Geobacillus

Geobacillus is a genus of thermophilic, rod-shaped, endospore-forming bacteria in the family Bacillaceae, within the phylum Firmicutes. Members are Gram-positive or Gram-variable and form resilient endospores that can survive environmental stresses. The genus was established to classify thermophilic species that were previously placed in Bacillus, and several species have since been reassigned to Geobacillus.

Geobacillus species are primarily aerobic or facultatively anaerobic chemoorganotrophs. They grow at elevated temperatures, with optima typically between 55 and 65°C, and some strains can tolerate or grow at temperatures up to about 75°C. They are commonly found in hot environments such as soils influenced by compost, hot springs, geothermal soils, and various man-made systems like oil reservoirs and industrial processing facilities.

Representative species include Geobacillus stearothermophilus, Geobacillus kaustophilus, Geobacillus thermoglucosidasius, and Geobacillus thermoleovorans. Geobacillus stearothermophilus, in particular, is known for producing spores used in sterilization process indicators.

Biotechnological relevance arises from their thermostable enzymes, including amylases, xylanases, proteases, and lipases, which have applications in biomass degradation, biofuel production, and other industrial processes that operate at high temperatures.

Safety and ecology: Geobacillus species are not generally regarded as human pathogens, though rare opportunistic infections can occur in immunocompromised individuals. They play ecological roles in the degradation of organic matter in hot environments. Genomic data from multiple Geobacillus species support studies of thermostability and enzyme production.