Statistical optimization of cultural conditions for chitinase production from fish scales waste by Aspergillus terreus

Aspergillus terreus, a local isolate from fishery polluted soil, was used successfully for the biodegradation of parrot fish-scales waste in favor of the production of highly active chitinase enzyme. Chitinase production was noticeably influenced by the culture medium and the highest enzyme production was attained through the acceleration growth phase (96 h). Pronounced decrease in chitinase production was concomitant with the sizes of fish-scales; larger sizes (normal, non-grinded) were the best for chitinase production than the finest grinded scales. Stagnant culture conditions were more favorite for chitinase production than shaked culture. Statistically based experimental designs were applied to optimize the production of chitinase by A. terreus. Eleven culture parameters were examined for their significance as effectors of chitinase expression using the Plackett-Burman factorial design. Concentrations of FeSO4.7H2O, glucose and MnSO4.2H2O were the most significant factors affecting the process of enzyme production. The second optimization step was to figure out the levels of these three independent variables that generate maximum chitinase activity, using the Box-Behnken design. Maximum enzyme activity (4.309 u/min), which is approximately 1.81 folds the activity expressed in the basal medium, has been assayed at concentrations (g/l): FeSO4.7H2O (9.5), glucose (6.5) and MnSO4.2H2O (4.7), after 90 h of fermentation. A verification experiment was accomplished and revealed approximately 99% model validity. The crude chitinase was characterized and maximum activity was obtained in reaction mixture of 50°C incubation temperature, 2 ml crude enzyme, 0.5 ml of 10% colloidal chitin, pH 6 and reaction time of 10 min. The enzyme is thermostable and lost only less than 10% of its activity when heated at 60°C for 60 min. The effect of metal ions in enzyme activity revealed that the enzyme have specific requirement of Cu, Ca, Zn and Mn ions for its activity.Key words: Chitinases, Aspergillus terreus, fish-scales, statistical optimization

Biosorption of mercury by capsulated and slime layerforming Gram -ve bacilli from an aqueous solution

The biosorption of mercury by two locally isolated Gram-ve bacilli: Klebsiella pneumoniae ssp. pneumonia (capsulated) and slime layer forming Pseudomonas aeruginosa, was characterized. Mercury adsorption was found to be influenced by the pH value of the biosorption solution, initial metal concentration, amount of the dried biomass and contact time. The optimum biosorption capacity of K. pneumoniae (about 15%) was recorded at pH 5, initial mercury concentration of 0.1 g/L and when contacted for less than 60 min with 1.0 g dried cells/L. While, the highest biosorption capacity of P. aeruginosa (about 25%) was reached at pH 5.8, initial mercury level of 0.15 g/L and for less than 60 min contacted with 1.0 g dried biomass/L. The efficiency average of slime layer forming P. aeruginosa, of high negatively charged components, showed more than 1.5 fold increase as compared to capsulated K. pneumoniae of low negatively charged constituents, under all the tested characteristics of mercury biosorption from aqueous solution.Key words: Biosorption, mercury, Klebsiella pneumoniae, Pseudomonas aeruginosa, capsulated and slime forming bacilli

Biosorption of lead by Gram-ve capsulated and non-capsulated bacteria

The biosorption of lead by two Gram-ve bacteria, either non-capsulated (Citrobacter freundii ) or capsulated (Klebsiella pneumoniae) was characterised. Lead biosorption was found to be influenced by the pH of the solution, initial metal concentration, and amount of the dried powdered cells and contact time. Thus, the optimum biosorption capacity, by the two tested bacteria, was attained at pH 4, initial lead concentration of about 481.2 mg/ℓ and contacted with 2 g dried cells/ℓ for 100 min. However, the dried powdered cells of both organisms can be safely stored for long periods (125 d) at room temperature (25 ± 2ْC) without any loss of their biosorption efficiency, i.e. their binding sites not affected by storage. The results revealed that the presence of capsule (K. pneumoniae) increased the biosorption efficiency of the bacterium. Water SA Vol.31 (3) 2005: pp.345-35

Characterization of native fungi responsible for degrading crude oil from the coastal area of Yanbu, Saudi Arabia

A total of 15 fungal isolates were obtained from oil-contaminated sites near the Red Sea in the Yanbu region. Based on the preliminary DCPIP (2,6-dichlorophenolindophenol) assay, three isolates showed promising oil degrading ability. The next-generation sequencing of the ITS-I and ITS-II internal transcribed spacer regions assigned the isolates to Aspergillus and Penicillium. Among these three strains, Y2 (Aspergillus oryzae) was the most efficient, degrading about 99% of the crude oil. The degradation rates were corroborated using spectrophotometric and gas chromatography–mass spectrometry analyses after two weeks of cultivation in Bushnell–Haas medium. All the three strains proved to be potent oil-degrading strains and, hence, can be utilized to degrade oil contaminants