Geobacillus stearothermophilus (GBPI_16): A Resilient Hyperthermophile Isolated From an Autoclaved Sediment Sample

A hyperthermophilic bacterium has been isolated from autoclaved sediments which were originally collected from a hot spring site (Soldhar) located in Tapovan area in District Chamoli of Indian Himalayan Region. The bacterium exhibited growth between 55 and 95 °C under laboratory conditions. The growth curves, drawn at different temperatures (55, 65, 75, 85 and 95 °C), showed clear preference for high temperature for production of cell biomass. Broth culture of the bacterium after exposure to boiling temperature, exhibited increase in the colony forming units up to 20 min. Microscopic observations showed Gram +ve cells arranged in clusters or short to long chains bearing endospore with swollen solitary sporangia at terminal positions, and developed coiling at a later stage after subcultures. The bacterium survived second round of autoclaving but with deteriorated cell arrangement. Following polyphasic approach, the bacterium was identified as Geobacillus stearothermophilus. In lipase producing medium, the bacterium exhibited maximum cell biomass at 65 °C, coinciding with maximum lipase activity (25.8 U/L) after 14 h of incubation. Relatively high amylase activity was recorded; maximum (47.2 U/L) at 95 °C after 8 h of incubation, not showing correlation with cell biomass which attained maximum value after 16 h. Distinct peaks of amylase activity were recorded twice at all the 4 temperatures, first on or before 8 h and the second after 14 h of incubation. Elasticity in morphological structures and the production of thermostable enzymes at elevated temperatures are likely to play important role in conferring resilience to bacterium for survival and multiplication under high temperatures. The bacterium and its 16S rDNA sequence have been assigned accession numbers MTCC11501 and MCC2050, and FJ548759, respectively.