Influence of Oxygen Supply on Growth and Laccases Production by Pleurotus sajor-caju PS-2001 in Submerged Process

Abstract (1) Background: Oxygen supply is an important parameter to be considered in submerged cultures. This study evaluated the influence of different conditions for dissolved oxygen (DO) concentration on laccases activities and growth of Pleurotus sajor-caju PS-2001 in submerged process in stirred-tank bioreactor. (2) Methods: Initially, three different conditions were tested: uncontrolled DO and minimum levels of 30% and 80% of saturation, with the pH controlled between 4.5 and 7.0. (3) Results: Best results were observed at 30% DO (26 U mL-1 of laccases at 96 h), whereas higher mycelial biomass was observed at 30% and 80% DO (above 4.5 g L-1). Four different conditions of DO (uncontrolled, 10%, 30% and 50% of saturation) were tested at pH 6.5, with higher laccases activity (80 U mL-1 at 66 h) and lower mycelial growth (1.36 g L-1 at 90 h) being achieved with DO of 30%. In this test, the highest values for volumetric productivity and specific yield factor were determined. Under the different pH conditions tested, the production of laccases is favoured at DO concentration of 30% of saturation, while superior DO levels favours fungal growth. (4) Conclusion: The results indicate that dissolved oxygen concentration is a critical factor for the culture of P. sajor-caju PS-2001 and has important effects not only on laccases production but also on fungal growth.

Production and characterization of endo-polygalacturonase from Aspergillus niger in solid-state fermentation in double-surface bioreactor

Endo-polygalacturonase (endo-PG) production by Aspergillus niger T0005/007-2 in solid medium with 170 mm of height was evaluated in a cylindrical double surface bioreactor in 96-h experiments. Cell concentration close to 92 mg.g -¹ dm (mg per g of dry medium) in the standard condition (static) was achieved, whereas in tests under forced aeration of 1.4 and 2.8 L.min-1. Kg-1 mm (L of air per minute per Kg of moist medium) and with the central shaft fungal biomass attained approximately 100 mg.g-1 dm. Superior endo-PG activity was obtained with the central-shaft system, 78 U.g-1 dm (units per g of dry medium). Forced aeration and pressure pulse showed no positive effect on the production of endo-PG, 45 U.g-1 dm and 28 U.g-1 dm, respectively. None of the conditions evaluated was efficient for medium temperature control. Endo-PG was stable up to 40ºC. The activity decreased in 50 percent after 120 minutes at 50ºC, which is a temperature normally found during this process.

Production of laccases in submerged process by Pleurotus sajor-caju PS-2001 in relation to carbon and organic nitrogen sources, antifoams and Tween 80.

Some conditions in media composition for laccases production, such as different sources of carbon and organic nitrogen, antifoams and a surfactant, were studied in liquid cultures of Pleurotus sajor-caju strain PS-2001. Cultivation with fructose or glucose as carbon sources produced maximum enzyme activities of 37 and 36 U mL(-1), respectively. When sucrose was present in the medium, the best results were obtained using 5 g L(-1) of this carbohydrate, on the 11th day of the process, attaining laccase titres of 13 U mL(-1). In a medium without casein, practically no enzyme was produced during the experiments; among the sources of nitrogen studied, pure casein led to the highest titres of laccase activity. Different concentrations of pure casein and sucrose were also tested. As to the different concentrations of casein, the addition of 1.5 g L(-1) resulted in the highest titres of laccase activity. Negligible levels of manganese peroxidase activity were also detected in the culture medium. In low concentrations, polypropylene glycol or silicon-based antifoams and the surfactant Tween 80 have no significant influence on the formation of laccases by P. sajor-caju. However, enhanced concentration of polypropylene glycol negatively affected the production of laccases but favored the titres in total peroxidases, lignin peroxidase and veratryl alcohol oxidase.