Lecture 47

Question 1

There are three major forms of bacterial horizontal gene transfer (keep in mind INTER-genus and species transfer plays an extremely important role in virulence and _______).

1. ______, the most efficient if the three, is mediated by a plasmid and requires cell-cell contact.
2. ______ is mediated by bacteriophage in a lytic life cycle, whereby a chopped up piece of host DNA equal in size to the viral genome is packaged into a phage and injected into a new cell.
3. ______ is the uptake of naked DNA from the environment.

Answer 1

Resistance

1. Conjugation
2. Transduction
3. Transformation

Question 2

There are three relevant classification criteria for plasmids.

1. _____, which describes whether or not the plasmid is capable of conjugation.
2. ______ significance, which is dependent on the virulence factors a plasmid encodes.
3. Antibiotic resistance, which describes whether or not a plasmid encodes an ___ factor (uptake of these plasmids via conjugation is the most common mech for acquiring resistance) –> Some plasmids have more than one contained within transposons.

Answer 2

1. Mobility
2. Pathogenic significance
3. R-factors

Question 3

_______ refers to the coupling of movement of a non-conjugative plasmid with a conjugative plasmid during conjugation. Keep in mind this is different from Mobility.

Answer 3

Mobilization

Question 4

R-plasmids are those that confer antibiotic resistance. They contain an ____ segment, which is comprised of the resistance genes, and an RTF segment.

Answer 4

RD (Resistance Determinant)

Question 5

Bacteriophages can have either ___ or ___ genomes, but NOT both. They can also be single or double stranded. Bacteriophages can exhibit a _____ or ________ life cylce (the latter accounts for about 90% of phages). Keep in mind bacteriophages can only infect a narrow range of hosts –> they are specific to one or few bacterial species.

Answer 5

DNA

RNA

Lytic

Lysogenic

Question 6

______ is the term used to describe a dormant intracellular form of a temperate (lysogenic) phage, and ______ is the term that describes the host cell that harbors it in its DNA.

Answer 6

Prophage

Lysogen

Question 7

Host _____-_____ (RM) is a way bacterial cells can defend against infection with exogenous DNA. RM consists of a restriction methylase and restriction endonuclease pair. Does the methylase methylate host or exogenous DNA? How does this help eliminate exogenous DNA and protect host DNA.

Answer 7

Restriction-Modification

The methylase methylates HOST DNA at particular sites, such that the endonuclease cleaves DNA that does not have this particular methylation pattern.

Question 8

______/____ immunity in bacteria is another mech bacterial cells use to degrade exogenous DNA. They essentially acquire immunity when phage DNA is incorporated into host DNA and is translated into RNA. This RNA combines with nucleases produced from _____ genes to form a ribonucloetide complex that recognizes exogenous DNA complimentary to the RNA from the phage DNA that had previously been incorporated into the host’s genome.

Answer 8

CRISPR/Cas

Cas genes

Question 9

“Male” bacterial cells are those that contain an ___ plasmid. These cells generate a sex pilus for which female cells have receptors. Keep in mind male cells do NOT have these receptors.

Answer 9

F plasmid

Question 10

There are three types of male bacterial cells:

1. ___+ males have an independent ___ plasmid.
2. ____ males have the plasmid integrated into the bacteria’s chromosome.
3. When the plasmid is removed from the host’s DNA with a copy of some of the host’s DNA, this is called ____’ males.

Keep in mind the ratio of ___+ to ___ males is 1000:1.

Answer 10

1. F+
2. HfR
3. F’

F+ : HfR

Question 11

Plasmid transfer via conjugation undergoes a process called “_____-_____” replication, whereby a copy of the plasmid is transcribed into the female cell where it recircularizes. This occurs through a Type 4 secretion system (T4SS) which involves nicking of the 5’ end of the original plasmid by _____, an enzyme contained within the relaxosome. This enzyme recircularizes ssDNA in the recipient cell, where that cell’s replication apparatus synthesizes a complementary strand, reforming dsDNA.
How do males cells become female again?

Answer 11

“Rolling-circle”

Relaxase

Under situations of stress, the male cell jettisons “extra baggage,” including its plasmids.

Question 12

HfR mating with female cells is basically the same as with F+ mating, but there is no plasmid to synthesized into the recipient cell. Instead, a portion of the host’s chromosome downstream of the oriT contained in the incorporated plasmid DNA is transcribed into the recipient cell where it undergoes ______ with the recipient genome and becomes a permanent feature of the host’s genome.

Answer 12

Recombination

Question 13

Transformation is different in Gram + and Gram - bacteria. Gram __ can only take up DNA from the environment when they are “competent,” which is not all the time. They can then uptake ONE strand of the exogenous DNA, and if it is homologous to the bacteria’s genome, it will recombine. Gram ___ are ALWAYS competent, but can only take up _____ DNA via receptors for a sequence motif. BOTH strand of exogenous DNA are transferred into the ______ space, but only one strand is transferred into the cytoplasm - the other is degraded in the cell.

Answer 13

Gram +

Gram -

Homologous DNA

Periplasmic space