Natarajan Subramani, Balachandar Dananjeyan, Paranidharan Vaikuntavasan
Department of Plant Pathology, Tamil Nadu Agricultural University, Coimbatore 641003, Tamil Nadu, India; School of Biology and Environment Science, Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland.
Department of Agricultural Microbiology, Tamil Nadu Agricultural University, Coimbatore 641003, Tamil Nadu, India.
Int J Food Microbiol. 2023 Dec 2;406:110368. doi: 10.1016/j.ijfoodmicro.2023.110368. Epub 2023 Aug 19.
Aspergillus flavus infection and subsequent aflatoxin contamination are considered the major constraints in senna (Cassia angustifolia Vahl.) export. Using native epiphytic yeast to control phytopathogens is a successful strategy for managing plant diseases. In the present investigation, we exploited the antagonistic potential of epiphytic yeast isolates obtained from senna against A. flavus growth and aflatoxin B (AFB) production. Four Kluyveromyces marxianus strains (YSL3, YSL16, YSP12, and YSF9) exhibited vigorous antagonistic activity with a maximum inhibition of 64 %. In vivo evaluation of senna pods showed that K. marxianus strains effectively reduced A. flavus colonization with a population range of 5.87 to 7.08 log CFU/g. In contrast, the untreated senna pods were found to have severe fungal colonization with a population of 7.84 log CFU/g. In addition, HPLC analysis showed that aflatoxin B in senna pods was drastically reduced upon yeast treatment up to 14 DAI. Furthermore, we demonstrated the antifungal action mechanisms of K. marxianus, such as surface colonizing ability on pods, production of antifungal volatiles (VOCs), siderophores, extracellular lytic enzymes, and cell wall binding ability to AFB. All four strains of K. marxianus showed rapid colonization on the senna pod, and YSP12 reached the maximum population of 7.18 log10 CFU/pod at 9 days after inoculation (DAI). The exposure of A. flavus to K. marxianus VOCs significantly reduced the growth by up to 99 and 93.2 % at 7 and 14 DAI, respectively. Scanning electron microscopic images demonstrated severe mycelial damage and hyphal deformities of A. flavus. In addition, yeast VOCs can reduce aflatoxin biosynthesis in A. flavus by up to 99 and 93.2 % at 7 and 14 DAI, respectively. Gas chromatography-mass spectrometry analysis confirmed the presence of antimicrobial compounds such as dimethyl trisulfide, ethyl acetate, ethanol, 3-methyl butanal, 2-methyl-1-butanol, and 3-methyl-1-butanol in the volatiles. K. marxianus strains produced siderophores and hydrolytic enzymes such as chitinase and β-1,3-glucanase. A higher AFB binding ability was observed in the heat-killed cells (47.5 to 70.65 %) than in the viable cells (43.16 to 60.98 %) of K. marxianus. The current study demonstrated that epiphytic K. marxianus isolated from senna could be a successful biocontrol source to reduce aflatoxin contamination in senna pods.
黄曲霉感染及随后的黄曲霉毒素污染被认为是番泻叶（Cassia angustifolia Vahl.）出口的主要限制因素。利用本地附生酵母控制植物病原体是管理植物病害的一种成功策略。在本研究中，我们利用从番泻叶中获得的附生酵母分离物对黄曲霉生长和黄曲霉毒素B（AFB）产生的拮抗潜力。四株马克斯克鲁维酵母菌株（YSL3、YSL16、YSP12和YSF9）表现出强烈的拮抗活性，最大抑制率为64%。对番泻叶荚的体内评估表明，马克斯克鲁维酵母菌株有效地减少了黄曲霉的定殖，其数量范围为5.87至7.08 log CFU/g。相比之下，未处理的番泻叶荚被发现有严重的真菌定殖，数量为7.84 log CFU/g。此外，高效液相色谱分析表明，在酵母处理后至接种后14天，番泻叶荚中的黄曲霉毒素B大幅减少。此外，我们证明了马克斯克鲁维酵母的抗真菌作用机制，如在荚上的表面定殖能力、抗真菌挥发性有机化合物（VOCs）的产生、铁载体、细胞外裂解酶以及与AFB的细胞壁结合能力。所有四株马克斯克鲁维酵母菌株在番泻叶荚上均表现出快速定殖，YSP12在接种后9天达到最大数量7.18 log10 CFU/荚。黄曲霉暴露于马克斯克鲁维酵母的VOCs中，在接种后7天和14天分别显著降低生长率达99%和93.2%。扫描电子显微镜图像显示黄曲霉的菌丝体严重受损和菌丝畸形。此外，酵母VOCs在接种后7天和14天分别可将黄曲霉中的黄曲霉毒素生物合成减少达99%和93.2%。气相色谱 - 质谱分析证实挥发物中存在抗菌化合物，如二甲基三硫、乙酸乙酯、乙醇、3 - 甲基丁醛、2 - 甲基 - 1 - 丁醇和3 - 甲基 - 1 - 丁醇。马克斯克鲁维酵母菌株产生铁载体和水解酶，如几丁质酶和β - 1,3 - 葡聚糖酶。在马克斯克鲁维酵母的热死细胞（47.5%至70.65%）中观察到比活细胞（43.16%至60.98%）更高的AFB结合能力。当前研究表明，从番泻叶中分离的附生马克斯克鲁维酵母可能是减少番泻叶荚中黄曲霉毒素污染的一种成功的生物防治来源。
