Abstract
BackgroundHeterologous expression of bacterial biosynthetic gene clusters is currently an indispensable tool for characterizing biosynthetic pathways. Development of an effective, general heterologous expression system that can be applied to bioprospecting from metagenomic DNA will enable the discovery of a wealth of new natural products.MethodologyWe have developed a new Escherichia coli-based heterologous expression system for polyketide biosynthetic gene clusters. We have demonstrated the over-expression of the alternative sigma factor σ54 directly and positively regulates heterologous expression of the oxytetracycline biosynthetic gene cluster in E. coli. Bioinformatics analysis indicates that σ54 promoters are present in nearly 70% of polyketide and non-ribosomal peptide biosynthetic pathways.ConclusionsWe have demonstrated a new mechanism for heterologous expression of the oxytetracycline polyketide biosynthetic pathway, where high-level pleiotropic sigma factors from the heterologous host directly and positively regulate transcription of the non-native biosynthetic gene cluster. Our bioinformatics analysis is consistent with the hypothesis that heterologous expression mediated by the alternative sigma factor σ54 may be a viable method for the production of additional polyketide products.
Highlights
Bacterial polyketides possess an enormous range of chemical diversity and biological function
We have demonstrated a new mechanism for heterologous expression of the oxytetracycline polyketide biosynthetic pathway, where high-level pleiotropic sigma factors from the heterologous host directly and positively regulate transcription of the non-native biosynthetic gene cluster
Our bioinformatics analysis is consistent with the hypothesis that heterologous expression mediated by the alternative sigma factor s54 may be a viable method for the production of additional polyketide products
Summary
Bacterial polyketides possess an enormous range of chemical diversity and biological function. Sequencing of bacterial genomes, especially those of major polyketide producers such as Actinomycetes and dproteobacteria, have shown that there are many more polyketide biosynthetic pathways than polyketides isolated from standard cultivation techniques [5,6,7]. These genetically encoded polyketide natural products from cultivatable and uncultivatable bacteria represent one of the greatest remaining untapped reservoirs of new natural product diversity. Methods to effectively access this diversity will have a major impact on drug discovery [8] To access this untapped diversity of polyketide products, a general method for heterologous expression of these pathways is needed. Development of an effective, general heterologous expression system that can be applied to bioprospecting from metagenomic DNA will enable the discovery of a wealth of new natural products
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