Case scenario A waste product for cheese making is whey. You have been tasked wi

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

6. What stage(s) of growth would you assume the antibiotic is produced and explain why it is produced at this/these stage(s)? Lag, exponential, log, stationary and/or death. (1 point)

You think you may have hit upon a gold mine in the newly identified antibiotic. You want to secure a private investor to help fund a biotech company startup. But before you can convince a billionaire to put up the funds, you have to make some changes to your microorganism. A major challenge in bio-production is minimizing biomass and maximizing product – essentially you want the cell to move more carbon away from making cellular components and into making the excreted product of the antibiotic without killing the cell. The antibiotic is an energy costly product so you must setup ideal conditions for maximum growth/production. You deduce that the antibiotic is a nucleotide analog and uses the same biosynthetic pathway as guanosine monophosphate (GMP). How can you genetically manipulate the organism to increase production of the antibiotic and decrease cellular biomass and grow it at a maximum output?

Table 1. Composition of milk, cheese whev and casein whev % by weight Fat Lactose (milk sugar) Casein protein Whey protein Minerals Minor components Water TOTAL Milk 4.7 4.5 2.7 0.55 0.85 0.20 86.5 100.00 Cheese whey 0.05 5.0 0.10 0.65 0.50 0.30 93.4 100.00

Explanation / Answer

5.During the lag phase of the bacterial growth cycle, synthesis of RNA, enzymes and other molecules occurs.

The log phase (sometimes called the logarithmic phase or the exponential phase) is a period characterized by cell doubling.The number of new bacteria appearing per unit time is proportional to the present population. If growth is not limited, doubling will continue at a constant rate so both the number of cells and the rate of population increase doubles with each consecutive time period.

The stationary phase is often due to a growth-limiting factor such as the depletion of an essential nutrient, and/or the formation of an inhibitory product such as an organic acid. Stationary phase results from a situation in which growth rate and death rate are equal.

At death phase (decline phase), bacteria die. This could be caused by lack of nutrients, environmental temperature above or below the tolerance band for the species, or other injurious conditions.

Antibiotics are produced in the log phase.

6.Batch culture is used to increase the production of antibiotic in this case and decrease cellular biomass as-

• Many secondary products are not growth associated
• Genetic instability
• Operability and reliability
• Economic considerations

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