Enzymes of Entomopathogenic Fungi, Advances and Insights

Abstract

Entomopathogenic fungi (EF) are recognized biological control agents of insects. Basically, the entomopathogenic fungi pathogen activity depends on the ability of its enzymatic equipment, consisting of lipases, proteases and chitinases, which are in charge of breaking down the insect's integument. Lipases are the first enzymes synthesized by the entomopathogenic fungi. Recently, a cytochrome P450 subfamily, referred as CYP52XI and MrCYP52 has been identified in Beauveria bassiana and Metarhizium robertsii, respectively. These break down long-chain alkenes and fatty acids to become initial nutrients. Subsequently, subtilisin type (Pr1) proteases sintetize; these enzymes are considered as virulence indicators and they are regulated by a signal transduction mechanism activated by the protein kinase A (PKA) mediated by AMPc. Through the employment of genetic engineering, it has been possible to increase virulence producing Pr1 recombinants with Androctonus australis neurotoxins or with chitinases, reducing the insect's time of death. In the course of time, the Pr1 protease gene has presented evolutionary adaptations by gene duplication or horizontal transfer infecting different orders of insects. In the same way, the entomopathogenic fungi chitinases have presented a functional diversification. Currently, these have been phylogenetically classified into three subgroups, in accordance to the catalytic site domain and the chitin binding domain. The chitinolytic activity has increased through a directed evolution processes and genetic recombination with Bombyx mori chitinase. Recently, enzymes have been employed as control agents for insects and phytopathogenic fungi (disease originator) opening new potentialities in order to improve the entomopathogenic fungi use. Solid state fermentation is a bioprocess that would produce at great scale enzymes and some other metabolites in grade of increasing the entomopathogenic fungi virulence, in the control of insects and potentially in some

Co-inoculum of Beauveria brongniartii and B. bassiana shows in vitro different metabolic behaviour in comparison to single inoculums

“…The differential use of substrates could also be associated to the different stages needed for the development of the infection in the host insect, that presumably require different metabolic abilities and the use of different carbon sources 34 . The interactions of entomopathogenic fungi, when playing the role of insect parasites, plant endophytes, rhizospheric colonizers, or simple soil inhabitants, as well as their change in trophic behaviour, require that their biosynthetic machinery undergo differential metabolic states of hyphae 35 , to fit their ecological niches 36 .…”

Conidia production of Isaria fumosorosea (Hypocreales: Cordycipitaceae) in organic substrates through two propagation techniques

“…In the present study, a nutritional analysis of each of the substrates used was not performed, however, according to the data reported by the United States Department of Agriculture (USDA 2016), about the nutritional information of the grains of rice, corn and barley that were the ones that obtained the best average yields in terms of the production of conidia per gram for both methods, for the grain of rice they report 79.95 g of available carbohydrates for only 7.13 g of protein, for corn 74.26 g of carbohydrates and 9.42 g of protein and for barley 73.48 g of carbohydrates and 12.48 g of proteins , all these values for every 100 g of each of these cereals. These values explain in a certain way the results obtained since in comparison with the corn cob, the canary seed and the peanut pericarp, their nutritional composition is more complete at least in these macronutrients, since for example for the grain bird seed each 100 g only 60.93 are available as carbohydrates (AGRICULTURE AND AGRI-FOOD CANADA, 2016) and for the peanut pericarp and the corn cob their main composition is based on lignocellulosic compounds such as cellulose, hemicellulose and lignin (RAVERA et al, 2008;CORDOBA et al, 2013), among others, which cannot be exploited in full by fungi such as I. fumosorosea because they lack the adequate enzymatic apparatus to do so (DE CAROLINA SÁNCHEZ-PÉREZ et al, 2014) and for other fungi such as Trichoderma harzianum, which agrees with that reported by Michel-Aceves et al (2008) who mention yields of up to 1.98 and 4.43 × 10 8 conidia g -1 in pericarp of peanut and corn cob, respectively. On the other hand it is known that enriched media, both in nitrogen and carbon, favor the production of biomass; however, it must be considered that higher mycelial growth does not necessarily result in high conidia production (MÉNDEZ et al, 2009), as mentioned by Moore (1996) that sporulation and mycelial growth can be favored by the presence of monosaccharides such as glucose or fructose, but not all nitrogen sources can favor these processes since amino acids such as asparagine and other ammonia compounds can accumulate during somatic growth by alkalizing the medium and inhibiting the processes of conidiation and growth, which agrees with Elósegui (2006) who mentions that to induce the sporulation process in fungi, it is necessary that the carbon source of the culture medium be abundant and the nitrogen content is the growth limiting factor.…”

The effect of entomopathogenic fungal culture filtrate on the immune response and haemolymph proteome of the large pine weevil, Hylobius abietis

“…Larvae co-injected with B. bassiana or B. caledonica filtrate and C. albicans showed significantly increased mortality. The proposed immunomodulation of larvae by the EPF that is rendering the host more susceptible to a subsequent pathogen is caused by spore-free culture filtrate which contains a diverse mixture of enzymes, proteases and secondary metabolites (Vey et al 2001;Sánchez-Pérez et al 2014). Destruxin, the most abundantly produced secondary metabolite in Metarhizium spp., induced a similar response in D. melanogaster (Pal et al 2007).…”