Chapter Six - A Genomic View of Secondary Metabolite Production in Cyanobacteria

Abstract

Abstract Cyanobacteria produce a wide range of secondary metabolites that are very diverse in chemical structure. These metabolites show also very diverse biological activities, including cytotoxicity, neurotoxicity, dermatotoxicity, and inhibition of proteases. The cyanotoxins that are harmful to animals, including humans, are essentially produced by freshwater cyanobacteria, while marine and terrestrial cyanobacteria produce some metabolites that are promising new drugs. Between 2001 and 2010, many biosyntheses of cyanobacterial secondary metabolites have been deciphered at the genetic and biochemical level. Thanks to the advent of genomic data on cyanobacterial genomes and to new powerful bioinformatic tools, about 30 clusters of genes responsible for the production of cyanobacterial secondary metabolites have been identified. The biosyntheses have also been studied in vitro, in certain cases. For instance, among the cyanotoxins, the microcystin, the cylindrospermopsin, the saxitoxin and the anatoxin-a biosyntheses have been elucidated. Almost all cyanobacterial secondary metabolites are the products of polyketide synthases, nonribosomal peptide synthases or hybrid thereof. However, ribosomal peptides are also produced by cyanobacteria, like the cyanobactins and recent genome mining data suggest that these metabolites are more represented than first thought in cyanobacteria. This review gives an overview of the connections between cyanobacterial secondary metabolites and their biosynthetic genes, with emphasis on the most significant cases like the cyanotoxins, sunscreens, alkanes and terpenes.