Meizhen Fan

Discovery and demonstration of the teleomorph ofBeauveria bassiana (Bals.) Vuill., an important entomogenous fungus

ACordyceps specimen was collected in Anhui, China, a strain ofBeauveria bassiana, an important entomopathogenic fungus for biological pest control, was isolated and their relationship was demonstrated by microcycle conidiation. The teleomorph is an undescribed species and is namedCordyceps bassiana.

Evaluation of Beauveria bassiana （Hyphomycetes） isolates as potential agents for control of Dendroctonus valens

Abstract  The red turpentine beetle (RTB), Dendroctonus valens LeConte, as a destructive invasive pest, has become one of the most economically important forest pest in China. Effective control measures are desperately needed. Entomopathogenic fungi, such as Beauveria bassiana, have shown great potential for the management of some bark beetle species. In this study, 12 isolates of B. bassiana from bark beetle were examined for biological characteristics and virulence, to assess their potential as biocontrol agents for RTB. There were significant differences (at P= 0.05) in colony growth rate, conidial yield, conidial germination, tolerance to UV light and extracellular proteases activity among the tested B. bassiana isolates. Isolates, including Bb1801, Bb1906, Bb789 and Bb773, exhibited the best characteristics, because they have faster hyphal growth rate, higher spore production and faster spore germination, higher UV tolerance and protease (Pr1) production. The results of a pathogenicity test of B. bassiana on RTB larvae showed that most isolates of B. bassiana have demonstrated high efficacy and the highest virulent isolate was Bb1801, which killed 100% of the treated insects and had a median lethal time (LT50) of 4.60 days at a concentration of 1×107 conidia/mL. Therefore, isolate Bb1801 has a great potential for sustainable control of RTB in the forest. The correlation between biological characteristics and virulence of the fungal isolates is discussed and the possibility of combination of entomopathogenic fungi with semiochemicals, as one of the promising strategy for RTB control, is considered.

Optimization of ultrasonic extraction of mycelial polysaccharides from Paecilomyces hepiali using response surface methodology and its antioxidant activity

Ultrasonic technology was applied to extract mycelial polysaccharides from Paecilomyces hepiali and the process was optimized by response surface methodology. Antioxidant activity of polysaccharides was also investigated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (%DPPHsc). Three independent variables were ratio of water to raw material (x 1 ), ultrasonic power (x 2 ) and extraction time (x 3 ). Statistical analysis indicated that x 1 , x 2 , x 1 2 , x 3 2 , x 1 x 2 , x 1 x 3 and x 2 x 3 had significant effect on the yields. Besides, x 2 , x 1 2 and x 2 2 shaped the %DPPHsc of polysaccharides significantly. Three dimensional surface plots and contour plots were drawn from the mathematical model. The optimal conditions for yield and %DPPHsc were as follows: condition (1) x 1 = 125 mL/g, x 2 = 300 W, x 3 = 12 min, and condition (2) x 1 = 125 mL/g and x 2 = 500 W, x 3 = 11 min, respectively. Under these conditions, the yield was 9.37%, and %DPPHsc was 45.34%. There existed good agreement between experimental and predicted values. Key words : Ultrasonic extraction, polysaccharides, Paecilomyces hepiali, response surface methodology, antioxidant activity.

Metabolic responses of Beauveria bassiana to hydrogen peroxide-induced oxidative stress using an LC-MS-based metabolomics approach.

The entomopathogenic fungus, Beauveria bassiana, is commonly used as a biological agent for pest control. Environmental and biological factors expose the fungus to oxidative stress; as a result, B. bassiana has adopted a number of anti-oxidant mechanisms. In this study, we investigated metabolites of B. bassiana that are formed in response to oxidative stress from hydrogen peroxide (H2O2) by using a liquid chromatography mass spectrometry (LC-MS) approach. Partial least-squares discriminant analysis (PLS-DA) revealed differences between the control and the H2O2-treated groups. Hierarchical cluster analysis (HCA) showed 18 up-regulated metabolites and 25 down-regulated metabolites in the H2O2-treated fungus. Pathway analysis indicated that B. bassiana may be able to alleviate oxidative stress by enhancing lipid catabolism and glycometabolism, thus decreasing membrane polarity and preventing polar H2O2 or ROS from permeating into fungal cells and protecting cells against oxidative injury. Meanwhile, most of the unsaturated fatty acids that are derived from glycerophospholipids hydrolysis can convert into oxylipins through autoxidation, which can prevent the reactive oxygen of H2O2 from attacking important macromolecules of the fungus. Results showed also that H2O2 treatment can enhance mycotoxins production which implies that oxidative stress may be able to increase the virulence of the fungus. In comparison to the control group, citric acid and UDP-N-acetylglucosamine were down-regulated, which suggested that metabolic flux was occurring to the TCA cycle and enhancing carbohydrate metabolism. The findings from this study will contribute to the understanding of how the molecular mechanisms of fungus respond to environmental and biological stress factors as well as how the manipulation of such metabolisms may lead to selection of more effective fungal strains for pest control.