Secondary Metabolites of the Rice Blast Fungus Pyricularia oryzae: Biosynthesis and Biological Function

Plant pathogenic fungi produce a wide variety of secondary metabolites with unique and complex structures. However, most fungal secondary metabolism genes are poorly expressed under laboratory conditions. Moreover, the relationship between pathogenicity and secondary metabolites remains unclear. To activate silent gene clusters in fungi, successful approaches such as epigenetic control, promoter exchange, and heterologous expression have been reported. Pyricularia oryzae, a well-characterized plant pathogenic fungus, is the causal pathogen of rice blast disease. P. oryzae is also rich in secondary metabolism genes. However, biosynthetic genes for only four groups of secondary metabolites have been well characterized in this fungus. Biosynthetic genes for two of the four groups of secondary metabolites have been identified by activating secondary metabolism. This review focuses on the biosynthesis and roles of the four groups of secondary metabolites produced by P. oryzae. These secondary metabolites include melanin, a polyketide compound required for rice infection; pyriculols, phytotoxic polyketide compounds; nectriapyrones, antibacterial polyketide compounds produced mainly by symbiotic fungi including endophytes and plant pathogens; and tenuazonic acid, a well-known mycotoxin produced by various plant pathogenic fungi and biosynthesized by a unique NRPS-PKS enzyme.     

Rhizopus oryzae产酸性蛋白酶条件及其酶学性质研究

本文以少孢根霉(Rhizopus oligosporus)为对照研究了豆豉中的一个分离菌株米根霉(Rhizopus oryzae)产生酸性蛋白酶的条件及所产蛋白酶的性质,结果表明这个菌株的产酶条件和蛋白酶的性质与少孢根霉相比有相似性但也存在一些差异:米根霉在水分含量57%~59%、pH2.5~3.0的酸性介质中、28~31℃下培养36h时产酸性蛋白酶能力最强,所分泌的蛋白酶系在pH4.0和pH6.0附近有最强的催化活性,在pH3.0~6.0的范围内有较好的稳定性,催化反应的最适作用温度为50℃,它的温度稳定性很差,在50℃保温30min已完全失活;少孢根霉在水分含量52%~55%、pH2.5~3.0的酸性介质中、31℃下培养48h时产酸性蛋白酶能力最强,在35℃条件下培养36h也能产生较高的酶活力,少孢根霉分泌的蛋白酶系在pH3.0和pH6.0附近有最强的催化活性,在pH4.0～6.0范围内很稳定,催化反应的最适作用温度可达55～60℃,但它的温度稳定性较差,在50℃保温30min,酶活力损失达到90%,保温120min酶几乎完全失活。     

聚乙烯醇丝固定化米根霉发酵产L（+）-乳酸

以聚乙烯醇(PVA)丝为吸附材料的立体载体,固定化米根霉菌种As3.3462发酵生产乳酸。与游离发酵相比,摇瓶单批固定化发酵乳酸的最终质量浓度提高了25%,发酵时间缩短了33%。分别在摇瓶和鼓泡式反应器中进行了载体的稳定性研究,摇瓶中可稳定发酵10批次,平均转化率为65%,平均产率为1.1g/(L.h);1L鼓泡式生物反应器的放大实验中进行了9批半连续发酵实验,乳酸质量浓度最高达到55.68g/L,转化率69.60%。     

Effect of mixed kojis on physiochemical and sensory properties of rapid‐fermented fish sauce made with freshwater fish by‐products

The objective of this study was to investigate the effect of mixed kojis on essential indices of fish sauce. Fish sauce inoculated with mixed kojis (FSB, Aspergillus oryzae koji:Aspergillus niger koji = 3:1) and A. oryzae koji (FSA, control) was prepared. At the end of fermentation, the content of amino nitrogen, total soluble nitrogen, Free amino acid (FAA) and glutamic acid in FSB increased by 7.50%, 7.84%, 9.80% and 28.43% compared to FSA, due to higher acid protease activity in mixed kojis. Moreover, flavour groups including phenols, ketones and nitrogen‐containing compounds in FSB were also improved. According to the results of sensory evaluation, FSB showed higher intensity of umami and caramel attributes, lower intensity of ammonia and sour attributes. All the results suggested that the usage of mixed kojis to produce fish sauce was an effective method that can accelerate the fermentation process and improve the flavour of fish sauce made with freshwater fish by‐products.     

高产L-乳酸米根霉RE3303菌株特性研究

为了获得更适于工业生产的产乳酸菌株 ,采用低能离子诱变方法 ,对出发菌米根霉PW 35 2进行改良 ,获得高产L(+) 乳酸菌株RE330 3,发酵周期为 36h ,产酸能力达 131～ 136g/L ,最高可达 14 0g/L ,体积产酸速率达 3.6 1g/ (L·h) ,产率为 86 %～ 90 % ,产酸比PW35 2提高 75 %。     

聚氨酯泡沫载体固定化米根霉的双层反应-扩散模型

根据聚氨酯泡沫固定化米根霉的生长特征,建立了描述固定化米根霉间歇发酵生产乳酸过程的双层反应──扩散理论模型,采用有限差分方法进行了数值求解．模型计算结果与实验结果吻合较好,证明该模型可用于过程的设计和优化．     

Reduction of raffinose oligosaccharides in chickpea (Cicer arietinum) flour by crude extracellular fungal α-galactosidase

The efficiency of crude extracelluar α-galactosidases from Cladosporium cladosporides, Aspergillus oryzae and A niger in reducing the raffinose and stachyose content in chickpea flours was studied and compared with other traditional treatments. The optimum pH for α-galactosidase activity was found to be 4·5 for A oryzae and 5·0 for Cl cladosporides and A niger, while the optimum temperature of enzyme activity was 40°C for Cl cladosporides and 50°C for A oryzae and A niger. The specific activities of α-galactosidase from Cl cladosporides, A oryzae and A niger were 3·35, 3·94 and 5·94 units μg⁻¹ protein, respectively. The enzyme activity was stable between pH 4·0 and 7·0 for A oryzae and A niger and between pH 5·0 and 7·0 for Cl cladosporides. The enzymes were thermostable when incubated at temperature ranges of 40–60°C for Cl cladosporides and 40–50°C for A oryzae and A niger. The optimum conditions for removing the raffinose and stachyose were obtained by incubating chickpea flours with 30 ml of crude fungal α-galactosidase extract (290, 210 and 130 units ml⁻¹ for Cl cladosporides, A oryzae and A niger, respectively) for 3 h at the optimum conditions of each strain. Crude fungal α-galactosidases reduced the raffinose oligosaccharides content in chickpea flours by 100%, while germination reduced the raffinose content by 69% and stachyose content by 75%. Other traditional techniques reduced the raffinose content by 13–49% and stachyose content by 10–32%. © 1998 Society of Chemical Industry     

Whole Genome Sequencing and Tn5-Insertion Mutagenesis of Pseudomonas taiwanensis CMS to Probe Its Antagonistic Activity Against Rice Bacterial Blight Disease

The Gram-negative bacterium Pseudomonas taiwanensis is a novel bacterium that uses shrimp shell waste as its sole sources of carbon and nitrogen. It is a versatile bacterium with potential for use in biological control, with activities including toxicity toward insects, fungi, and the rice pathogen Xanthomonas oryzae pv.oryzae (Xoo). In this study, the complete 5.08-Mb genome sequence of P. taiwanensis CMS was determined by a combination of NGS/Sanger sequencing and optical mapping. Comparison of optical maps of seven Pseudomonas species showed that P. taiwanensis is most closely related to P. putida KT 2400. We screened a total of 11,646 individual Tn5-transponson tagged strains to identify genes that are involved in the production and regulation of the iron-chelator pyoverdine in P. taiwanensis, which is a key anti-Xoo factor. Our results indicated that the two-component system (TCS) EnvZ/OmpR plays a positive regulatory role in the production of pyoverdine, whereas the sigma factor RpoS functions as a repressor. The knowledge of the molecular basis of the regulation of pyoverdine by P. taiwanensis provided herein will be useful for its development for use in biological control, including as an anti-Xoo agent.     

海洋细菌抗菌筛选及深海独岛枝芽胞杆菌A493活性物质分离鉴定

以水稻黄单胞菌等植物病原菌为指示菌,采用平板对峙法对411株海洋细菌进行了抗菌筛选,初筛获得具有抗菌活性的海洋菌株81株,复筛获得具有稳定抗菌活性的菌株7株,最后通过测定抗菌谱,得到1株抗菌谱特异并且稳定拮抗水稻黄单胞菌的深海独岛枝芽胞杆菌（Virgibacillus dokdonensis）A493.对水稻白叶枯病害的温室生防实验表明,经过A493无菌发酵上清波处理,水稻生长20 d后对水稻白叶枯病害的防治效果达到了66.7％,且对水稻的正常生长无不良影响.通过离子交换色谱法提取,再经2次薄层层析硅胶板回收分离,得到了纯化活性物质,经过ESI-MS＂分析,初步判断活性物质分子量为317 Da.Doskochilova系统纸层析结果显示活性物质很可能为新的氨基糖苷类物质.