Efficacy of metabolites of a Streptomyces strain (AS1) to control growth and mycotoxin production by Penicillium verrucosum, Fusarium verticillioides and Aspergillus fumigatus in culture

Abstract

The objectives of this study were to determine the efficacy of metabolites of a Streptomyces strain AS1 on (a) spore germination, (b) mycelial growth, (c) control of mycotoxins produced by Penicillium verrucosum (ochratoxin A, OTA), Fusarium verticillioides (fumonisins, FUMs) and Aspergillus fumigatus (gliotoxin) and (d) identify the predominant metabolites involved in control. Initial screening showed that the Streptomyces AS1 strain was able to inhibit the mycelial growth of the three species at a distance, due to the release of secondary metabolites. A macroscopic screening system showed that the overall Index of Dominance against all three toxigenic fungi was inhibition at a distance. Subsequent studies showed that the metabolite mixture from the Streptomyces AS1 strain was very effective at inhibiting conidial germination of P. verrucosum, but less so against conidia of A. fumigatus and F. verticillioides. The efficacy was confirmed in studies on a conducive semi-solid YES medium in BioScreen C assays. Using the BioScreen C and the criteria of Time to Detection (TTD) at an OD = 0.1 showed good efficacy against P. verrucosum when treated with the Streptomyces AS1 extract at 0.95 and 0.99 water activity (a w) when compared to the other two species tested, indicating good efficacy. The effective dose for 50% control of growth (ED 50) at 0.95 and 0.99 a w were approx. 0.005 ng/ml and 0.15 μg/ml, respectively, with the minimum inhibitory concentration (MIC) at both a w levels requiring > 40 μg/ml. In addition, OTA production was completely inhibited by 2.5 μg/ml AS1 extract at both a w levels in the in vitro assays. Ten metabolites were identified with four of these being predominant in concentrations > 2 μg/g dry weight biomass. These were identified as valinomycin, cyclo(L-Pro-L-Tyr), cyclo(L-Pro-L-Val) and brevianamide F.

The Nonribosomal Peptide Valinomycin: From Discovery to Bioactivity and Biosynthesis

“…This suggests that valinomycin might be a potential antifungal agent for the control of Botrytis diseases in agriculture. Furthermore, valinomycin displays antifungal activity against other fungal species such as Aspergillus niger , Fusarium graminearum , Sclerotinia minor , Penicillium verrucosum , and Rhizoctonia solani [ 49 , 50 , 51 ]. However, the antifungal mechanism of valinomycin was not elucidated in these above-mentioned studies.…”

Proof of concept: could snake venoms be a potential source of bioactive compounds for control of mould growth and mycotoxin production

“…Strains of five mycotoxigenic fungal species were used in this study. These were A. flavus (NRRL 3357, an AFB 1 /B 2 producer), P. verrucosum (OTA 11, a OTA producer), A. westerdijkiae (IBT 23971, OTA producer), F. langsethiae (UK oats, 2004/54, a T-2 producer) and F. graminearum (FgB (L1-2/2D), NIV producer) Nierman et al 2016;Mohd Danial et al 2020).…”

“…The presence of these compounds in food products is strictly regulated worldwide (European Union 2006;Wu and Khlangwiset 2010). Research has been focused on screening alternative sources of naturally produced antimicrobial compounds from extreme environments, micro-organisms and plant extracts, especially essential oils (Aldred et al 2008;Bluma et al 2008;Verheecke et al 2014;El Khoury et al 2016;Lahoum et al 2016;Mylona et al 2019;Mohd Danial et al 2020;Garc ıa-D ıaz et al 2020). However, there have been few new lead compounds which have been found for use in food and feed chains to reduce mould growth and mycotoxin contamination, without impacting on the organoleptic properties of the final product.…”

Novel Metabolites Identified From Bacillus Safensis and Their Antifungal Property Against Alternaria Alternata 

“…Among all, phytopathogens (including bacteria and fungi) account for yearly loss of USD 120 billion during crop production and after harvesting (Shuping et al 2017). Decrease in the crop yields and impact on economy due to phytopathogens are often more severe in developing and poor countries, particularly where economy largely depends on agriculture (Danial et al 2020).…”

“…A. alternata is known to cause leaf spot disease in several crops including Stevia rebaudiana (Meena et al 2017). The leaf spot disease is identi ed by the presence of dark brown color or necrotic lesions on the leaf (Danial et al 2020). The symptoms of this disease appear after infection and during pathogenesis, when fungal metabolites impact the plant during active phase of growth (Thomma 2003).…”