Poly(hydroxybutyric acid) (PHB) and other biodegradable polyesters are promising candidates for the development of environment-friendly, totally biodegradable plastics. The use of cane molasses and corn steep liquor, two of the cheapest substrates available in Egypt, may help to reduce the cost of producing such biopolyesters. In this work, the effect of different carbon sources was studied. Maximum production of PHB was obtained with cane molasses and glucose as sole carbon sources (40.8, 39.9 per mg cell dry matter, respectively). The best growth was obtained with 3% molasses, while maximum yield of PHB (46.2% per mg cell dry matter) was obtained with 2% molasses. Corn steep liquor was the best nitrogen source for PHB synthesis (32.7 mg per cell dry matter), on the other hand, best growth was observed when ammonium chloride, ammonium sulphate, ammonium oxalate or ammonium phosphate were used as nitrogen sources.

Lipid accumulation by Gordonia sp. DG using sodium gluconate as carbon source in comparison with Rhodococcus opacus PD630 was studied. Maximum lipid content 80% was observed at the beginning of the stationary phase for R. opacus and 72% at the end of stationary phase for Gordonia sp. Different agro-industrial wastes were used as carbon source. The cells of the two organism accumulated lipid more than 50% of the biomass with most tested agro-industrial wastes. The maximum value was in presence of sugar cane molasses (93 and 96%) for R. opacus and Gordonia sp. respectively. Maximum triacyglycerols (TAGs), 88.9 and 57.8 mg/l, was obtained using carob and orange waste by R. opacus and Gordonia sp. respectively. The use of orange waste as carbon source by R. opacus, increased lipid unsaturation with C18:3 as the major unsaturated fatty acid. On the other hand, C22:0 and C6:0 were the dominant fatty acids (54.5% of the total identified fatty acids) produced by Gordonia sp. in presence of orange waste as carbon source. Statistical optimization of the medium revealed that maximum lipid content was achieved with 60% orange waste, 0.05 g/l ammonium chloride and 0.2 g/l magnesium sulphate.

The production of a polyester-degrading hydrolase from the thermophilic actinomycete Thermomonospora fusca was investigated with regard to its potential technical application. Only in the presence of a polyester (random aliphatic-aromatic copolyester from 1,4-butanediol, terephthalic acid, and adipic acid with around 40-50 mol % terephthalic acid in the acid component), the excretion of the extracellular enzyme could be achieved with an optimized synthetic medium using pectin and NH(4)Cl as nitrogen source. Compared to complex media, a significantly higher specific activity at comparable volumetric yields could be obtained, thus reducing the expenditure for purification. The activity profile in the medium is controlled by a complex process involving (1) induction of enzyme excretion, (2) enzyme adsorption on the hydrophobic polyester surface, (3) inhibition of enzyme generation by monomers produced by polyester cleavage, and (4) enzyme denaturation. Diafiltration with cellulose acetate membranes as the sole downstream processing step led to a product of high purity and with sufficient yield (60% of total activity). Scaling-up from shaking flasks to a fermentor scale of 100 L revealed no specific problems. However, the excretion of the hydrolase by the actinomycete turned out to be inhibited by the degradation products (monomers) of the aliphatic-aromatic copolyester used as inductor for the enzyme production. The crude enzyme exhibited generally similar properties (temperature and pH optimum) as the highly purified hydrolase described previously; however, the storage capability and thermal stability is improved when the crude enzyme solution is diafiltrated.

Xylanase from Aspergillus tamarii was covalently immobilized on Duolite A147 pretreated with the bifunctional agent glutaraldehyde. The bound enzyme retained 54.2% of the original specific activity exhibited by the free enzyme (120 U/mg protein). Compared to the free enzyme, the immobilized enzyme exhibited lower optimum pH, higher optimum reaction temperature, lower energy of activation, higher Km (Michaelis constant), lower Vmax (maximal reaction rate). The half-life for the free enzyme was 186.0, 93.0, and 50.0 min for 40, 50, and 60 degrees C, respectively, whereas the immobilized form at the same temperatures had half-life of 320, 136, and 65 min. The deactivation rate constant at 60 degrees C for the immobilized enzyme is about 6.0 x 10(-3), which is lower than that of the free enzyme (7.77 x 10(-3) min). The energy of thermal deactivation was 15.22 and 20.72 kcal/mol, respectively for the free and immobilized enzyme, confirming stabilization by immobilization. An external mass transfer resistance was identified with the immobilization carrier (Duolite A147). The effect of some metal ions on the activity of the free and immobilized xylanase has been investigated. The immobilized enzyme retained about 73.0% of the initial catalytic activity even after being used 8 cycles.

Acetone fractionation o f Bacillus lentus culture filtrate yielded the highest a-amylase activity and the 66.6% fraction reached 13-fold that o f the crude enzyme preparation. Gel filtration and ion exchange chrom a t o g r a p h y afforded a pure a-amylase (relative molecular mass, 42000). The pure enzyme was highly active on starch and dextrin~ It produced a mixture o f oligosaccharides as major products o f starch hydrolysis. Maximal activity was reached at 70°C and p H 6.1. Ca 2÷, N a +, K + and Sr 2+ ions stabilized or slightly stimulated the enzyme whereas A g +, Co 2+, H g z+, Zn 2+, Cd z+ and Fe 3÷ ions strongly inhibited the activity. The enzyme contained 16 amino acids, o f which aspartic and glutamic acids were present in the highest proportions.