Comparative study of the growth of Trichoderma reesei and Penicillium occitanie

During the last years, a great deal of research on the production of energetic substances was directed to the use of cellulosic by-products. A technique of special interest is the production of fermentissible sugars by the enzymatic hydrolysis of cellulose. Mandels and Reese (1960) showed that a fungi strain of Trichoderma reesei is the best performant microorganism in the production of cellulolytic enzymes. Nevertheless, recent investigation indicated that the rate and the yield of conversion of cellulose to glucose of this strain are limited by its poor beta-glucosidase activity. In order to increase the efficiency of the hydrolytic power of the cellulasic complex two approaches can be considered. Beta-glucosidase enrichment of Trichoderma reesei enzymes. The selection and use of strains with a better performance. In our laboratory, we chose the second approach using Penicillium occitanie comparing it to Trichoderma reesei.     

Optimization of cellulase production by Penicillium occitanis

The mutant Pol6 of Penicillium occitanis is an interesting strain for producing cellulases and hemicellulases. The nitrogen source and substrate that regulate cellulase production were evaluated in shake-flask and fermentor (batch and fed-batch) culture. The nature of the nitrogen source and the C/N ratio markedly affected cellulase production by P. occitanis. When nitrate was used in Mandels and Weber's basal growth medium with a C/N ratio below 20.2, it resulted in more cellulase production than from urea or ammonium sulphate. Crude substrates such as wheat bran and wheat flour residues, used in combination with a local cellulose esparto grass paper pulp as an alternative nitrogen source and cellulose substrates, also gave high cellulase yields. Greatest cellulase yields and productivity were obtained by fed-batch cultivation [23 filter-paper activity units (FPU)/ml and 168 FPUI^–1h^–1].     

Roles of Lignin Peroxidase and Manganese Peroxidase from Phanerochaete chrysosporium in the Decolorization of Olive Mill Wastewaters

The relative contributions of lignin peroxidase (LiP) and manganese peroxidase (MnP) to the decolorization of olive mill wastewaters (OMW) by Phanerochaete chrysosporium were investigated. A relatively low level (25%) of OMW decolorization was found with P. chrysosporium which was grown in a medium with a high Mn(II) concentration and in which a high level of MnP (0.65 (mu)M) was produced. In contrast, a high degree of OMW decolorization (more than 70%) was observed with P. chrysosporium which was grown in a medium with a low Mn(II) concentration but which resulted in a high level of LiP activity (0.3 (mu)M). In this culture medium, increasing the Mn(II) concentration resulted in decreased levels of OMW decolorization and LiP activity. Decolorization by reconstituted cultures of P. chrysosporium was found to be more enhanced by the addition of isolated LiP than by the addition of isolated MnP. The highest OMW decolorization levels were obtained at low initial chemical oxygen demands combined with high levels of extracellular LiP. These data, plus the positive effect of veratryl alcohol on OMW decolorization and LiP activity, indicate that culture conditions which yield high levels of LiP activity lead to high levels of OMW decolorization.     

Study of the δ-endotoxins produced by three recently isolated strains of Bacillus thuringiensis

Abstract Three different strains of Bacillus thuringiensis , subsp. toumanoffi, sotto and kurstaki , producing parasporal inclusion crystals, have recently been isolated in Tunisia. The δ-endotoxins produced by the different strains gave distinct patterns on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Polymerase chain reaction screening of these three strains, using oligonucleotides specific for the genes cryIA, cryIII and cryIV , did not generate amplified fragment profiles characteristic of these genes. For each of the strains, the presence of one or more δ-endotoxin coding genes having partial sequence similarities to one or more genes of these three groups was found.     

Minimal structural requirements for adjuvant activity of bacterial peptidoglycan derivatives

We have recently shown that the monomeric subunit of mesodiaminopimelic acid containing bacterial peptidoglycans, i. e. the disaccharide tetrapeptide N-acetyl glucosaminyl-N-acetyl muramyl-L-alanyl-D-isoglutaminyl-meso-diaminopimelyl-D-alanine can replace whole killed mycobacteria in Freund's adjuvant. We now report further structural simplifications of the active molecule; natural N-acetyl-muramyl-tripeptides have been found active; the smallest adjuvant molecule found is a synthetic N-acetyl muramyl-dipeptide prepared by Sinaÿ $\text{et al.}$ (1).     

Hydrolytic efficiency of Penicillium occitanis cellulase: kinetic aspects

Summary The parameters controlling the activity of the hyper-cellulolytic mutant Pol 6 of Penicillium occitanis cellulase were studied with regard to its efficiency for the hydrolysis of esparto grass cellulose. The optimal operational hydrolysis parameters were pH 5.0, temperature 45–55°C and 32 enzyme units/g of substrate. The maximum conversion ratio to reducing sugars was 84%. The cellulase was thermally quite stable, its activity decreasing by 20% when held at 50°C for 48 h. The cellulase was subject to end-product inhibition, with filter paper activity decreasing by 30% in the presence of 5% glucose. The results generally indicate the high efficiency of P. occitanis cellulase. It compares well with that from other microorganisms such as Trichoderma reesei.     

Optimization of the fermentation of olive mill waste-waters by Aspergillus niger

Summary The fermentation of olive mill waste-waters (OMW) by Aspergillus niger was studied. On the basis of factorial design experiments, suspended solids and concentration of OMW, nitrogen source, sulphate and size of inocula were all found to be significant by affecting mycelium growth and chemical oxygen demand (COD) removal. Neither the absence of yeast extract, magnesium, sodium, potassium nor of calcium limited the growth of A. niger. With media lacking additional nitrogen and sulphate, the growth was limited. The optimal inoculum obtained was between 10⁶ and 10⁷ spores/g COD. The highest biomass and the greatest COD removal were obtained with removed COD to N:SO _inf4 ^sup¨- ratios averaging 100 to 3:1.5. Offprint requests to: M. Hamdi