Ueki Atsuko, Takehara Toshiaki, Ishioka Gen, Kaku Nobuo, Ueki Katsuji
Faculty of Agriculture, Yamagata University, 1-23, Wakaba-machi, Tsuruoka, Yamagata, 997-8555, Japan.
NARO Western Region Agricultural Research Center, Hiroshima, 721-8514, Japan.
AMB Express. 2019 Jul 23;9(1):114. doi: 10.1186/s13568-019-0842-1.
Biological soil disinfestation (BSD) or anaerobic (reductive) soil disinfestation (ASD/RSD) is a bioremediation method used to eliminate soil-borne plant pathogens by exploiting the activities of anaerobic bacteria in soil. In this study, two obligate anaerobic bacterial strains isolated from BSD-treated soil and identified as Clostridium beijerinckii were examined for their abilities to suppress the spinach wilt disease pathogen (Fusarium oxysporum f. sp. spinaciae) as a representative soil-borne fungal plant pathogen. Both strains degraded β-1,3-glucan and chitosan, two major polysaccharide components of ascomycetes fungal cell wall, supplemented in the medium. β-1,3-Glucanase was detected in the supernatants of cultures supplemented with different types of glucan. Similarly, chitosanase was detected in cultures supplemented with chitosan. Both the enzyme activities were also detected in cultures containing glucose as a substrate. Live cells of F. oxysporum f. sp. spinaciae that were co-incubated with each anaerobic strain under anaerobic conditions using glucose as a substrate died during incubation. Freeze-dried dead fungal biomass of the pathogen, when added to the culture, supported good growth of both anaerobes and production of both enzymes. Severe and nearly complete degradation of both live and dead fungal cells during incubation with anaerobic bacteria was observed by fluorescence microscopy. When individual anaerobic bacterial strain was co-incubated with live pathogenic fungal cells in wheat bran, a popular material for BSD-treatment, both the strains grew well and killed the fungal pathogen promptly by producing both enzymes. These results indicate that both the bacterial strains attack the fungal cells by releasing extracellular fungal cell wall-degrading enzymes, thereby eliminating the pathogen.
生物土壤熏蒸（BSD）或厌氧（还原）土壤熏蒸（ASD/RSD）是一种生物修复方法，通过利用土壤中厌氧细菌的活性来消除土壤传播的植物病原体。在本研究中，对从BSD处理土壤中分离出的两种专性厌氧细菌菌株进行了检测，这两种菌株被鉴定为拜氏梭菌，检测它们抑制菠菜枯萎病病原体（尖孢镰刀菌菠菜专化型）的能力，该病原体是一种典型的土壤传播真菌性植物病原体。两种菌株都能降解培养基中添加的β-1,3-葡聚糖和壳聚糖，这是子囊菌真菌细胞壁的两种主要多糖成分。在添加不同类型葡聚糖的培养上清液中检测到了β-1,3-葡聚糖酶。同样，在添加壳聚糖的培养物中检测到了壳聚糖酶。在以葡萄糖为底物的培养物中也检测到了这两种酶的活性。在厌氧条件下，以葡萄糖为底物与每种厌氧菌株共同孵育的尖孢镰刀菌菠菜专化型活细胞在孵育过程中死亡。将病原体的冻干死亡真菌生物质添加到培养物中，有利于两种厌氧菌的生长以及两种酶的产生。通过荧光显微镜观察到，在与厌氧细菌孵育过程中，活的和死的真菌细胞都发生了严重且几乎完全的降解。当将单个厌氧细菌菌株与活的致病真菌细胞在麦麸（一种常用于BSD处理的材料）中共同孵育时，两种菌株都生长良好，并通过产生两种酶迅速杀死真菌病原体。这些结果表明，两种细菌菌株都通过释放细胞外真菌细胞壁降解酶来攻击真菌细胞，从而消除病原体。
