Isolation and identification of an actinomycete strain with a biocontrol effect on the phytopathogenic Erwinia chrysanthemi 3937VIII responsible for soft rot disease

Abstract

Erwinia chrysanthemi is a phytopathogenic bacterium causing soft rot disease in several agricultural products. Conventional techniques used in the control of this phytopathology have serious limitations due to the emergence of resistant strains and the undesirable effect on the environment of chemical treatments. In this work, we report the isolation of an actinomycete strain from a Moroccan biotope that inhibits the growth of Erwinia chrysanthemi 3937VIII. PCR amplification and DNA sequencing of the 16 S ribosomal RNA gene allowed the identification of this strain as Streptomyces cinereoruber. The concentrated culture supernatant of this actinomycete strain exhibited activity against the growth of Erwinia chrysanthemi 3937VIII and two Gram-positive bacteria, Staphylococcus aureus and Bacillus amylolitiquefaciens, but had no effect on other Gram-negative bacteria tested (Erwinia carotovora 197stpR, Escherichia coli TG1 and Pseudomonas sp.), suggesting that this actinomycete strain secretes into the extracellular medium a substance that inhibits selectively the growth of other bacteria, especially the phytopathogenic Erwinia chrysanthemi 3937VIII. The antibacterial activity of Streptomyces cinereoruber found in this study highlights the importance of actinomycetes strains as candidates for the biological control of pathogenic bacteria. The identification and characterization of the active substance would open the way for further technological and therapeutic investigations.