ISOLATION OF SOIL STREPTOMYCES STRAINS CAPABLE OF DEGRADING HUMIC ACIDS AND ANALYSIS OF THEIR PEROXIDASE-ACTIVITY

Fifteen Streptomyces strains capable of decolorizing humic acids in pr esence of glucose were isolated from soil samples using the dilute sus pension technique and spread on agar plates. Six strains, displaying a significant and stable activity, were selected for further characteri zation. Some features of these isolates (carbon source utilization, en zyme production, antibiotic resistance) were compared with those of th e reference strain Streptomyces viridosporus ATCC 39115. Degradation p roperties studied in batch cultures at pH 7.0 showed that the cataboli c activity on humic acids was generally stimulated by incubation with 100% oxygen and was cell surface-associated. Peroxidase activity from cell-free extracts was analysed by using the oxidation of N,N,N',N'-te tramethyl-phenylene-diamine. PAGE analysis revealed the existence of t wo major types of peroxidases (molecular mass: about 39.2 and 61.6 kDa ), dividing the strains into two groups. The role of cell surface-asso ciated peroxidase activity in the breakdown of humic acids is discusse d.