Bacterial EcologyBacterial Ecology

Bacterial EcologyBacterial Ecology

DefinitionDefinition

- Relation between bacteria and non-living environment

- Relation between bacteria and other living organisms

- Relation between bacteria with each other

Relation with non-living environmentRelation with non-living environment

Bacteria plays roles as:Bacteria plays roles as:

ProductionProductionProducers

DegradationDegradationDegeneratersConsumers

Relation with other living organisms Relation with other living organisms (Symbiosis)(Symbiosis)

Mutualism

(Transient and resident microflora)

Commensalism

Parasitism

Relation with each other Relation with each other (Symbiosis)(Symbiosis)

Indifference

Competition

Antagonism

Synergism

Bacterial traits changes are due to:

1. Changes in environmental conditions

2. Changes in the genetic codes

Bacterial GeneticsBacterial Genetics(Studying heritage variations in bacterial traits)(Studying heritage variations in bacterial traits)

Changes in environmental conditions Changes in environmental conditions

Brucella species are bacillus in 21 ○C and coccobacillus in 37 ○C

Mycobacterium tuberculosis shows filamentous in 24 ○C when exposing glycerin.

pneumococcus loses its capsule after some invitro culture.

Staphylococcus aureus is not able to produce golden pigment in absence of oxygen.

Salmonella species loses flagella when exposing phenol on culture.

Adding calcium to Bacillus anthracis culture stops converting bacteria to spore form.

Changes in bacterial traitsChanges in bacterial traits

Changes in the genetic codes

1- Intermicrobial exchange

2- Mutations

(point mutations, insertions, deletions)

Intermicrobial exchangeIntermicrobial exchange

Transformation

(Capturing DNA from solution)

Transduction

(Phage-mediated)

Conjugation

(Bacterial Sex)

Explored by F. Griffith (1928) using pneumococci

The DNA released from a degenerated bacterium enters into another bacterium.

There is no vector or mediation in this type of gene exchange.

Transformation Transformation

DN

A-M

edia

ted

Tra

nsf

orm

atio

nD

NA

-Med

iate

d T

ran

sfor

mat

ion

DN

A-M

edia

ted

Tra

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nD

NA

-Med

iate

d T

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Intermicrobial exchanges by vectorsIntermicrobial exchanges by vectors

15

Characteristics of genetic vectorsCharacteristics of genetic vectors

must be capable of carrying a significant piece of donor DNAmust be readily accepted by the host

Plasmids – small, well characterized, easy to manipulate & can be transferred into appropriate host cells through transformation Bacteriophages – have the natural ability to inject their DNA into bacterial hosts through transduction

TransductionTransduction(madiated by phage)(madiated by phage)

Microbe Library, American Society for Microbiology

www.microbelibrary.org

Lytic versus LysogenicLytic versus Lysogenic

Gen

eral

ized

Tra

nsd

uct

ion

Gen

eral

ized

Tra

nsd

uct

ion

Gen

eral

ized

Tra

nsd

uct

ion

Gen

eral

ized

Tra

nsd

uct

ion

TransductionTransduction

Specialized (Restricted):

Transduction in which only certain donor genes can be transferred.

TransductionTransduction(Restricted)(Restricted)

Restricted TransductionRestricted Transduction(Lysogenic Phage)(Lysogenic Phage)

gal

bio

gal bio

gal bio

gal

bio

bio

gal

TransductionTransduction

Significance

– Common in Gram+ bacteria

– Lysogenic (phage) conversion

• e.g. Corynebacterium diptheriae toxin

–Toxin derived from lysogenic phage

ConjugationConjugation

Definition: Gene transfer from a donor to a recipient by direct physical contact between cells

Mating types in bacteriaDonor

F factor (Fertility factor)

F (sex) pilusRecipient

Lacks an F factor

ConjugationConjugation

Significance Gram - bacteria

Antibiotic resistance Gram + bacteria

Production of adhesive material by donor cells

ConjugationConjugation

Con

juga

tion

: S

ex o

r F

Pil

us

Con

juga

tion

: S

ex o

r F

Pil

us

Pla

smid

sP

lasm

ids

PlasmidsPlasmids

Definition:

Extrachromosomal genetic elements that are capable of autonomous replication (replicon)

Plasmid Types:

Congugative & Non-congugativeCongugative & Non-congugativeEpisome - a plasmid that can integrate into the

chromosomeCasmid – An integration of a plasmid and a

bacteriophage

Phenotypic effectsPhenotypic effects

Fertility (F factor)

Bacteriocinogenic (or encoding some other toxins)

Resistance (R factors)

Structure of R FactorsStructure of R Factors

RTFConjugative

plasmidTransfer genes

Tn 9

Tn 2

1

Tn 10Tn 8

RTF

R determinant

R determinantResistance genes

Sel

f-T

ran

smis

sib

le R

Pla

smid

Sel

f-T

ran

smis

sib

le R

Pla

smid

Con

juga

tion

: F

Pla

smid

C

onju

gati

on:

F P

lasm

id

Tra

nsf

erT

ran

sfer

ConjugationConjugation

FF+ + andand HFr cellsHFr cells

Integrated (Hfr)(High Frequency of Recombination)

F+ Hfr

Hfr and F’ cellsHfr and F’ cells

Hfr F’

Mechanism of Hfr x FMechanism of Hfr x F-- Crosses Crosses

Hfr F- Hfr F-

Hfr F-Hfr F-

Mechanism of F’ x FMechanism of F’ x F-- Crosses Crosses

F’ F’F’ F’

F’ F- F’ F-

Transposable Genetic ElementsTransposable Genetic Elements

Definition: Segments of DNA that are able to move from one location to another (across the genome or from one genome to another)

Properties

– “Random” movement

• Transposase

– Transposition may be accompanied by duplication

Types of Transposable Genetic ElementsTypes of Transposable Genetic Elements

Transposons (Tn)/ Insertion elements (IS)Definition: Elements that carry other genes in

addition to those involved in transpositionNomenclature - Tn10, IS6110Structure

Composite Tns Importance

Antibiotic resistance

Epidemiology and evolutionary studies

IS ISResistance Gene(s)

IS ISResistance Gene(s)