Question

1. What are the four possible results of a fermentation experiment and what does each indicate?
2. What does a pH indicator tell you? Which pH indicator did we use in fermentation tubes?
3. Explain why E. coli would ferment glucose to acid/gas result while Pseudomonas does not?
4. Why would a bacterium oxidize a molecule instead of fermenting it?
5. If an inoculated OF tube turns yellow and DOES not have mineral oil on top – what process(es) caused the color change?

Answer 1

1. FERMENTATION

Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes.

In microorganisms, fermentation is the primary means of producing ATP by the degradation of organic nutrients anaerobically.fermentation is a way of extracting energy from molecules, but it is the only one common to all bacteria and eukaryotes.

The possible products formed from fermentation are

1. Ethanol

In ethanol fermentation, one glucose molecule is converted into two ethanol molecules and two carbondioxide molecules.

2. Lactic acid

Homolactic fermentation (producing only lactic acid) is the simplest type of fermentation. The pyruvate from glycolysis undergoes a simple redox reaction, forming lactic acid.

3. Hydrogen gas

Hydrogen gas is produced in many types of fermentation (mixed acid fermentation, butyric acid fermentation, caproatefermentation, butanol fermentation, glyoxylatefermentation) as a way to regenerate NAD⁺from NADH.

4. Glucose

Glucose could theoretically be converted into just CO₂ and H₂, but the global reaction releases little energy.

2. pH indicators

A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH of the solution can be determined visually. Hence, a pH indicator is a chemical detector for hydronium ions or hydrogen ions in a substance.

Carbohydrate fermentation, as in the other tests, produces acidic wastes. The pH indicator phenol red is used to detect the change in pH. In addition, a small, inverted tube called a Durham tube is placed in the media to collect any carbon dioxide produced as a waste product of fermentation.

3. E coli is used for fermentation while other pseudomonas is not :

All enteric bacteria can ferment glucose to produce acid and gas. E. coli, specifically, is physiologically versatile. Under anaerobic conditions it can grow by fermentation or anaerobic respiration. This allows E. coli to adapt to both the anaerobic environment inside the intestine and external aerobic environments.

Acetic acid bacteria (AAB) are a group of Gram-negative bacteria which oxidize sugarsor ethanol and produce acetic acid during fermentation.The acetic acid bacteria consist of 10 genera in the family Acetobacteraceae. Several species of acetic acid bacteria are used in industry for production of certain foods and chemicals.