the presence of endosymbiotic bacteria in its endoplasmic reticulum, however, like most such endosymbionts neither the identity nor functional association with its host were known. We generated both amplification-free shotgun metagenomics and whole genome amplification sequencing data fromS.scintillans strains RCC257 and RCC24, but were unable to detect any sequences from known lineages of endosymbiotic bacteria. The absence of endobacteria was further verified with FISH analyses. Instead, numerous contigs in assemblies from both RCC24 and RCC257 were closely related to prasinoviruses infecting the green algaeOstreococcus lucimarinus,Bathycoccus prasinos, andMicromonas pusilla (OlV, BpV, and MpV, respectively). Using the BpV genome as a reference, we assembled a near-complete 190 kbp draft genome encoding all hallmark prasinovirus genes, as well as two additional incomplete assemblies of closely related but distinct viruses from RCC247, and three similar draft viral genomes from RCC24, which we collectively call SsVs. A multi-gene tree showed the three SsV genome types branched within highly supported clades with each of BpV2, OlVs, and MpVs, respectively. Interestingly, transmission electron microscopy als...

Source: PLoS Genetics - April 1, 2024 Category: Genetics & Stem Cells Authors: Anna Cho Source Type: research