Strain JAU4234, identified as Streptomyces padanus, was isolated from soil collected in Jiangxi Province, China. It produced actinomycin X2, fungichromin, and a new polyene macrolide compound with antifungal activity, antifungalmycin 702. Antifungalmycin 702 had good general antifungal activity and may have potential future agricultural and/or clinical applications.

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Antifungalmycin 702, a new polyene macrolide antibiotic produced by Streptomyces padanus JAU4234, has a broad antifungal activity and may have potential future agricultural and/or clinical applications. However, the mechanism of antifungal action of antifungalmycin 702 remains unknown. Antifungalmycin 702 strongly inhibited mycelial growth and sclerotia formation/germination of Rhizoctonia solani. When treated with antifungalmycin 702, the hyphae morphology of R . solani became more irregular. The membrane and the cellular organelles were disrupted and there were many vacuoles in the cellular space. The lesion in the plasma membrane was detected through the increase of membrane permeability, lipid peroxidation and leakage of cell constituents. In summary, antifungalmycin 702 may exert its antifungal activity against R . solani by changing the structure of cell membranes and the cytoskeleton and interacting with the organelles.

Antifungalmycin 702, a novel polyene macrolide antibiotic produced by Streptomyces padanus JAU4234, strongly inhibited mycelial growth of the rice blast fungus, Magnaporthe grisea, with EC50 of 37 μg/ml and EC90 of 136 μg/ml. Significant reduction in the number of conidia was observed at above 20 μg/ml. Conidia germination and appressorium formation were also suppressed and were not viable with >40 μg/ml. When treated with antifungalmycin 702, hyphae morphology became irregular. Based on microscopic examination, antifungalmycin 702 may exert its antifungal activity by changing the structure of cell membranes and the cytoskeleton and interacting with the organelles. Antifungalmycin 702 thus has potential as a new fungicide in the treatment of rice blast disease.

BACKGROUND: There are two different routes for vitamin B12 biosynthesis, which results in discrepancies and uncertainties of the dissolved oxygen (DO) concentration for vitamin B12 fermentation. In this paper, the DO control strategy was explored for industrial vitamin B12 fermentation by Pesudomonas denitrificans in 120000‐L fermenter.RESULTS: A DO‐stat strategy was first successfully scaled up from a 9000 L fermenter to a 120 000 L fermenter. Then a multi‐stage DO control strategy was further established in the 120 000 L fermenter, in which the DO level was shifted from 8–10% (20–48 h) to 2–5% (49–106 h) and below 2% (107–168 h) by gradually reducing the rate of aeration and agitation. As a result, 198.80 mg L−1 of vitamin B12 was obtained, which was significantly higher than those obtained under the fermentations with one‐stage DO control.CONCLUSIONS: The comparatively low DO level was favorable for vitamin B12 biosynthesis, but it would have an extremely negative effect on cell growth. Compared with the low DO level maintained at all times of the fermentation process, a multi‐stage DO control strategy could not only increase the biomass but also improve vitamin B12 biosynthesis. Copyright © 2012 Society of Chemical Industry