Abstract
Carbon-limited chemostat cultures were performed using different carbon sources (glucose, 10 and 20 g/L; sucrose, 10 g/L; fructose/glucose, 5.26/5.26 g/L; carboxymethyl cellulose, 10 g/L; and carboxymethyl cellulose/glucose, 5/5 g/L) to verify the capability of the wild type strain Trichoderma harzianum to produce extracellular enzymes. All chemostat cultures were carried out at a fixed dilution rate of 0.05 h−1. Experiments using glucose, fructose/glucose and sucrose were performed in duplicate. Glucose condition was found to induce the production of enzymes that can catalyse the hydrolysis of p-nitrophenyl-β-d-glucopyranoside (PNPGase). A concentration of 20 g/L of glucose in the feed provided the highest productivity (1048 ± 16 U/mol h). Extracellular polysaccharides were considered the source of inducers. Based on the obtained results, a new PNPGase production process was developed using mainly glucose. This process raises interesting possibilities of synthesizing the inducer substrate and the induced enzymes in a single step using an easily assimilated carbon source under carbon-limited conditions.
Highlights
Continuous processes provide possibilities for attaining higher productivity in comparison with batch cultures
This study shows the potential of this microorganism to produce PNPGase continuously and suggests that the optimization of the operating conditions as well as the strain could lead to a promising enzyme production process using mainly glucose
Sucrose was used as the carbon source in carbon-limited chemostat cultures to verify whether the synthesis of PNPGase would occur in this condition
Summary
Continuous processes provide possibilities for attaining higher productivity in comparison with batch cultures. According to Peebo and Neubauer (2018), experiments in continuous cultures result in a steady-state operation that is easier to characterize and can have economic benefits. A major advantage of chemostat cultures is the option of maintaining cells in a producing state for extended periods, which can lead to high volumetric productivities (Peebo and Neubauer, 2018). Carbon catabolite repression (CCR) is one of the mechanisms that prevent the unnecessary synthesis of cellulase. In this mechanism, the presence of an assimilated substrate (e.g. glucose) activates the repression of the production of enzymes responsible for the degradation of complex substrates (Suto and Tomita, 2001).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
