Bioactive antifungal metabolites produced by Streptomyces albus CINv1 against strawberry anthracnose pathogen

Abstract

The endophytic Streptomyces albus CINv1, isolated from Cinnamomum verum, has previously demonstrated the ability to promote plant growth, colonize effectively, and exhibit antifungal activity against Colletotrichum sp. isolate CA0110, the causal agent of strawberry anthracnose. This study aims to assess the in vitro antifungal potential of ethyl acetate from S. albus CINv1. The investigated including culture broth medium, optimal incubation conditions as well as determining their antifungal activities, comparing with their standard phenolic compounds through LC-MS analysis. The culture broth medium and optimal incubation conditions for antifungal production by S. albus CINv1 were investigated. The results revealed that the ISP-2 culture broth, at a pH range
of 6–9 with incubation periods of 7–10 days, achieved the highest percentage inhibition of radial growth (PIRG)
of Colletotrichum sp. CA0110. As the concentration of the culture filtrate increased from 20% to 100%, the percentage of conidial germination inhibition (%PCGI) also increased, ranging from 22.77% to 91.80%. The ethyl acetate crude extract of S. albus CINv1 exhibited the highest antifungal activity against Colletotrichum sp. CA0110,
with a percentage inhibition of radial growth (%PIRG) of 92.25%. The crude extract was subsequently fractionated using column chromatography and evaluated for its %PCGI against Colletotrichum sp. CA0110. Among
the 15 fractions, five (F2, F9, F10, F11, and F12) showed the highest %PCGI, ranging from 92.67% to 100%. LC-MS analysis of the five fractions, using 16 standard phenolic compounds, revealed varying quantities of detected phenolics. The results exhibited the predominant antifungal compounds, such Naringenin, Hydroxybenzoic acid, O-coumaric acid, Quercetin, Kaempferol, and Chlorogenic acid. Notably, ferulic acid was identified as a well-known fungicide and antifungal compound. The findings suggest that the metabolites of endophytic S. albus CINv1, particularly phenolics, hold significant promise for developing potent biocontrol agents or bio-fungicide to control anthracnose disease in various crops in Thailand.