De novo Transcriptome of the Non-saxitoxin Producing Alexandrium tamutum Reveals New Insights on Harmful Dinoflagellates.

Giorgio Maria Vingiani,Pasquale De Luca,Dārta Štālberga,Daniele De Luca,Chiara Lauritano,Adrianna Ianora

doi:10.3390/md18080386

Abstract

Many dinoflagellates species, especially of the Alexandrium genus, produce a series of toxins with tremendous impacts on human and environmental health, and tourism economies. Alexandrium tamutum was discovered for the first time in the Gulf of Naples, and it is not known to produce saxitoxins. However, a clone of A. tamutum from the same Gulf showed copepod reproduction impairment and antiproliferative activity. In this study, the full transcriptome of the dinoflagellate A. tamutum is presented in both control and phosphate starvation conditions. RNA-seq approach was used for in silico identification of transcripts that can be involved in the synthesis of toxic compounds. Phosphate starvation was selected because it is known to induce toxin production for other Alexandrium spp. Results showed the presence of three transcripts related to saxitoxin synthesis (sxtA, sxtG and sxtU), and others potentially related to the synthesis of additional toxic compounds (e.g., 44 transcripts annotated as “polyketide synthase”). These data suggest that even if this A. tamutum clone does not produce saxitoxins, it has the potential to produce toxic metabolites, in line with the previously observed activity. These data give new insights into toxic microalgae, toxin production and their potential applications for the treatment of human pathologies.

Highlights

Harmful algal blooms (HABs) are intense algal proliferations that can profoundly disrupt the habitat where they occur via the production of high biomass accumulation, which causes oxygen depletion and the production of high amounts of toxins [1,2]
Despite the fact that type I polyketide synthases (PKS) are typically multifunctional enzymes organized into modules, each harbouring a set of distinct domains, we only found single domain type I PKSs, as reported for other toxic dinoflagellate studies [98,99,100]
There is an increased need to study toxin biosynthetic pathways and the enzymes involved in their metabolism, in order to rapidly detect harmful algal blooms, monitor their distribution and toxicity, contrast these occurrences, and when possible, reduce their detrimental effects

Summary

Introduction

Harmful algal blooms (HABs) are intense algal proliferations that can profoundly disrupt the habitat where they occur via the production of high biomass accumulation, which causes oxygen depletion and the production of high amounts of toxins [1,2]. HABs induce detrimental effects on marine organisms, humans, environments and economies [1,3]. They are often associated to toxin-producing freshwater cyanobacteria and marine dinoflagellates [4]. Dinoflagellates, together with diatoms, are the main primary producers in aquatic ecosystems. Alexandrium spp. is one of the most common marine dinoflagellates known to be responsible for seasonal HABs; there are more than. 40 species, half of which are known to produce toxins [5]. Microalgae are known to produce a series of compounds, generally derived from secondary metabolism, known to regulate and control algal

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Conclusion