6 research outputs found
Complete Genome Sequence of Vibrio gazogenes ATCC 43942
Vibrio gazogenes ATCC 43942 has the potential to synthesize a plethora of metabolites which are of clinical and agricultural significance in response to environmental triggers. The complete genomic sequence of Vibrio gazogenes ATCC 43942 is reported herein, contributing to the knowledge base of strains in the Vibrio genus
Aflatoxin-Exposure of Vibrio gazogenes as a Novel System for the Generation of Aflatoxin Synthesis Inhibitors
Aflatoxin is a mycotoxin and a secondary metabolite, and the most potent known liver carcinogen that contaminates several important crops, and represents a significant threat to public health and the economy. Available approaches reported thus far have been insufficient to eliminate this threat, and therefore provide the rational to explore novel methods for preventing aflatoxin accumulation in the environment. Many terrestrial plants and microbes that share ecological niches and encounter the aflatoxin producers have the ability to synthesize compounds that inhibit aflatoxin synthesis. However, reports of natural aflatoxin inhibitors from marine ecosystem components that do not share ecological niches with the aflatoxin producers are rare. Here, we show that a non-pathogenic marine bacterium, Vibrio gazogenes, when exposed to low non-toxic doses of aflatoxin B1, demonstrates a shift in its metabolic output and synthesizes a metabolite fraction that inhibits aflatoxin synthesis without affecting hyphal growth in the model aflatoxin producer, Aspergillus parasiticus. The molecular mass of the predominant metabolite in this fraction was also different from the known prodigiosins, which are the known antifungal secondary metabolites synthesized by this Vibrio. Gene expression analyses using RT-PCR demonstrate that this metabolite fraction inhibits aflatoxin synthesis by down-regulating the expression of early-, middle-, and late- growth stage aflatoxin genes, the aflatoxin pathway regulator, aflR and one global regulator of secondary metabolism, laeA. Our study establishes a novel system for generation of aflatoxin synthesis inhibitors, and emphasizes the potential of the under-explored Vibrio’s silent genome for generating new modulators of fungal secondary metabolism
Vibrio gazogenes Inhibits Aflatoxin Production Through Downregulation of Aflatoxin Biosynthetic Genes in Aspergillus flavus
Aspergillus flavus is an opportunistic pathogen of oilseed crops such as maize, peanut, cottonseed, and tree nuts and produces carcinogenic secondary metabolites known as aflatoxins during seed colonization. Aflatoxin contamination not only reduces the value of the produce but is also a health hazard to humans and animals. Previously, we observed inhibition of A. flavus aflatoxin biosynthesis on exposure to the marine bacterium Vibrio gazogenes (Vg). In this study, we used RNA sequencing to examine the transcriptional profiles of A. flavus treated with both live and heat-inactivated dead Vg and control samples. Fungal biomass, total accumulated aflatoxins, and expression profiles of genes constituting secondary metabolite biosynthetic gene clusters were determined at 24, 30, and 40 h after treatment. Statistically significant reductions in total aflatoxins were detected in Vg-treated samples as compared with control samples at 40 h. However, no statistical difference in fungal biomass was observed on these treatments. The Vg treatments were most effective on aflatoxin biosynthesis, as was reflected in significant downregulation of most genes in the aflatoxin gene cluster, including the aflatoxin pathway regulator gene, aflR. Along with aflatoxin genes, we also observed significant downregulation in some other secondary metabolite gene clusters, including cyclopiazonic acid and aflavarin, suggesting that the treatment could inhibit other secondary metabolites as well. Finally, a weighted gene correlation network analysis identified an upregulation of 10 genes that were most strongly associated with Vg-dependent aflatoxin inhibition and provide a novel starting point in understanding the mechanisms that result in this phenomenon. [Graphic: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2022
Citrate-Coated Silver Nanoparticles Growth-Independently Inhibit Aflatoxin Synthesis in <i>Aspergillus parasiticus</i>
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<sub>1</sub> in the filamentous fungus and an important
plant pathogen, <i>Aspergillus parasiticus</i>, 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, <i>laeA</i> and <i>veA,</i> 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
Activation of Aflatoxin Biosynthesis Alleviates Total ROS in Aspergillus parasiticus
An aspect of mycotoxin biosynthesis that remains unclear is its relationship with the cellular management of reactive oxygen species (ROS). Here we conduct a comparative study of the total ROS production in the wild-type strain (SU-1) of the plant pathogen and aflatoxin producer, Aspergillus parasiticus, and its mutant strain, AFS10, in which the aflatoxin biosynthesis pathway is blocked by disruption of its pathway regulator, aflR. We show that SU-1 demonstrates a significantly faster decrease in total ROS than AFS10 between 24 h to 48 h, a time window within which aflatoxin synthesis is activated and reaches peak levels in SU-1. The impact of aflatoxin synthesis in alleviation of ROS correlated well with the transcriptional activation of five superoxide dismutases (SOD), a group of enzymes that protect cells from elevated levels of a class of ROS, the superoxide radicals (O2−). Finally, we show that aflatoxin supplementation to AFS10 growth medium results in a significant reduction of total ROS only in 24 h cultures, without resulting in significant changes in SOD gene expression. Our findings show that the activation of aflatoxin biosynthesis in A. parasiticus alleviates ROS generation, which in turn, can be both aflR dependent and aflatoxin dependent