Proteorhodopsins are light-driven proton pumps involved in widespread phototrophy. Discovered in marine proteobacteria just 10 years ago, proteorhodopsins are now known to have been spread by lateral gene transfer across diverse prokaryotes, but are curiously absent from eukaryotes. In this study, we show that proteorhodopsins have been acquired by horizontal gene transfer from bacteria at least twice independently in dinoflagellate protists. We find that in the marine predator Oxyrrhis marina,…

Microsporidia are a group of highly adapted unicellular fungi that are known to infect a wide range of animals, including humans and species of great economic importance. These organisms are best known for their very simple cellular and genomic features, an adaptive consequence of their obligate intracellular parasitism. In the last decade, the acquisition of a large amount of genomic and transcriptomic data from several microsporidian species has greatly improved our understanding of the…

With malaria parasites (Plasmodium spp.), Toxoplasma, and many other species of medical and veterinary importance its iconic representatives, the protistan phylum Apicomplexa has long been defined as a group composed entirely of parasites and pathogens. We present here a report of a beneficial apicomplexan: the mutualistic marine endosymbiont Nephromyces. For more than a century, the peculiar structural and developmental features of Nephromyces, and its unusual habitat, have thwarted…

Intron reduction and loss is a significant component of genome compaction in many eukaryotic lineages, including yeasts, microsporidia, and some nucleomorphs. Nucleomorphs are the extremely reduced relicts of algal endosymbiont nuclei found in two lineages, cryptomonads and chlorarachniophytes. In cryptomonads, introns are rare or even lost altogether. In contrast, the nucleomorph of the chlorarachniophyte Bigelowiella natans contains the smallest nuclear genome known but paradoxically also…

Dinoflagellates have among the largest nuclear genomes known, but we know little about their contents or organisation. Given the interest in dinoflagellate ecology, cell biology, and evolutionary biology, there are many reasons to thoroughly investigate the contents of dinoflagellate genomes, but because of their large size the only thorough samples to date have relied on expressed sequence tag surveys to analyse cDNAs. To complement this, there are some studies of the physical properties of…

No abstract

Reconstructing the history of plastid acquisition and loss in the alveolate protists is a difficult problem because our knowledge of the distribution of plastids in extant lineages is incomplete due to the possible presence of cryptic, nonphotosynthetic plastids in several lineages. The discovery of the apicoplast in apicomplexan parasites has drawn attention to this problem and, more specifically, to the question of whether many other nonphotosynthetic lineages also contain cryptic plastids or…

The mitochondrial genome and the expression of the genes within it have evolved to be highly unusual in several lineages. Within alveolates, apicomplexans and dinoflagellates share the most reduced mitochondrial gene content on record, but differ from one another in organisation and function. To clarify how these characteristics originated, we examined mitochondrial genome form and expression in a key lineage that arose close to the divergence of apicomplexans and dinoflagellates, Oxyrrhis…

Sequence variability of RPCS (repetitive PuvII Ctenomys sequence), the major satellite DNA of octodontid Ctenomys rodents, was analysed in species belonging to three groups of species representing the two patterns of karyotypic evolution in the genus: stable and dynamic karyotypes among closely related species. The studied species represent the overall range of RPCS copy number (2000–6.6×10(6) copies per haploid genome) in the genus. RPCS sequence was characterised by PCR amplification of the…