Citrate-Coated Silver Nanoparticles Growth-Independently Inhibit Aflatoxin Synthesis in Aspergillus parasiticus

Abstract

Manufactured silver nanoparticles (Ag NPs) have long been used as antimicrobials. However, little is known about how these NPs affect fungal cell functions. While multiple previous studies reveal that Ag NPs inhibit secondary metabolite syntheses in several mycotoxin producing filamentous fungi, these effects are associated with growth repression and hence need sublethal to lethal NP doses, which besides stopping fungal growth, can potentially accumulate in the environment. Here we demonstrate that citrate-coated Ag NPs of size 20 nm, when applied at a selected nonlethal dose, can result in a >2 fold inhibition of biosynthesis of the carcinogenic mycotoxin and secondary metabolite, aflatoxin B in the filamentous fungus and an important plant pathogen, Aspergillus parasiticus, without inhibiting fungal growth. We also show that the observed inhibition was not due to Ag ions, but was specifically associated with the mycelial uptake of Ag NPs. The NP exposure resulted in a significant decrease in transcript levels of five aflatoxin genes and at least two key global regulators of secondary metabolism, laeA and veA, with a concomitant reduction of total reactive oxygen species (ROS). Finally, the depletion of Ag NPs in the growth medium allowed the fungus to regain completely its ability of aflatoxin biosynthesis. Our results therefore demonstrate the feasibility of Ag NPs to inhibit fungal secondary metabolism at nonlethal concentrations, hence providing a novel starting point for discovery of custom designed engineered nanoparticles that can efficiently prevent mycotoxins with minimal risk to health and environment.

Biofabrication of Zinc Oxide Nanoparticles With Syzygium aromaticum Flower Buds Extract and Finding Its Novel Application in Controlling the Growth and Mycotoxins of Fusarium graminearum

“…Antifungal and antimycotoxin activities of SaZnO NPs might be due to an elevation of ROS and thus, it could induce death of fungi by oxidative-stress mediated apoptosis. In support of the present study, several studies have evidenced that nanoparticles (Mitra et al, 2017), physical agents (Calado et al, 2014; Kalagatur et al, 2018d,e), synthetic fungicides (Delattin et al, 2014) and bio-fungicides (Sebaaly et al, 2016; Sellamani et al, 2016) could induce the death of fungi through oxidative-stress mediated apoptosis by elevation of ROS. Specifically concerning to nanomaterials, few reports were available on antifungal and antimycotoxin capabilities of nanomaterials.…”

“…Besides, Savi et al (2013) proved that zinc compounds could generate intracellular ROS and exhibit strong inhibitory activity on growth and fumonisin mycotoxin production of F. verticillioides by detrimental action on hyphae and conidia. Captivatingly, Mitra et al (2017) reported that citrate decorated silver nanoparticles independently inhibit the fungal growth and aflatoxin production in A. parasiticus and revealed that silver nanoparticles inhibit aflatoxin production by downregulating the aflatoxin biosynthesis genes at its below the lethal dose.…”

Extracellular biosynthesis of silver nanoparticles using Streptomyces griseoplanus SAI-25 and its antifungal activity against Macrophomina phaseolina , the charcoal rot pathogen of sorghum

“…It is observed that Streptomyces mediated AgNPs can able to inhibit the phytopathogens such as Aspergillus niger, Aspergillus flavus and Aspergillus fumigatus (Thenmozhi et al, 2013). Recent studies by Mitra et al (2017) documented AgNPs mediated inhibition of aflatoxin synthesis in Aspergillus parasiticus which further substantiates the role of AgNPs in agriculture.…”

New insight into the effect of mass transfer on the synthesis of silver and gold nanoparticles

“…Noble metal nanoparticles (NPs) offer unique properties as compared to their bulk counterpart, offering potential for a variety of applications. Silver NPs for instance are successfully used in catalysis, 1,2 surface enhanced Raman scattering, 3,4 electronics, 5,6 and as antimicrobial or anti-inflammatory agents [7][8][9][10] and sensors. 11,12 Likewise, gold NPs have been utilised for biological/biomedical, [13][14][15][16][17][18] electrochemical, 19,20 catalytic, 21,22 and optical applications.…”