Genome size of chrysophytes varies with cell size and nutritional mode

Abstract

The cellular content of nuclear DNA varies up to 200,000-fold between eukaryotes. These differences can arise via different mechanisms. In particular, cell size and nutritional mode may influence evolution of the nuclear DNA content. Chrysophytes comprise organisms with different cell organizations and nutritional modes. Heterotrophic clades evolved independently several times from phototrophic or mixotrophic ancestors. Thus, chrysophytes are an ideal model taxon for investigating the effect of the nutritional mode on cellular DNA content. We investigated the genome size of heterotrophic, mixotrophic, and phototrophic chrysophytes. We demonstrate that cell sizes and genome sizes differ significantly between taxa with different nutritional modes. Phototrophic strains tend to have larger cell volumes and larger genomes than heterotrophic strains do. The investigated mixotrophic strains had intermediate cell volumes and small to intermediate genome sizes. Heterotrophic chrysophytes had the smallest genomes and cell volumes compared to other chrysophytes. In general, genome size increased with cell volume, but cell volume only partially explained the variation in genome size. In particular, genome sizes of mixotrophic strains were smaller than expected based on cell sizes.

Intraspecific Variation in Protists: Clues for Microevolution from Poteriospumella lacustris (Chrysophyceae)

“…2017) was used to assemble the PacBio reads of strain JBM10. The genome size parameter was chosen based on estimates from Olefeld et al. (2018).…”

Comparative Plastid Genomics of Non-Photosynthetic Chrysophytes: Genome Reduction and Compaction

“…The chrysophyte Hydrurus foetidus forms filamentous branches within a soft polysaccharide coat and is a putatively facultative phototrophic species (Klaveness and Lindstrøm, 2011;Lavoie et al, 2018). Genome size and cell size differ significantly among species exhibiting different nutritional modes (Olefeld et al, 2018). Where known, heterotrophic chrysophytes have the smallest genomes and cell volumes, phototrophs have the largest, and mixotrophs are generally in between the two.…”

“…The extreme reduction in the plastid genome of the non-photosynthetic Spumella-like flagellates examined herein surely results from the evolution of a heterotrophic lifestyle concomitant with the loss of genes for photosynthesis that are no longer needed. According to Olefeld et al, 2018, the loss of photosynthesis in chrysophytes may be due to energetic factors. Chrysophytes generally do not have a carbon-concentrating mechanism (CCM), indicating that they do not use bicarbonate (HCO 3 -) as a carbon source in diverse water environments (Maberly et al, 2009) and that they are subject to carbon limitation as a selection pressure.…”

Morphology, Ultrastructure, and Mitochondrial Genome of the Marine Non-Photosynthetic Bicosoecid Cafileria marina Gen. et sp. nov.

“…Stramenopila can be divided into obligate heterotrophs, the apparently plastid-less labyrinthulomycetes, oomycetes, opalinids, and bicosoecids [10,11]; a plastid-containing group, mostly phototrophic Ochrophyta [13,14], that also includes known non-photosynthetic species such as apochlorotic nonphagotrophic diatoms from the genera Nitzschia [15,16] and Pseudonitzschia [15]; and phagotrophic chrysophytes, e.g., Mallomonas annulate and Spumella sp. [17,18], to name a few. Interestingly, the ochrophytes also retain their plastids when they lose their autotrophic lifestyle [19], while convincing evidence for the presence of a plastid has not been reported for any of the other groups of stramenopiles, which are all non-photosynthetic.…”