Authentication of the proteins expression profiles (PEPs) identification methodology in a bloom of Karenia digitata, the most damaging harmful algal bloom causative agent in the history of Hong Kong

Identification of harmful algal bloom (HAB) causative agents makes use either of morphology-based techniques or genetic tools. These techniques are often time-consuming, labor intensive, and/or based on subjective judgment. Recently, matching with protein/peptide expression profiles (PEPs) obtained with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI–TOF–MS) has emerged as a new technique for species identification of various microorganisms. We were the first group to adopt this rapid and simple methodology for the identification of dinoflagellates (Lee et al., 2008). In the present study, we evaluated the use of PEPs from MALDI–TOF–MS for species identification of field samples obtained from a local red-tide caused by Karenia digitata. PEPs obtained from direct MALDI–TOF–MS analysis of field samples were compared to that of established monospecific reference culture. Several species-specific peaks of K. digitata were found in the reference monoculture and most of these observed peaks could be matched to the PEPs of the field samples. Matched species-specific peaks observed from the PEPs of field samples would allow rapid identification of the causative agents in corresponding and future HABs. Furthermore, as K. digitata is the most damaging dinoflagellate in Hong Kong's history, we were interested in obtaining its SSU, partial LSU rDNA and ITS sequences for future studies. In the present study, besides reporting on the ITS and rDNA sequences of K. digitata, phylogenetic tree analysis was also performed. The results showed that K. digitata fell within the Karlodinium clade and had a closer relationship with the Karlodinium species than the Karenia species.

► We had developed a rapid and simple methodology for the identification of dinoflagellates by using PEPs obtained with MALDI–TOF–MS. ► PEPs of local red-tide field samples caused by K.digitata were obtained successfully. ► Most of the observed peaks from the PEPs of monoclonal culture could be matched to the PEPs of red-tide field samples. ► ITS and rDNA sequences as well as phylogenetic analysis revealed that K.digitata bears a striking similarity to Karlodinium spp.