Production of hybrids of Streptomyces bikiniensis strain HD-087 by genome shuffling and enhancement of its bio-control activity against Fusarium oxysporum f. sp. cucumerinum

Summary

Fusarium wilt, caused by Fusarium oxysporum Schlecht. emend. Snyd. Hans. f. sp. cucumerinum, is one of the major constraints on cucumber (Cucumis sativus L.) production worldwide. We previously isolated and identified a novel strain of Streptomyces bikiniensis, HD-087, which had anti-fungal activity against F. oxysporum f. sp. cucumerinum. Here, we have applied four rounds of genome shuffling (GS) to S. bikiniensis strain HD-087 to enhance its bio-control activity. An improved strain, HD-087-18, was obtained, with a zone of growth-inhibition against F. oxysporum f. sp. cucumerinum up to 30.52 mm in diameter, substantially greater than that of the parental strain (24.30 mm). The antibiotics present in the culture broth of HD-087-18 which were active against F. oxysporum f. sp. cucumerinum were water-soluble and stable under UV light for 13 h, although they were de-activated by heating to 100ºC for 10 min, or by exposure to pH 11.0. Soaking cucumber seeds in broth of the genome-shuffled strain resulted in an improved bio-control effect (67.5%) that was statistically significant compared to 61.2% for broth of the wild-type strain, and its plant growth-promoting activity was also enhanced relative to that of the wild-type strain.