Chapter 7 Microbial Genetics Plasmids Circular genetic elements that reproduce autonomously and have an extra-chromosomal existence. ·1-1000 KB in size Typical plasmid 1/20 of chromosome Most are circular double-stranded DNA. some linear ds dna Transmitted from cell to cell via conjugation process Some can integrated into chromosome Can carry a variety of genes for production of toxin, resistance to antibiotics and heavy metals et al
Chapter 7 Microbial Genetics Plasmids • 1-1000 KB in size • Typical plasmid 1/20 of chromosome • Most are circular double-stranded DNA, some linear ds DNA • Transmitted from cell to cell via conjugation process • Some can integrated into chromosome • Can carry a variety of genes for production of toxin, resistance to antibiotics and heavy metals et al. Circular genetic elements that reproduce autonomously and have an extra-chromosomal existence:
Plasmid Conjugative: plasmids which govern their own transfer by cell-to-cell contact are called conjugative Tra region: a set of genes within the plasmid that control the transmissability by conjugation Hfr(high frequency of recombination): strains of bacteria that transfer large amounts of chromosomal dna during conjugation Supercoil: plasmids isolated from the cells are in supercoiled configuration Curing of plasmids: elimination of plasmids from host cel Plasmid separation: by ultracentrifugation or electrophores by various treatments
Plasmid • Conjugative: plasmids which govern their own transfer by cell-to-cell contact are called conjugative • Tra region: a set of genes within the plasmid that control the transmissability by conjugation • Hfr (high frequency of recombination): strains of bacteria that transfer large amounts of chromosomal DNA during conjugation • Supercoil: plasmids isolated from the cells are in supercoiled configuration • Plasmid separation: by ultracentrifugation or electrophoresis • Curing of plasmids: elimination of plasmids from host cells by various treatments
Plasmids Replication: Most plasmids of gram-positive bacteria replicate by a rolling circle mechanism Copy number: The number of plasmids in a cell, can range from only 1-3 copies to 100 copies. Incompatibility: Two different types of Plasmids can not coexist in a cell pl Episomes: Plasmids having the ability to integrate into host chromosome
Plasmids • Replication: Most plasmids of gram-positive bacteria replicate by a rolling circle mechanism. • Copy number: The number of plasmids in a cell, can range from only 1-3 copies to 100 copies. • Incompatibility: Two different types of plasmids can not coexist in a cell. • Episomes: Plasmids having the ability to integrate into host chromosome
F-Plasmid-Fertility plasmids 1s3 100KB Tn1000 Can be cured with 1000 acridine orange tra region s· compatibility(imc) Origin of replication (oriS) Transposable elements 75 25 tra region phi: phage inhibition Is (insertion sequence) rep: replication functions inc, rep, oris, phi
F-Plasmid-Fertility Plasmids • 100 KB • Can be cured with acridine orange • Incompatibility (inc) • Origin of replication (oriS) • Transposable elements (Tn) • tra region • phi: phage inhibition • IS (insertion sequence) • rep: replication functions
Cell to Cell transfer of plasmids Conjugative: Plasmids that govern their own transfer by cell-to-cell contact are called conjugative(not all plasmids are conjugative) Some conjugative plasmids can transfer genetic information between distintly related organisms (between gram-positive and gram-negative bacteria, between bacteria and plant cells, and between bacteria and fungi), it is important for evolution. Chromosome Plasmid Conjugation(接合作用)
Cell to Cell Transfer of Plasmids • Conjugative: Plasmids that govern their own transfer by cell-to-cell contact are called conjugative (not all plasmids are conjugative) • Some conjugative plasmids can transfer genetic information between distintly related organisms (between gram-positive and gram-negative bacteria, between bacteria and plant cells, and between bacteria and fungi), it is important for evolution. Conjugation (接合作用）
Plasmid biology Chromosome (a)Plasmid replication inde of chromosom (c)Cell-to-cell transfer during conjugation p Somes (a) Integration of plasmid into chromosome
Plasmid Biology Episomes
Plasmid Biology Growth cuning (b) Curing of plasmid
Plasmid Biology
Types of Plasmids and Their Biological significance The presence of plasmids in a cell can have a profound influence on the cells phenotype the ability of conjugation the ability of rhizobium to interact with plants the resistance to antibiotics and heavy metals the degradation of octane, camphor et al the production of enterotoxin the applications in genetic engineering
Types of Plasmids and Their Biological Significance • The presence of plasmids in a cell can have a profound influence on the cell’s phenotype: – the ability of conjugation – the ability of Rhizobium to interact with plants – the resistance to antibiotics and heavy metals – the degradation of octane, camphor et al – the production of enterotoxin – the applications in genetic engineering
Types of Plasmids and Their functions TABLE9.3 Types of plasmids lype Organisms Conjugative plasmids F plasmid, Escherichia coli; Pfdm, K, Pseudomonas: P, Vibrio cholerae: SCP, Streptomyces R Wide variety of antibiotics(ao Section 11.13) Enteric bacteria, Staphylococcus Resistance to mercury, cadmium, nickel, cobalt, zinc, arsenic pseudomonas aO Section 14.18) Bacteriocin and antibiotic production Enteric bacteria; Clostridium; Streptomyces Physiological functions Lactose, sucrose, urea utilization, nitrogen fixation Enteric bacteria Degradation of octane, camphor, naphthalene, salicylate Ps seudomonas Pigment production Erwinia, Staphylococcus Nodulation and symbiotic nitrogen fixation(o Section 14.23 Rhizobium Virulence plasmids Enterotoxin, K antigen, endotoxin(oo Sections 19.8-19.11) Escherichia coli Tumorigenic plasmid (aD Section 14.22) Agrobacterium tumefaciens Adherence to teeth(dextran)(oo Section 19.3 Streptococcus mutans Coagulase, hemolysin, fibrinolysin, enterotoxin(oo Sections 19.7 and 19.9) Staphylococcus aureus "Plasmids have been found in most bacterial genera
Types of Plasmids and Their Functions
Resistance Plasmids(r-plasmids the most well studied plasmids onv The emergence of bacteria resistant to several antibiotics is IS medically Significant Resistance can be transferred via cell-to-cell contact 890 This could be one of the reasons for the rapid rise of multiply 75 resistant strains Plasmid recombination is one cml 725 mean by which multiply resistant organisms might have 50 first arisen Infectious nature of the r plasmids permits rapid spread of the characteristic through populations onT ter Typical example: plasmid R100
Resistance Plasmids (R-Plasmids): the most well studied plasmids • The emergence of bacteria resistant to several antibiotics is medically significant • Resistance can be transferred via cell-to-cell contact • This could be one of the reasons for the rapid rise of multiply resistant strains • Plasmid recombination is one mean by which multiply resistant organisms might have first arisen • Infectious nature of the R plasmids permits rapid spread of the characteristic through populations • Typical example: plasmid R100
