California Sea Grant College Program

During the last three decades, tropical marine cyanobacteria have emerged as an extraordinarily prolific source of promising biomedical natural products (NPs). Creative endeavors have been used to explore this novel chemical diversity, but lagging behind is the recognition and description of the biological diversity responsible for these NPs. Instead of being recognized as unique taxa, tropical marine NP-producing groups have been identified, with few exceptions, based on classification systems tied to morphospecies of terrestrial and freshwater specimens from temperate regions. This lack of proper classification systems is primarily due to the fact that tropical marine cyanobacteria have only recently been explored. As a result, our current perspective of the taxonomic origin and distribution of NPs in marine cyanobacteria is extraordinarily incomplete.

A major aspect of this thesis research has focused on providing a better understanding of how NPs are distributed among different cyanobacterial groups so as to improve the efficiency of future investigations. The initial perception was that bioactive secondary metabolites are unequally distributed among different taxonomic groups with a few groups being responsible for the majority of the isolated NPs. However, based on polyphasic characterization of globally distributed populations, many of the most chemically prolific groups were found to constitute polyphyletic groups. Moreover, a large proportion of the secondary metabolites attributed to these groups are in fact produced by morphologically similar but evolutionarily distant cyanobacteria. I argue that this morphological resemblance of different cyanobacterial lineages is a major reason why some cyanobacterial groups have such an apparent richness of secondary metabolites.

In my efforts to provide taxonomic clarity as well as to better guide future natural product drug discovery investigations, I have proposed a revision of the NP-rich genus Lyngbya on the basis of phylogenetic, genomic, secondary metabolism and ultrastructural comparisons with the genus reference strain PCC 7419^T. In conclusion, this proposed revision of "tropical marine Lyngbya" as a new genus (Mooreagen. nov.) highlights the underestimated biodiversity of tropical marine cyanobacteria.