Bacterial genetics involves the study of bacterial chromosomes, plasmids, transcription, translation, replication, and genetic variation. Bacteria store DNA in circular chromosomes and small plasmids. Transcription and translation allow genes to be expressed. Replication duplicates genetic material. Bacteria undergo genetic variation through mutation, transformation, conjugation, and transduction, allowing them to adapt. Genetic engineering uses bacteria to produce recombinant proteins for research and medical purposes like vaccines.

1. Bacterial genetics
Group 15

2. Objective
 By the end of this presentation we expect you to
know:
 About bacterial chromosome and plasmids
 About translation and transcription
 Replication
 Genetic variation in bacteria
 Uses of bacteria in genetic engineering

3. Introduction
 Genetics is the study of genes including the
structure of genetic materials, what information is
stored in the genes, how the genes are
expressed and how the genetic information is
transferred.
 Genetics is the study of heredity and variation.
 Two essential function of genetic material is
replication and expression.
 The genome of an organism is defined as the
totality of its genetic material.
 Genotype vs. phenotype

4. Introduction
 Bacteria are one of the three domains in
taxonomy, they are also prokaryotes;
 Bacteria store DNA in two places the
chromosome and the small circular plasmid.
 Bacteria’s DNA is about thousand times the size
of the cell.
 Has both DNA and RNA

5. Structure of bacterial genetic material
Chromosome
 Most bacteria's has a single haploid circular
chromosome. But some may have more than one:
For example, Vibrio cholerae and Brucella melitensis
,leptospira, have two or more dissimilar
chromosomes. There are also exceptions to this rule
of circularity because some prokaryotes (eg, Borrelia
burgdorferi and Streptomyces coelicolor) have been
shown to have a linear chromosome.
Plasmids
 are autonomously replicating DNA molecules of
varying size located in the cytoplasm. Could contain
transposons,
Virulence plasmid
 plasmid
Resistance plasmid

6. Significance of plasmids:
1. Codes for resistance to several antibiotics. Gram-negative
bacteria carry plasmids that give resistance to antibiotics such
as neomycin, kanamycin, streptomycin, chloramphenicol,
tetracycline, penicillins and sulfonamides.
2. Codes for the production of bacteriocines.
3. Codes for the production of toxins
4. Plasmids carry virulence determinant genes. Eg, the plasmid
Col V of Escherichia coli contains genes for iron sequestering
compounds.
5. Codes resistance to uv light (DNA repair enzymes are coded
in the plasmid).
6. Codes for colonization factors that is necessary for their
attachment.
7. Contains genes coding for enzymes that allow bacteria unique
or unusual materials for carbon or energy sources. Some
strains are used for clearing oil spillage.

7. Replication

8. Transcription
 Transcription enables the DNA to direct the
synthesis of RNA,
 Types of RNA:
 mRNA rRNA
 tRNA snRNA
 siRNA miRNA
 The process will be explained in the next slide

9.  Initiation


10. Termination

11. Translation

12. Initiation
elongation
From class lecture slide

13. DNA damage
Causes
 Endogenous –e.g. Reactive oxygen (metabolic
byproducts)
 Exogenous - external agents (radiations)
 Types of DNA damage:
• Deamination: (e.g. C->U )
• Depurination : ( purine base A or G lost)
• T-T and T-C dimers: (bases become cross-linked)
• Alkaylation : ( an alkyle group e.g. CH3 added to base
• Oxidative damage: (guanine oxidizes to 8 –oxo-guanine
• cause SS and DS breaks
• Replication error: wrong nuceotide or modified neuclotide
inserted
• Double strand breaks (DSB): induced by ionizing radiations,
transposons,, endonucleases, mechanical stress, etc

14. Repair against damage
 Damage caused by UV
 Mismatch
 Proofreading
 Nucleotide Excision repair
 SOS response ( there are over set of 17 genes
that are involved tin this)
 Base excision repair

15. mutation
 Mutation is random it can happen to any gene
and to any bacteria.
 But in bacteria it may seem like the environment
has a role in changing the genotype but it
doesn’t.
Lederberg’s concept

16.  There are different types of mutation
 Mutation on a coding stand
Point mutation Nonsense
Missense
Frame shift
 Lethal mutation
 Conditional
 Resistance mutation
 Auxotrophic mutation
 Reversion
 suppression

17.  Mutation on noncoding strand
 Polar mutation
 Mutation on enhancer, promoter,

18. Genetic exchange
 Bacteria can not adopt simply because of
mutation, because mutation is to rare, they need
other system.
 Sharing of genetic material
 Donor Vs. recipient, exogenoate Vs.
endogenoate
 This along with mutation is the cause of genetic
variation amongst bacteria's.
 A type of horizontal transfer

19. Transformation
 Transformation involves the uptake of free or
naked DNA released by donor by a recipient. By
using surface proteins that recognize and snatch
naked DNA.
 The competence is determined by genes that
become active under certain conditions. But can
also be artificial.
 N.B. not all bacteria’s are capable of carrying out
only competent bacteria’s like ( Bacillus,
Haemophilus, Neisseria, Pneumococcus) can.
 The classic example for transformation is the
griffith experiment.

21. steps
 The steps involved in transformation are:
 1. A donor bacterium dies and is degraded.
 2. A fragment of DNA (usually about 20 genes long)
from the dead donor bacterium binds to DNA binding
proteins
 on the cell wall of a competent, living recipient
bacterium.
 3. Nuclease enzymes then cut the bound DNA into
fragments.
 4. One strand is destroyed and the other penetrates
the recipient bacterium.
 3. The Rec A protein promotes genetic exchange
(recombination) between a fragment of the donor's
DNA and the

22. Conjugation
 Bacterial conjugation is the transfer of DNA from
a living donor bacterium to a recipient bacterium.
 It requires intimate cell contact
 The male donates its plasmid to the female
 Conjugate(f) plasmid directs it’s own process, of
conjugation
Because it has tra genes.
 Transfer replication
 Plasmid mobilization
 There are various types
Of conjugation

23. Conjugation
 Bacterial conjugation is the transfer of DNA from
a living donor bacterium to a recipient bacterium.
 It requires intimate cell contact
 The male donates its plasmid to the female
 Conjugate(f) plasmid directs it’s own process, of
conjugation
Because it has tra genes.
 Transfer replication
 Plasmid mobilization
 There are various types
Of conjugation

24. F+ conjugation
 In which plasmid called F plasmid induces f pilli,
formation, and enzymes involved in the process
and the donor bateria gives F plasmid to the
recipient.
 the bacterial plasmid to be transferred will be
separated in to two single strands, one to be
exchanged the other will stay with in the cell and
both of them will replicate to be double stranded
DNA,
 Exchange occurs across the conjugation tube
 Then both bacteria’s will be F+

25. Hfr conjugation
 Plasmids may integrate into the bacterial
chromosome by a recombination event depending
upon the extent of DNA homology between the two.
The plasmid is called episome.
 And forms HFR cell because they are able to pass
both chromosomal and plasmid genes.
 Process is their will be a nick around the area of origin
of transfer, and the chromosome will be replicated,
and pass through the conjugation tube to the F- cell
but most of the time the conjugation bridge collapse.
 The integration of the chromosome with the plasmid
isn’t stable so the chromosome and the plasmid
separate, but through this process the plasmid might
take some genes of the chromosome along with it.

27. Transduction
 Transduction is virus-mediated transfer of genetic
information from donor to recipient cell.
 This is mediated by bacteriophages.
 Bacteriophage’s can be of two types
 Lytic
 Lysogenic
 Depending on the type of bacteriophage used
transduction can be classified as general and
specialized transduction.

28. General transduction
 Lytic bacteriophage infects
the bacteria, the process is
descibed in the image to the
right.
 Pseudovirus:- virus that
contains bacterial DNA
 Happens 1 in 1000 virus
formed

29. Specialized transduction
 Caused by lysogenic bacteria
 The viral DNA attaches to a particular site of the
chromosome, and it may drag along with it the
genes next to it but this is of low probability but as
this integration replicates it becomes of high
probability and then when it infects other bacteria
it would have that gene.
 Is valuable for sequencing genes, knowing about
the function and regulation of that gene, cloning
and antibiotic resistance.

30. transposable DNA elements
 Transposable genetic elements are segments of
DNA that have the capacity to move from one
location to another
 They synthesize transposase protein that aids
transposition,
 The three major kinds of transposable elements
are insertion sequence elements, transposons
and transposable bacteriophage;
 Insertion sequences

31.  Transposon are like insertion sequences but they
also cary additional genes between the
transposition gene/ IS segment.
 They are important because they might carry
genes for antibiotic resistance
 While IS can deactivate a gene by inserting with
in it.
 Direct transposition vs. replicative transposition
 One such conjugative transposon is Tn916,
found originally in a strain of E. faecalis.

32. Mechanism of drug resistance
 Decreased uptake (or increased efflux) of antibiotic: For
example, gram-negative organisms can limit the
penetration of certain agents, including β-lactam
antibiotics, tetracyclines, and chloramphenicol, as a result
of alteration in the number and structure of porins (proteins
that form chanels) in the outer membrane.
 Alteration of the target site for antibiotic: For example,
Staphylococcus pneumoniae resistance to β-lactam
antibiotics involves alterations in one or more of the major
bacterial penicillin-binding proteins (see p. 75), which
results in decreased binding of the antibiotic to its target.
 Acquisition of the ability to destroy or modify the antibiotic:
Examples of antibiotic inactivating enzymes include: 1) β-
lactamases that hydrolytically inactivate the β-lactam ring
of penicillins, cephalosporins, and related drugs; 2)
acetyltransferases that transfer an acetyl group to the
antibiotic, inactivating chloramphenicol or
aminoglycosides; 3) esterases that hydrolyze the lactone
ring of macrolides.

33. Genetic engineering
 Development of vectors or vehicles allowing the
cloning of any DNA sequences
 Eucaryotic genes may be expressed in
procaryotic systems
 Many genetic diseases are caused by lack of
protein
 Production in bacteria of recombinant vaccines
 Replacement therapy - bacterial interference

35. Molecular technologies in diagnosis
 Use of nucleic acid (DNA) probes to diagnose
and study diseases
 DNA of interest is inserted to bacterium and
amplified to high copy numbers and labeled - in
situ hybridization
 PCR - generation of millions copies of specific
pieces of nucleic acid of suspected
microorganism

36. References
 Prescott’s microbiology
 Sherri’s microbiology
 Lippincott's illustrated review of microbiology

37. THANK YOU