Productivity in case of filamentous fungi is heavily depend upon the morphology of the fungi. But during submerged fermentation, morphology is function of impeller design, speed and orientation of the impeller, besides other factors like pH. Right now, my fermentation 3L is equipped with the fixed blade rushton impeller due to which I have observed a lot of shearing. Is there any impeller which is suitable for the fungal fermentation specifically in chemostat mode?
Morphology depends on many factors of which scale is also important. E.g. on large scale pellet morphology, and on small scale hyphae. Look for research on A.awamori our publications (search for Yi-Qing Cui on RG)
As already stated, many factors affect the morphology of the fungi in a bioreactor as well as how much shear or lysis occurs. The Rushton turbine impeller is suitable for most filamentous fungi in a bioreactor, also in chemostat operation. You should consider tip speed as well as impeller shape. You can try a marine impeller to reduce shear, but you may then have difficulties with adequate oxygen transfer. The biomass concentration you are trying to maintain may contribute to lysis problems which you may mistake as a problem with shear. The species of filamentous fungus is also a critical factor. While many common Ascomycetes should do well in a high shear environment, Zygomycetes may not. But we have also had chemostats with Mucor using Rushton turbine impellers. And indeed, there are a lot of publications to look into on this topic.
Thanks @Prof. Marilyn for your response. It would be great, if you can elaborate more on this "biomass concentration you are trying to maintain may contribute to lysis problems which you may mistake as a problem with shear". Second I will look the chemostats with mucor.
Dear AAdarsh,
As already mentioned Rushton turbine impeller can be used for filamentous fungi culture in submerged fermentation.
If you find that the shearing effect is a problem during your fermentation, you can use the marine impeller.
As also mentioned, certain parameters such as the distance between two turbines can also cause shearing effects (D
Depending on your bioreactor, biomass levels between about 4 and 8 g/L are probably okay for chemostat cultures with a filamentous fungus. If the biomass concentration is too low you are likely to have problems obtaining a steady state because of biomass attachment to surfaces and possibly also some pellet formation (depending on the species). If the biomass concentration is too high you are likely to have problems with providing sufficient aeration and uniform mixing. Dense biomass can also result in more autolysis though I don't know whether that has been investigated scientifically. Our work with Mucor in chemostats was not published, but there are publications for chemostats with Fusarium, Aspergillus and Penicillium from the APJ Trinci group, Trichoderma from VTT group, Aspergillus and Penicillium from other groups... The medium composition can affect the success of achieving good steady states. The choice of limiting substrate can affect how much hyphae adhere to surfaces and can affect the steady state. As hinted above, pH will impact the morphology and because of that the steady state...
Marilyn Wiebe I have read the papers form Trinci group and Pirt papers on penicillin fermentation, with the information given in those papers I have prepared my media composition. And I maintained the limiting substrate ( in my case it is Inorganic nitrogen) is such a way that biomass should not go beyond the microbial oxygen demand. Biomass level are between 4 to 6 g.L in my case. As far as lysis I will check other group papers. pH side I will revisit my data once again.
Thanks a lot for your valuable time and response.
Interesting. Sporulation is usually more of a problem than lysis under those conditions. You need some fragmentation in order to maintain the population.
Marilyn Wiebe Yes Prof. Even in my case I have observed intense sporulation (green color) especially when I have nitrogen concentration lower than the Kn (saturation constant for nitrogen). To maintain fragmentation, people did the experiments at higher rpm, in most of the cases. Thanks! for all the help.
In my opinion for fungal fermentation (mycelial fungus), the bottom impeller is Ruston, the second impeller may be Ruston/axial impeller and the third impeller may be Axial or Rushton and this configuration is for Large scale (50 KL and above production fermenter). But for laboratory fermenters it is usually Ruston impellers, and you may change and check the yield.
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