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

• Published in: Toxins 2017-10, Vol.9 (10), p.322
• Main Authors: Cirés, Samuel, Delgado, Adrián, González-Pleiter, Miguel, Quesada, Antonio
• Format: Article
• Language: English
• Subjects: Aphanizomenon gracile; Biosynthesis; Cyanobacteria; Drug Metabolite Transporter (DMT); Environmental gradient; extracellular; Fresh water; Gene expression; Genes; High temperature; Maxima; Neurotoxins; NorM-MATE; qPCR; Saxitoxin; sxtA; sxtM; sxtPer; Temperature; Temperature effects; Transcription; Transport
• ISSN: 2072-6651; 2072-6651
• DOI: 10.3390/toxins9100322

The cyanobacterium 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 ( ) and transport ( , ) were assessed in 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 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 at both 12 °C and 30 °C (3.8-4.1 fold respectively), and yet with just a slight upregulation of at 30 °C (2.1-fold). Nitrate depletion also induced a high extracellular saxitoxin release (51.2%), although without variations of and transcription, and showing evidence of membrane damage. This is the first study analysing the transcriptional response of under environmental gradients, as well as the effect of temperature on putative saxitoxin transporters ( and ) in cyanobacteria in general.