Effects of pellet morphology on broth rheology in fermentations of Aspergillus terreus

Abstract Effects of pellet morphology on broth rheology are reported for pelleted submerged cultures of the lovastatin producing filamentous fungus Aspergillus terreus, growing in fluidized bed and stirred tank bioreactors. The pellet diameter and compactness were affected by the agitation intensity of the broth; however, the total biomass productivity was not affected. In fluidized beds and stirred tanks with agitation intensity of up to 300 rpm (impeller tip speed of 1.02 m s−1), the fungal pellets were stable at diameters of up to about 2300 μm. In more intensely agitated stirred tanks (≥600 rpm; impeller tip speed of ≥2.03 m s−1), the stable pellet size was only about ≤900 μm. The biomass concentration and the pellet diameter were the main factors that influenced the flow index and the consistency index of the power-law broths. Because the biomass productivity was the same in all experiments in a given type of reactor and the oxygen concentration was kept at ∼400% of air saturation, the pellet size and morphology were not influenced by oxygen mass transfer effects. Pellets were always dense in the core region and no necrosis of the biomass occurred.

[1]  K. Luyben,et al.  Effect of agitation intensities on fungal morphology of submerged fermentation. , 1997, Biotechnology and bioengineering.

[2]  G. C. Paul,et al.  Characterisation of mycelial morphology using image analysis. , 1998, Advances in biochemical engineering/biotechnology.

[3]  N. Kossen,et al.  The rheology of mould suspensions , 1979 .

[4]  Amanullah,et al.  Effects of agitation intensity on mycelial morphology and protein production in chemostat cultures of recombinant Aspergillus oryzae. , 1999, Biotechnology and bioengineering.

[5]  Mark R. Marten,et al.  Effects of Increased Impeller Power in a Production‐Scale Aspergillusoryzae Fermentation , 2002, Biotechnology progress.

[6]  A. Nienow,et al.  Dependence of penicillium chrysogenum growth, morphology, vacuolation, and productivity in fed-batch fermentations on impeller type and agitation intensity , 1998, Biotechnology and bioengineering.

[7]  Y. Chisti,et al.  Pellet morphology, culture rheology and lovastatin production in cultures of Aspergillus terreus. , 2005, Journal of biotechnology.

[8]  J. C. van Suijdam,et al.  Influence of engineering variables upon the morphology of filamentous molds , 1981 .

[9]  A. Nienow,et al.  Dependence of mycelial morphology on impeller type and agitation intensity , 2000, Biotechnology and bioengineering.

[10]  Michael C. Flickinger,et al.  Encyclopedia of bioprocess technology : fermentation, biocatalysis, and bioseparation , 1999 .

[11]  N. Kossen,et al.  The growth of molds in the form of pellets–a literature review , 1977 .

[12]  Mark R. Marten,et al.  Fungal morphology and fragmentation behavior in a fed-batch Aspergillus oryzae fermentation at the production scale. , 2000, Biotechnology and bioengineering.