Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bacteria Staphylococcus bacteria in nose

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Structure Unicellular Some species form colonies 0.5–10 µm, much smaller than the 10–100 µm of many eukaryotic cells Most common shapes: spheres (cocci) rods (bacilli) and spirals

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bacterial Cell Wall maintains cell shape provides physical protection, prevents the cell from bursting in a hypotonic environment Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides (proteins) sugar polypeptide

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Using the Gram stain, scientists classify bacterial into Gram + or Gram - groups based on cell wall composition Gram - bacteria: less peptidoglycan outer membrane that can be toxic  more likely to be antibiotic resistant Many antibiotics target peptidoglycan and damage bacterial cell walls Gram Stain Classification Gram +Gram -

Cell wall Peptidoglycan layer Plasma membrane Protein (a) Gram-positive: peptidoglycan traps crystal violet.

Cell wall Peptidoglycan layer Plasma membrane Protein (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. Outer membrane Carbohydrate portion of lipopolysaccharide

Gram- positive bacteria Gram- negative bacteria 20 µm

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings A polysaccharide or protein layer called a capsule covers many bacteria Structure

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bacterial Motility Most motile bacteria use flagella to propel themselvesflagella Many exhibit taxis, the ability to move toward or away from certain stimuli Video: Prokaryotic Flagella (Salmonella typhimurium) Video: Prokaryotic Flagella (Salmonella typhimurium)

Flagellum Filament Hook Basal apparatus Cell wall Plasma membrane 50 nm

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fimbriae (also called attachment pili) allows them to stick to their substrate or other individuals in a colony Fimbriae

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Internal Organization lack complex compartmentalization (ex. no nucleus, ER, mitochondrion, etc.) Often perform metabolic functions using highly folded extensions of plasma membrane

(a) Aerobic prokaryote (b) Photosynthetic prokaryote Thylakoid membranes Respiratory membrane 0.2 µm 1 µm

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Most of the genome consists of a circular chromosome located in a nucleoid region Some have smaller rings of DNA called plasmids Plasmids w/ short codes of DNA that may be beneficial to bacteria (Ex. some code for antibiotic resistance) Genome

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Sex pili are longer than fimbriae and allow prokaryotes to exchange DNA Genome

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cells containing the F plasmid function as DNA donors during a process called conjugation Cells without the F factor function as DNA recipients during conjugation The F factor is transferable during conjugation Plasmid F factor

F plasmid F + cell F – cell Mating bridge Bacterial chromosome Bacterial chromosome (a) Conjugation and transfer of an F plasmid Plasmid F factor

F plasmid F + cell F – cell Mating bridge Bacterial chromosome Bacterial chromosome (a) Conjugation and transfer of an F plasmid Plasmid F factor

F plasmid F + cell F – cell Mating bridge Bacterial chromosome Bacterial chromosome (a) Conjugation and transfer of an F plasmid F + cell Plasmid F factor

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings R plasmids carry genes for antibiotic resistance Antibiotics select for bacteria with genes that are resistant to the antibiotics R Plasmids and Antibiotic Resistance

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Reproduction and Adaptation Quick reproduction by binary fission every 1–3 hours Beneficial mutations can accumulate rapidly in a population, allowing for rapid evolution ex. Antibiotic resistant strains are becoming more common Many form inactive endospores to remain viable in harsh conditions

Endospore 0.3 µm

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Genetic Recombination DNA from different individuals can be brought together by conjugation, transformation, transduction

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Transformation and Transduction A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation Transduction is the movement of genes between bacteria by vectors like bacteriophages (viruses that infect bacteria)

Donor cell A+A+ B+B+ A+A+ B+B+ Phage DNA

A+A+ Donor cell A+A+ B+B+ A+A+ B+B+ Phage DNA

Recipient cell B–B– A+A+ A–A– Recombination A+A+ Donor cell A+A+ B+B+ A+A+ B+B+ Phage DNA

Recombinant cell Recipient cell A+A+ B–B– B–B– A+A+ A–A– Recombination A+A+ Donor cell A+A+ B+B+ A+A+ B+B+ Phage DNA

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Pathogenic Prokaryotes Prokaryotes cause about half of all human diseases Lyme disease is an example

5 µm

Fig a Deer tick

Fig c Lyme disease rash

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bacteria typically cause disease by releasing exotoxins or endotoxins Exotoxins cause disease even if the prokaryotes that produce them are not present Endotoxins are released only when bacteria die and their cell walls break down Many pathogenic bacteria are potential weapons of bioterrorism Pathogenic Prokaryotes