Genome size of colonial chrysophytes

Genome size is a fundamental characteristic of the cell and is associated with a number of key features of the organism, such as cell size, division rate or metabolic rate. Knowledge of the genome size is also a prerequisite for many areas of research (e.g. selection of suitable organisms for whole genome sequencing or cell cycle analysis). However, genome size analysis in microalgae is often difficult and involves many methodological challenges. As a result, genome size data for microalgae are largely lacking. In this study, we focused on fragile, poorly growing colonial chrysophytes. We analysed their genome size using flow cytometry and tested the difference between colonial and solitary living chrysophytes on all published genome size data using analysis of variance. We successfully established nine cultures that were further determined to belong to six species of colonial chrysophytes. We estimated their genome size to be on average 0.24 pg·cell–1 for Chrysosphaerella longispina Lauterborn, 1.70 pg·cell–1 for Neotessella lapponica (Skuja) B.Y.Jo, J.I.Kim, W.Shin, P.Škaloud & P.A.Siver, 0.25 pg·cell–1 for Uroglenopsis turfosa (Skuja) R.H.Thompson & D.E.Wujek, 0.31 pg·cell–1 for Urostipulosphaera articulata (Korshikov) Pusztai & Škaloud, 0.22 pg·cell–1 for U. granulata Pusztai & Škaloud and 0.19 pg·cell–1 for U. lindiae (Bourrelly) Pusztai & Škaloud. It was also shown that colonial chrysophytes have larger genomes compared to solitary living species. This study further revealed the smallest genome among colonial chrysophytes, belonging to Urostipulosphaera lindiae. Nevertheless, colonial chrysophytes have lower variance in genome size, possibly due to evolutionary constraints on cell size (and genome size) variation to maintain the functionality of the whole colony movement.