Properties of an extracellular -galactosidase secreted by Neurospora crassa

New β-galactosidase producers with potential for prebiotic synthesis

β-Galactosidases (EC 3.2.1.23) are interesting enzymes with potential application in the pharmaceutical and food industry. In this work, a screening study was carried out to identify new fungal sources of β-galactosidase. A total of 50 fungi were evaluated using a chromogenic test performed in agar plates. The most promising microorganisms were validated as effective β-galactosidase producers under submerged fermentation conditions. The crude β-galactosidases were characterized regarding their optimal pH (3.0-5.5) and temperature (45-65 °C). All enzymes showed ability to synthesize lactose-based prebiotics, namely lactulose (maximal yield 3.3%) and a galacto-oligosaccharide (GOS) (maximal yield 20%). Additionally, some enzymatic extracts with fructosyltransferase activity allowed to produce other type of prebiotics, namely fructo-oligosaccharides (FOS). This work, reports for the first time the simultaneous synthesis of different mixtures of GOS (2-15% yield and 0.07-0.5 g/L·h^-1 productivity) and FOS (4-30% yield and 0.1-1 g/L·h^-1 productivity) by crude extracts exhibiting dual enzymatic activity.

Microbial technologies in the production of low-lactose dairy foods / Tecnologías microbiológicas para la elaboración de productos lácteos con bajo contenido en lactosa

Low-lactose milk products with 70% or more of the lactose hydrolysed by food grade β-galac tosidase enzymes of yeasts or fungi have become widely accepted for alleviating the symptoms of lactose maldigestion. This condition limits the intake of nutritious dairy foods by large segments of the world's population. Alternative approaches recently proposed for dealing with lactose maldigestion include the supplementation of milk with dormant dairy cultures, treatment of milk with sonicated or permeabilized cultures as food-grade sources of β-galactosidase and the use of cold-active enzymes to hydrolyse lactose in milk under refrigerated storage conditions.

Extra- and intracellular lactose catabolism in Penicillium chrysogenum: phylogenetic and expression analysis of the putative permease and hydrolase genes

Penicillium chrysogenum is used as an industrial producer of penicillin. We investigated its catabolism of lactose, an abundant component of whey used in penicillin fermentation, comparing the type strain NRRL 1951 with the high producing strain AS-P-78. Both strains grew similarly on lactose as the sole carbon source under batch conditions, exhibiting almost identical time profiles of sugar depletion. In silico analysis of the genome sequences revealed that P. chrysogenum features at least five putative β-galactosidase (bGal)-encoding genes at the annotated loci Pc22g14540, Pc12g11750, Pc16g12750, Pc14g01510 and Pc06g00600. The first two proteins appear to be orthologs of two Aspergillus nidulans family 2 intracellular glycosyl hydrolases expressed on lactose. The latter three P. chrysogenum proteins appear to be distinct paralogs of the extracellular bGal from A. niger, LacA, a family 35 glycosyl hydrolase. The P. chrysogenum genome also specifies two putative lactose transporter genes at the annotated loci Pc16g06850 and Pc13g08630. These are orthologs of paralogs of the gene encoding the high-affinity lactose permease (lacpA) in A. nidulans for which P. chrysogenum appears to lack the ortholog. Transcript analysis of Pc22g14540 showed that it was expressed exclusively on lactose, whereas Pc12g11750 was weakly expressed on all carbon sources tested, including D-glucose. Pc16g12750 was co-expressed with the two putative intracellular bGal genes on lactose and also responded on L-arabinose. The Pc13g08630 transcript was formed exclusively on lactose. The data strongly suggest that P. chrysogenum exhibits a dual assimilation strategy for lactose, simultaneously employing extracellular and intracellular hydrolysis, without any correlation to the penicillin-producing potential of the studied strains.

Localization of beta-(1,3)-glucanase in the mycelium of Sclerotium rolfsii

The role of the lytic enzyme beta-(1,3)-glucanase in cell wall synthesis and its distribution in the mycelium of the fungus Sclerotium rolfsii were studied. Enzyme activity was determined after enzyme extraction with Triton X-100 from a cell wall preparation. Specific zones of immunofluorescence appeared in the hyphal tips, clamp connections, new septa, and lateral branching when a specific antiserum was used with the indirect method of the fluorescent antibody staining. Enzymatic activity in the cell wall preparation was inactivated by diethylpyrocarbonate. However, 69% of the total enzymatic activity was present in a latent form which was not affected by the ester. This result suggests that most of the beta-(1,3)-glucanase was present along the hyphal cell walls in a "masked" form. An active enzyme appeared only in those regions which showed immunofluorescence. The activity of glucan synthetase, an enzyme essential for wall formation, was higher in the branching funus grown on L-threonine-supplemented synthetic medium than in the synthetic medium-grown fungus.

Influence of the carbon source on glycerol kinase activity in Neurospora crassa

The level of glycerol kinase activity in Neurospora crassa was shown to change in response to resuspension of sucrose-grown mycelia in fresh medium containing a new carbon source: the magnitude of the change depended on the new carbon source provided. Certain carbon sources, such as glucose and fructose, inhibited the small increase that occurred in the absence of any carbon source. Others, and in particular deoxyribose, galactose, glycerol and ribose, greatly enhanced this increase. The activity induced by deoxyribose and galactose had the same stability, both in vivo and in vitro, as that induced by glycerol, and as that induced by incubation of Neurospora cultures at low temperatures. The inhibitory carbon sources, such as glucose and fructose, also restricted the increases induced by deoxyribose, galactose and glycerol: they had more effect on the increases induced by glycerol and deoxyribose than on that induced by galactose. The increase in activity that occurs at low temperature was also inhibited by glucose and sucrose.

Control of Extracellular beta-1,3-glucanase activity in a basidiomycete species

The basidiomycete QM 806 excreted large amounts of beta-1,3-glucanase into the culture medium. Synthesis and excretion of the enzyme were triggered by a critically low concentration of carbon source. The extracellular beta-1,3-glucanase exhibited a remarkable stability. Addition of glucose or other carbon sources to a culture after consumption of the initial carbon source led to an inactivation of the extracellular beta-1,3-glucanase by an inactivating system, which could be separated from the cells. The inactivation of beta-1,3-glucanse was prevented by cycloheximide. This indicates the necessity of active protein synthesis for the inactivation process but does not prove that the inactivating system itself is a protein. Marked changes in the electrophoretic mobility and immunological properties of beta-1,3-glucanase indicate rather profound alterations of the enzyme protein in the course of inactivation.