Geobacillus thermoleovorans: growth and lipase production

English: The aim of this study was to elucidate factors, specifically media composition and growth conditions that would improve the thermophilic lipase production by Geobacillus thermoleovorans. A semi-starved state where carbon and or nitrogen becomes limiting was found not to be conducive to optimum lipase production. Instead, the notion that lipase activity peaks at these limiting conditions, normally during stationary phase was disproved as we could get a 25% increase in biomass obtained under optimized conditions, yielding a 100% increase in lipase production. This showed that the availability of specific nutrients has a direct positive effect on the amount of enzyme produced. The occurrence of free fatty acids (products of lipolysis) under these conditions was found to be the main signal for the commencement of lipase production. This was shown by the almost immediate production of lipase once free fatty acids were present at the initial point of inoculation (stearic acid induction), showing that the presence of free fatty acids does not repress the production of inducible lipases by Geobacillus thermoleovorans but that it rather acts as a signal for lipase induction. The presence of glucose as a second utilizable carbon source at inoculation was not inhibitory to lipase production. The consumption of glucose and stearic acid occurred simultaneously, with the consumption of free fatty acids being enhanced by the presence of glucose. The pH of the media also had a noticeable effect on the physiology surrounding lipase production, specifically effecting the rate of uptake of free fatty acids. This indicated that not only the presence but also the rate of uptake of free fatty acids probably plays a direct role in the regulation and/or secretion of lipases. The optimum temperature for lipase production and the optimum for growth differed. The optimum temperature for lipase production was found to be 55ºC with little or no lipase production occurring at 65ºC, which is the optimum growth temperature. The addition of NaCl increased lipase yield and/or activity further. It is however not clear whether the presence of NaCl has an effect on lipase production or merely acts as a stabilizer of lipase activity. We propose that the presence of free fatty acids in the culture media is the primary signal for lipase production, possibly by inducing the transcription of an inducible lipase gene.