Prokaryotes Chapter 28. Prokaryotic Diversity Oldest, structurally simplest, and most abundant forms of life Abundant for over a billion years before

Prokaryotes

Chapter 28

Prokaryotic Diversity• Oldest, structurally simplest, and most

abundant forms of life

• Abundant for over a billion years before eukaryotes

• 90 and 99% unknown and undescribed

• Fall into 2 domains– Bacteria (also called Eubacteria) – Archaea (formerly called Archaebacteria)

• Many archaeans are extremophiles2

• Unicellularity– Most are single-celled– May stick together to form associations and biofilms

• Cell size – Size varies tremendously– Most are less than 1 m in diameter

• Nucleoid– Chromosome is single circular double-stranded DNA – Found in the nucleoid region of cell– Often have plasmids

• Cell division and genetic recombination– Most divide by binary fission – exchange genetic material extensively

3

• Genetic recombination – Occurs through horizontal gene transfer – NOT a form of reproduction

• Internal compartmentalization– No membrane-bounded organelles– No internal compartment– Ribosomes differ from eukaryotic form

• Flagella– Simple in structure– Different from eukaryotic flagella

• Metabolic diversity– Oxygenic and anoxygenic photosynthesis– Chemolithotrophic

4

• They differ in four key areas:– Plasma membranes– Cell walls– DNA replication– Gene expression

5

Bacteria and archaea differ fundamentally

• Plasma membranes– Plasma membranes of archaea differ from

bacteria and eukaryotes• Archaean membrane lipids composed of glycerol

linked to hydrocarbon chains by ether linkages• Ester linkages in bacteria and eukaryotes

6

Bacteria and archaea differ fundamentally

• Cell walls– Both kinds of prokaryotes typically have cell

walls covering the plasma membrane• Archeae cell walls lack peptidoglycan• Bacteria cell walls have peptidoglycan, but a

variety of proteins and carbohydrates

7

• Gene expression– Gene expression differs between archaea and

bacteria• Archaea have more than one RNA polymerase• These enzymes closely resemble the eukaryotic

RNA polymerase• Translation machinery is more similar to that of

eukaryotes

8

9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Common ancestor

DomainBacteria

DomainArchaea

DomainEukarya

The three-domain system of phylogeny originated by Carl Woese

Tree is based onrRNA sequences.


Crenarchaeota Euryarchaeota Aquificae Thermotogae Chloroflexi

Thermophiles

BacteriaArchaea

Bacilli Clostridium Actinobacteria

Gram-positive bacteria

High G/CLow G/C (Firmicutes)

Euryarchaeota Aquificae Bacilli Actinobacteria Spirochaetes

25.96 µm

Archaea differ greatlyfrom bacteria.Although both areprokaryotes, archaealcell walls lackpeptidoglycan; plasmamembranes are madeof different kinds oflipids than bacterialplasma membranes;RNA and ribosomalproteins are more likeeukaryotes thanbacteria. Mostlyanaerobic. Examplesinclude Methanococcus,Thermoproteus,Halobacterium.

The Aquificaerepresent the deepestor oldest branch ofbacteria. Aquifexpyrophilus is a rod-shaped hyper-thermophile with atemperature optimumat 85°C; a chemo-autotroph, it oxidizeshydrogen or sulfur.Several other relatedphyla are alsothermophiles.

Gram-positivebacteria. Largely solitary;many form endospores.Responsible for manysignificant humandiseases, includinganthrax (Bacillusanthracis); botulism(Clostridium botulinum);and other commondiseases(staphylococcus,streptococcus).

Some gram-positivebacteria formbranching filamentsand some producespores; often mistakenfor fungi. Producemany commonly usedantibiotics, includingstreptomycin andtetracycline. One ofthe most common typesof soil bacteria; alsocommon in dentalplaque. Streptomyces,Actinomyces.

Long, coil-shapedcells that stain gram-negative. Common inaquaticenvironments.Rotation of internalfilaments produces acorkscrewmovement. Somespirochetes such asTreponema pallidum(syphilis) andBorrelia burgdorferi(Lyme disease) aresignificant humanpathogens.

1.37 µm

1 µm

23.80 µm 22.15 µm

Deinococcus-Thermus

a: © SPL/Photo Researchers, Inc.; b; © Dr. R. Rachel and Prof. Dr. K. O. Stetten, University of Regensburg, Lehrstuhl fuer Mikrobiologie, Regensburg, Germany;c: © Andrew Syred/SPL/Photo Researchers, Inc.; d: © Microfiield Scientific Ltd/SPL/Photo Researchers, Inc.; e: © Alfred Paseika/SPL/Photo Researchers, Inc.

10

11


f: © Dr. Robert Calentine/Visuals Unlimited; g: © Science VU/S. Watson/Visuals Unlimited; h: © Dennis Kunkel Microscopy, Inc.;i: © Prof. Dr. Hans Reichenbach, Helmholtz Centre for Infection Research, Braunschweig

Cyanobacteria Chlorobi Beta Gamma Delta

ProteobacteriaPhotosynthetic

Spirochaetes

Cyanobacteria Beta Gamma Delta

25.04 µm

10.57 µm 750 µmCyanobacteria are aform of photosyntheticbacterium common inboth marine andfreshwater environ-ments. Deeplypigmented; oftenresponsible for “blooms”in polluted waters.Both colonial andsolitary forms arecommon. Somefilamentous forms havecells specialized fornitrogen fixation.

A nutritionally diversegroup that includes soil bacteria like thelithotrophNitrosomonas thatrecycle nitrogen within ecosystems byoxidizing theammonium ion(NH4

+). Other membersare heterotrophs andphotoheterotrophs.

Gammas are adiverse group includingphotosynthetic sulfurbacteria, pathogens,like Legionella, andthe enteric bacteriathat inhabit animalintestines. Entericsinclude Escherichiacoli, Salmonella (foodpoisoning), andVibrio cholerae(cholera).Pseudomonas are acommon form of soilbacteria, responsiblefor many plantdiseases, and areimportant opportunisticpathogens.

The cells ofmyxobacteria exhibitgliding motility bysecreting slimypolysaccharides overwhich masses of cellsglide; when the soildries out, cellsaggregate to formupright multicellularcolonies calledfruiting bodies. Otherdelta bacteria aresolitary predators thatattack other bacteria(Bdellovibrio) andbacteria used inbioremediation(Geobacter).

Epsilon–Helicobacter

Alpha–Rickettsia

Prokaryotic Cell Structure

• 3 basic shapes– Bacillus – Rod-shaped – Coccus – Spherical– Spirillum – Helical-shaped

12

Bacillus Coccus Spirillum

3 µm2 µm0.5 µm


(left): © Dr. Gary Gaugler/SPL/Photo Researchers, Inc.; (middle): © CNRI/Photo Researchers, Inc.; (right): © Dr. Richard Kessel & Dr. Gene Shih/Visuals Unlimited

• Cell wall– Peptidoglycan forms a rigid network

• Maintains shape• Withstands hypotonic environments• Archaea have a similar molecule

– Gram stain• Gram-positive bacteria have a thicker peptidoglycan

wall and stain a purple color• Gram-negative bacteria contain less peptidoglycan

and do not retain the purple-colored dye – retain counterstain and look pink

13


Gram-positive Gram-negative Gram-positive Gram-negative Gram-positive Gram-negative Gram-positive Gram-negative

a.

b. 10 µm

Crystal violet–iodine complexformed inside cells.

All one color.

Alcoholdehydrates thickPG layer trapping

dye complex.

Alcoholhas minimaleffect on thin

PG layer.

Dark Purplemasks thered dye.

Red dye stains the

colorless cell.Both cell walls affix the dye.

1. Crystal violet is applied.

2. Gram’s iodine is applied.

3. Alcohol wash is applied.

4. Safranin (red dye) is applied.

b: © Jack Bostrack/Visuals Unlimited

14

The Gram stain

• Endospores– Develop a thick wall around their genome and a

small portion of the cytoplasm– When exposed to environmental stress– Highly resistant to environmental stress

• Especially heat

– When conditions improve can germinate and return to normal cell division

– Bacteria causing tetanus, botulism, and anthrax

15

Prokaryotic Genetics

• Prokaryotes do not reproduce sexually

• 3 types of horizontal gene transfer– Conjugation – cell-to-cell contact– Transduction – by bacteriophages– Transformation – from the environment

• All 3 processes also observed in archaea

16

Conjugation

• Plasmids may encode advantageous info– Are not required for normal

function

• In E. coli, conjugation is based on the presence of the F plasmid (fertility factor)– F+ cells contain the plasmid

– F- cells do not

17


a. 2 µm© Dr. Dennis Kunkel/Visuals Unlimited

Transduction

• Generalized transduction– Virtually any gene can be transferred– Occurs via accidents in the lytic cycle– Viruses package bacterial DNA and transfer it

in a subsequent infection

• Specialized transduction– Occurs via accidents in the lysogenic cycle– Imprecise excision of prophage DNA– Only a few host genes can be transferred

18

19

Infection with Phage

Phage adheres to cell. Phage DNA is injected in to cell.Phage DNA is replicated andhost DNA is degraded.

Phage particles are packagedwith DNA and are released.

Infection with Transducing Phage

Cell contains DNA from donor. Transducing phageadheres to cell.

Phage injects a piece ofchromosomal DNA.

DNA is incorporated byhomologous recombination.


Transformation

• Natural transformation– Occurs in many bacterial species, including

Streptococcus which was studied by Griffith– DNA that is released from a dead cell is

picked up by another live cell – Encoded by bacterial chromosome

• Not an accident of plasmid or phage biology

20

Tuberculosis (TB)

• Scourge for thousands of years

• Mycobacterium tuberculosis

• Afflicts the respiratory system

• Thwarts immune system

• Easily transferred from person to person through the air

• Multidrug-resistant (MDR) strains are very alarming

21

Beneficial Prokaryotes

• Decomposers release a dead organism’s atoms to the environment

• Fixation– Photosynthesizers fix carbon into sugars

• Ancient cyanobacteria added oxygen to air

– Nitrogen fixers reduce N2 to NH3 (ammonia) • Anabaena in aquatic environments• Rhizobium in soil

22

• Symbiosis refers to the ecological relationship between different species that live in direct contact with each other– Mutualism – both parties benefit

• Nitrogen-fixing bacteria on plant roots• Cellulase-producing bacteria in animals

– Commensalism – one organism benefits and the other is unaffected

– Parasitism – one organism benefits and the other is harmed

23

• Bacteria are used in genetic engineering – “Biofactories” that produce various chemicals,

including insulin and antibiotics

• Bacteria are used for bioremediation– Remove pollutants from water, air, and soil– Biostimulation – adds nutrients to encourage

growth of naturally occurring microbes• Exxon Valdez oil spill

24

Documents

Prokaryotes Chapter 28. Prokaryotic Diversity Oldest, structurally simplest, and most abundant forms of life Abundant for over a billion years before