Department of Entomology and Acarology, Escola Superior de Agricultura "Luiz de Queiroz", University of São Paulo (ESALQ-USP), Av. Pádua Dias, 11, C.P. 9, Piracicaba, SP, 13418-900, Brazil.
Laboratory of Environmental Microbiology, Brazilian Agricultural Research Corporation, Embrapa Environment, Rodovia SP 340, Km 127.5, Jaguariúna, 13820-000, Brazil.
World J Microbiol Biotechnol. 2020 Apr 28;36(5):71. doi: 10.1007/s11274-020-02844-z.
The cosmopolitan entomopathogenic and root endophytic fungus Metarhizium robertsii has a versatile lifestyle and during liquid fermentation undergoes a dimorphic transformation from hyphae to conidia or microsclerotia, or from hyphae to blastospores. In all cases, these processes are mediated by environmental and nutritional cues. Blastospores could be used in spray applications to control arthropod pests above ground and may serve as an attractive alternative to the traditional solid-grown aerial conidial spores of Metarhizium spp. found in commercial products. Nitrogen is a vital nutrient in cell metabolism and growth; however, it is the expensive component in liquid cultures of entomopathogenic fungi. Our goals in this study were to optimize nitrogen sources and titers for maximum production of M. robertsii blastospores cultured in shake flasks at highly aerated conditions and to further determine their virulence against the corn leafhopper Dalbulus maidis, an important vector of serious pathogens in maize crops worldwide. Our fermentation studies revealed that the low-cost corn steep liquor (CSL) was the most suitable nitrogen source to improve blastospore growth in M. robertsii. The growth kinetic assays determined the optimal titer of 80 g L and a yield up to 4.7 × 10 cells mL within 5 days of cultivation (3 days preculture and 2 days culture), at a total cost of US$0.30 L. Moreover, the blastospore growth kinetic was strongly dependent on glucose and nitrogen consumptions accompanied by a slight drop in the culture pH. Insect bioassays evidenced a high virulence of these blastospores, either as dried or fresh cells, to D. maidis adults fed on maize plants. Our findings provide insights into the nutritional requirements for optimal and cost-efficient production of M. robertsii blastospores and elucidate the potential of blastospores as an ecofriendly tool against the corn leafhopper.
具有世界性的昆虫病原真菌和根内生真菌玫烟色棒束孢（Metarhizium robertsii）具有多样的生活方式，在液体发酵过程中会经历从菌丝到分生孢子或微菌核，或从菌丝到芽生孢子的二态转化。在所有情况下，这些过程都受到环境和营养线索的调节。芽生孢子可用于喷雾应用，以控制地上节肢动物害虫，并且可能是对商业产品中发现的传统固体生长的空气中的分生孢子的有吸引力的替代物。氮是细胞代谢和生长的重要营养物质；然而，它是昆虫病原真菌液体培养中的昂贵成分。我们在这项研究中的目标是优化氮源和浓度，以最大限度地生产在高通气条件下摇瓶培养的玫烟色棒束孢芽生孢子，并进一步确定它们对玉米叶蝉（Dalbulus maidis）的毒力，玉米叶蝉是全世界玉米作物中严重病原体的重要载体。我们的发酵研究表明，低成本的玉米浆（CSL）是改善玫烟色棒束孢芽生孢子生长的最合适氮源。生长动力学测定确定了最佳浓度为 80 g/L，在 5 天的培养期内（3 天预培养和 2 天培养）达到 4.7×10 个细胞/mL 的产量，总成本为 0.30 美元/L。此外，芽生孢子生长动力学强烈依赖于葡萄糖和氮的消耗，同时培养 pH 值略有下降。昆虫生物测定证明，这些芽生孢子无论是干燥细胞还是新鲜细胞，对以玉米植株为食的玉米叶蝉成虫都具有很高的毒力。我们的研究结果提供了关于玫烟色棒束孢最佳和成本效益生产的营养需求的见解，并阐明了芽生孢子作为防治玉米叶蝉的环保工具的潜力。
