The endophytic capacity of the entomopathogenic fungus Beauveria bassiana caused inherent physiological response in two barley (Hordeum vulgare) varieties.

In this study, the endophytic capacity of B. bassiana was determined for two barley (Hordeum vulgare) varieties, Josefa and Esmeralda, inoculated with a seedling immersion at three different concentrations (1 × 106, 1 × 107 and 1 × 108 conidia/mL). Seedling length and chlorophyll content were found to be not affected when inoculated with the entomopathogenic fungus, in both barley varieties. However, the colonisation percentage was found to be significantly lower with the inoculum concentration 1 × 106 conidia/mL for both barley varieties (P < 0.05) when compared to the other concentrations. Furthermore, a principal component analysis indicated that 96.23% of the variability in the data could be explained with two components. This analysis showed that the seedling length and chlorophyll content were positively correlated in both barley varieties for the 1 × 107 conidia/mL concentration. Likewise, a positive correlation was observed for colonisation percentage and treatment with 1 × 108 conidia/mL in the Josefa variety only. This is the first study in which the endophytic capacity of B. bassiana was evaluated in two different barley varieties, with the Josefa variety found to be the most susceptible.

Comparison between superficial and solid-state cultures of Isaria fumosorosea: conidial yields, quality and sensitivity to oxidant conditions.

Conidia production and quality from mycoinsecticides in solid-state cultures (SSC) are frequently inferred from superficial culture (SC) results. Both parameters were evaluated for two Isaria fumosorosea strains (ARSEF 3302 and CNRCB1), in SC and SSC, using culture media with the same chemical composition. For both strains, conidia production was higher in SC than SSC in terms of conidia per gram of dry substrate. Germination in both strains did not show significant differences between SC and SSC (>90 %). Similarly, conidia viability in ARSEF 3302 strain did not show differences at early stages between SC and SSC, but was higher in SC compared to SSC in the late stage of culture; in contrast, conidia from CNRCB1 strain did not differ between both culture systems. Some infectivity parameters improved in conidia from SSC, compared to SC at the early stages, but these differences disappeared at the final stage, independently of the strain. Both strains showed decreased conidia production when 26 % O2 pulses were applied; nevertheless, conidiation in SSC was two orders of magnitude more sensitive to oxidant pulses. In SC with 26 % O2 pulses, conidia viability for both strains at early stages, was higher than in normal atmospheric conditions. Infectivity towards Galleria mellonella larvae was similar between conidia from normal atmosphere and oxidant conditions; notably, for the strain ARSEF 3302 infectivity decreased at the final stage. This study shows the intrinsic differences between SC and SSC, which should be considered when using SC as a model to design production processes in SSC.

Variations in oxygen concentration cause differential antioxidant response and expression of related genes in Beauveria bassiana.

The entomopathogenic fungus Beauveria bassiana is widely used in pest biocontrol strategies. We evaluated both the antioxidant response mediated by compatible solutes, trehalose or mannitol, and the expression of related genes using oxygen pulses at three oxygen concentrations in solid state culture (SSC): normal atmosphere (21% O2), low oxygen (16% O2) and enriched oxygen (26% O2). Trehalose concentration decreased 75% after atmospheric modifications in the cultures, whereas mannitol synthesis was three-fold higher under the 16% O2 pulses relative to normal atmosphere (100 and 30 µg mannitol mg(-1) biomass, respectively). Confirming this result, expression of the mpd gene, coding for mannitol-1-P dehydrogenase (MPD), increased up to 1.4 times after O2 pulses. The expression of the bbrgs1 gene, encoding a regulatory G protein related to conidiation, was analysed to explain previously reported differences in conidial production. Surprisingly, expression of bbrgs1 decreased after atmospheric modification. Finally, principal component analysis (PCA) indicated that 83.39% of the variability in the data could be explained by two components. This analysis corroborated the positive correlation between mannitol concentration and mpd gene expression, as well as the negative correlation between conidial production and bbrgs1 gene expression. This study contributes to understanding of antioxidant and molecular response of B. bassiana induced under oxidant conditions.

Physiological and antioxidant response by Beauveria bassiana Bals (Vuill.) to different oxygen concentrations.

The effect of three levels of oxygen (normal atmosphere (21% O(2)), low oxygen (16% O(2)) and enriched oxygen (26% O(2))) on the production and germination of conidia by Beauveria bassiana was evaluated using rice as a substrate. The maximum yield of conidia was achieved under hypoxia (16% O(2)) after 8 days of culture (1.51 × 10(9) conidia per gram of initial dry substrate), representing an increase of 32% compared to the normal atmosphere. However, germination was reduced by at least 27% due to atmospheric modifications. Comparison of antioxidant enzyme activity (superoxide dismutases and catalases) with the oxidation profiles of biomolecules (proteins and lipids) showed that a decrease in catalase activity in the final days of culture coincided with an increase in the amount of oxidized lipids, showing that oxidative stress was a consequence of pulses of different concentrations of O(2). This is the first study describing oxidative stress induction by atmospheric modification, with practical implications for conidia production.