Lab URL: http://www.mhhe.com/biosci/genbio/tlw3/virtual_labs/lab11/labs/lab11/ex

Question

Lab URL: http://www.mhhe.com/biosci/genbio/tlw3/virtual_labs/lab11/labs/lab11/exp2/index.html

Lab Overview: http://www.mhhe.com/biosci/genbio/tlw3/virtual_labs/lab11/labs/lab11/resources/overview.pdf

1.) If CV103 can use acetate as a source of carbon, why couldn’t CV103 grow on CV101 filtrate? (hint: see observation #6)

2.) Explain how the interaction between CV101 and CV103 could maintain strain CV101 in the population grown on glucose-limiting media.

3.) Do your results support or reject your hypothesis?

Explanation / Answer

1. Even if CV103 can use acetate as a source of carbon, it cannot grow on CV101 filtrate. This is because CV101 does not produce acetate as a by-product of aerobic fermentation; so the filtrate of media for CV101 is devoid of acetate. So, if CV103 is allowed to grow on the CV101 filtrate, it will not find any carbon source & will fail to grow.
( references - observation 5 & 6).

2. In a glucose- limiting media, both CV101 & CV103 survive due to mutual interactions taking place between them (commensalism). CV101 & CV103 do not compete for the limited amount of glucose in the media; instead CV103 uses the glucose as a carbon source for metabolism. Due to aerobic fermentation of glucose, CV103 produces acetate as a by-product & this acetate acts as carbon source for CV101. Thus instead of competing with each other for glucose, there is resource partitioning between them where CV103 feeds off glucose & CV101 feeds off acetate- a by-product of CV103.

3. The results of the experiment conducted inferred to :

(A)- Both CV101 & CV103 can utilise acetate as carbon source, but CV101 can do it more efficiently.

(B)- Since CV101 can grow well in acetate media, it can also grow in glucose -limited media along with CV103 assuming CV103 can produce acetate as by product of its metabolism. ( observation 5- refers to the presence of acetate in filtrate of CV103 media).

So, the results support the hypothesis.

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