Physiological and transcriptional responses to inorganic nutrition in a tropical Pacific strain of Alexandrium minutum: Implications for the saxitoxin genes and toxin production
Saxitoxins (STXs) constitute a family of potent sodium channel blocking toxins, causative agents of paralytic shellfish poisoning (PSP), and are produced by several species of marine dinoflagellates and cyanobacteria. Two STX-core genes, sxtA and sxtG, have been well elucidated in Alexandrium but...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | en |
| Published: |
Elsevier Ltd.
2016
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| Subjects: | |
| Online Access: | http://ir.unimas.my/id/eprint/13417/1/Physiological.pdf http://ir.unimas.my/id/eprint/13417/ http://www.sciencedirect.com/science/article/pii/S1568988316300117 http://dx.doi.org/10.1016/j.hal.2016.04.005 |
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| Summary: | Saxitoxins (STXs) constitute a family of potent sodium channel blocking toxins, causative agents of
paralytic shellfish poisoning (PSP), and are produced by several species of marine dinoflagellates and
cyanobacteria. Two STX-core genes, sxtA and sxtG, have been well elucidated in Alexandrium but the
expression of these genes under various nutritional modes in tropical species remains unclear. This study
investigates the physiological responses of a tropical Pacific strain of Alexandrium minutum growing with
nitrate or ammonium, and with various nitrogen to phosphorus (N:P) supply ratios. The transcriptional
responses of the sxt genes were observed. Likewise, a putative sxtI encoding O-carbamoyltransferase
(herein designated as AmsxtI) was recovered from the transcriptomic data, and its expression was
investigated. The results revealed that the cellular toxin quota (Qt) was higher in P-depleted, nitrate-
grown cultures. With cultures at similar N:P (<16), cells grown with excess ammonium showed a higher
Qt than those grown with nitrate. sxtA1 was not expressed under any culture conditions, suggesting that
this gene might not be involved in STX biosynthesis by this strain. Conversely, sxtA4 and sxtG showed
positive correlations with Qt, and were up-regulated in P-depleted, nitrate-grown cultures and with
excess ambient ammonium. On the other hand, AmsxtI was expressed only when induced by P-depletion,
suggesting that this gene may play an important role in P-recycling metabolism, while simultaneously
enhancing toxin production. |
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