Identification of phytoplankton isolates from the eastern Canadian waters using long-read sequencing

As important primary producers and key components of biogeochemical processes, phytoplankton communities are highly diverse and continually adapt to changes in the environment, impacting the entire marine ecosystem. Consequently, it remains important to isolate, culture and properly describe new phytoplankton strains to provide relevant model organisms for laboratory research and accurate reference sequences for identification. Here, 73 phytoplankton strains from the eastern Canadian waters were isolated and genetically characterized using a long rRNA fragment (~4000 bp) covering the 18S, ITS and 28S rRNA regions generated with long-read sequencing technology. While most strains (66%) were accurately identified using the partial 18S rRNA gene (~1200 bp-V4-V9), this study broadens the current 28S rRNA reference database by incorporating 41 distinct strains including 30 unique species. In addition, previously unpublished long-read reference sequences were generated for a few genera, including Picochlorum and Droopiella. Species that were previously poorly described in the eastern Canadian waters were also genetically characterized, including a Chaetoceros similis strain. Overall, this work expands the total number of long-read references, an essential resource for accurate identification of phytoplankton and environmental sequences, thereby advancing the taxonomic resolution that could lead to a better understanding of environmental microbial diversity.