title: Impact of nitrogen sources on gene expression and toxin production in the diazotroph Cylindrospermopsis raciborskii CS-505 and non-diazotroph Raphidiopsis brookii D9.
abstract: Different environmental nitrogen sources play selective roles in the development of cyanobacterial blooms and noxious effects are often exacerbated when toxic cyanobacteria are dominant. Cylindrospermopsis raciborskii CS-505 (heterocystous, nitrogen fixing) and Raphidiopsis brookii D9 (non-N₂ fixing) produce the nitrogenous toxins cylindrospermopsin (CYN) and paralytic shellfish toxins (PSTs), respectively. These toxin groups are biosynthesized constitutively by two independent putative gene clusters, whose flanking genes are target for nitrogen (N) regulation. It is not yet known how or if toxin biosynthetic genes are regulated, particularly by N-source dependency. Here we show that binding boxes for NtcA, the master regulator of N metabolism, are located within both gene clusters as potential regulators of toxin biosynthesis. Quantification of intra- and extracellular toxin content in cultures at early stages of growth under nitrate, ammonium, urea and N-free media showed that N-sources influence neither CYN nor PST production. However, CYN and PST profiles were altered under N-free medium resulting in a decrease in the predicted precursor toxins (doCYN and STX, respectively). Reduced STX amounts were also observed under growth in ammonium. Quantification of toxin biosynthesis and transport gene transcripts revealed a constitutive transcription under all tested N-sources. Our data support the hypothesis that PSTs and CYN are constitutive metabolites whose biosynthesis is correlated to cyanobacterial growth rather than directly to specific environmental conditions. Overall, the constant biosynthesis of toxins and expression of the putative toxin-biosynthesis genes supports the usage of qPCR probes in water quality monitoring of toxic cyanobacteria.
authors: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany. kstuckenm@gmail.com.
authors: Karina
authors: K
authors: Stucken
authors: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany. Uwe.John@awi.de.
authors: Uwe
authors: U
authors: John
authors: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany. Allan.Cembella@awi.de.
authors: Allan
authors: A
authors: Cembella
authors: Department of Molecular Genetics and Microbiology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile. katiasotoliebe@gmail.com.
authors: Katia
authors: K
authors: Soto-Liebe
authors: Department of Molecular Genetics and Microbiology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile. mvasquez@bio.puc.cl.
authors: Mónica
authors: M
authors: Vásquez
mesh_terms: D000470:Alkaloids; D064751:Ammonium Compounds / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000096:biosynthesis* / Q000737:chemistry; D061249:Batch Cell Culture Techniques; D001938:Brazil; D000458:Cyanobacteria / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism*; D000087522:Cyanobacteria Toxins; D046891:Cylindrospermopsis / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism*; D005618:Fresh Water / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D015394:Molecular Structure; D009566:Nitrates / Q000378:metabolism; D009586:Nitrogen Fixation; D011042:Poisons / Q000737:chemistry / Q000378:metabolism*; D011793:Queensland; D014498:Uracil / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000737:chemistry; D014508:Urea / Q000378:metabolism
chemical_list: D000470:Alkaloids; D064751:Ammonium Compounds; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D000087522:Cyanobacteria Toxins; D009566:Nitrates; D011042:Poisons; C089595:cylindrospermopsin; D014498:Uracil; D014508:Urea