Geobacillus thermoleovorans: growth and lipase production

[摘要] English: The aim of this study was to elucidate factors, specifically media composition andgrowth conditions that would improve the thermophilic lipase production byGeobacillus thermoleovorans.A semi-starved state where carbon and or nitrogen becomes limiting was foundnot to be conducive to optimum lipase production. Instead, the notion that lipaseactivity peaks at these limiting conditions, normally during stationary phase wasdisproved as we could get a 25% increase in biomass obtained under optimizedconditions, yielding a 100% increase in lipase production. This showed that theavailability of specific nutrients has a direct positive effect on the amount ofenzyme produced. The occurrence of free fatty acids (products of lipolysis) underthese conditions was found to be the main signal for the commencement oflipase production. This was shown by the almost immediate production of lipaseonce free fatty acids were present at the initial point of inoculation (stearic acidinduction), showing that the presence of free fatty acids does not repress theproduction of inducible lipases by Geobacillus thermoleovorans but that it ratheracts as a signal for lipase induction.The presence of glucose as a second utilizable carbon source at inoculation wasnot inhibitory to lipase production. The consumption of glucose and stearic acidoccurred simultaneously, with the consumption of free fatty acids beingenhanced by the presence of glucose.The pH of the media also had a noticeable effect on the physiology surroundinglipase production, specifically effecting the rate of uptake of free fatty acids. Thisindicated that not only the presence but also the rate of uptake of free fatty acidsprobably plays a direct role in the regulation and/or secretion of lipases.The optimum temperature for lipase production and the optimum for growthdiffered. The optimum temperature for lipase production was found to be 55ºCwith little or no lipase production occurring at 65ºC, which is the optimum growthtemperature.The addition of NaCl increased lipase yield and/or activity further. It is howevernot clear whether the presence of NaCl has an effect on lipase production ormerely acts as a stabilizer of lipase activity.We propose that the presence of free fatty acids in the culture media is theprimary signal for lipase production, possibly by inducing the transcription of aninducible lipase gene.

[发布机构] University of the Free State