Prymnesium parvum is a toxin-producing haptophyte that causes harmful algal blooms (HABs) globally, leading to large scale fish kills that have severe ecological and economic implications.
A HAB on the Norfolk Broads, U.K, in 2015 caused the deaths of thousands of fish. Using optical microscopy and 16S rRNA gene sequencing of water samples, P. parvum was shown to dominate the microbial community during the fish-kill. Using liquid chromatography-mass spectrometry (LC-MS), the ladder-frame polyether prymnesin-B1 was detected in natural water samples for the first time. Furthermore, prymnesin-B1 was detected in the gill tissue of a deceased pike (Exos lucius) taken from the site of the bloom; clearing up literature doubt on the biologically relevant toxins and their targets.
Using microscopy, natural P. parvum populations from Hickling Broad were shown to be infected by a virus during the fish-kill. A new species of lytic virus that infects P. parvum was subsequently isolated, Prymnesium parvum DNA virus (PpDNAV-BW1). Morphological analysis and genome sequencing revealed PpDNAV-BW1 to belong to the Megaviridae family of algal viruses. We propose that viral lysis of P. parvum may act as a novel release mechanism for intracellular toxins.
The sialic acid, 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN) has recently been shown to be important in viral infections of microalgae. LC-MS was used to demonstrate that P. parvum contains KDN. Candidate sequences for KDN biosynthesis from P. parvum were cloned and expressed and shown to produce cytidine monophosphate-activated KDN (CMPKDN). Using the newly characterized sequences in BLASTp analysis, we revealed that sialic acid biosynthesis is widespread amongst algae.
Using bioinformatics, NDP-β-L-rhamnose biosynthesis was explored in P. parvum and across other algae. We propose that the haptophytes have acquired bacterial TDP-β-L-rhamnose biosynthetic genes from horizontal gene transfer and subsequently passed them on to some dinoflagellate species. Sugar-nucleotide profiling of two representative algae support this proposition
