Prokaryote: Bacteria and Archaea Characteristics

Life’s 7 major defining properties

• cellular organization

• growth and development

• heredity and DNA

• reproduction

• metabolism and enzymes

• transport

• responsiveness

One of the main reasons viruses are generally
considered nonliving is that they are _______.

cellular

Viruses do show some traits of life such as ______.

heredity, development, and evolution, they do
not display these characteristics independent of their living host cell.

• Outside of their host, they lack most other
  features of life we just described and are
  inactive and inert.

Bacteria and archaea

• First appear 3.5 to 3.8 billion years
  ago

• Most diverse group of cellular
  microbes

• Habitats - ubiquitous
  • From Antarctic glaciers to
  thermal hot springs
  • From colons of animals to
  cytoplasm of other organisms
  • From water to brine
  • From rocks to air vents

• Only a few cause diseases

Only Two domains contain
prokaryotes _______.

bacteria and archaea

Classification Systems for Bacteria and
Archaea

Bergey’s Manual of Systematic Bacteriology and Bergey’s Manual of Determinative Bacteriology

Bergey’s Manual of Systematic Bacteriology

• Comprehensive view of bacterial and archaeal relatedness

• Based on rRNA sequencing

Bergey’s Manual of Determinative Bacteriology

• Based entirely on phenotypic characteristics

• Categorizes organisms based on traits commonly assayed in clinical, teaching, and research labs such as shape as seen in a microscope, or metabolic capabilities
  (what they need to grow)

Bacterial species

• A collection of bacterial cells, all of which share an overall similar pattern of traits

• Should share at least 95% of their genes as matches

Subspecies, strain, or type

Bacteria of the same species that have differing characteristics

Serotype

Representatives of a species that stimulate a distinct pattern of antibody (serum) responses because of unique surface molecules

Common bacterial shapes

coccus, bacillus, spiral (spirochete and spirillum)

Cocci

can be perfect spheres, but they also can exist as oval, bean-shaped, elongated, flattened on one side, or even pointed variants

Diplococci

pairs of cocci

Streptococci

chain of cocci

Tetrads

group of four cocci

• has two planes

Sacrinae

cubelike groups of eight cocci

• has three planes

Staphylcocci

grapelike clusters of cocci

• has multiple planes

bacillus

cell that is cylindrical is termed a rod

• only divide across their short axis - - > fewer arrangements than cocci

Diplobacillus

pairs of rods after division

Streptobacilli

chain-like rods

Coccobacillus

oval to the point where they resemble cocci

Palisades

cells of a chain remain partially attached by a
small hinge region at the ends

Spiral bacteria have one or more _____.

twists

Vibrio

Singly occurring rods that are gently curved (comma-shaped)

Spirillum/spirillia

slightly curled or spiral-shaped body

Spirochete

flexible form that resembles a spring

• Contains a periplasmic flagella/axial filament
  used for movement

Most bacteria are monomorphic ________.

that is, they maintain a single shape. However, a
number of environmental conditions can
alter that shape.

Pleomorphism

variations in cell wall structure caused by slight genetic or
nutritional differences

• Can even find square or star shaped
  bacterial cells!

All cells possess:

1. Cytoplasmic membrane

2. Cytoplasm

3. Ribosomes

4. DNA Genome

How organisms are different from
eukaryotes:

1. The way their DNA is packaged: lack of nucleus and histones (proteins we wrap our DNA around)

2. The makeup of their cell wall: peptidoglycan and other unique chemicals

3. Their internal structures: lack of membrane-bound organelles

Prokaryotic cell structure

Cell envelope

Lies outside the cytoplasm
• Composed of two or three basic layers
that each perform a distinct function, but
together act as a single protective unit:

1. Cytoplasmic membrane

2. Cell wall

3. Outer membrane (in some
   bacteria)

Cytoplasmic membrane

• surrounds cytoplasm

• A lipid bilayer with proteins embedded
  • Bacteria and Archaea have different lipids

• selectively permeable = special carrier mechanisms for passage of most molecules
  • Regulates transport of nutrients and waste

Cell wall

• Helps determine the shape of a bacterium

• Provides strong structural support to keep the bacterium from bursting (lysis) or collapsing because of changes in osmotic pressure

• Gains its relative rigidity from peptidoglycan

Certain drugs target the cell wall, disrupting its integrity and causing _______.

cell lysis (disintegration or rupture) of the cell

Peptidoglycan

• Compound composed of a repeating framework
  of long glycan (sugar) chains cross-linked by
  short peptide (protein) fragments

• Provides a strong but flexible support
  framework (not found in archaea or eukarya)

• Target for some antibiotics

Gram-positive cell wall

• Thick, homogenous sheet of peptidoglycan: 20 to 80 nm in thickness

• Contains teichoic acid and lipoteichoic acid:
  • Function in cell wall maintenance and
  enlargement
  • Contribute to the acidic charge on the
  cell surface

Gram-negative cell wall

• Single, thin sheet of peptidoglycan: 1 to 3 nm in thickness

• Thinness gives Gram-negative cells more susceptibility to lysis

gram-negative outer membrane

• Similar in composition to most
  membranes, except it contains
  specialized polysaccharides and proteins (Lipopolysaccharide and porin proteins)

  
  

Lipopolysaccharide

• Signaling molecules and receptors

• Endotoxin (Lipid A)

Porin proteins

Special membrane channels that only the outer membrane allows certain chemicals to penetrate

Outer membrane of gram-negative bacteria contributes an _______.

extra barrier

• Resistant to certain antimicrobial chemicals

• More difficult to inhibit or kill than gram-positive bacteria

Alcohol-based compounds dissolve ________ .

lipids in the outer membrane and therefore
damage the cell
• Alcohol swabs used to cleanse the skin before certain medical procedures

Treatment of infections caused by gram-negative bacteria requires drugs that can _______.

cross the outer membrane

Gram-positive cells have _______.

cytoplasmic and cell wall

Gram-negative cells have ______.

cytoplasmic, cell wall, and outer membrane

What component provides structural support in most bacterial cells walls?

peptidoglycan

Which type of bacteria are classified as gram negative?

bacteria with a thin peptidoglycan layer and an outer membrane

Which bacterial shape is best described as spherical?

coccus

What term describes rod-shaped bacteria arranged in chains?

streptobacillus

Which of the following is an example of an acid-fast bacteria?

mycobacterium tuberculosis

Which component is not present in archaea?

peptidoglycan

Which bacteria lack a typical cell wall structure and instead contain sterols for membrane stability?

mycoplasma

What unique lipid Is found in the cell walls of acid-fast bacteria like mycobacterium?

mycolic acid

What is the main function of the bacterial cytoplasmic membrane?

regulating transport of nutrients and waste

What type of flagellar arrangement has flagella located at both poles of the cell?

amphitrichous

Which structure allows bacteria to exchange genetic material during conjugation?

pili (type IV)

What type of bacteria forms endospores to survive extreme conditions?

gram positive bacillus

Acid-fast bacteria

• Mycobacterium and Norcardia: contain peptidoglycan and stain Gram-positive, but
  bulk of cell wall is composed of unique lipids (mycolic acid)

• “laugh in the face of alcohol”

• Acid-fast staining required

• β-Lactams (include Penicillin) are
  ineffective

Mycolic acid

• Very-long-chain fatty acid

• Found in the cell walls of acid-fast bacteria

• Contributes to the pathogenicity of the bacteria

• Makes bacteria highly resistant to certain chemicals and dyes

Common medical examples of acid-fast bacteria

Mycobacterium tuberculosis, Mycobacterium leprae,
and Nocardia species

Archaeal cell walls

• Exhibit unusual and chemically distinct cell walls

• All lack true peptidoglycan structure (pseudomurein)

• Most lack an outer membrane

• Some have cell walls composed entirely of
  polysaccharides or protein

• some can also lack a cell wall

Pseudomurein is immune from destruction by
both _________.

lysozyme and penicillin

• present in archaea cell walls

S layers

a rigid protein shell that functions to prevent osmotic lysis just as does the bacterial cell wall

• present in Archaea which lack a polysaccharide-containing cell wall

• When present, is always the outermost layer of the cell envelope

In many Archaea, thick S-layers can take on the role of the _______.

cell wall and are responsible for providing structural strength, protecting the cell from osmotic lysis, and conferring cell shape

Mycoplasmas

• Naturally lack a cell wall

• Sterols in the cell membrane stabilize the cell
  against lysis

• Mycoplasma pneumoniae: “walking
  pneumonia

L forms

• Some bacteria that naturally have a cell wall
  but lose it during part of their life cycle

• Role in persistent infections

• Resistant to some antibiotics

Mycoplasma (cont.)

• Naturally lack cell wall (not L–form bacteria)

• MUST contain steroids for membrane stability

• Parasitic and saprophytic

• Highly pleomorphic

• causes several human pathogens

Mycoplasmas are the _______.

Smallest prokaryotic organisms grown in cell-free culture
medium

Mycoplasmas may have little need for a cell wall because ________.

they experience little osmotic pressure when living within the cytoplasm of another cell
• Absence of peptidoglycan may help evade the host immune system

Glycocalyx

General term for a gelatinous polymer surrounding a cell

• can be a slime layer or capsule

• role in biolfim production

Slime layer

loose, protects against loss of water
and nutrients

• type of glycocalyx

capsule

more tightly bound, denser, and thicker;
produce a sticky (mucoid) character to colonies on
agar

• type of glycocalyx

  
  

Specialized functions of capsules

• Formed by many pathogenic bacteria

• Have greater disease-causing abilities

• Protect against host white blood cells called
  phagocytes

• Helps prevent cell dehydration

Appendages for motility

flagella and axial filaments

Appendages for Attachment points or channels

fimbriae, pili, hami, and nanotubes/nanowires

Flagellum

• primary function is motility

• has three parts: filament, hook (sheath), and basal body

flagellar function

• Chemotaxis: movement of bacteria in response to chemical signals

• Phototaxis – response to light signals

• Runs (linear directions) and tumbles (stop and go)

Positive chemotaxis

movement toward favorable chemical stimulus

Negative chemotaxis

movement away from a repellant

Polar arrangement

flagella attached at one or both ends of the
cell

types:

• Monotrichous: single flagellum

• Lophotrichous: small bunches
  or tufts of flagella emerging from the same site

• Amphitrichous: flagella at
  both poles of the cell

Peritrichous arrangement

flagella are dispersed randomly over the surface of the cell

Periplasmic Flagella (Axial Filaments)

• Internal flagellum enclosed in the space between the cell wall and the cytoplasmic membrane

• Spirochetes possess an unusual, wriggly mode of locomotion caused by two or more long,
  coiled threads, the periplasmic flagella or
  axial filaments

Archaella proteins are unrelated to those of __________.

flagella, and in evolutionary terms are more
closely related to type IV pili

• Somewhat simpler than flagella

• Generally slower than bacterial flagella

Fimbriae

• type of attachment or channel formation

• Small, bristle-like fibers sprouting off the surface of many bacterial cells

• Allow tight adhesion between fimbriae and
  epithelial cells, allowing bacteria to colonize and
  infect host tissues

• Escherichia coli colonizes the intestine and begins its invasion of tissues by use of this adhesion

• Mutant forms of these pathogens that lack fimbriae are unable to cause infections

Pili/pilus

• type of Attachment or Channel Formation
  Appendages

• usually longer than fimbriae and only one or two found per cell

• Involved with motility and DNA transfer

  
  

Twitching motility of pili

pilus extends then contacts surface then retracts
(powerstroke). Results in short, jerky, intermittent movements.

Gliding motility of pili

smooth gliding movement

Type IV pili aka conjugation sex pili

the conjugation pilus of one bacterium called an
F+ cell connects to receptors on the surface of another bacterium. The two cells make physical contact, and DNA from the F+ cell is transferred to the other cell.

• Found only in Gram-negative bacteria

Type IV pilus can transfer ______.

genetic material, act like fimbriae and assist in attachment, and act like flagella and make a bacterium motile

Type IV pili are major contributor to the infectiousness of:

• Neisseria gonorrhoeae (gonorrhea)

• Vibrio cholerae (cholera)

• Streptococcus pyrogenes (strep throat and scarlet fever)

nanotubes

• Very thin, long, tubular extensions of the
  cytoplasmic membrane

• Used as channels to transfer amino acids or
  to harvest energy by shuttling electrons to
  iron-rich substances (“breathing rock
  instead of oxygen”)

• used by bacteria in nutrient poor environments

• type of Attachment or Channel Formation Appendage

Hamus/Hami

• type of Attachment or Channel Formation Appendages

• Present within the SM1 group of Archaea

• “Tiny grappling hook” = holds archaea in place to collect nutrients

• Ecological strategy that helps trap scare nutrients within habitat

• Aids in biofilm formation

• present in archaea that Inhabit anoxic groundwater - - > Earth’s deep subsurface

Cytoplasm

• 70 to 80% water

• Complex mixture of sugars,
  amino acids, and salts

Cell inclusions

• function as energy reserves, carbon or phosphorus reservoirs, and/or have special functions

• Enclosed by thin protein membrane
  • Reduces osmotic stress = Storing carbon or other substances in an insoluble form within the cytoplasm reduces osmotic stress and takes up less space compared with storing these
  substances in a soluble form

Common examples of storage cell inclusions

storage for carbonate mineral, Polyphosphate, and sulfur

Gas vesicle cell inclusions

structures that confer buoyancy and allow the cells to
position themselves in regions of the water column that best suit their metabolisms

• present in Cyanobacteria (algae blooms)

Magnetosomes cell inclusions

impart a magnetic dipole on a cell, allowing it to orient itself in a magnetic field

Endospores

dormant survival structures

• Produced by some Gram-positive bacilli

• Vegetative cell: metabolically active

• resist extremes of heat, drying, freezing, radiation, and chemicals that would kill vegetative cells

• Require special stains (Endospore stain) to view