In many aquatic ecosystems world-wide cyanobacteria can proliferate into so-called “harmful algal blooms”. Members of this bacterial phylum produce an unparalleled array of bioactive secondary metabolites; some of which are potent toxins. The past 30 years has witnessed major advances in our understanding of the genetic basis for toxin production by a number of groups of cyanobacteria. The ecophysiological role of these chemically diverse toxins and the molecular responses of their biosynthesis genes to the environment remains contentious.
Genomic information related to toxin synthesis has indicated their environmental and cellular regulators, as well as associated transport mechanisms. Light quality and quantity have been shown to regulate cyanobacterial toxin gene expression and it appears that other cellular interactions, possibly involving nitrogen metabolism and quorum sensing also affect toxin levels. Correlations between toxicity and salt tolerance raise future concerns for Australia’s inland rivers and coastal zones.
The pattern of acquisition of genes responsible for cyanobacterial and marine microalgae toxicity is not generally related to the evolution of potentially toxic species and their global distribution has been the topic of several phylogeographical studies. Toxin biosynthesis gene cluster-associated transposition and the natural transformability of certain species allude to a broader distribution of toxic taxa.
The information gained from the discovery of these toxin biosynthesis pathways has enabled the genetic screening of various environments for water quality management. The ratio of toxin genes to 16S rRNA allows the estimation of the extent of the toxic populations among the entire cyanobacterial community present along spatial and temporal grades.
So why do some and not other species produce a particular toxin and why only on certain continents at certain times? Pre- and post-omic data from the lab and field will be presented. This talk is a tribute to all those students and scientists that have accompanied me on this journey.