An environmental isolate of Pseudomonas, 20EI1, reduces Aspergillus flavus growth in an iron-dependent manner and alters secondary metabolism

Authors: WYMAN, ELIZABETH - Northern Illinois University; GRAYBURN, SCOTT - Northern Illinois University; Gilbert, Matthew; Lebar, Matthew; Lohmar, Jessica; Cary, Jeffrey; SAUTERS, THOMAS - Vanderbilt University Medical Center; ROKAS, ANTONIS - Vanderbilt University Medical Center; CALVO, ANA - Northern Illinois University

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2024
Publication Date: 1/19/2025
Citation: Wyman, E.M., Grayburn, S., Gilbert, M.K., Lebar, M.D., Lohmar, J.M., Cary, J.W., Sauters, T.J., Rokas, A., Calvo, A.M. 2025. An environmental isolate of Pseudomonas, 20EI1, reduces Aspergillus flavus growth in an iron-dependent manner and alters secondary metabolism. Frontiers in Microbiology. 15. Article151450. https://doi.org/10.3389/fmicb.2024.1514950.
DOI: https://doi.org/10.3389/fmicb.2024.1514950

Interpretive Summary: Aspergillus flavus is an opportunistic pathogenic fungus that infects oilseed crops such as corn, peanuts, and cotton. During infection of crops, the fungus produces carcinogenic mycotoxins such as aflatoxins, cyclopiazonic acid (CPA), and aflatrems making them unsuitable for human and animal consumption. This leads to leads to large economic losses to the agricultural industry every year. Progress has made in mitigating A. flavus mycotoxin related crop losses, but a permanent solution has not been found leading to the need to develop novel control strategies aimed at controlling the ability of A. flavus to grow, disseminate , infect crops and produce mycotoxins. This study identified a novel environmental bacterial isolate of the Pseudomonas genus named 20EI1. Experimental results demonstrate that 20El1 is capable of inhibiting A. flavus growth in an iron-dependent manner and also can suppress the ability of the fungus to produce aflatoxin, CPA, and kojic acid. When co-cultured with A. flavus, 20El1 was also capable of suppressing the expression of genes in the aflatoxin, CPA, kojic acid and imazoquin biosynthesis gene clusters. Collectively, the results from this study demonstrate that Pseudomonas 20El1 is a promising biocontrol agent that can be used to control the growth of A. flavus and the ability of the fungus to produce mycotoxins.

Technical Abstract: Aspergillus flavus is an opportunistic pathogenic fungus that infects oilseed crops worldwide. When colonizing the plants, it produces mycotoxins, including carcinogenic compounds such as aflatoxins. Mycotoxin contamination results in an important economic and health impact. The design of new strategies to control A. flavus colonization and mycotoxin contamination is paramount. In this study, we identified a promising new isolate of Pseudomonas spp., 20EI1, and observed that it is able to reduce the growth of A. flavus. Furthermore, we determined that this growth inhibition is iron-dependent. To further elucidate the nature of this bacterial-fungus interaction, we performed chemical and transcriptomics analyses. In the present study, Pseudomonas 20EI1 reduced or blocked the production of aflatoxin, as well as cyclopiazonic acid and kojic acid. Expression of iron-related genes was altered in the presence of the bacteria and genes involved in the production of aflatoxin were down-regulated. Iron supplementation partially reestablished their expression. Expression of other secondary metabolite genes was also reduced by the bacteria, including genes of clusters involved in cyclopiazonic acid, kojic acid and imazoquin biosynthesis, while genes of the cluster corresponding to aspergillicin, a siderophore, were upregulated. Interestingly, the global SM regulatory gene mtfA was significantly upregulated by 20EI1, which could have contributed to the observed alterations in SM. Our results suggest that Pseudomonas 20EI1 is a promising biocontrol against A. flavus, and provide further insight into this bacterial-fungal interaction affecting the expression of numerous genes, among them those involved in secondary metabolism.