Kamil Isik

Representatives of fifteen validly described and three non-validly described species of Nocardia were assigned to nineteen groups based on an optimised PCR-randomly amplified polymorphic DNA fingerprinting technique. Species specific banding patterns were recognised for the representatives of N. brasiliensis, N. crassostreae, N. farcinica, N. otitidiscaviarum and N. seriola. Unique banding patterns were also seen for the type strains of N. brevicatena, N. carnea, N. salmonicida, N. uniformis and N. vaccinii, and for the single representatives of "N. fusca", "N. pseudosporangifera", and "N. violaceofusca". More than one banding pattern was detected for the N. asteroides, N. flavorosea, N. nova, N. pseudobrasiliensis and N. transvalensis strains though in the case of the representative strains of N. nova and N. transvalensis the patterns were similar for each of these species. The results are in line with current trends in nocardial systematics thereby indicating that PCR-randomly amplified polymorphic DNA fingerprinting provides valuable data for the classification and identification of pathogenic nocardiae to the species level.

Streptomyces sp. F6616 was found to produce higher levels of extracellular peroxidase activity (0.535 U/mL) without any inducers than other actinobacteria which are previously reported. Maximum specific peroxidase activity (6.21 U/mg of protein) was obtained after 72 h of incubation at 30°C in a minimal salt medium (pH 8.0) containing (in wt/v) 0.6% yeast extract and 0.8% ball-milled wheat straw corresponding to a C:N ratio of 4.6:1. Characterization of the peroxidase revealed that the optimal temperature for the enzyme activity, using the standard 2,4-dichlorophenol (2,4-DCP) assay was 50°C, when the enzyme reaction was performed at pH 8.0. A study of the effect of temperature on the stability of peroxidase over time, showed that the enzyme was stable at 50°C, with a half-life of 145 min, while at higher temperature the stability and activity was reduced such that at 60°C the half-life of the enzyme was 30 min. The optimum pH for the activity of the enzyme occurred between pH 9.0 and 10.0. The apparentK m andV max values for the peroxidase preparations were determined to be 1.52 mmol/L and 1.84 U/mg protein, respectively using 2,4-DCP as a substrate. Characterization of the peroxidase activity revealed activity against 2,4-DCP, L-3,4-dihydroxyphenylalanine (L-DOPA), 2,4,5-trichlorophenol and other chlorophenols in the presence of hydrogen peroxide. However, inhibition of peroxidase activity with the addition of potassium cyanide and sodium azide, suggested the presence of heme component in the tertiary structure of the enzyme.