Abstract
Ayeast isolate, selected for its lipolytic activity from a meat product, was characterized as Pichia anomala. Lipolytic activity, determined on p-NPA as esterase, was maximum at 28 °C, pH 6.5, and induced by the short chain triglyceride tributyrin. Fermentations in 2 L and 10 L stirred tank bioreactors, with 20 and 60 g/L glucose respectively, showed that in the second case lipolytic activity increased 1.74-fold, while the biomass increased 1.57-fold. Under otherwise identical aeration conditions, improved mixing in the 10 L reactor maintained higher dissolved oxygen levels which, along with the elevated glucose concentration, resulted in significant increase of specific rates of lipolytic activity (51 vs. 7 U/g/L), while specific rates of growth and glucose consumption maintained lower. The Crabtree-negative yeast (glucose insensitive growth) exhibited a Pasteur effect at lower dissolved oxygen concentrations while elevated glucose prevented ethanol formation under oxygen saturation. The particular physiological traits can be exploited to obtain significant lipolytic activity in a scalable aerobic process.
Highlights
The P. anomala M1 strain was cultivated in stirred tank bioreactors and produced significant lipolytic activity compared to known sources
Anomala grew exponentially with aa Figure 7 shows the time-courses of biomass,−1 lipolytic activity and residual glucose concentrations maximum specific growth rate μ max of 0.17 h −1 and a biomass yield Yx/s of 0.43 g of cell dry weight (CDW) g of maximum specific growthtank ratebioreactor
Oxygen is the main regulator of the central energy metabolism while glucose does not repress respiration but possibly repress the ethanol assimilation pathway. Having this metabolic and physiological background, lipolytic enzyme production by P. anomala appears to be advantageous compared to other sources as it can take place under oxygen-saturated conditions using substrates with elevated glucose concentrations
Summary
Pichia isolates were tested for lipolytic activity and upon obtaining positive results, further studies were carried out which are reported in the present work. The P. anomala M1 strain was cultivated in stirred tank bioreactors and produced significant lipolytic activity compared to known sources. As a Crabtree-negative yeast and insensitive to elevated levels of glucose concentrations in its substrate, it can be grown in batch fermenters without the need of fed-batch cultivation. These characteristics show an organism of practical significance and a potential industrial microorganism in the case of effective production of a valuable metabolite
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