Development of sensitive genotype-specific quantitative polymerase chain reaction methods for detection of Phaeocystis globosa in the South China Sea

Since 1997, dense blooms of the alga Phaeocystis globosa have occurred in the South China Sea (SCS), and previous studies have revealed the co-existence in this sea of two types of P. globosa cell characterized by different marker pigment profiles. However, owing to a lack of quantitative methods for the detection of different types of P. globosa cells, the dynamics of P. globosa blooms in the SCS are still poorly understood. In this study, on the basis of phylogenetic analysis of the mitochondrial atp8 (Mit atp8) gene and pigment profiles, the P. globosa strains from Pacific and Atlantic coastal waters were divided into four genotypes, of which Type I and Type IV strains co-exist in the SCS. Furthermore, two genotype-specific quantitative polymerase chain reaction (qPCR) methods were developed targeting the Mit atp8 gene for quantitative determinations of the densities of Type I and Type IV P. globosa cells. Both qPCR methods were reproducible, highly sensitive, and specific with a wide range of detection (from 30 to 1 x 10(8) cells L-1) for target P. globosa genotypes in the field, thereby facilitating the detection of low cell densities prior to bloom development, as well as high cell densities during bloom periods. Finally, the developed qPCR assays were successfully applied to determine the distribution patterns of Type I and Type IV P. globosa in the Beibu Gulf, a region of the SCS characterized by a high frequency of P. globosa blooms.

Automated summary

This study divided Phaeocystis globosa strains into four genotypes based on genetic and pigment profile analysis, identifying the co-existence of Type I and Type IV strains in the South China Sea. The developed qPCR methods proved reproducible, sensitive, and specific with a wide detection range, allowing for accurate quantification of algae densities in different growth stages. The assays were successfully applied to determine the distribution patterns in a region characterized by a high frequency of Phaeocystis globosa blooms.