Aspergillus terreus Broth Rheology, Oxygen Transfer, and Lovastatin Production in a Gas-Agitated Slurry Reactor

Abstract

A 20 L gas-agitated slurry bubble column bioreactor was used to investigate the effects of nonmechanical low-intensity agitation on development of broth rheology and fungal pellet morphology during production of lovastatin by the filamentous fungus Aspergillus terreus. Fermentations were carried out under elevated dissolved oxygen levels (400% of air saturation) at gassing rates that ranged from 0.5 to 1.5 vvm. Various initial concentrations of the growth limiting nitrogen source were used to attain different total biomass concentrations, to observe the effect of this variable on development of pellets and the rheology of the fermentation broth. The non-Newtonian rheology of the fermentation broth was influenced both by the biomass concentration and the size of the fungal pellets. The stable pellet diameter ranged from ∼2300 to ∼2900 µm. Too low turbulence (gassing rate of 0.5 vvm) and low dissolved oxygen levels adversely affected lovastatin production. The best biomass specific production of lovastatin was attained at high biomass concentrations under oxygen-rich conditions that were not excessively turbulent. In fermentation broths with various rheologies, the oxygen-transfer coefficient in the bubble column correlated with the aeration velocity, biomass concentration, and effective viscosity of the broth. The correlations obtained were significantly different for broths with pelleted growth and those with filamentous growth.

Impact of bioreactor scale on lovastatin biosynthesis by Aspergillus terreus ATCC 20542 in a batch culture

“…This treatment resulted in the increase of lovastatin production from 20 to 80 mg LOV l -1 . Rodriguez Porcel et al (2006), also proved that the control of dissolved oxygen on the high level (400%) in the broth was necessary for attaining suitable lovastatin production in the slurry bioreactor. Lai et al (2005) received the best results, when dissolved oxygen was controlled at the level of 20%.…”

“…3). The researchers who conducted lovastatin biosynthesis in bioreactors claimed that there were several factors that may have played an important role in these processes (Bizukojć and Ledakowicz, 2008;Casas Lopez et al, 2004;Lai et al, 2005;Rodriguez Porcel et al, 2006). Among these factors the initial concentration of nitrogen sources, pH control and pO 2 control were mentioned.…”

“…In the experiments performed in shake flasks a significant impact on the course of lovastatin biosynthesis had, first of all, type and concentration of carbon and nitrogen sources (Bizukojć and Ledakowicz, 2007a;Casas Lopez et al, 2003). In bioreactors it was also necessary to use optimal pH (Bizukojć and Ledakowicz, 2008;Lai et al, 2005), oxygen saturation of broth and aeration rate (Casas Lopez et al, 2005;Lai et al, 2005;Rodriguez Porcel et al, 2006). Lovastatin titres obtained with ATCC 20542 were usually moderate, compared to those, which were the effect of the application of other strains, including the mutant ones (Hajjaj et al, 2001;Kumar et al, 2000;Manzoni et al, 1998).…”

“…Some of the presented results came from bioreactor cultures only (Bizukojć and Ledakowicz, 2008;Lai et al, 2005;Rodriguez Porcel et al, 2006). Thus, it is difficult to find a comparative study analysing simultaneously lovastatin biosynthesis both in shake flasks and bioreactors.…”

Bioprocess Engineering Aspects of the Cultivation of a Lovastatin Producer Aspergillus terreus

“…Rodriguez Porcel et al [62] Pellets formed by A. terreus in a fluidized bed bioreactor are larger than those in a stirred tank bioreactor; the compactness and fluffiness of pellets is affected by stirring intensity and so is the size of pellets; rheological parameters of the broth are affected by biomass concentration pellets size and pellet fluffiness 10 Rodriguez Porcel et al [63] In a fluidized bed bioreactor, aeration with oxygen-enriched air is required to obtain high lovastatin titres at aeration rate equal to 1 L air L −1 min…”