Thermophiles that produce extracellular hydrolases are of great importance due to their applications in various industries. Thermophilic enzymes are of interest for industrial applications due to their compatibility with industrial processes, and the availability of the organisms is essential to develop their full potential. In this study, a culture-dependent approach was used to identify thermophilic bacteria from five hot springs in Republic of Korea. Characterization, taxonomic identification, and extracellular hydrolase (amylase, lipase, and protease) activity of 29 thermophilic bacterial isolates from the Neungam carbonate, Mungang sulfur, Deokgu, Baegam, and Dongnae hot springs were investigated. Identification based on the full-length 16S rRNA gene sequence revealed that strains belonged to the phylum Bacillota and were classified as Aeribacillus, Bacillus, Caldibacillus, Geobacillus, and Thermoactinomyces genera. It was found that 22 isolates could produce at least one extracellular enzyme. Geobacillus, representing 41.4% of the isolates, was the most abundant. The highest amount of proteolytic and lipolytic enzymes was secreted by strains of the genus Geobacillus, whereas Caldibacillus species produced the highest amount of amylolytic enzyme. The Geobacillus species producing hydrolytic extracellular enzymes appeared to be the most promising.
Keywords: Geobacillus; amylase; extracellular hydrolase; hot spring; lipase; protease; thermophiles.