Chapter 27 Bacteria and Archaea

Overview: Masters of Adaptation Prokaryotes: Thrive almost everywhere In too acidic, salty, cold, or hot for most other organisms Most are microscopic Lack in size but make up for it in numbers Have an astonishing genetic diversity Divided into two domains: Bacteria Archaea

Fig. 27-1 Figure 27.1 Why is this lakebed red?

Most prokaryotes are unicellular Some form colonies Concept 27.1: Structural and functional adaptations contribute to prokaryotic success Most prokaryotes are unicellular Some form colonies Cells are much smaller (0.5–5 µm) than eukaryotic cells (10–100 µm) The cell wall is a key feature in nearly all of them Cells have a variety of shapes The three most common cell shapes are: Spheres (cocci) Rods (bacilli) Spirals

(a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral 1 µm 2 µm Fig. 27-2 Figure 27.2 The most common shapes of prokaryotes 1 µm 2 µm 5 µm (a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral

Cell-Surface Structures The importance of prokaryotic cell wall: Maintains cell shape Provides physical protection Protect the cell from bursting in a hypotonic environment Bacterial cell walls: Contain peptidoglycan (a network of sugar polymers cross-linked by polypeptides)

Gram-negative bacteria: Archaea: Contain polysaccharides and proteins But lack peptidoglycan Using Gram stain, & based on cell wall composition, many bacteria are classified into: Gram-positive Gram-negative Gram-negative bacteria: Have less peptidoglycan Have an outer membrane that can be toxic More likely to be antibiotic resistant

Many antibiotics work by: Targeting peptidoglycan & damage the bacterial cell walls Carbohydrate portion of lipopolysaccharide Outer membrane Peptidoglycan layer Cell wall Cell wall Peptidoglycan layer Plasma membrane Plasma membrane Protein Protein Gram- positive bacteria Gram- negative bacteria Figure 27.3 Gram staining 20 µm (a) Gram-positive: peptidoglycan traps crystal violet. (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. Fig. 27-3

(a) Gram-positive: peptidoglycan traps crystal violet. Fig. 27-3a Peptidoglycan layer Cell wall Plasma membrane Protein Figure 27.3 Gram staining (a) Gram-positive: peptidoglycan traps crystal violet.

of lipopolysaccharide Fig. 27-3b Carbohydrate portion of lipopolysaccharide Outer membrane Cell wall Peptidoglycan layer Plasma membrane Protein Figure 27.3 Gram staining (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye.

Gram- Gram- positive negative bacteria bacteria 20 µm Fig. 27-3c Figure 27.3 Gram staining Gram- positive bacteria Gram- negative bacteria 20 µm

Capsule: A polysaccharide or protein layer covers many prokaryotes 200 nm Capsule

Fimbriae (attachment pili): Found in some prokaryotes Allow prokaryotes to stick to their substrate or other individuals in a colony Sex pili: Are longer than fimbriae, and Allow prokaryotes to exchange DNA

Fig. 27-5 Figure 27.5 Fimbriae Fimbriae 200 nm

Video: Prokaryotic Flagella (Salmonella typhimurium) Motility Most motile bacteria propel themselves by flagella Prokaryotic flagella are structurally and functionally different from eukaryotic flagella In a heterogeneous environment, many bacteria exhibit a phenomenon called taxis Taxis: is the ability to move toward or away from certain stimuli Video: Prokaryotic Flagella (Salmonella typhimurium)

Flagellum Filament Cell wall Hook Basal apparatus Plasma membrane Fig. 27-6 Flagellum Filament 50 nm Cell wall Hook Basal apparatus Figure 27.6 Prokaryotic flagellum Plasma membrane

Filament Cell wall Hook Basal apparatus Plasma membrane Fig. 27-6a Figure 27.6 Prokaryotic flagellum Plasma membrane

Prokaryotic flagellum (TEM) Fig. 27-6b 50 nm Figure 27.6 Prokaryotic flagellum Prokaryotic flagellum (TEM)

Internal and Genomic Organization Prokaryotic cells: Usually lack complex compartmentalization Some do have specialized membranes that perform metabolic functions

(a) Aerobic prokaryote (b) Photosynthetic prokaryote Fig. 27-7 0.2 µm 1 µm Respiratory membrane Figure 27.7 Specialized membranes of prokaryotes Thylakoid membranes (a) Aerobic prokaryote (b) Photosynthetic prokaryote

Some species of bacteria also have: Prokaryotic genome: Has less DNA than the eukaryotic genome Mostly consists of a circular chromosome Some species of bacteria also have: Smaller rings of DNA called plasmids

Chromosome Plasmids 1 µm Fig. 27-8 Figure 27.8 A prokaryotic chromosome and plasmids 1 µm

The typical prokaryotic genome is: A ring of DNA The DNA is: Not surrounded by a membrane Located in a nucleoid region

Reproduction and Adaptation Prokaryotes reproduce quickly by: Binary fission & divide every 1–3 hours Some every 20 min Many form metabolically inactive endospores Endospores can be viable in harsh conditions for centuries Prokaryotes can evolve rapidly because of their short generation times

Fig. 27-9 Endospore Figure 27.9 An endospore 0.3 µm

0.1 mL (population sample) Fitness relative to ancestor Fig. 27-10 EXPERIMENT Daily serial transfer 0.1 mL (population sample) Old tube (discarded after transfer) New tube (9.9 mL growth medium) RESULTS 1.8 1.6 Figure 27.10 Can prokaryotes evolve rapidly in response to environmental change? Fitness relative to ancestor 1.4 1.2 1.0 5,000 10,000 15,000 20,000 Generation

Promotion of genetic diversity in prokaryotes Prokaryotes have considerable genetic variation Three factors contribute to this genetic diversity: Rapid reproduction Mutation Genetic recombination

Rapid Reproduction and Mutation Prokaryotes reproduce by binary fission Offspring cells are generally identical Mutation rates during binary fission are low But mutations can accumulate rapidly in a population, due to rapid reproduction High diversity from mutations allows for rapid evolution

Genetic Recombination Additional diversity arises from genetic recomb-ination Prokaryotic DNA from different individuals can be brought together by: Transformation: Incorporation of foreign DNA from the environment Transduction: Movement of genes between bacteria by bacteriophages (bacterial viruses) Conjugation: Transfer of genetic material between bacterial cells

Fig. 27-11-4 Phage DNA A+ B+ What type of proccess? A+ B+ Donor cell A+ Recombination Figure 27.11 Transduction A+ A– B– Recipient cell A+ B– Recombinant cell

Conjugation and Plasmids In conjugation: Sex pili allow cells to connect & pull together for DNA transfer A piece of DNA called the F factor is required for the production of sex pili The F factor can exist as a separate plasmid or as DNA within the bacterial chromosome

Fig. 27-12 Figure 27.12 Bacterial conjugation 1 µm Sex pilus

The F Factor as a Plasmid Cells containing the F plasmid function as DNA donors during conjugation Cells without the F factor function as DNA recipients during conjugation The F factor is transferable during conjugation

Fig. 27-13 F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell F+ cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid Recombinant F– bacterium Hfr cell A+ A+ A+ F factor Figure 27.13 Conjugation and recombination in E. coli A+ A– A+ A– A– A+ A– F– cell (b) Conjugation and transfer of part of an Hfr bacterial chromosome

The F Factor in the Chromosome The donor cell (during conjugation): The cell with the F factor built into its chromosomes The recipient bacterium: : The recombinant bacterium with DNA from two different cells It is assumed that horizontal gene transfer is also important in archaea

R Plasmids and Antibiotic Resistance R plasmids carry genes for antibiotic resistance Antibiotics select for bacteria with genes that are resistant to the antibiotics Antibiotic resistant strains of bacteria are becoming more common

Phototrophs obtain energy from light Evolvement of diverse nutritional & metabolic adaptations in prokaryotes Phototrophs obtain energy from light Chemotrophs obtain energy from chemicals Autotrophs require CO2 as a carbon source Heterotrophs require an organic nutrient to make organic compounds Accordingly, the four major modes of nutrition: Photoautotrophy Chemoautotrophy Photoheterotrophy Chemoheterotrophy

Table 27-1 Table 27-1

The Role of Oxygen in Metabolism Prokaryotic metabolism varies with respect to O2: Obligate aerobes require O2 for cellular respiration Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration Facultative anaerobes can survive with or without O2

Prokaryotes can metabolize nitrogen in a variety of ways: Nitrogen Metabolism Prokaryotes can metabolize nitrogen in a variety of ways: Nitrogen fixation: Some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3) Cooperatve use of environmental resources that can’t be used by individual cells; Example: photosynthetic cells & nitrogen-fixing cells called heterocytes (in cyanobacterium Anabaena) exchange metabolic products

Photosynthetic cells Heterocyte 20 µm Fig. 27-14 Figure 27.14 Metabolic cooperation in a colonial prokaryote 20 µm

Concept 27.4: Molecular systematics is illuminating prokaryotic phylogeny Until the late 20th century prokaryotic taxonomy was based on phenotypic criteria Later use of molecular systematics has produced dramatic results Polymerase chain reaction (PCR) allowed for more rapid sequencing of prokaryote genomes

Archaea Archaea share certain traits with bacteria and other traits with eukaryotes Eukarya Archaea Bacteria

Table 27-2 Table 27.2

Extremophiles: Archaea that live in extreme environments: Extreme halophiles: Those live in highly saline environments Extreme thermophiles: Those thrive in very hot environments

Fig. 27-17 Figure 27.17 Extreme thermophiles

Methanogens: Live in swamps and marshes Produce methane as a waste product Strict anaerobes and are poisoned by O2

Bacteria Bacteria: Include the vast majority of prokaryotes Diverse nutritional types are scattered among the major groups of bacteria

Gram-negative bacteria Include: Proteobacteria Gram-negative bacteria Include: Photoautotrophs Chemoautotrophs Heterotrophs Some are anaerobic, others aerobic