Plastic waste disposal is a huge ecotechnological problem and one of the approaches to solving this problem is the development of biodegradable plastics This review summarizes data on their use, biodegradability, commercial reliability and production from renewable resources Some commercially successful biodegradable plastics are based on chemical synthesis (ie polyglycolic acid, polylactic acid, polycaprolactone, and polyvinyl alcohol) Others are products of microbial fermentations (ie polyesters and neutral polysaccharides) or are prepared from chemically modified natural products (eg, starch, cellulose, chitin or soy protein)

Biodegradable plastics from renewable sources

Fungal β-mannanases: Mannan hydrolysis, heterologous production and biotechnological applications

In the present work, the use of low-cost substrates to produce Trichoderma spores was evaluated. Rice, corn bran, and wheat bran were used as solid substrate to grow Trichoderma harzanium sp., Trichoderma viride sp., Tricho- derma koningii sp., and Trichoderma polysporum sp. No external nutrient sources were added to the solid substrate that was only moisturized with deonized water, sterilized, inoculated, and cultivated at 30 °C for 7 days. Wheat bran showed to be the most suitable substrate to produce Trichoderma spores for all strains that were evaluated. High spore counts were obtained for T. harzianum sp. (28.30×10 8 /gds) and T. viride sp. (24.10×10 8 spores/gds).

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Effect of Moisture on Trichoderma Conidia Production on Corn and Wheat Bran by Solid State Fermentation

Association of beet necrotic yellow vein virus with isolates of Polymyxa betae Keskin.

β-Glucosidase from the fungusThermoascus 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, β-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°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 β-d-glucopyranoside as substrate,K
 m 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+.

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

Conditions for conidiation of a natural isolate ofTrichoderma atroviride during submerged cultivation in Erlenmeyer flasks and in a laboratory stirred-tank fermenter were optimized. From the simple sugars tested, cellobiose was the best substrate for conidia production while cellulose fines from paper mill waste proved to be a suitable cheap complex carbon source. Optimum temperature for conidiation was 24–26°C, and the required dissolved oxygen level was >40% saturation. After initial slight decrease during the 1st d after inoculation, the pH of the culture medium constantly increased throughout the sporulation period. Attempts to regulate the pH during fermentation did not improve the spore yields. The most intense formation of conidia took place between 2nd and 3rd d of growth and the overall volumetric productivity of conidia was 4.1–8.2 × 109 conidia per L/h.

Conidiation of Trichoderma atroviride isolate during submerged cultivation in a laboratory stirred-tank fermenter.

Polysaccharide hydrolase activity was assayed in a group of 28 selectedRhizopus strains. The production of lichenases, mannanases, cellulases, xylanases, amylases and pullulanases was demonstrated using the gel-testing method during growth of the strains on suitably meshed polysaccharide gels.

N. Kolarova

Papers

Conidiation of Trichoderma atroviride isolate during submerged cultivation in a laboratory stirred-tank fermenter.

Production of polysaccharide hydrolases in the genus Rhizopus.