Identification and detection of Cyanobacteria and their toxins in Pacific oysters

Abstract

During a cyanobacterial bloom in Lake Omapere, cyanobacterial toxins were detected in Crassostrea gigas (Pacific oyster) from the Hokianga Harbour using Enzyme-Linked immunosorbent assay (ELISA). However, Detection and confirmation of these results by Liquid-Chromatography Mass-spectrometry (LCMS) were negative. This research investigated whether Pacific oysters were able to uptake cyanobacteria and accumulate cyanobacterial toxins, as well as, characterising cyanobacteria from the Hokianga Harbour region. Results obtained in this project determined Pacific oysters do feed on cyanobacteria; however using LCMS no microcystins could be detected in Pacific oysters that had been fed microcystin producing cyanobacteria. Furthermore, ELISA tests were demonstrated to be unsuitable for detection of microcystins in Pacific oyster tissue due to cross reactivity giving false positives. As Pacific oysters were shown to be capable of feeding on cyanobacteria, identification of isolates obtained from the Hokianga Harbour was undertaken to determine if the isolates were from toxin producing genera. Using morphological and molecular techniques some of the isolates were determined to be related to known toxin producers. To test the potential of these isolates to produce the toxins, PCR primers targeted to the microcystin, cylindrospermopsin, saxitoxin and anatoxin genes were used. The mcyE gene was detected in isolates JW02 and JW04 and this was confirmed by comparing the microcystin genes from known species. This study indicates further work is necessary before the Pacific oysters beds at Hokianga Harbour are reopened. It is currently unclear whether Pacific oysters accumulate cyanobacterial toxins and cyanobacteria with toxin-producing potential have been identified in the Harbour.