Dynamics of Cylindrospermopsin Production and Toxin Gene Expression in Aphanizomenon ovalisporum

Aphanizomenon ovalisporum is a cylindrospermopsin (CYN)-producing cyanobacteria species that due to its increasing worldwide distribution has become an important health alarm in the last few years. Several clusters of genes involved in CYN production have been described in different CYN+ cyanobacteria genera, named aoa for Aphanizomenon and cyr for Cylindrospermopsis and others strains. The sequences of those genes are highly similar, but a rearrangement in gene order is also observed. The information on the control of CYN production by gene expression is still scarce, especially in Aphanizomenon. To obtain further information about the control of CYN production in A. ovalisporum, we have quantified the intra and extracellular CYN content, during nine days in BG11 batch cultures under optimal conditions. In parallel, the expression of four genes related to CYN synthesis, aoaA-C and cyrJ, has been analyzed by real time q-PCR. The results show a similar pattern of total CYN accumulation and gene expression. Most of the CYN is found intracellularly. Considering the high nitrogen content in the CYN molecule, we have explored if nitrogen assimilation could be related to CYN synthesis. We found inside the aoaA and aoaC sequences several putative binding domains for the global nitrogen regulator NtcA. The pattern of the ntcA expression along the culture is similar to that of CYN accumulation. Our data suggest that CYN production in A. ovalisporum seems to be controlled both by the expression of genesaoa and ntcA, this last one suggesting the influence of available nitrogen; however, other regulation mechanisms of CYN synthesis cannot be discarded.