Evolutionary analysis of polyketide synthases in symbionts of marine sponges

JÖRN PIEL
Kekulé Institut für Organische Chemie und Biochemie
Rheinische Friedrich-Wilhelms-Universität Bonn
Gerhard-Domagk-Str. 1
53121 Bonn
joern.piel@uni-bonn.de
http://www.chemie.uni-bonn.de/oc/ak_piel

Many sponges harbor an enormous diversity of as-yet unculturable bacteria, which are suspected to be responsible for the production of many bioactive compounds isolated from the animals. Heterologous expression of symbiont biosynthetic pathways in culturable microorganisms could therefore generate renewable sources of rare or novel metabolites. To systematically exploit the biotechnological potential of sponge symbionts, a detailed understanding of their secondary metabolism is required. We have previously shown that a phylogenetic analysis of PCR-amplified ketosynthase regions of modular polyketide synthases (PKSs) allows to target gene clusters belonging to specific polyketide classes even in very large sponge metagenomes. Unexpectedly, in the sponge Theonella swinhoei these studies revealed the presence of a dominant type of PKS unrelated to any other enzyme group. In an analysis of 20 different sponge species of diverse geographic origin the PKS type was found in all bacteriosponges and is therefore ubiquitously distributed, but highly sponge-specific. Three gene clusters cloned from T. swinhoei and Aplysina aerophoba exhibited a similar architecture consisting of a single complete PKS module with a type I fatty acid synthase-like domain set, suggesting their involvement in the production of methyl-branched fatty acids. An analysis of housekeeping genes strongly indicates that at least one of the systems belongs to a bacterium of the Deinococcus/Thermus group. Methyl-branched fatty acids are commonly found in sponges and have often been suggested to be of bacterial origin. The evolutionary and biological implications of these findings are discussed in the talk.

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