Nuclei isolation protocols for flow cytometry allowing nuclear DNA content estimation in problematic microalgal groups

Microalgae are fundamentally important organisms for global ecosystem functioning with high potential in biotechnology and its applications. The knowledge of their nuclear DNA content has become a prerequisite for many areas of microalgal research. Due to common presence of various pigments, secondary metabolites and complex cell walls, the nuclear DNA content estimation using flow cytometry (FCM) is, however, often laborious or even impossible with the currently used protocols. In this study the performance of six nuclei isolation protocols was compared on various problematic microalgae using FCM. The nuclei isolation methods involved osmotic bursting of cells, razor blade chopping of fresh biomass and two newly introduced protocols, razor blade chopping of desiccated biomass and bead beating. These techniques also involved the use of two different nuclei isolation solutions, Otto I + II solutions, and LB01 buffer. Performance of the particular protocols differed greatly, depending on the used nuclei isolation solution and microalgal group. The most successful method was a newly adopted chopping of desiccated biomass in LB01 buffer. This method seems more appropriate for nuclei isolation in filamentous microalgae; on the other hand, bead beating appears to be more suitable for nuclei isolation in solitarily living algae. Using the optimal protocol for a given species, their nuclear DNA content was estimated, resulting in first DNA content estimates for four investigated taxa (Chlamydomonas noctigama, Gonyostomum semen, Microglena sp. and Stigeoclonium sp.). The estimated DNA content spanned from 0.15 to 32.52 pg.

Automated summary

Microalgae are important organisms for global ecosystem functioning and biotechnology. Knowledge of their nuclear DNA content is crucial for research, but estimating it using flow cytometry can be difficult due to their complex cell structures. Different nuclei isolation methods and solutions were compared, with chopping desiccated biomass in LB01 buffer showing the most success. The study also provided the first DNA content estimates for four investigated taxa.