Purification and characterization of a β-glucosidase from the phytopathogenic fungus Fusarium oxysporum f. sp. melonis

Unravelling the temporal and spatial variation of fungal phylotypes from embryo to adult stages in Atlantic salmon

Early microbial colonization has a profound impact on host physiology during different stages of ontogeny. Although several studies have focused on early bacterial colonization and succession, the composition and role of fungal communities are poorly known in fish. Here, we sequenced the internal transcribed spacer 2 (ITS2) region of fungi to profile the mycobiome associated with the eggs, hatchlings and intestine of Atlantic salmon at various freshwater and marine stages. In most of the stages studied, fungal diversity was lower than bacterial diversity. There were several stage-specific fungal phylotypes belonging to different stages of ontogeny but some groups, such as Candida tropicalis, Saccharomyces cerevisiae, Alternaria metachromatica, Davidiella tassiana and Humicola nigrescens, persisted during successive stages of ontogeny. We observed significant changes in the intestinal fungal communities during the first feeding. Prior to first feeding, Humicola nigrescens dominated, but Saccharomyces cerevisiae (10 weeks post hatch) and Candida tropicalis (12 weeks post hatch) became dominant subsequently. Seawater transfer resulted in a decrease in alpha diversity and an increase in Candida tropicalis abundance. We also observed notable variations in beta diversity and composition between the different farms. Overall, the present study sheds light on the fungal communities of Atlantic salmon from early ontogeny to adulthood. These novel findings will also be useful in future studies investigating host-microbiota interactions in the context of developing better nutritional and health management strategies for Atlantic salmon farming.

β-Glucosidase VmGlu2 Contributes to the Virulence of Valsa mali in Apple Tree

The apple tree canker is caused by Valsa mali, which produces major pathogenic factors involving multiple cell wall-degrading enzymes (CWDEs) and toxins. The β-glucosidases are among the main CWDEs, and thus, they play important roles in the virulence of necrotrophic pathogens. However, the specific roles of β-glucosidases in the virulence of V. mlai remain largely unknown. In this study, we identified a β-glucosidase gene, VmGlu2, which was upregulated during the V. mali infection. We found that VmGlu2 protein had high enzyme activity of β-glucosidase using p-nitrophenyl-β-D-glucopyranoside (pNPG) as a substrate, while the VmGlu2 could convert phloridzin to phloretin with the release of glucose. The deletion and overexpression of VmGlu2 showed no effect on vegetative growth, but gene deletion mutants of V. mlai showed significantly reduced pycnidia formation. The gene deletion mutants had lower β-glucosidase activities and toxin levels as compared to the wild-type strain. Therefore, these mutants showed a reduced virulence. Moreover, the overexpression of VmGlu2 did not affect toxin levels, but it significantly enhanced β-glucosidase activities, which resulted in an increased pathogenicity. Thus, we conclude that VmGlu2 is required for the full virulence of V. mali. These results provide valuable evidence to the complex role of CWDEs in the fungal pathogenicity.

Investigation into the fungal diversity within different regions of the gastrointestinal tract of Panaque nigrolineatus, a wood-eating fish

The Amazonian catfish, Panaque nigrolineatus have several physiological adaptions enabling the scraping and consumption of wood (xylivory), facilitating a detritivorous dietary strategy. Composed of lignocellulose, wood is a difficult substrate to degrade and as yet, it is unclear whether the fish obtains any direct nutritional benefits from wood ingestion and degradation. However, there are numerous systems that rely on microbial symbioses to provide energy and other nutritional benefits for host organisms via lignocellulose decomposition. While previous studies on the microbial community of P. nigrolineatus have focused upon the bacterial population, the role of fungi in lignocellulose degradation in the fish has not yet been examined. This study describes the detection of fungi within the fish gastrointestinal tract. Using next generation sequencing, the effects of diet on enteric fungal populations were examined in each gastrointestinal tract region. Fungal species were found to vary in different regions of the gastrointestinal tract as a function of diet. This study is the first to examine the fungal community in a xylivorous fish and results support the hypothesis that diet influences fungal distribution and diversity within the gastrointestinal tract of P. nigrolineatus.

Optimization of phytase production by Penicillium purpurogenum GE1 under solid state fermentation by using Box-Behnken design

Phytase production by Penicillium purpurogenum GE1 isolated from soil around bean root nodules was investigated by solid state fermentation (SSF) using mixed substrates consisted of corn cob and corn bran. The SSF conditions were optimized by using one-variable-at-a-time strategy. The optimum conditions for phytase production were at 27 °C, pH 8 and 66% moisture content. The study of different carbon and nitrogen sources revealed that glucose and peptone registered the highest enzyme productivity (92 ± 5.6 U/g ds, 125 ± 4.9 U/g ds). Among different surfactants, maximum phytase productivity was observed with Tween 80 at 0.001 concentrations (170 ± 4.2 U/g ds). A Box-Behnken design was employed to investigate the optimization of the most significant variables affecting the enzyme production. Maximal phytase production was detected after the addition of (g/5 g ds): 0.75 glucose, 0.375 peptone and 0, 01 tween 80. This result represented an improvement in phytase production of 2.6 folds when compared to that previously obtained using the basal medium under the same cultivation conditions. The generated model was found to be very adequate for phytase production (90% accuracy) as the experimental value was 444 ± 3.5 U/g ds compared to 401 U/g ds for the predicted value. In brief, the production of phytase using corn cob and corn bran is a novel and cheap way for the production of this important enzyme and opens a new way for researchers to discover and explore this arena.

Purification and characterization of two beta-glucosidases from the thermophilic fungus Thermoascus aurantiacus

beta-Glucosidase from the fungus Thermoascus aurantiacus grown on semi-solid fermentation medium (using ground corncob as substrate) was partially purified in 5 steps--ultrafiltration, ethanol precipitation, gel filtration and 2 anion exchange chromatography runs, and characterized. After the first anion exchange chromatography, beta-glucosidase activity was eluted in 3 peaks (Gl-1, Gl-2, Gl-3). Only the Gl-2 and Gl-3 fractions were adsorbed on the gel matrix. Gl-2 and Gl-3 exhibited optimum pH at 4.5 and 4.0, respectively. The temperature optimum of both glucosidases was at 75-80 degrees C. The pH stability of Gl-2 (4.0-9.0) was higher than Gl-3 (5.5-8.5); both enzyme activities showed similar patterns of thermostability. Under conditions of denaturing gel chromatography the molar mass of Gl-2 and Gl-3 was 175 and 157 kDa, respectively. Using 4-nitrophenyl beta-D-glucopyranoside as substrate, Km values of 1.17 +/- 0.35 and 1.38 +/- 0.86 mmol/L were determined for Gl-2 and Gl-3, respectively. Both enzymes were inhibited by Ag+ and stimulated by Ca2+.