MANIPULATING METABOLISM

The objective in most fermentation industries are:
1 To produce the desired fermentation product using the microbes
2 Produce the products in high concentration and volume

The ability of the microorganisms to produce the fermentation product is ultimately determined by its genetic set up. Within the genetic make up or the genes are all the instructions needed to produce the enzymes which transform the substrate through a series of metabolic pathways to form the products

Trouble is the formation of a particular fermentation product is not exclusively held or controlled by one particular metabolic pathway, Although we often simplify the picture of product formation as:

[A]--> B--> C--> D--> E -->[F]

Where A is the initial substrate to be converted to F the final fermentation product.

From the above simple hypothetical pathway we know for the substrate to be converted to the final fermentation product, it has to pass through a number of enzyme mediated transformations

The problem of the above is seen from two main views:
1 The metabolic pathway is not independent by itself and form part of the intricate metabolic maze with other pathways,substrates, products and intermediates capable of influencing the metabolic pathway forming the fermentation product
2 Each metabolic pathway forming the fermentation product is controlled by the various steps of metabolic reactions which can affect the ultimate fate of the formation of the fermentation product. The activity of each step of enzymatic conversion are affected by the incoming substrate, concentration of the intermediate product formed


We must note that in analyzing the metabolic pathway, in terms of substrate and product formed controlling the metabolic pathway, there are other kinds of substrate and product contributing to the efficiency of the fermentation product formation


A -----------------------> B
SUBSTRATE PRODUCT

H2O, OH- and H+
NADP, NADPH2, ATP
METABOLIC GASES

These 'other products and intermediates' do influence the metabolic fermentation pathway.

Some of the most significant changes that may occur during the fermentation process from these side products are:
1 Affecting the ph of the reaction
2 Affecting the dissociation of NADH2 to NAD+ vice versa
3 High hydrostatic pressure built up in the fermentor will affect the release of gaseous products of the metabolism thus preventing the gas from escaping from the metabolism of the cell. This might cause diversion in the pathway resulting in the formation of unwanted fermentation side products

EFFECT OF PH
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The ph could be explained as the measure of acidity or the concentration of hydrogen ions in the media. If the fermentation broth contains a lot of [H+] then the broth will be acidic. The contribution of the [H*] in the fermentation media could be initially caused by the acid components of the nutrients in the media or by the addition of chemicals that changes the ph of the media or it sould be the resultant changes to the media brought about by the microbial actions such as the formation of strongly acidic fermentation products.

In whatever the case the high acidity produced is the reflection of high [H+] in the fermentation media.
The impact of high ph could result in:

1 Changes in the optimal of of the fermentation reactions making it no longer optimal for the reactions to occur
2 It might affect the growth and behaviour of the microorganisms in the fermentor
3 It might affect the toxicity of certain acids by favouring ionizations or dissociations of certain molecules
4 It might affect precipitations of nutrients

AFFECTING NADH2 DISSOCIATION
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In a normal metabolic reaction in the generation of energy, the redox carrier NADH2 is a very important electron carrier. It functions in the metabolic redox reactions by receiving and donating electrons

The simple equation could be seen as follows:

NADH2---------> NAD+ + H2
<--------- It is a two way reaction in which H+ is liberated During very acidic conditions, if there are too much H+ then the overall reaction might favour the formation of NADH2. This would lead to a condition where there would not be enough NAD+ for the metabolism to function HIGH HYDROSTATIC PRESSURE ------------------------- This is the situation which often occurs in very large fermentors where the hydrostatic pressure could be very significant affecting microorganisms at the bottom of the fermentor. Under very high hydrostatic pressure it could lead to the diversion of the metabolism of the microorganism resulting in the formation of other products. Gases could be one of the products released during the metabolism of the cells. The high hydrostatic pressure on the microorganisms could prevent the release of the gases produced during the metabolism