Concomitant biosynthesis of Aspergillus niger pectolytic enzymes and citric acid on sucrose

By-products from the biodiesel chain as a substrate to citric acid production by solid-state fermentation

In this study, we propose the use of tung cake for the production of organic acids, with an emphasis on citric acid by solid-state fermentation. We evaluated the conditions of production and the by-products from the biodiesel chain as raw materials involved in this bioprocess. First, we standardized the conditions of solid-state fermentation in tung cake with and without residual fat and with different concentrations of glycerine using the fungus Aspergillus niger The solid-state fermentation process was monitored for 7 days considering the biomass growth and pH level. Citric acid production was determined by high-performance liquid chromatography. Fungal development was better in the crude tung cake, consisting of 20% glycerine. The highest citric acid yield was 350 g kg(-1) of biomass. Therefore, the solid-state fermentation of the tung cake with glycerine led to citric acid production using the Aspergillus niger fungus.

Biotechnological Potential of Agro-Industrial Wastes as a Carbon Source to Thermostable Polygalacturonase Production in Aspergillus niveus

Agro-industrial wastes are mainly composed of complex polysaccharides that might serve as nutrients for microbial growth and production of enzymes. The aim of this work was to study polygalacturonase (PG) production by Aspergillus niveus cultured on liquid or solid media supplemented with agro-industrial wastes. Submerged fermentation (SbmF) was tested using Czapeck media supplemented with 28 different carbon sources. Among these, orange peel was the best PG inducer. On the other hand, for solid state fermentation (SSF), lemon peel was the best inducer. By comparing SbmF with SSF, both supplemented with lemon peel, it was observed that PG levels were 4.4-fold higher under SSF. Maximum PG activity was observed at 55°C and pH 4.0. The enzyme was stable at 60°C for 90 min and at pH 3.0–5.0. The properties of this enzyme, produced on inexpensive fermentation substrates, were interesting and suggested several biotechnological applications.

Microbial pectic transeliminases

Pectic transeliminases, also known as pectic lyases or pectinases, are involved in the degradation of pectic substances. They have a wide range of applications in food and textile processing. Although Aspergillus and Penicillium spp. produce pectin lyases, bacteria are the major producers of polygalacturonate lyase. The yields of pectic transeliminases are less than other pectinases. Since new applications for pectic transeliminases are emerging, an improved process for the production of these enzymes is necessary.

Production of pectin-degrading enzymes by ericoid mycorrhizal fungi

Production of enzymes which degrade plant cell wall macromoleculea has been studied in relatively few ericoid fungal isolates, although these polymers arc a major component of the organic litter and an important source of nutrients for these fungi. Our aims were to investigate whether the ability to degrade the wall pectic component, only reported for one isolate, is a general feature of ericoid fungi. Of about 35 isolates from different geographic regions, all were capable of growing on pectin as the sole carbon source. Polygalacturonase (PG) activity was detected to a different degree in the culture filtrates and independently of the fungal growth rate. Solid and liquid isoelectric focusing allowed separation and identification of several polygalacturonase isoforms. Among the fungal isolates investigated, those from the northern hemisphere produced mostly acidic isoforms, whereas isolates from South Africa secreted more abundantly basic isoforms. However, purification and biochemical characterization of several PG isoforms from the different isolates revealed an optimal activity in the acidic pH range for all the PG enzymes tested. Polygalacturonase enzymes seem to be an important component of the enzymatic arsenal secreted by ericoid fungi during their saprotrophic life. In addition, they could also play a role during root colonization, since penetration across the plant cell wall is a prerequisite for the establishment of endomycorrhizal symbiosis.