Biotic and abiotic factors affecting stability of Beauveria bassiana conidia in soil

Beauveria bassiana conidia were stored in sterile and nonsterile soil under various temperature, relative humidity, soil water content, and pH regimes. Survival of the conidia was primarily dependent on temperature and soil water content. Conidia half-lives ranged from 14 days at 25°C and 75% water saturation to 276 days at 10°C and 25% water saturation. Conidia held at ?15°C exhibited little or no loss in viability regardless of water content, relative humidity, or pH. Conidia were not recoverable after 10 days from soils held at 55°C. Conidia survival in nonsterile soil that was amended with carbon sources, nitrogen sources, or combinations of carbon and nitrogen was greatly decreased and loss was often complete in less than 22 days whereas sterile soil treated in the same manner showed dramatic increases in number, demonstrating that B. bassiana is capable of growth in sterile soil. The obvious fungistatic effect in amended nonsterile soils was possibly related to Penicillium urticae which was routinely isolated from the soils and is shown to produce a water-soluble inhibitor of B. bassiana. The fungistatic effect was shown to be an active inhibition rather than due to competition.     

拟南芥HyPRP蛋白AZI1在大肠杆菌中的表达及其抗真菌活性分析

AZI1(AZELAIC ACID INDUCED 1)基因位于拟南芥4号染色体上,编码产物是脂质转移蛋白(lipid transfer protein, LTP)家族的一个成员。该基因在系统获得抗性(systemic acquired resistance, SAR)中具有重要功能,名称来自它可以被壬二酸(azelaic acid, AzA)诱导。已有的研究结果显示,在拟南芥中由AzA和甘油-3-磷酸(glycerol-3-phosphate, G3P)诱导的SAR反应需要AZI1和DIR1,这两个脂质转移蛋白有助于G3P的积累。为了确定AZI1蛋白是否具有抗真菌活性,本工作构建了原核表达载体pET28a-AZI1,利用大肠杆菌BL21(DE3)受体细胞制备了没有信号肽的AZI1重组蛋白。Western免疫印迹分析发现通过半乳糖苷类似物IPTG诱导表达的AZI1重组蛋白主要以包涵体的形式存在。体外抑菌实验以及激光共聚焦显微观察结果表明,用镍离子亲和层析树脂纯化的AZI1重组蛋白对灰霉菌、赤霉菌、棉花枯萎病菌和酿酒酵母细胞的生长/分裂均具有抑制作用。     

Fungistatic activity of different Indian soils againstFusarium udum Butler

Summary The fungistatic activity of different Indian soils againstF. udum, causing wilt disease of pigeon-pea, has been assessed in relation to soil pH and organic matter. Correlation co-efficient between soil characteristics and fungistasis has been calculated to evaluate relationship. High fungistatic activity was exhibited generally by the soils having low pH but high organic matter. The soils exhibiting high fungistatic activity againstF. udum have low incidence of wilt disease of pigeon-pea. There was no definite correlation between volatile and non-volatile fungistasis and, therefore, the origins of volatile and non-volatile fungistasis are different. In the usual biological limit pH had insignificant impact on fungistasis.     

Autecology of Fusarium oxysporum f. sp. raphani in soils suppressive and conducive to Fusarium-wilt of radish

Abstract Effects of organic amendments and alterations of environmental conditions on the inoculum potential of Fusarium oxysporum f. sp. raphani PEG-4 (PEG-4), estimated from its population dynamics and spore germinability, were investigated using soils suppressive (S-soil) and conducive (C-soil) to Fusarium-wilt of radish. The results on the population dynamics of PEG-4 in S- and C-soils showed that the germination-lysis mechanism, proposed by Chinn and Ledingham (Can. J. Bot. (1962) 39, 739–748), seemed to be applicable to S-soil, while not application to C-soil. Germination of PEG-4 microconidia in soils supplemented with glucose and asparagine (1 mg g⁻¹ of soil) was higher in C-soil than in S-soil, showing that S-soil possessed a greater degree of fungistasis than C-soil. Organic amendments, especially rice straw and fresh radish residue (FRR), brought about suppressive effects on the germination of PEG-4 in both soils along with their decomposition. These results suggest that the autecology of PEG-4 in S- and C-soils was quite different depending on incubation conditions, and presence or absence of organic amendments.     

In vitro suppression of fungi caused by combinations of apparently non-antagonistic soil bacteria

We hypothesized that apparently non-antagonistic soil bacteria may contribute to suppression of fungi during competitive interactions with other bacteria. Four soil bacteria (Brevundimonas sp., Luteibacter sp., Pedobacter sp. and Pseudomonas sp.) that exhibited little or no visible antifungal activity on different agar media were prescribed. Single and mixed strains of these species were tested for antagonism on a nutrient-poor agar medium against the plant pathogenic fungi Fusarium culmorum and Rhizoctonia solani and the saprotrophic fungus Trichoderma harzianum. Single bacterial strains caused little to moderate growth reduction of fungi (quantified as ergosterol), most probably due to nutrient withdrawal from the media. Growth reduction of fungi by the bacterial mixture was much stronger than that by the single strains. This appeared to be mostly due to competitive interactions between the Pseudomonas and Pedobacter strains. We argue that cohabitation of these strains triggered antibiotic production via interspecific interactions and that the growth reduction of fungi was a side-effect caused by the sensitivity of the fungi to bacterial secondary metabolites. Induction of gliding behavior in the Pedobacter strain by other strains was also observed. Our results indicate that apparently non-antagonistic soil bacteria may be important contributors to soil suppressiveness and fungistasis when in a community context.     

拮抗北细辛菌核病木霉菌的分离、鉴定及生防效果

[背景] 菌核病是北细辛根部主要病害之一,木霉菌作为目前应用最广泛的生物防治真菌,利用木霉菌防治北细辛菌核病是目前研究的热点。[目的] 通过稀释分离法对健康北细辛植株根际土壤进行菌株分离,以期筛选出有效拮抗北细辛菌核病的生防木霉菌。[方法] 以北细辛菌核病菌为靶标菌,采用平板对峙培养、挥发性与非挥发性物质抑菌的方法对分离得到的木霉菌进行筛选,采用生长速率法对筛选出的木霉菌的发酵液进行抑菌效果测定,并采用硫代巴比妥酸法测定筛选出的木霉对北细辛菌核病菌的丙二醛（Malondialdehyde,MDA）含量、紫外吸收法测定过氧化氢酶（Catalase,CAT）活性、氮蓝四唑法测定超氧化物歧化酶（Superoxide Dismutase,SOD）活性、愈创木酚法测定过氧化物酶（Peroxidase,POD）活性的影响。[结果] 从土壤中分离出木霉菌共14株,通过形态学和ITS-RPB2双基因联合构建系统发育树,鉴定其为哈茨木霉（Trichoderma harzianum）、钩状木霉（Trichoderma hamatum）、拟康氏木霉（Trichoderma koningiopsis）、深绿木霉（Trichoderma atroviride）、短密木霉（Trichoderma brevicompactum）和装絮木霉（Trichoderma tomentosum）。对峙培养试验表明,钩状木霉A26、拟康氏木霉B30、钩状木霉C6、哈茨木霉A17对北细辛菌核病菌抑制率均在90%以上,挥发性物质抑制测定结果显示钩状木霉C6抑制率最高,为53.73%±0.07%,木霉菌的非挥发性物质抑菌作用较强,哈茨木霉A17、钩状木霉A26、钩状木霉C6的非挥发性物质对细辛菌核病菌的抑制率均在75%以上,而拟康氏木霉B30抑制率可达100%。因此,筛选出的哈茨木霉A17、钩状木霉A26、拟康氏木霉B30、钩状木霉C6为拮抗效果较强的生防木霉菌,这4株木霉菌的发酵液对北细辛菌核病菌的抑制率分别为56.33%±0.12%、77.22%±0.06%、82.28%±0.03%、46.20%±0.04%。经这4株木霉菌的非挥发性物质处理7 d后,菌核病菌MDA含量显著增加,钩状木霉A26是对照组的7.7倍,最为显著;菌核病菌抗氧化酶活性均降低,与对照组相比,CAT、SOD、POD活性分别下降了19.67%-75.84%、4.71%-68.71%和3.57%-67.86%。[结论] 从北细辛健康植株根际土壤中分离的木霉菌株哈茨木霉A17、钩状木霉A26、拟康氏木霉B30、钩状木霉C6对北细辛菌核病菌均有较好的抑制效果,可用于北细辛菌核病的生物防治。     

Edible dates (Phoenix dactylifera), a potentialsource of Cladosporium cladosporioides andSporobolomyces roseus: Implications for public health

The non-steroidal anti-inflammatory drug niflumic acid was found to inhibit growth of the yeast form of Candida albicans. Niflumic acid inhibited respiratory oxygen uptake and it is hypothesised that this was achieved by cytosolic acidification and block of glycolysis. Inhibitory concentrations are compatible with current practice of topical application. This revised version was published online in June 2006 with corrections to the Cover Date.     

Failure of a Mycelial Formulation of the Nematophagous FungusHirsutella rhossiliensisto Suppress the NematodeHeterodera schachtii

Research was conducted to determine whether pelletized hyphae ofHirsutella rhossiliensissuppressed invasion of roots by the sugarbeet cyst nematodeHeterodera schachtiiin field microplots. The loamy sand in the microplots was infested withH. schachtiibut not withH. rhossiliensis.Alginate pellets, with or without hyphae ofH. rhossiliensis,were mixed into soil removed from the microplots (1 pellet/cm³of soil). The soil was placed in cylinders positioned vertically in microplots; cylinders (6/microplot) were 10.1 cm wide and 15.3 cm deep and contained 1200 cm³of soil. Pellets and soil also were placed in soil observation chambers, which were buried in the cylinders or kept at 20°C in moisture chambers in the laboratory. After 12 days, cabbage seeds were planted in each cylinder, and after 10 days of growth, the seedlings were removed from the soil andH. schachtiiin the roots were counted. The number ofH. schachtiiin roots was large and was unaffected by addition ofH. rhossiliensis.In soil observation chambers,H. rhossiliensisgrew vigorously from the pellets in heat-treated soil but not in nonheated soil, and enchytraeids and collembolans were observed near damaged pellets. We suspect that organisms, possibly including enchytraeids and collembolans, fed upon or otherwise inhibitedH. rhossil- iensis.     

Antifungal Activity of Schinifoline Against Candida Albicans in Caenorhabditis Elegans

Zanthoxylum schinifolium has been used as spices and traditional medicine in China for hundreds of years. A variety of active substances have been isolated from Zanthoxylum schinifolium using biological and chemical techniques. Among these substances, the effect of schinifoline has gradually attracted much attention. Candida albicans is one of the most common pathogens isolated from the gastrointestinal tract, vagina, and mouth in healthy individuals. In a healthy population, there are various mechanisms in host, such as the microbial flora, the epithelial barriers, and the innate immune system, that can control the presence of Candida albicans. However, when host immunity is compromised, an invasive fungal infection is more likely to occur. In this study, we explored the antifungal activity of schinifoline against Candida albicans in Caenorhabditis elegans. To determine the optimal concentration of schinifoline, we investigated the lifespan, defecation cycle and locomotion behavior of Caenorhabditis elegans after treatment with schinifoline. In addition, we examined colony formation in the intestine of Caenorhabditis elegans after Candida albicans infection. The results indicated that 100 and 200 mg/L of schinifoline could prolonged the lifespan, shorten the defecation cycle and increased the locomotion behavior of Caenorhabditis elegans, with 100 mg/L of schinifoline being the optimal concentration. Moreover, 100 mg/L of schinifoline increased the lifespan of Caenorhabditis elegans after infection and inhibited the colony formation of Candida albicans in Caenorhabditis elegans intestine. Therefore, we concluded that schinifoline exhibits anti-fungal effects and its potential use as natural drugs should be further explored in future studies.