Evolution of Type III PKS from cyanobacteria and investigation of a Type III PKS gene cluster

Joachim S. Larsen, Michelle Quezada, Konstantinos Vavitsas, Claudia Vickers and Brett A. Neilan


Cyanobacteria are known as prolific producers of bioactive metabolites many of which are assembled by specialized enzymes called polyketide synthases (PKSs) found co-localized in genomic clusters. Genome mining has greatly advanced discovery of gene clusters. Here, a phylogenomic study has been carried out, with the aim of studying type III PKS found in cyanobacteria. Through genome mining all gene clusters from cyanobacteria containing type III PKS were identified. A total of 90 type III PKS were identified, with the genera Synechococcus, Prochlorococcus and Microcystis showing the most abundance of type III PKS. Surprisingly, phylogenetic analysis of cyanobacterial type III PKS showed that they form two distinct branches, depending on the architecture of the gene clusters they were retrieved from. Through these phylogenetic analysis, a type I/III PKS hybrid gene cluster (MKS gene cluster) from Microcystis aeruginosa PCC 7806 was identified for further investigation. We focused on the MKS cluster due to its novelty and because its expression has shown to be regulated inversely to the biosynthesis of the cyanotoxin microcystin [1, 2], an hepatotoxin critical in water management. Using the novel cloning technology Golden Gate MoClo, the MKS gene cluster will be heterologous expressed in E. coli for in vitro characterization studies and in a cyanobacterial host for in vivo identification of the metabolite produced by the gene cluster. The role of the MKS metabolite in microcystin regulation will be investigated through disruption mutants, transcriptomic and metabolomic studies. Together, this study will expand the knowledge on the specialized metabolite capacities of the toxic organism M. aeruginosa PCC 7806 and the role of biosynthetic gene clusters in toxin regulation.


  1. Sandrini G, Cunsolo S, Schuurmans JM, Matthijs HC, Huisman J: Changes in gene expression, cell physiology and toxicity of the harmful cyanobacterium Microcystis aeruginosa at elevated CO2. Front Microbiol 2015, 6:401.
  2. Makower AK, Schuurmans JM, Groth D, Zilliges Y, Matthijs HC, Dittmann E: Transcriptomics-aided dissection of the intracellular and extracellular roles of microcystin in Microcystis aeruginosa PCC 7806. Appl Environ Microbiol 2015, 81(2):544-554.

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