Vibrio gazogenes-dependent disruption of aflatoxin biosynthesis in Aspergillus flavus: the connection with endosomal uptake and hyphal morphogenesis

Authors: JESMIN, RUBAIYA - University Of South Carolina; Cary, Jeffrey; Lebar, Matthew; Majumdar, Raj; GUMMADIDALA, PHANI - University Of South Carolina; DIAS, TRAVIS - University Of South Carolina; CHANDLER, SAVANNAH - University Of South Carolina; BASU, PARAMITA - Touro College; DECHO, ALAN - University Of South Carolina; KELLER, NANCY - University Of Wisconsin; CHANDA, ANINDYA - University Of South Carolina

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2023
Publication Date: 9/8/2023
Citation: Jesmin, R., Cary, J.W., Lebar, M.D., Majumdar, R., Gummadidala, P.M., Dias, T., Chandler, S., Basu, P., Decho, A.W., Keller, N.P., Chanda, A. 2023. Vibrio gazogenes-dependent disruption of aflatoxin biosynthesis in Aspergillus flavus: the connection with endosomal uptake and hyphal morphogenesis. Frontiers in Microbiology. 14:1208961. https://doi.org/10.3389/fmicb.2023.1208961.
DOI: https://doi.org/10.3389/fmicb.2023.1208961

Interpretive Summary: This work describes experiments that have been conducted in an effort to better understand the genetic mechanisms that control aflatoxin production in the fungus, Aspergillus (A.) flavus. Aflatoxins are toxic and carcinogenic compounds often produced by the fungi, Aspergillus flavus during growth on crops such as corn, peanuts, cottonseed, and treenuts. Because of the potential health risks, aflatoxin contamination of food and feed crops is also of great economic importance to farmers who cannot sell their crops due to strict domestic and international regulatory guidelines with regards to aflatoxin contamination. Here we show that placing the bacterium, Vibrio (V.) gazogenes, in the growth medium of A. flavus results in an almost complete inhibition (>99%) of aflatoxin biosynthesis. Light and electron microscopy suggested that V. gazogenes-dependent aflatoxin inhibition was associated with internalization of bacterial cell materials but not intact bacteria, into specialized cell compartments in the fungus. Identification of the mechanism by which V. gazongenes inhibits aflatoxin production will add to our knowledge of regulation of growth and toxin production in A. flavus and this in turn will help in devising strategies for eliminating fungal toxin contamination of food and feed crops.

Technical Abstract: Aflatoxin is a liver carcinogen, mycotoxin, and a secondary metabolite that is produced by some plant pathogens within the genus Aspergillus when they infect crops such as corn, peanuts, and cotton. Given the significant adverse health and economic impacts of aflatoxin and a predicted rise of crop contamination with mycotoxins caused by a changing climate, there is a pressing need for exploring new aflatoxin mitigation methods. Previous studies in our laboratory have shown that metabolites from Vibrio gazogenes, an estuarine non-pathogenic bacterium, can inhibit aflatoxin synthesis. However, a direct interaction study between V. gazogenes and aflatoxin producing strains has not been conducted thus far. Here we show that administration of V. gazogenes in the growth medium of Aspergillus flavus, an aflatoxin producing pathogen in corn, results in an almost complete inhibition (>99%) of aflatoxin biosynthesis at the level of gene expression. Dry weight comparisons of control and treated mycelia suggested that the inhibition was not a growth effect. Light and electron microscopy suggested that V. gazogenes dependent aflatoxin inhibition was associated with internalization of bacterial cell materials but not intact bacteria, in endosome-like compartments. Administration of equal concentrations of heat-inactivated non-viable V. gazogenes cells to the growth medium resulted in a similar reduction in aflatoxin production, supporting that bacterial viability was not necessary for this inhibitory effect. We also show that V. gazogenes uptake results in an almost complete (>98%) block of hyphal fusion and an ~3-fold decrease of polar growth, processes that depend on endosomal functions, and transport. Sclerotial development that depends on hyphal fusion decreased by more than 2-fold as well. Mycelia upon V. gazogenes administration showed early conidiation; however, conidia harvested from the treated colonies produced ~2-fold less aflatoxin than the earlier generation. Collectively, our study introduces a novel cellular perturbation tool through V. gazogenes that can allow us to identify the interconnected molecular and cellular mechanisms that co-regulate secondary metabolism and hyphal development in filamentous fungi. The study also unlocks an opportunity for furthering fundamental science and developing practically applicable strategies for intervening in Aspergillus toxin accumulation in the environment.