Genetic, metabolic and toxicological diversity within Prymnesium parvum (Haptophyte) from Polish waterbodies.

Toxic blooms of Prymnesium parvum pose one of the most serious environmental threats. This alga occurs worldwide and has devastating effects on gill-breathing organisms inhabiting inland waters. In 2022, Polish society was faced with the problem for the first time. A high biomass of P. parvum in the Gliwice Canal, the Odra River and the oxbow lakes resulted in large-scale fish kills and significant economic losses. Since then, the toxic alga has become a permanent component of the Gliwice Canal phytoplankton community. Studies on P. parvum from other geographical regions have revealed existence of genotypic and phenotypic variation between and within the populations. Therefore, it was important to examine the specific characteristics of P. parvum from Polish water bodies. Here, we present the results of studies on the dynamics of B-type prymnesins (PRMs) production by P. parvum in the Gliwice Canal in 2023. For the purpose of the study, three B-type PRM variants were isolated and used as standards for toxins quantification and toxicity assessment. Differences in cytotoxicity of three isolated B-type prymnesins against fish (RTgill-W1) and human cells (fibroblasts - HDFa and lung cancer cells - A549) were documented for the first time. The lack of a clear correlation between the number of P. parvum cells and PRMs concentration indicates the heterogeneity of the population. Molecular characterisation of P. parvum CCNP2001 strain from Polish waters was also performed. The genome of the strain was sequenced, and the organisation of the PKZILLA genes involved in the biosynthesis of PRMs was described. These genes were present in all analysed bloom samples and in the isolated P. parvum strain. Analysis of the 5.8S rRNA gene sequence yielded unexpected results which indicated that CCNP2001 belongs to a type A prymnesin-producing strain. Additionally, high-resolution mass spectrometry analyses revealed the presence of A-type prymnesin in CCNP2001, supporting the findings of the genetic studies. This study also represents the first investigation into the impact of environmental conditions on the expression of the PKZILLA-1 and PKZILLA-2 genes in P. parvum. The obtained results were compared to prymnesin production level. Our broad-scale studies provided new data on the dynamics, toxicity of PRMs, and molecular characteristics of P. parvum from Polish waterbodies. The results also highlighted existing gaps in knowledge regarding population diversity, the role of prymnesins, and potentially other metabolites, in harmful effects of P. parvum blooms.