EXPLORATION OF ACTINOMYCETES DIVERSITY IN DIVERSE SOILS OF SOLAPUR–RAICHUR REGION AND OPTIMIZATION OF CULTURE CONDITIONS FOR MICROBIAL TRANSFORMATION OF COMPACTIN INTO PRAVASTATIN

Abstract

Actinomycetes remain one of the most prolific sources of clinically and industrially important secondary metabolites, yet their diversity in many Indian agro-industrial soils is still incompletely documented. In this study, soil samples were collected from 14 distinct habitats across the Solapur–Raichur belt of Maharashtra and Karnataka, India — including industrial, agricultural, riverine and compost-associated sites — and screened for actinomycete diversity using a combination of selective isolation media, antibiotic supplementation, and physical/chemical pretreatment strategies. Yeast extract–malt extract–dextrose agar supplemented with cycloheximide (25 µg/mL), fluconazole (50 µg/mL), nystatin (25 µg/mL) and rifampicin (50 µg/mL) gave contamination-free recovery and was selected for the study. Among pretreatments, a combination of dry heat (40 °C), 0.5% calcium carbonate and 0.5% phenol yielded the highest isolate recovery. A total of 308 morphologically distinct actinomycete isolates were recovered, dominated by white, grey, black and creamish aerial-mycelium morphotypes, with black and brown soils yielding the greatest isolate density. All 308 isolates were screened by thin-layer chromatography for their ability to bioconvert compactin to pravastatin via whole-cell hydroxylation; isolates G4 and G7 (from Sangvi village soil, Akkalkot) showed the strongest reaction intensity. Fermentation parameters were subsequently optimized for these two isolates: starch–casein–dextrose broth (SCDM), pH 7.0 7.5 and 28 °C gave the best bioconversion activity. These findings identify G4 and G7 as promising candidates for further scale-up, enzyme characterization and molecular identification as industrial biocatalysts for pravastatin production.