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Toxins 2017, 9(10), 322; doi:10.3390/toxins9100322

Temperature Influences the Production and Transport of Saxitoxin and the Expression of sxt Genes in the Cyanobacterium Aphanizomenon gracile

Departamento de Biología, Darwin, 2, Universidad Autónoma de Madrid, 28049 Madrid, Spain
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Academic Editor: Luis M. Botana
Received: 28 September 2017 / Revised: 7 October 2017 / Accepted: 9 October 2017 / Published: 13 October 2017
(This article belongs to the Special Issue Selected Papers from the 5th Iberoamerican Cyanotoxins Meeting)
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Abstract

The cyanobacterium Aphanizomenon gracile is the most widely distributed producer of the potent neurotoxin saxitoxin in freshwaters. In this work, total and extracellular saxitoxin and the transcriptional response of three genes linked to saxitoxin biosynthesis (sxtA) and transport (sxtM, sxtPer) were assessed in Aphanizomenon gracile UAM529 cultures under temperatures covering its annual cycle (12 °C, 23 °C, and 30 °C). Temperature influenced saxitoxin production being maximum at high temperatures (30 °C) above the growth optimum (23 °C), concurring with a 4.3-fold increased sxtA expression at 30 °C. Extracellular saxitoxin transport was temperature-dependent, with maxima at extremes of temperature (12 °C with 16.9% extracellular saxitoxin; and especially 30 °C with 53.8%) outside the growth optimum (23 °C), coinciding with a clear upregulation of sxtM at both 12 °C and 30 °C (3.8–4.1 fold respectively), and yet with just a slight upregulation of sxtPer at 30 °C (2.1-fold). Nitrate depletion also induced a high extracellular saxitoxin release (51.2%), although without variations of sxtM and sxtPer transcription, and showing evidence of membrane damage. This is the first study analysing the transcriptional response of sxtPer under environmental gradients, as well as the effect of temperature on putative saxitoxin transporters (sxtM and sxtPer) in cyanobacteria in general. View Full-Text
Keywords: cyanobacteria; saxitoxin; transport; extracellular; sxtA; sxtM; sxtPer; NorM-MATE; Drug Metabolite Transporter (DMT); qPCR cyanobacteria; saxitoxin; transport; extracellular; sxtA; sxtM; sxtPer; NorM-MATE; Drug Metabolite Transporter (DMT); qPCR
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Cirés, S.; Delgado, A.; González-Pleiter, M.; Quesada, A. Temperature Influences the Production and Transport of Saxitoxin and the Expression of sxt Genes in the Cyanobacterium Aphanizomenon gracile. Toxins 2017, 9, 322.

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