Effects of Oxygen Transference on Protease Production by Rhodotorula mucilaginosa CBMAI 1528 in a Stirred Tank Bioreactor

Abstract

Microbial proteases, especially aspartic proteases, are an essential group of enzymes produced from different microorganisms. Microbial proteases have several applications, mainly in the food, beverage, cosmetic, and pharmaceutical industries, due to their efficiency in the processing and in the manufacturing stages. The yeast Rhodotorula mucilaginosa CBMAI 1528 was isolated from the Antarctic environment and was previously reported to have higher extracellular aspartic protease production. In addition, advances in the operational conditions of bioreactors for enzyme production are important to reduce the gap associated with scaling−up processes. This is the first study that evaluates the influence of oxygen transference (kLa) on the protease production of R. mucilaginosa yeast. To that end, batch cultures were created in a stirred tank bioreactor using Sabouraud dextrose broth at 25 °C for 72h under kLa values from 18 to 135 h−1. The results show that kLa (121 h−1) obtained at 500 rpm and 1.5 vvm plays an important role in protease production (124.9 U/mL) and productivity (6.784 U/L.h) as well as biomass (10.4 g/L), μmax (0.14 h−1) and Yx/s (0.484 g/g). In conclusion, R. mucilaginosa showed high yield production in aerobic culture with the efficiency of protease expression and secretion influenced by kLa. In this sense, our results could be used for further industrial investment.

Biotechnological potential of red yeast isolated from birch forests in Poland

“…R. colostri strains also showed no proteolytic activity in this study. Machado et al ( 2022 ) isolated the yeast strain R. mucilaginosa from the Antarctic continent, which synthesised proteases with an activity of 124.9 U mL −1 . Enzyme unit was defined as the amount of enzyme at which an increase in absorbance of 0.001 was found under the experimental conditions.…”

Bacterial Fermentation for Protease Production in Fermenters: Impact of Oxygen Transfer Characteristics and Rheological Features on Scale up Process

“…It was reported earlier that the k L a values for protease production from Bacillus strains varied in the range of 0.01 to 0.055 s − 1 (Calik et al, 2000;2003). Another recent study reported that the values for increased protease production by Rhodotorula mucilaginosa ranges from 18 to 135 h − 1 with agitation ranging from 100 to 500 rpm and aeration ranging from 1.0 to 2.5 vvm (Machado et al, 2022). The DO concentration in the culture broth depends on the OTR from the gas to the liquid phase and also on the rate of its consumption by the microorganism, OUR.…”

“…due to inadequate oxygen transfer (Calik et Agitation is reported to be more effective than aeration for enzyme production as high agitation generates bubbles that increase the gas-liquid interface area as well as the residence time in the culture medium causing a higher rate of DO (Teruasmaki et al, 2018). Shear stress due to oxygen supply through high aeration rate adversely affect the organism's morphology, physiology, and consequently, the biomass generation and enzyme production (Machado et al, 2022).…”

“…Gas liquid mass transfer is of paramount importance in bioprocess because of the requirement of oxygen in aerobic fermentations. Growth and protease production in bioreactors are adversely impacted by oxygen due to its effect on the physiology of bacteria by means of changes in metabolic pathways and metabolic uxes (Calik et al, 2000;Garcia-Ochoa and Gomez, 2009;Machado et al, 2022). Though oxygen transfer is essential for bacterial protease production; the extent of that requirement varies among microorganisms as well as the type of proteases produced in diverse operating conditions (Calik et al, 2003;Bhunia et al, 2012).…”