Inhibitory Effect of Volatiles from <i>Flavobacterium johnsoniae</i> TR-18 on <i>Aspergillus flavus</i> Growth and Aflatoxin Production

<i>Aspergillus</i> <i>flavus</i> and the produced aflatoxins cause great damage to crop production, food security, and human health. The control of <i>A. flavus</i> and aflatoxins in the grains during storage is a great challenge to humans worldwide. In this study, we investigated the potential of the strain TR-18, isolated from the rhizosphere of tea plants, in controlling <i>A. flavus</i> and aflatoxins. The results demonstrated that TR-18 greatly inhibited <i>A. flavus</i> growth in dual cultural tests by the production of antifungal volatiles. TR-18 was identified as <i>Flavobacterium johnsoniae</i> through biochemical analysis and a 16S rRNA phylogenetic tree. Moreover, TR-18 effectively inhibited <i>A. flavus</i> growth and aflatoxin production in peanuts during storage. Further analysis of TR-18's volatiles was conducted by gas chromatography-tandem mass spectrometry. Five authentic compounds were identified in the volatiles of TR-18: methyl thiolacetate, dimethyl disulfide (DMDS), methyl isovalerate, 5-methyl-3-hexanone, and S-methyl 3-methylbutanethioate. DMDS with a relative content of 54.92% (peak area normalization) was the most abundant compound in the volatiles. The minimal inhibitory concentration of DMDS against <i>A. flavus</i> growth was 50 μl/liter (compound volume/airspace volume). The other compounds also showed a great inhibition rate (more than 90%) to <i>A. flavus</i> at 200 μl/liter. In addition, TR-18 exhibited broad antifungal activity against other six important phytopathogens, that is, <i>Fusarium graminearum</i>, <i>F. verticillioides</i>, <i>Colletotrichum graminicola</i>, <i>C. fructicola</i>, <i>Alternaria alternata</i>, and <i>Botrytis cinerea</i>, with inhibition rates ranging from 52.90 to 98.70%. In conclusion, <i>F. johnsoniae</i> TR-18 with the production of five types of antifungal volatiles could be used as potential biocontrol agents in controlling pathogenic fungi and associated mycotoxins in the grains during storage.