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Bioeconomy goals for using biomass feedstock for biofuels and bio-based production has arisen the demand for fungal strains and enzymes for biomass processing. Despite well-known Trichoderma and Aspergillus commercial strains, continuous bioprospecting has revealed the fungal biodiversity potential for production of biomass degrading enzymes. The strain Aspergillus fumigatus LMB-35Aa has revealed a great potential as source of lignocellulose-degrading enzymes. Nevertheless, genetic improvement should be considered to increase its biotechnological potential. Molecular manipulation based on homologous direct recombination (HDR) in filamentous fungi poses a challenge since its low recombination rate. Currently, CRISPR/Cas9-mediated mutagenesis can enable precise and efficient editing of filamentous fungi genomes. In this study, a CRISPR/Cas9-mediated gene editing strategy for improving endoglucanase activity of A. fumigatus LMB-35Aa strain was successfully used, which constitutes the first report of heterologous cellulase production in filamentous fungi using this technology. For this, eglA gene from A. niger ATCC 10,864 was integrated into conidial melanin pksP gene locus, which facilitated the selection of edited events discerned by the emergence of albino colonies. Heterologous production of the EglA enzyme in a biofilm fermentation system resulted in a 40% improvement in endoglucanase activity of the mutant strain compared to the wild type., (© 2024. The Author(s).)

Photochemical reactions in snow can have an important impact on the composition of the atmosphere over snow-covered areas as well as on the composition of the snow itself. One of the major photochemical processes is the photolysis of nitrate leading to the formation of volatile nitrogen compounds. We report nitrite concentrations determined together with nitrate and hydrogen peroxide in surface snow collected at the coastal site of Barrow, Alaska. The results demonstrate that nitrite likely plays a significant role as a precursor for reactive hydroxyl radicals as well as volatile nitrogen oxides in the snow. Pollution events leading to high concentrations of nitrous acid in the atmosphere contributed to an observed increase in nitrite in the surface snow layer during nighttime. Observed daytime nitrite concentrations are much higher than values predicted from steady-state concentrations based on photolysis of nitrate and nitrite indicating that we do not fully understand the production of nitrite and nitrous acid in snow. The discrepancy between observed and expected nitrite concentrations is probably due to a combination of factors, including an incomplete understanding of the reactive environment and chemical processes in snow, and a lack of consideration of the vertical structure of snow.

Biomass organization of Aspergillus niger biofilms and pellets stained with fluorescein isothiocyanate were analyzed by means of confocal laser scanning microscopy and detectable differences between both types of growth were found. Three-dimensional surface plot analysis of biofilm structure revealed interstitial voids and vertical growth compared with pellets. Growth was lower in biofilm and according to fluorescence profile obtained, biomass density increased at the surface (0-20 microm). However, a decrease in fluorescence intensity was observed through optical sections of pellets even though growth was significantly higher than biofilms. Cryo scanning electron microscopy also showed structural differences. While biofilms showed a spatially ordered mycelium and well structured hyphal channels, pellets were characterized by an entangled and notoriously compacted mycelium. These findings revealed common structural characteristics between A. niger biofilms and those found in other microbial biofilms. Thus, biofilm microstructure may represent a key determinant of biofilm growth and physiology of filamentous fungi., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)

Aims: To study the morphological patterns of Aspergillus niger during biofilm formation on polyester cloth by using cryo-scanning electron microscopy related to lignocellulolytic enzyme productivity., Methods and Results: Biofilm and pellet samples obtained from flask cultures were examined at -80 degrees C in a LEO PV scanning electron microscope. Spore adhesion depends on both its rough surface and adhesive substances that form a pad between spore and support. An extracellular matrix surrounding germ tubes and hyphae was also seen. Biofilm mycelia showed an orderly distribution forming surface and inner channels, while pellets showed highly intertwined superficial hyphae and a densely packed deep mycelium. Morphological differences between both types of culture correlated with differences in enzyme volumetric and specific productivities. Biofilm cultures produced higher filter paper cellulase, endoglucanase, beta-glucosidase and xylanase volumetric and specific productivities than submerged cultures., Conclusions: Fungal biofilms are morphologically efficient systems for enzyme production. Favourable physiological aspects are shared with solid state fermentation, but fungal biofilms present better possibilities for process control and scale-up., Significance and Impact of the Study: The results of this study support the importance of morphology in the productivity of fungal submerged processes, placing biofilms in a preferential category.

Aims: To compare cellulase production by Aspergillus niger ATCC 10864 biofilms on polyester cloth and freely suspended cultures in shaken flasks and microbioreactors of bubble column type., Methods and Results: Both shaken flasks and oxygenated microbioreactors containing 40 ml of production medium were used to compare cellulase secretion by free mycelium and biofilm cultures. Free mycelium cultures grew better in flasks than in microbioreactors producing compact and fluffy pellets, respectively, while the opposite was found for biofilm cultures without any visible change in biofilm morphology. Cellulase activities and volumetric productivities attained by biofilms in flask cultures were 70% higher than that produced by free mycelium cultures and threefold higher when biofilms were grown in microbioreactors., Conclusions: Fungal biofilms developed on polyester cloth in both flasks and microbioreactors produce higher cellulase yields and volumetric productivities than free mycelium cultures at lower biomass levels., Significance and Impact of the Study: The results of the present study are of commercial and biological interest. All productivity parameters revealed that fungal biofilms may be used for the production of cellulase and other proteins in various types of bioreactors. Moreover, they may be used as model systems to study differential gene expression related to cell adhesion.

Peroxides present in Santiago City dew waters readily decompose with first order kinetics. In order to minimize the loss of peroxides during the time elapsed between deposition and collection, the collectors were pre-treated with a mercury chloride solution. This reduces, but not completely eliminates, the decomposition. A correction is introduced by a comparison of the levels and decomposition kinetics of the samples collected in treated and untreated collectors. The average concentration estimated by this procedure was 8.1 microM. The mechanism of peroxide decomposition and its stabilization is discussed.