A steam steriliser is used to sterilise liquid medium for fermentation. The initial concentration of contaminating organisms is 10⁸ per litre. For design purposes, the final acceptable level of contamination is usually taken to be 10^-3cells; this corresponds to a risk that one batch in a thousand will remain contaminated even after the sterilisation process is complete. For how long should 1 m³ medium be treated if the temperature is 140⁰C ________________.

        To be safe, assume that the contaminants present are spores of Bacillus stearothermophilus, one of the most heat-resistant microorganisms known. For these spores the activation energy for thermal death is 283 kJ gmo1^-1 and the Arrhenius constant is 10^36.2 s^-1

#Question id: 5249

#Section 3: Genetics, Cellular and Molecular Biology

What is the best explanation for why Bernard Davis didn't observe generalized transduction in his U tube experiments?

#Question id: 5250

#Section 3: Genetics, Cellular and Molecular Biology

A researcher would like to map the location of galE and trpA genes in a new species of bacterium that appears to be closely related to E. coli. He decides to use cotransduction, and generatesnappropriate donor and recipient strains. He is disappointed when cotransduction is not seen in his experiement. What is the most reasonable explanation for this situation?

#Question id: 5252

#Section 3: Genetics, Cellular and Molecular Biology

Which type(s) of genetic transfer lead to incorporation of new DNA into the bacterial chromosome?

I. Conjugation mediated by F factor

II. Hfr mediated conjugation

III. Transduction

IV. Transformation

#Question id: 5253

#Section 3: Genetics, Cellular and Molecular Biology

In a hypothetical situation, the genes for sex pilus construction and for tetracycline resistance are located together on the same plasmid within a particular bacterium. If this bacterium readily performs conjugation involving a copy of this plasmid, then the resultshould be

#Question id: 5255

#Section 3: Genetics, Cellular and Molecular Biology

Which of the following is a structure that permits conjugation to occur?

#Question id: 5256

#Section 3: Genetics, Cellular and Molecular Biology

If the experimental population of E. coli lacks an F factor or F plasmid, and if bacteriophage are excluded from the bacterial cultures, then which of these is a means by which beneficial mutations might be transmitted horizontally to other E. coli cells?