Exploring Bacterial Endophytes as Potential Biocontrol Agents Against Aspergillus parasiticus Colonisation and Aflatoxin Contamination in Maize

Abstract

Aflatoxin is one of the most deleterious types of mycotoxins commonly found in maize. Using native endophytic bacteria to control phytopathogens can be a successful strategy for managing plant diseases. A total of 26 endophytic bacterial strains were isolated from different parts of maize plants and their efficacy tested against the mycelial growth of highly toxigenic Aspergillus parasiticus Asp23. Among the endophytic isolates, EPL2 and EPL3 showed the highest inhibition (51.1% inhibition over control after 7 days of co-culture) followed by EPR2, EPR4 and EPC1. All effective bacterial isolates were tentatively identified by 16S rRNA gene sequence analysis and homology analysis with the NCBI nucleotide database using BLAST search. A detoxification assay indicated that endophytic bacterial isolates EPR2, EPL2 and EPL3 were superior in detoxifying both aflatoxin B1 and B2. Furthermore, we demonstrated the antifungal mechanisms of endophytic bacteria, such as the production of extracellular lytic enzymes, antifungal volatiles and siderophores. Finally, the effect of endophytic bacterial isolates EPL3, EPR2 and EPC2 was tested against A. parasiticus and aflatoxin contamination in maize grains in vivo. The results revealed that there was a significant reduction in colonisation of A. parasiticus and the lowest population was recorded in EPL3-treated maize grains, followed by EPR2. Similarly, the endophyte EPL3 showed the highest reduction in aflatoxin levels of 94.8% (to 23.05 ppb), followed by EPR2 (94.4% reduction to 24.71 ppb), whereas in the untreated control the aflatoxin level was 445.37 ppb. This study demonstrated that endophytic bacteria isolated from maize could be a successful biocontrol source to suppress Aspergillus growth and reduce aflatoxin contamination in maize grains.