Evolutionary mechanisms underlying polyketide diversity in bacteria: Implications from cyanobacteria
ELKE DITTMANN
Humboldt University
Institute of Biology
Department of Molecular Ecology
Chausseestr. 117
D-10115 Berlin
Germany
Elke.Dittmann@rz.hu-berlin.de
http://www.biologie.hu-berlin.de/moloeko/
Modular
polyketide synthases (PKS I) of bacteria provide an enormous reservoir
of natural chemical diversity. Even though a minority of bacterial strains
has maintained and expanded the ability to produce PKS I the list of individual
strains include members from all major bacterial groups. This raises the
question whether there are differences between these groups in acquiring,
retaining, and expanding their PKS stock. Using phylogenetic approaches
we have assessed the different driving forces for the evolution of multimodular
PKS gene clusters. Our data revealed that duplication and homologous recombination
have shaped the modular enzymes found in extant bacteria. The impact of
horizontal gene transfer (HGT) seems to differ between the bacterial groups.
Strongest evidence for HGT was found for proteobacteria, including myxobacteria
(Jenke-Kodama et al., 2005). In a second part of our project we have investigated
a cyanobacterial PKS gene cluster in more detail that encodes enzyme components
with close similarity to characterized myxobacterial PKS. Our specific
questions are:
1) is there a structural relationship between the cyanometabolite and
known myxobacterial metabolites?
2) How similar are mechanistic and biochemical features of such related
biosynthesis enzymes?
3) Are similar biosynthetic pathways in different bacteria under the control
of similar regulatory elements?
4) Do related metabolites play similar roles in different bacterial groups?
Beside of the evolutionary relevance of the project the study represents
the first thorough study of a modular PKS pathway in terrestric cyanobacteria
that are presently largely unexplored.
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