Chrysochromulina: Genomic assessment and taxonomic diagnosis of the type species for an oleaginous algal clade

Background: Until recent studies documented their extensive contribution to primary productivity and carbon sequestration, haptophytes remained underappreciated players in global ecosystem processes. Contemporary analyses, augmented by the use of molecular probes, show the haptophyte taxon Chrysochromulina to be seminal to the ecology of both marine and freshwater ecosystems. Unfortunately, description for the type species for this clade remains enigmatic. Results: Chrysochromulina parva Lackey was re-isolated from Big Walnut Creek (Ohio), the site where the original isolate was obtained. The sequenced haploid genome of this organism is 65.7 Mb in size. Several noteworthy nuclear-encoded genes identified include a novel ftsZ (mediates organelle division) that phylogenetically clusters with the Chloroarachniophytes. Also revealed, is a complement of genes associated with meiosis and DNA repair, indicating the presence of a sexual cycle in this alga. Mitochondrial genes lost to the nucleus include all extrinsic components of the nad complex, completing a punctate pattern of transfer that is observed among algal taxa. Comparison of the newly sequenced Chrysochromulina parva Lacky isolate was made with that of Chrysochromulina tobinii (59.1 Mb) - a fresh water strain isolated from a lake in Colorado. Conclusion: Genomic analysis suggests that fresh water Chrysochromulina isolates, though geographically well separated, from a related clade. The name of the type species of Chrysochromulina parva Lacky is anchored with a lectotype and epitype, and the second isolate is described as Chrysochromulina tobinii sp. nov. Chrysochromulina represents a new, extremely tractable model organism for experimental studies. This oleaginous alga has a small genome and because it represents only the second haptophyte taxon to be sequenced and assembled, presents new opportunity to examine the evolution of an algal taxon that plays an intrinsic role in ecosystem function.