micro - bacteria genetics

Question 1

What is the genetic material of bacteria found?

Answer 1

in Chromosome

(circular dsDNA, 2000-4000 genes; 1copy/cell)

replicates in concert with cell growth & division

and in PLASMIDS

(circular dsDNA, 5-100 genes, 1-20 copies/cell - THIS IS WHERE THE VIRULENCE FACTORS ARE LOCATED)

replicates independant of chromosome
may be transferred from 1 cell to another

may contain toxin genes or antibiotic resistance genes, some on transposable elements

Question 2

How does genetic variation happen?

Answer 2

Mutation
_{<span>Gene Regulation (not discussed here)</span>}

Gene Transfer:

• Transformation - transfer of naked bacterial chromosomal DNA from dead cell to living cell*
• Conjugation - transfer of bacterial chromosomal DNA through a pilus from livign cell to living cell*
• Transduction - transfer of bacterial chromosomeal DNA in a bacterial virus (phage) from a dead host cell to a live host cell*
• Transposiiton - transfer of DNA sequences from 1 DNA site to another which may be on a plasmid*

Question 3

Steps of Transformation:

Answer 3

1) bacterium dies, its DNA is released into the medium
2) another bacterium may take up that DNA by a process called transformation
3) recipient cell may incorporate that DNA into its DNA, exchanging its genes for the other bacterium’s genes
- this is assoc. with competance factor in that cell: only certian cells in specific physiological states can take it up.

Question 4

Which of the 4 types of gene transfer is used in recombinant DNA work?

Answer 4

Transformation:

the gene is place in a plasmid and added to a bacterial suspension under conditions favorable for DNA uptake.

recipient bacterium takes up the plasmid DNA bearing the gene in question and expresses the gene.

The gene product (like IFN-alpha or IFN-beta) is harvested and used clinically

Question 5

What type of gene transfer occurs between male and female bacteria?

Answer 5

conjugation:

• male bacteria have F factor and express F pili on their surface
• female bacteria have no F factor and no F pili

The F factor is found in several states:

it may be integrated in the host bacterial chromosome: Hfr bacterium (Hfr=high frequency recombination)

it may be free in the cytoplasm: F⁺ bacterium

rarely, a previously integrated F factor may excise itself incorrectly from the host bacterial DNA and pick up a piece of host DNA: F` bacterium

Question 6

Notes on Hfr Conjugation:

Answer 6

• In Hfr bacteria, the F factor is integrated into the host chromosome at one of a very few particular points.
• Upon mating with an F- bacterium, the Hfr begins replicating the host bacterial chromosomal DNA, beginning just downstream of the integrated F factor.
• The newly replicated DNA is transferred to the F- bacterium.
• Thus, the Hfr bacterium transfers first host bacterial chromosomal DNA. Only if conjugation continues for 90 minutes does the F factor get transferred to the F- bacterium, converting it to an Hfr bacterium.

Question 7

Steps of Hfr Conjugation

Answer 7

1) A male bacterium that contains
integrated F factor
approaches a female
bacterium that has no
F factor and attaches
by an F pilus.

2) The F factor activates
replication of the DNA and
transfers the DNA either
across the F pilus or by means
of a cytoplasmic bridge.

3) The transferred DNA
can be incorporated
into the recipient
chromosome, replacing
its own DNA. The last factor to transfer is the F factor.

Question 8

What is an F⁺ bacterium?

Answer 8

One that has an F factor free in the cytoplasm.

Question 9

What happens when a single F+ bacterium is introduced into a culture of F- bacteria?

Answer 9

Basically all the bacteria will become F+

Question 10

What is the difference between Hfr conjugation and F+ conjugation?

Answer 10

Only the F factor is exchanged in F+ conjugation, which converts the F- bacterium into an F + bacterium

Question 11

What is important about F` Conjugation?

Answer 11

Occasionally, an integrated F factor will excise itself from the host bacterial chromosome to become an F+ bacterium.

If the excision is incorrect, a bit of host bacterial DNA may be excised as part of the F factor.

An F factor carrying a piece of host chromosomal DNA is called an F’ factor.

The bacteria with a F’ factor are called F’ bacteria.

Because F factors integrate at only a few specific sites on the host bacterial chromosome, the piece of DNA excised is limited to specific host genes.

Question 12

Why do F factors integrate at Specific Sites?

Answer 12

F factors contain a transposon, and can use it to integrate into host DNA, which only has a limited number of complementary transposon sites.

Question 13

What do transposons collect?

Answer 13

antibiotic resistan genes…

Question 14

What are resistance transfer factors (RTFs)?

Answer 14

plasmids that contain transposons - similar to F factors…they can be exchanged by conjugation, and they get their name because they can contain genes fro resistance to antibiotics.

**Thus, resistance to antibiotics can be rapidly transferred from one bacterium to another by conjugation. **

Question 15

3 Types of Antibiotic Resistance Genes:

Answer 15

• change permeability to decrease taking in antibiotic or increase getting rid of it
• alter target site for antibiotic so antibiotic can’t bind
• destroy or modify the antibiotic so it no longer works

Question 16

Review of Conjugation:

Answer 16

Genes may be transferred from one bacterium to another, without the death of the donor bacterium through the action of a plasmid such as the F factor or the resistance transfer factor (RTF) that confers maleness.
~The F factor can exist as a free plasmid or integrated into the bacterial chromosome.
-If the F factor is a plasmid (F+ bacterium), the F factor alone may be transmitted.
-If the F factor is integrated into the bacterial chromosome (Hfr bacterium), the chromosomal genes alone are transmitted.
-If the F factor was integrated and, upon again becoming a plasmid, picked up a few host chromosomal genes (F’ bacterium), the F’ factor carrying those few host chromosomal genes is transmitted.
~The RTF is a free plasmid carries genes encoding resistance to certain antibiotics. If it is transferred by conjugation, the recipient bacterium now becomes resistant to those antibiotics.

Question 17

What are the 2 types of phages?

Answer 17

• virulent phage
• temperate phage

(If phage is removed from bacteria, the bacteria can’t produce disease)

Question 18

What kind of phages infect a bacterium and replicate, killing the bacterium in the process?

Answer 18

VIRULENT PHAGES

Each type of bacterium has its own unique set of phages that can recognize it and infect it.

Once the bacterial cell wall has been breached, the replication cycle of the T phages occurs in about 20 minutes.

The replication cycle of the phage uses phage encoded genes to take over control of the host bacterial biosynthetic machinery to make hundreds of progeny.

Replication involves separate synthesis of viral genome and viral proteins, with self-assembly creating progeny phages.

The phage then lyses the bacterium, releasing hundreds of progeny phages.

In the process of their replication cycle, the phages may degrade bacterial chromosomal DNA to large or small pieces.

These phages may give rise to generalized transduction.

Question 19

What are the steps of phage replication?

Answer 19

attachment

penetration

transcription

translation

nucleic acid replication

phage assembly

bacterial lysis

phage release

Question 20

What kind of phages infect a bacterium and can either replicate, killing the bacterium (lytic cycle) or integrate into the bacterial chromosome to be replicated along with the bacterial genome (lysogenic cycle)?

Answer 20

TEMPERATE PHAGES

Another name for a temperate phage is a lysogenic phage. Diptheria is one of these

The integrated phage is called a prophage.

The bacterium with an integrated prophage is called a lysogenic bacterium and is said to be lysogenized.

The integrated prophage is repressed by a phage protein and will stay repressed indefinitely, unless the phage protein is degraded by something like UV-light or heat.

If the repressor protein is degraded, the prophage cuts itself out of the host chromosome by a process called induction and begins to replicate in a lytic cycle. Can also pull off a piece of host DNA on either side as it does this, and then when making more phages, that phage DNA now contains host DNA as well.

These phages may give rise to specialized transduction. Only certain genes are copied, others aren’t possible.

Question 21

What are the steps of Lysogeny?

Answer 21

• attachment
• penetration
• limited transcription
• limited translation
• prophage in lysogenic state
• induction
• lytic cycle begins

Question 22

What are the 2 types of transduction?

Answer 22

GENERALIZED TRANSDUCTION

Lytic phage partially degrades host bacterial chromosome during replication cycle.

Pieces of host bacterial chromosome are randomly (and accidentally) encapsidated into phage virions.

These transducing phage virions can enter a second bacterial host and bacterial DNA from the first host can be incorporated into the chromosome of the second host.

Because of the random nature of the encapsidation of host bacterial DNA, any gene can be transduced from one bacterium to another: generalized transduction.

SPECIALIZED TRANSDUCTION

Lysogenic phages integrate at specific sites in the host bacterial chromosome.

When the prophage is induced to excise itself from the host bacterial chromosome, on rare occasions, the phage inaccurately excises itself from the bacterial chromosome, picking up a piece of the host bacterial chromosome that now becomes a part of the phage genome.

The phage with bacterial DNA replicates and is encapsidated.

A second bacterium is infected by this phage and the phage and the bacterial DNA from the first bacterial host are integrated as a prophage in the second bacterial chromosome.

Because the prophage inserts at a specific point in the host bacterial chromosome, it picks up a specific host gene from the chromosome upon inaccurate excision: specialized transduction

Question 23

What are transposons?

Answer 23

Are moveable genetic elements incapable of independent replication.

Can involve transposons that contain insertion sequences (ISs),a transposase enzyme gene, and other genes related to antibiotic resistance or virulence.

Can involve integrons that consist of ISs, a transposase enzyme gene, and a series of antibiotic resistant genes controlled by a promoter. can help transposon integrate

**Can involve pathogenicity islands that consist of ISs, a transposase enzyme gene, and groups of virulence-associated genes. **

Most of the time, PI ARE COMPONANTS OF GRAM- BACTERIA. some gram- bacteria virulance is because of PIs.

Question 24

What are cassettes?

Answer 24

series of resistance genes that accumulate on the gene or plasmid - multi-antiresistnace things going on in single bacteria

Question 25

What does Corynecbacterium Diptheria cause and how?

Answer 25

an alpha toxin inhibits protein synthesis via ADP Ribosylates Elongation Factor 2 - located on the phage.

Causes diptheria.

Question 26

Where are Pathogenicity Islands?

Answer 26

Common features of PAI

Presence of virulence genes

Specific presence in pathogens, absence in benign relatives

Large distinct chromosomal regions (10 to 200 kb)

Characteristic base composition different from core genome

Insertion of PAI adjacent to tRNA genes

Frequent association with mobile genetic elements, i.e., presence of: DR, cryptic or functional integrase or transposase, IS elements, and chromosomally integrated conjugative transposons, plasmids, and phages

Genetic instability (if functional mobility elements are present)

Mosaic structures of several acquisitions

Question 27

What is important about PIs?

Answer 27

they’re pathogenicity islands:

usually components of and found in Gram - bacteria…they code for virulence factors

Question 28

What is the one gram + bacteria with pathogenicty islands?

Answer 28

STAPHYLOCOCCUS AUREUS

Question 29

What are the major virulence features encoded by PIs?

Answer 29

• adherence factors

toxins

Iron uptake systems

invasions, modulins, effectors

Type III secretion systems

Type IV secreation system

Question 30

What is Bactofection?

Answer 30