Niche adaptations and plasticity within the fungal entomopathogenic genus Metarhizium in Brazil

• Autor(a) principal: Couceiro, Joel da Cruz
• Data de Publicação: 2021
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/11/11146/tde-14022022-165125/
• topic: Metarhizium; Metarhizium; Expressão gênica; Gene expression; Genômica; Genomics; Microbiota do solo; Radiação UV-B; Soil microbiota; Temperatura; Temperature; UV-B radiation; Virulence; Virulência

The entomopathogenic fungal genus Metarhizium has a worldwide distribution. Natural abundance and distribution of Metarhizium spp. can be explained by diverse factors. In Brazil, Metarhizium anisopliae subclade Mani 2 causes most of the infections of insects above-ground, while Metarhizium robertsii is the most abundant Metarhizium species in the soil and is probably more associated with plant roots. The main objective of this PhD studies was to evaluate the effects of biotic and abiotic factors on selected isolates of Metarhizium anisopliae subclade Mani 2, Metarhizium robertsii and Metarhizium brunneum, a rare species in Brazil. The first aspect studied was the influence of UV-B radiation and high temperatures on conidial viability and mycelia activity. Considerable intra- and interspecific variability was found in tolerance to these abiotic factors. Exposure to UV-B radiation for 8 h harshly reduced survival of conidia. Mycelia of M. robertsii isolates showed optimum growth at 33 °C, but their conidia could not tolerate the highest temperature tested (40 °C), while mycelia of M. anisopliae isolates had optimum growth at 25 °C and their conidia were the most tolerant to incubation at 40 °C. It was demonstrated that conspecific isolates responded differently to abiotic factors. The second aspect studied was genomic features and relative gene expression of six target genes in two substrates (root exudate solution and insect cuticle suspension). Sequencing of the genomes, insect adhesin gene Mad1 and plant adhesin gene Mad2 of the twelve Brazilian isolates and two well-known reference isolates of M. robertsii revealed genotypic variability related to the geographic origin of the isolates. Gene expression variability was more pronounced for Mad2, protease Pr1A and hydrophobin hyd1, possibly relating to the lifestyles of each species. The third aspect was the interaction of the isolates with an insect host, evaluated through virulence bioassays. Two methods of inoculation were tested, representing exposure to aerial conidia in the above-ground environment and exposure to conidia in the soil environment. Mortality and sporulation on cadavers varied depending on the isolate. In most cases, isolates of M. brunneum and M. robertsii showed lower sporulation when contamination occurred in the soil compared to the above-ground spraying method. The last aspect studied was the interaction of the twelve isolates with native soil microbiota, evaluating their persistence for 120 days through assessment of colony forming units per gram of soil. The densities of the isolates decreased over time, and although there was variability between replicates in time, within each replicate the densities among isolates did not differ. The results obtained in all four studies indicate that isolates of M. robertsii are more adapted to develop mycelia in the soil, where they can associate with plants in the rhizosphere, while isolates of M. anisopliae Mani 2 are more adapted to develop conidia in the above-ground environment. The results emphasize the importance of evaluating ecological aspects of fungal isolates in order to conduct isolate selection and to include these entomopathogens in biological control programs.