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1. Biochemistry of peptide and polyketide biosynthesis in cyanobacteria

Cyanobacteria produce numerous and structurally diverse secondary metabolites, in particular nonribosomal peptide (NRP) and polyketide (PK) structures. Various bioactivities could be assigned to these compounds, and some may prove useful either for development into commercial drugs or as biochemical research tools. Microcystin, a worldwide common cyanobacterial hepatotoxin, was the first metabolite whose nonribosomal biosynthesis could be confirmed by knock-out mutagenesis. The microcystin synthetase complex consists of peptide synthetases, polyketide synthases, and hybrid enzymes, and reveals a number of novel enzymatic features, signifying the potential of cyanobacterial biosynthetic systems for combinatorial biochemistry. Recent studies have shown the presence of peptide synthetase genes and polyketide synthase genes within a number of cyanobacterial genomes. This knowledge may be very valuable for future screening projects aimed at the detection of new bioactive compounds. We are currently investigating biosynthesis gene clusters and enzymes from Microcystis, Planktothrix, Anabaena PCC 7120 and Nostoc punctiforme. The main focus of these studies are unique biochemical features of cyanobacterial systems and evolutionary aspects of NRPS and PKS enzymes in cyanobacteria

2. Functional role of cyanobacterial secondary metabolites

We are interested in the functional role of metabolites of the nonribosomal peptide/polyketide class in planktonic cyanobacteria, in particular in the role of the cyclic hetapeptide toxin microcystin for Microcystis. Community structure is very important for toxin producing cyanobacteria and may contribute to its success in the field. Our data support a functional role of microcystin as an intercellular signaling mediator within and between Microcystis colonies. We observed a reception of microcystin depending on light conditions and cell density and an autoinduction of microcystin biosynthesis genes. We are currently investigating the complement of proteins regulated by a microcystin signal and we are keen to understand the role these processes in the freshwater ecosystems.