Freshwater protists: unveiling the unexplored in a large floodplain system

Area of Science:

• Ecology
• Microbiology
• Genomics

Background:

• Protists are vital to ecosystem function, yet their full diversity, especially in freshwater environments, is largely unknown.
• Estimating protist diversity is challenging due to the vast number of species and limited reference data.

Purpose of the Study:

• To assess protist diversity in the Paraná River using metabarcoding.
• To evaluate the novelty of protist genetic sequences against the PR2 database.
• To identify understudied protist groups in freshwater ecosystems.

Main Methods:

• Metabarcoding of environmental DNA from the Paraná River.
• Sequence similarity and phylogenetic analyses to identify novel sequences.
• Comparison against the PR2 reference database for protist sequences.

Main Results:

• Approximately 28% of identified amplicon sequence variants (ASVs) were novel compared to the PR2 database.
• Novel sequences were predominantly associated with heterotrophic protists, often overlooked in freshwater studies.
• New genetic clusters were identified within well-known groups like green algae (Mamiellophyceae, Pedinophyceae) and understudied groups such as Bicosoecida, Codosiga, and Perkinsea.

Conclusions:

• Significant genetic novelty exists within freshwater protist communities, indicating substantial undiscovered diversity.
• Current knowledge gaps extend to both well-documented and less-studied protist lineages.
• Further research, including organism isolation and cultivation, is essential to understand the ecological significance of novel freshwater protists.