Case scenario A waste product for cheese making is whey. You have been tasked wi
ID: 95528 • Letter: C
Question
Case scenario A waste product for cheese making is whey. You have been tasked with finding a use for the whey from Swiss cheese (aside from a dietary supplement for humans). You isolate a microbe that is genetically related to Lactobacillus. This microbe is able to grow exceptionally well on the whey when you allow for aeration of the culture - it grows weakly without aeration and the pH drops dramatically over time due to an acidic waste product. See Figure 1 and Table 1 for the structure of lactose and the composition of whey. When you sequence the genome you identify genes for Embden Meyerhoff Parnas as well as oxidoreductases and quinones. You also notice it produces an interesting antibiotic when grown in a closed batch system. Using Figure 1 and Table 1, what compound(s) found in whey may be the carbon and energy source for the newly isolated microorganism described in the case study? Describe this microbe in regards to its carbon, energy and electron usage. (chemoorgano/litho-, photo-, auto-, hetero-)Explanation / Answer
1.
Microorganism is probably using lactose as carbon source. Cheese whey has 5% lactose. Upon hydrolysis, lactose yields galactose and glucose. Glucose can enter glycolysis (embden meyerhof parnas pathway) directly.
Galactose is phosphorylated by galactokinase to form galactose 1-phosphate. It will be converted to glucose 1-phosphate by uridyl phosphate. This will enter glycolysis.
This microorganism is genetically related to Lactobacillus which uses an extensive range of fermentatable carbon sources. Lactose is on of them.
Aeration (oxygen supply) is essential suggesting that it is aerobe. Slow down of growth and production of acidic waste product after withdrawing aeration is indication of anaerobic glycolysis which produces lactic acid. Slow growth in this condition suggests that it is primarily an aerobe.
The organism is capable of aerobic glycolysis and when oxygen is limited, it will grow slowly suggesting that it is not anaerobe.
The microorganism has genes coding for glycolysis, oxidoreductases and quinones indicating that it follows aerobic metabolism.
Therefore, main carbon source is lactose. However, we cannot rule out possibility of using fat and proteins also as carbon source when lactose levels deplete in the medium.
2.
It is a chemoorganotroph because it utilizes chemical compounds to supply energy and organic compounds as electron donors.