Gul Ozyilmaz

Phylogenetic analysis and characterization of lipolytic activity of halophilic archaeal isolates

Five isolates designated as B45, D83A, A206A, A85 and E49 found to possess lipolytic activities were taxonomically classified on the basis of their phylogenetic, phenotypic and chemotaxonomic characteristics. The isolates were determined to be gram-negative, catalase and oxidase positive, hydrolyzing Tween 80 and 60 but not starch, need 3.5–4 M NaCl for optimal growth and lack of anaerobic growth with arginine or DMSO. All isolates had the highest lipolytic activity at pH 8.5. Lipase and esterase activities increased with salt concentration up to 3–4.5 M NaCl, and decreased at 5 M NaCl. Esterase and lipase showed their maximal activities at 50–55°C and 60–65°C, respectively. The phylogenetic tree constructed by the neighbor-joining method indicated that the strain B45 and A85 were closely related to the members of genera Halovivax and Natrinema, respectively. The closest relative of the strain A206A and D83A were found to be Haloterrigena saccharevitans. The strain E49 displayed a more distant relationship to known strains.

Using Response Surface Methodology for Amperometric Glucose Biosensor Construction

In this study, construction of amperometric glucose biosensor was carried out by immobilizing of glucose oxidase (GOD) on platinum electrode with 0.09 cm2 surface area which coated with polypyrrole (PPy) by cyclic voltammetry technique. Because measured current values in the presence of glucose would be affected from the electrode preparing and working conditions, experimental parameters should be optimized by response surface methodology (RSM). To this, State Ease Design Expert 8.0.7.1. (Serial Number:0021-6578) programe was used. PPy synthesis conditions of pyrrole (Py) monomer concentration and scan rate were optimized according to current response in presence of glucose. Optimal Py monomer concentration and scan rate for PPy synthesis were determined as 10 mM and 50 mV/s, respectively. Immobilization parameters such as concentrations of chitosan, GOD and glutaraldehyde (GAL) also were optimized by RSM as 1.0 %, 4 mg/ml and 0.0625 %, respectively. The digital photos of electrodes at each stage were obtained. All electrodes well characterized in absence and in the presence of glucose by cyclic voltammetry and impedance techniques and it was observed that electrodes were sensitive to glucose molecule. Finally the effect of working pH and applied potential on the current response was investigated by RSM. The highest current response was obsreved when pH of glucose solution and applied potential were 6.0 and 0.8, respectively.