Why transgenic biocontrol agents?
Genetic engineering offers an approach to enhance the consistency of performance, spectrum of activity and colonising ability of BCAs. All mechanisms of biocontrol (competition/pre-emptive exclusion, parasitism/predation, induction of systemic resistance and antibiosis/toxin production) have been targeted for improvement during the last 25 years. Selected examples of proof of concept studies are given below.
Expression of the Pseudomonas putida WCS358 ferric siderophore receptor pupA in strain WCS374 increased the competitiveness of WCS374 against WCS358 when both strains were co-inoculated (Raaijmakers et al., 1995). Increasing the copy number of the Pseudomonas fluorescens WCS365 site-specific recombinase gene sss in F113 and WCS307 increased the competitive colonisation ability of the recombinant strains on tomato root tips (Dekkers et al., 2000). This gene plays a role in DNA rearrangements and is thought to help keep bacterial cells from becoming “locked in” a state unfavourable for competitive colonisation.