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-1 and a yield up to 4.7 × 108 cells mL-1 within 5 days of cultivation (3 days preculture and 2 days culture), at a total cost of US$0.30 L-1. 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.

中文翻译：

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罗伯氏绿僵菌液体培养发酵的生长动力学和氮源优化及对玉米叶蝉 Dalbulus maidis 的生物效应

世界性昆虫病原真菌和根内生真菌绿僵菌具有多种生活方式，在液体发酵过程中经历了从菌丝到分生孢子或微菌核，或从菌丝到芽生孢子的双态转化。在所有情况下，这些过程都是由环境和营养线索介导的。芽孢可用于喷雾应用以控制地上节肢动物害虫，并可作为绿僵菌属的传统固体生长气生分生孢子的有吸引力的替代品。在商业产品中发现。氮是细胞代谢和生长的重要营养素；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滴度，以最大程度地生产 M. robertsii 芽生孢子在摇瓶中在高度通风的条件下培养，并进一步确定它们对玉米叶蝉 Dalbulus maidis 的毒力，玉米叶蝉是全球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) 是最适合改善 M. robertsii 芽生孢子生长的氮源。生长动力学分析确定了 80 g L-1 的最佳滴度和在培养 5 天内（3 天预培养和 2 天培养）的产量高达 4.7 × 108 个细胞 mL-1，总成本为 0.30 美元 L- 1. 此外，芽生孢子的生长动力学强烈依赖于葡萄糖和氮的消耗，伴随着培养物 pH 值的轻微下降。昆虫生物测定证明这些芽生孢子，无论是干细胞还是新鲜细胞，对 D. maidis 成虫以玉米植物为食。我们的研究结果提供了对 M. robertsii 胚芽孢子最佳和经济高效生产的营养需求的见解，并阐明了胚芽孢子作为对抗玉米叶蝉的生态友好工具的潜力。