Abstract
Burkholderia have potential as biocontrol agents because they encode diverse biosynthetic gene clusters (BGCs) for a range of antimicrobial metabolites. Given the opportunistic pathogenicity associated with Burkholderia species, heterologous BGC expression within non-pathogenic hosts is a strategy to construct safe biocontrol strains. We constructed a yeast-adapted Burkholderia-Escherichia shuttle vector (pMLBAD_yeast) with a yeast replication origin 2 mu and URA3 selection marker and optimised it for cloning BGCs using the in vivo recombination ability of Saccharomyces cerevisiae. Two Burkholderia polyyne BGCs, cepacin (13kb) and caryoynencin (11kb), were PCR-amplified as three overlapping fragments, cloned downstream of the pBAD arabinose promoter in pMLBAD_yeast and mobilised into Burkholderia and Paraburkholderia heterologous hosts. Paraburkholderia phytofirmans carrying the heterologous polyyne constructs displayed in vitro bioactivity against a variety of fungal and bacterial plant pathogens similar to the native polyyne producers. Thirteen Paraburkholderia strains with preferential growth at 30 degrees C compared with 37 degrees C were also identified, and four of these were amenable to genetic manipulation and heterologous expression of the caryoynencin construct. The cloning and successful heterologous expression of Burkholderia biosynthetic gene clusters within Paraburkholderia with restricted growth at 37 degrees C opens avenues for engineering non-pathogenic biocontrol strains.