CHARACTERISTICS OF MICROBIAL CELLS AND FERMENTATION

The type of fermentation carried out will also reflect the type of microorganisms or even cells that are used in the fermentation studies. Different microbes and different cells used in the fermentation will affect the choice of the most suitable fermentor for the studies. Thus the physical characteristics of the cells,its physiology will have to be considered in choosing the right fermentation system for the fermentation studies.

The golden rule of fermentation is simple:

MICROORGANISMS WILL AFFECT THE FERMENTATION PROCESS AND FERMENTATION PROCESS OR THE TYPE OF FERMENTORS USED WILL AFFECT THE PHYSIOLOGY OF THE ORGANISMS

As we said earlier the choice of microorganisms is diverse to be used in the fermentation studies. Bacteria, Unicellular fungi, Virus, Algal cells have all been cultivated in fermentors. Now more and more attempts are tried to cultivate single plant and animal cells in fermentors.

It is very important for us to know the physical and physiological characteristics of the type of cells which we use in the fermentation as we will know the limitations and optimum conditions for us to operate the fermentor.

BACTERIA
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These unicellular microorganisms are often used in various fermentation. They are procaryotes and do not show presence of membrane bound organelles. The bacteria are very microscopic particles when compared to protozoa, algal, fungal and plant and animal cells.

One of their most unique physical characteristics is that they have very strong cell wall and very high internal osmotic pressure. These factors make the bacterial cells very strong and thus they can with stand strong shear forces emanating from the shear action of the impellers and intense liquid circulations

Due to their very small size they do not really get "entangled" or spliced by the shearing blades of the impellers and will be carried away by the flow of the broth circulations

FUNGI
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When we talk about fungal fermentation using fermentors, we are specifically referring here to unicellular yeasts or those simple hyphal fungal sich as actinomycetes or streptomycetes.

These unicelluar fungi are eucaryotes and are clearly larger compared to bacterial cells. The yeasts are small and occur unicellularly and they have very strong cell walls which protect them against the shear forces within the fermentor.

In the case of streptomycetes and actinomycetes they occur more as filamentous or hyphal morphology At such under fermentation mixing by the impellers there is great tendency for cell or filamental breakages to occur, as their cell walls are rigid

PROTOZOA
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Protozoa are unicellular animal cells and are eucaryotes. They have larger cells and they really do not have protective cell walls. Strong mixing or shear forces such as by the use of impellers will easily damage the cells

ALGAE
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Algae used in the fermentors are large unicellular plant cells. They have very strong cell wall. However these strong cell walls are rigid and are easily damaged by the impellers and shearing forces generated

VIRUS
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The most microscopic of all cells and are therefore not affected by the shearing forces