Geni cromosomici, geni plasmidici 1 o più cromosomi 1 o più tipi di plasmidi Assenza di introni Assenza di esporto nucleare Trascrizione e traduzione sono accoppiate

organizzazione in operoni (co-regolazione trascrizionale) aploidia diploidia parziale fluidità

Promoter Coding region mRNA

operons Promoter ATG TGA ATG TAA Polycistronic mRNA Polycistronic mRNA

16S____23S__5S Ribosomal DNA genes 6-7 operons/cell species-specific genes

cromosoma plasmide

Fluidità genomica Il genoma di molte specie batteriche è in equilibrio dinamico e può essere rimodellato da differenti processi che determinano perdita o acquisizione di DNA

coniugazione, trasformazione, trasduzione stessa specie differente specie coniugazione, trasformazione, trasduzione ricombinazione, transposizione

cromosoma DNA plasmide ricombinazione, transposizione

Plasmidi di fertilità Plasmidi di resistenza Plasmidi di patogenicità

Gene di interesse inserito in E. coli cromosoma plasmide Plasmidi di clonaggio Gene di interesse inserito in E. coli artificialmente

LGT lateral gene transfer Vertical evolution Horizontal evolution

Conjugation between Hfr (left) and – (right) strains of E. coli.

coniugazione

Figure: 10-22 Caption: Integration of an F plasmid into the chromosome with the formation of an Hfr. The insertion of the F plasmid occurs at a variety of specific sites where IS elements are located, the one here being an IS3 located between the chromosomal genes pro and lac. Some of the genes on the F plasmid are shown. The arrow indicates the origin of transfer, oriT, with the arrow as the leading end. Thus, in this Hfr pro would be the first chromosomal gene to be transferred and lac would be among the last.

The insertion of the F plasmid occurs at a variety of sites where IS elements are located

HFR High Frequency of Recombination Ceppo HFR 1 Ceppo HFR 2

Figure: 10-23 Caption: Breakage of the Hfr chromosome at the origin of transfer and the beginning of DNA transfer to the recipient. Replication occurs during transfer (see Figure 10.21). Please note that the figure is not drawn to scale. The inserted F plasmid is less than 3% of the size of the Escherichia coli chromosome.

Figure 9.2 Lederberg and Tatum experiment showing that sexual recombination occurs between cells of E. coli. After the cells from strain A and strain B have been mixed and the mixture plated, a few colonies grow on the minimal medium, indicating that they can now make the essential constituents. These colonies are recombinants produced by an exchange of genetic material between the strains.

Figure: 10-24a-b Caption: Manner of formation of different Hfr strains, which donate genes in different orders and from different origins. The bacterial chromosome is a circle (a) that can open at various insertion sequences, at which F plasmids become inserted. The gene orders are shown in part (b).

Figure: 10-24a-b Caption: Manner of formation of different Hfr strains, which donate genes in different orders and from different origins. The bacterial chromosome is a circle (a) that can open at various insertion sequences, at which F plasmids become inserted. The gene orders are shown in part (b).

Figure: 10-26 Caption: Rate of formation of recombinants containing different genes after mixing Hfr and bacteria by the process known as interrupted mating. The location of the genes along the Hfr chromosome is shown at the upper left. Note that the genes closest to the origin (0 min) are the first ones detected in the recombinants. The experiment is done by mixing Hfr and cells under conditions in which essentially all Hfr cells find mates. The recipient was streptomycin-resistant but auxotrophic for the markers being scored. The Hfr donor was streptomycin-sensitive. At various times, samples of the mixture are shaken violently to separate the mating pairs and plated on a selective medium in which only the recombinants can grow and form colonies.

Figure: 10-22 Caption: Integration of an F plasmid into the chromosome with the formation of an Hfr. The insertion of the F plasmid occurs at a variety of specific sites where IS elements are located, the one here being an IS3 located between the chromosomal genes pro and lac. Some of the genes on the F plasmid are shown. The arrow indicates the origin of transfer, oriT, with the arrow as the leading end. Thus, in this Hfr pro would be the first chromosomal gene to be transferred and lac would be among the last.

IS3 Figure: 10-22 Caption: Integration of an F plasmid into the chromosome with the formation of an Hfr. The insertion of the F plasmid occurs at a variety of specific sites where IS elements are located, the one here being an IS3 located between the chromosomal genes pro and lac. Some of the genes on the F plasmid are shown. The arrow indicates the origin of transfer, oriT, with the arrow as the leading end. Thus, in this Hfr pro would be the first chromosomal gene to be transferred and lac would be among the last.

F F’ Diploidia parziale

penicillina tetraciclina cloramfenicolo Plasmidi R

RTF resistance transfer factor

Sequenze di inserzione (IS) Geni di resistenza sono spesso associati a segmenti di DNA mobili che possono entrare e uscire dal cromosoma Sequenze di inserzione (IS) Trasposoni

conseguenze della trasposizione mobilizzazione di geni inattivazione di geni

TRASFORMAZIONE

Non tutte le specie batteriche sono trasformabili Trasformazione naturale Streptococcus pneumoniae Pneumoniae Bacillus subtilis Neisseria meningitidis Neisseria gonorrhoeae Haemophilus influenzae Pasteurella multocida

Trasformazione plasmidica E. coli Permeabilizzazione membrana Mediante 1) ioni calcio 2) Shock elettrico Antibiotico resistenza DNA “clonato”

Plasmidi di clonaggio

Lytic life cycle

LISOGENIA

TRASDUZIONE SPECIALIZZATA (˜10-6)

TRASDUZIONE GENERALIZZATA (˜10-6)

Batterio auxotrofo (his-) Batterio autotrofo (his+)

109 fagi infettano 1010 batteri auxotrofi his- autotrofi his+

plasmide F 100 kb Plasmidi R 10-100kb Plasmidi clonaggio 3-4 Kb Fago lambda 48kb Fago P1 89 Kb

1 fago infetta 1 batterio 102 fagi sono prodotti da un ciclo litico Se ogni fago infetta un batterio, dopo 30’ saranno prodotti 104 fagi, che infettando 104 batteri produrrano 106 fagi in 30’

Bacteriophages are the world's most numerous organisms. 1031 phages worldwide (1021 stars in the universe) Approximately half of all bacteria are killed daily by phages. Phages can carry virulence and antibiotic resistance genes, and can be used therapeutically against pathogenic diseases.

Conversione lisogenica Geni fagici determinano o accrescono la virulenza del batterio

Lysogenic Conversion Examples of Virulence Factors Carried by Phage Batterio fago Prodotto genico fenotipo Vibrio cholerae CTX phage cholerae toxin cholera Escherichia coli lambda phage shigalike toxin hemorrhagic diarrhea Clostridium botulinum clostridial phages botulinum toxin botulism Corynebacterium diphtheriae corynephage beta diphtheria toxin diphtheria Streptococcus pyogenes T12 erythrogenic toxins scarlet fever