Pamamycin Disrupts the Cell Envelope and Mitochondrial Potential to Inhibit Aspergillus flavus and Aflatoxin Production in a Peanut Kernel Model

TL;DR

Pamamycin, an antibiotic, effectively inhibits Aspergillus flavus growth and aflatoxin production in peanuts by disrupting cell membranes and mitochondrial function.

Contribution

This study reveals pamamycin's novel antifungal mechanism and efficacy in a peanut model for aflatoxin mitigation.

Findings

Pamamycin inhibits A. flavus colony formation and aflatoxin production in vitro and in peanut kernels.

Pamamycin disrupts cell envelope integrity and mitochondrial membrane potential in A. flavus.

Transcriptomic changes show repression of aflatoxin biosynthesis genes at effective concentrations.

Abstract

Aspergillus flavus contaminates food commodities and produces carcinogenic aflatoxins. Pamamycin, a macrodiolide antibiotic from Streptomyces alboflavus TD-1, shows potent antifungal activity, yet its action against A. flavus and efficacy in complex food matrices largely remains unknown. Here, pamamycin was purified and evaluated using in vitro assays together with a peanut kernel model. Pamamycin reduced colony formation of A. flavus on PDA in a concentration-dependent manner, with near-complete inhibition at 4.0 mg/L on surface-treated PDA plates. Microscopy revealed progressive deformation and collapse of conidia and hyphae. Pamamycin increased membrane permeability, as indicated by elevated extracellular nucleic acid leakage, and impaired cell envelope integrity, as reflected by alkaline phosphatase release. In addition, pamamycin reduced Rh123-associated fluorescence, indicating an apparent dissipation of mitochondrial membrane potential under the tested conditions. Notably, at pamamycin concentrations of ≥0.5 mg/L, AFB1 accumulation was markedly reduced and fell below the limit of detection (LOD). This suppression was accompanied by distinct transcriptional changes in the aflatoxin regulatory network. RT–qPCR showed concentration-dependent repression of the pathway-specific regulators aflR and aflS, whereas the global regulator veA displayed a biphasic response with transient upregulation at lower concentrations. Notably, at 0.5 mg/L, multiple structural genes (aflC, aflD, aflK, aflP, and aflQ) were reduced to near-background transcript levels, coinciding with the loss of detectable AFB1. In inoculated peanut kernels incubated under high-humidity conditions, pamamycin significantly reduced fungal colonization and decreased AFB1 accumulation by >99%. Transcriptomic analysis of cultures treated with 0.5 mg/L pamamycin further revealed extensive transcriptional reprogramming, with enrichment of pathways related to branched-chain amino acid biosynthesis, central carbon metabolism, and ABC transporters. Collectively, pamamycin inhibits A. flavus through combined disruption of cell envelope integrity, apparent mitochondrial potential collapse, and broad suppression of the aflatoxin biosynthetic pathway, supporting its potential utility for mitigating aflatoxin contamination in peanut kernels, pending further safety evaluation.

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