In this study, we describe the screening for amylolytic activity of 17 thermophilic Actinobacteria isolates obtained from the soil of Cisolok geysers, a geothermal area in West Java, Indonesia. All isolates were screened for amylolytic activity by the starch-agar plate method at various temperatures. The results showed that all of isolates were able to grow at 45°C. The growth abilities of the isolates grown in ISP 1 medium varied at temperatures from 45 to 60°C. Fifteen of the 17 isolates showed amylolytic activity at 45°C, 13 showed such activity at 50°C, and four showed activity at 55°C. Only three isolates, designated SL1-2-R-2, SL1-2-R-3, and SL1-2-R-4, showed growth and amylolytic activity at 60°C. These three isolates were selected for molecular identification. The nearly full-length of 16S rRNA gene sequences data showed that these three isolates have a similarity of 99.93-100% with Actinomadura keratinilytica WCC-2265T and of 98.74-98.91% with A. miaoliensis BC 44T-5T. Phylogenetic tree shows that all three isolates are clustered together in a monophyletic group with the type strain of A. keratinilytica WCC-2265T as their most closely related species, with 100% bootstrap support. Based on sequencing of the 16S rRNA gene, phylogenetic comparison, and phenotypic characterization, the three isolates were identified as A. keratinilytica.
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