The impact of EGFP transformation on fitness of bioactive streptomycetes

Streptomycetes have been extensively studied for the production of bioactive compounds in pharmaceutical industry and to a lesser extent for their potential biological control activity in agriculture. The EGFP (enhanced green fluorescence protein) approach was applied to study Streptomyces-mediated biological control of soil-borne fungal pathogens of horticultural crops, and to visualize their localization and interactions in/with the host plant. Five wild-type Streptomyces strains that showed strong in vitro antagonistic activity against Sclerotinia sclerotiorum were transformed with the EGFP gene by conjugation. The conjugation efficiencies varied among strains from 5.81×10−8 to 4.64×10−5 ex-conjugants/recipient cell. The successful transformation and expression of EGFP was verified by fluorescence microscopy, and additionally confirmed by PCR. Horizontal gene transfer may change the fitness or activity of the biological control agents (BCAs), which can interfere with studies on the mode of action and plant-microbe interactions. Therefore, the influences of the EGFP transformation on the in vitro antagonistic activity against S. sclerotiorum, growth rate and sporulation ability in the EGFP-transformed BCAs were evaluated. The results indicated that none of the characters were significantly altered, except for one ex-conjugant of the EGFP-FT05W strain showing reduced antagonistic activity. Further studies about the impact of the EGFP transformation on the production of secondary metabolites important for biological control are needed. The EGFP-tagged Streptomyces strains that do not show altered fitness and biological control activity will be utilized to study plant-pathogen-microbe interactions, and will contribute to further understanding of biological control mechanisms of plant soil-borne fungal pathogens.