The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

Morphological observation and chemical composition analysis of P. globosa strains isolated from different geographical regions showed differences in single-cell surface structures, colony sizes, toxicity level and pigment compositions, suggesting that P. globosa has high genetic diversity. However, how to distinguish different P. globosa genotypes and monitor the dynamics of genotypes in the field remain to be established. In this study, we ascertained genetic diversity of P. globosa with different molecular markers.
Single-strain sequencing of the common molecular marker 18S rDNA V4 amplicons of 54 P. globosa strains revealed that these strains could be divided into two genotypes (18S1 and 18S2). As pigment analysis revealed the possible existence of higher number of P. globosa genotypes, we further carried single-strain sequencing of pgcp1 amplicons of these strains, which yielded 12 genotypes, suggesting that P. globosa has high recognizable genetic diversity. Single-strain analysis indicated that pgcp1 not only has higher resolution compared to 18S rDNA V4 that has high levels of intragenomic variations (IGVs), but also has almost no IGVs, making it an ideal molecular marker for probing and tracking genetic diversity of P. globosa in the field.
We further examined the composition and dynamic changes of P. globosa genotypes during a P. globosa bloom from January to April on 2019 through metabarcoding analysis using these two molecular markers. 18S rDNA V4-based metabarcoding analysis revealed both genotypes (18S1 and 18S2) uncovered above in the single-strain analysis, together with an additional genotype (18S3) that was not identified in the single-strains analysis, suggesting that P. globosa genetic diversity in the field was higher than those captured by the 54 strains. Dynamic analysis revealed that these genotypes showed differential spatiotemporal patterns, with two genotypes (18S1 and 18S3) showing similar patterns with the bloom development, suggesting that these two genotypes contributed to the development of the P. globosa bloom, while the 18S2 genotype showed little change during the bloom, suggesting that this genotype might not contributed to the development of the P. globosa bloom. Similarly, pgcp1-based metabarcoding analysis revealed 76 genotypes (pgcp1-pgcp76), revealing high P. globosa genetic diversity. Differential contribution of these genotypes to the development of P. globosa bloom, and the correlation of different genotypes with environmental factors will be presented.
We also evaluated pigment compositions and cell size variations of different genotypes of P. globosa, which will be helpful to provide more effective evidence for the genetic diversity of P. globosa.

Phaeocystis globosa, metabarcoding analysis, 18S rDNA V4, pgcp1