Phylogeny of type I polyketide synthases (PKSs) in fungal entomopathogens and expression analysis of PKS genes in Beauveria bassiana BCC 2660.

Entomopathogenic fungi are able to invade and kill insects. Various secondary metabolites can mediate the interaction of a fungal pathogen with an insect host and also help the fungus compete with other microbes. Here we screened 23 isolates of entomopathogenic fungi for polyketide synthase (PKS) genes and amplified 72 PKS gene fragments using degenerate PCR. We performed a phylogenetic analysis of conserved ketosynthase and acyltransferase regions in these 72 sequences and 72 PKSs identified from four insect fungal genome sequences. The resulting genealogy indicated 47 orthologous groups with 99-100 % bootstrap support, suggesting shared biosynthesis of identical or closely related compounds from different fungi. Three insect-specific groups were identified among the PKSs in reducing clades IIa, IIb, and III, which comprised PKSs from 12, 9, and 30 fungal isolates, respectively. A IIa-IIb pair could be found in seven fungi. Expression analyses revealed that eleven out of twelve PKS genes identified in Beauveria bassiana BCC 2660 were expressed in culture. PKS genes from insect-specific clades IIa and IIb were expressed only in insect-containing medium, while others were expressed only in PDB or in CYB, PDB and SDY. The data suggest the potential production of several polyketides in culture.

On the trail of an elusive flux sensor.

The hexokinase PII isozyme has been implicated as an essential component of multiple glucose sensing pathways in the yeast Saccharomyces cerevisiae. Several lines of evidence suggest that the flux through this enzymatic step, but not the levels of substrates, cofactors or products, is the critical process detected by downstream sensing machinery. In spite of intensive research efforts, how the activity of this enzyme is translated into a quantitative signal remains an unresolved question.