Fermentation
In fermentation, ATP is synthesized by substrate level phosphorylation at the.
The growth of fermenting bacteria is limited by the fact that the organic acids they produce in the cell as a result of their low energy and metabolism are toxic to the cell.
Pyruvate formed by oxidation of glucose by
fermentative bacteria is converted to various compounds such as ethanol, lactate, butyrate.
Fermentations are referred to, for example, alcohol fermentation, lactic acid fermentation.
Pyruvate is fermented by microorganisms in five main ways.
Pasteur Effect:
Some microorganisms (such as yeasts) can perform both fermentation and respiration. If conditions are anoxic
fermentation occurs, and when O2 is present (as last electron acceptor) the cell obtains and prefers more energy by
respiration.
Hydrolysis of lignocellulosic biomass produces sugars such as glucose, xylose, arabinose, galactose and mannose.
Unfortunately, S. cerevisae, used in the production of
industrial ethanol, can only metabolize glucose to ethanol under anaerobic conditions.
Therefore, different strategies have been developed to obtain microorganisms capable of metabolizing other sugars in addition to glucose.
These strategies include:
Selection of a good ethanol producer but a host who can use narrow range sugars or a weak ethanol producer but a host
that can use wide range sugars
Transmitting plasmids containing genes to promote the use of a wide range of sugars or improve ethanol production to
this host
Improvement of experiments
Integration of genes to chromosome to increase genetic stability
In order to improve ethanol production, it can be
summarized as inactivation of biosynthetic pathways that lead to the formation of unwanted by-products.
Another strategy is the development of organisms capable of directly metabolizing cellulose and hemicellulose. In this way, the hydrolysis step with the enzyme is eliminated. This method is the latest technology developed for the
production of ethanol from lignocellulosic raw materials.
Therefore, it is not as advanced as other strategies.
A good ethanol producer microorganism should have:
Able to convert sugars from multi-biomass into ethanol
Be able to tolerate inhibitory compounds formed during pretreatment
No need for expensive nutrients
It should have high growth rate and ethanol production capacity even under undesirable conditions such as low pH and high
temperatures.
Mesophilic microorganisms are generally
used in ethanol production. However, some strains capable of using thermophilic sugar can also be used for this purpose, and this has some advantages:
High fermentation temperature eliminates contamination problem.
High volatility of ethanol at fermentation temperature reduces the recovery cost of ethanol.
Continuous removal of the product under vacuum reduces ethanol inhibition.
