Introduction to Microbiology/Prokaryotes

Dr. Cory L. BlackwellJanuary 13, 2015

Changing Paradigms

• Before the 1880’s it was believed that diseases came from demons and witchcraft

• With the new concept of biogenesis and the realization that microorganisms can physically and chemically change organic materials, scientists/physicians began to develop The Germ Theory of Disease.

GERM THEORY OF DISEASE

• The Germ Theory of Disease states that a particular microbe might cause a specific disease– 1865 Joseph Lister, English surgeon, began treating

surgical wounds with phenol (acid) resulting in the significant reduction of infections and deaths

– 1876 Robert Koch discovered that the bacterium Bacillus anthracis was present in the blood of cattle that died of the disease anthrax

• Koch eventually established Koch’s Postulates

Koch’s Postulates

1. The same pathogen must be isolated in each case of the disease

2. Pathogen must be isolated from the diseased host and grown in a pure culture

3. The pathogen from the culture must cause the same disease when used to inoculate a healthy organism

4. Microorganism must be isolated from the newly diseased animal and be identical to the original pathogen

Prokaryotic and Eukaryotic Cells

Prokaryote or Eukaryote?

Prokaryotes• Bacteria

• Archaea

Eukaryotes• Humans

• Plants

• Yeast

• Fungi

• Amoebas

Prokaryote and Eukaryote

• Prokaryotes and Eukaryotes have four common features1. Cell Membrane 2. Cytoplasm3. Nucleic Acid4. Ribosomes– Both utilize similar chemical reactions to

metabolize food, build proteins, and store energy

Eukaryotic or Prokaryotic

• Prokaryotes and Eukaryotes differ in several ways:

DNA Location

• DNA of Eukaryotes are found in the cell’s nucleus—membrane bound organelle that contains the genetic material

• DNA of Prokaryotes is not enclosed in a membrane bound organelle

DNA Location

Eukaryote Prokaryote

DNA Structure

• Eukaryotic DNA is bound by chromosomal proteins called histones and is found in multiple chromosomes

• Prokaryotic DNA is usually takes the form of a singular circularly arranged chromosome. No histones are present

Prokaryotic DNA Eukaryotic DNA

Organelles

• Eukaryotes possess membrane-enclosed organelles – Mitochondria, endoplasmic reticulum, golgi

apparatus, lysosomes, nucleus, etc.

• Prokaryotes are void of an membrane-enclosed organelles

Organelles

Cell Wall Composition

• Prokaryotes contain peptidoglycan (complex polysaccharide) within its cell walls– Lipotechoic acids (LTA)– Lipopolysaccharides (LPS)

• Eukaryotes cell wall (only in plant cells and fungi) are made of simple molecules (cellulose and chitin)

Cell Wall Composition

Eukaryotic Cell Membrane Prokaryotic Cell Wall

Growth and Division

• Prokaryotes divide by binary fission– Requires relatively few structure and processes

• Eukaryotes divide utilizing mitosis– More complex than binary fission– Interphase, prophase, metaphase, anaphase,

telophase

PROKARYOTES

Prokaryotes

• Prokaryotes are subdivided into two groups– Bacteria– Archaea

• Both bacteria and archaea are unicellular organisms• Although bacteria (constitutes the majority of prokaryotes)

and archaea look similar, their chemical composition is different– Archaea lack peptidoglycan in their cell walls– Archaea usually live in extreme environments

• Methanogens• Extreme Halophiles• Hypothermophiles

BACTERIA

Bacterial Size, Shape, and Arrangement

• Most bacteria range between 2 to 8 µm in length– That is roughly 1,000X less than the size of an ant

• Bacteria have three different cellular shapes– Coccus “spherical”– Bacillus “rod-shaped”– Spiral “spiral-shaped”

Cocci

• Bacterial cells that are cocci can be oval, elongated, or flat on one side

Cocci

Cocci

• The cocci are also distinguished based on how the bacteria group with one another (bacterial arrangement)

Spatial Arrangement of Cocci

• Diplo—pairs of bacteria

• Strepto—chains of bacteria

• Staphyl—grapelike clusters

• Tetrads—groups of four

• Sarcinae—cube like structures consisting of 8 bacteria

Bacilli

• Bacilli divide only across their short axis, therefore there are less arrangement groupings

• Diplo—pairs of bacteria

Bacillus anthracis

Bacilli

• Bacilli divide only across their short axis, therefore there are less arrangement groupings

• Diplo—pairs of bacteria• Strepto—chains of

bacteria arranged from tip to tail

Bacilli

• Coccobacilli—combination of rod and oval shapes

Brucella melitensis

Spiral

• Spiral bacteria form twists and are never found in a straight conformation

• Spiral bacteria come in three varieties:– Vibrio– Spirillum– Spirochete

• Vibrio are in the shape of curved rods

Vibrio cholera

• Spirilla have a helical “corkscrew” shape

• Have rigid bodies

Camplyobacter jejuni

• Spirochetes are helical in nature

• Bodies are FLEXIBLE– Difference between

spirilla and spirochetes

Treponema pallidum

Bacterial Shapes

• Bacterial shape is determined by heredity– If the parent cells are of a certain shape their progeny

will be of similar shape• Most bacteria are monomorphic, or maintain a

single shape– Although the environment may play a role in

changing a bacterium’s shape– When a bacterium can change its shape it is referred

to as pleomorphic (Corynebacterium)– Leads to difficulty in identifying bacteria

Critical Thinking

• The name of a bacterium is often associated with its shape. Draw these organisms based on their names– Streptococcus pneumoniae– Staphlycoccus aureus– Bacillus anthracis– Vibrio cholera

Functional Anatomy of Prokaryotic and Eukaryotic Cells

External Cell Wall Structures

• The cell wall is a crucial component of the bacteria

• There are several structures that line the outside of the cell wall that have a variety of functions

Glycocalyx

• Glycocalyx—substance that is secreted on the surface of the cell walls by prokaryotes– Glycocalyx (sugar coat) is a sticky, gelatinous

polymer that is composed of a polysaccharide, polypeptide, or both

– If the glycocalyx is organized and firmly attached to the cell wall, it is referred to as a capsule

– Inversely, if the glycocalyx is unorganized and loosely attached it is called a slime layer

Glycocalyx

Capsule

Slime Layer

Glycocalyx

• The glycocalyx serves a variety of functions– Helps anchor bacteria to specific surfaces– Used as a source of nutrients for the bacterial cells– Prevents phagocytosis (ingestion by immune cells) thus

aiding in their pathogenicity – Forms biofilms that not only shield the bacteria from

external stimuli (salt concentrations or antibiotics) but also aid in the communication between the bacteria• Up to 80% of all human infections are linked to biofilms

(NIH)• Biofilm Impact on Health

Flagella

• Some prokaryotes have flagella which are long filamentous appendages that aid in bacterial motility (ability of a bacteria to move by itself)

• H antigen—flagellar proteins. Aids in distinguishing serovars of bacteria– Serovars—variations within a species

• The type of flagella can be categorized based on its arrangement on the bacteria

Flagellar Arrangement

• Atrichous—bacteria that lacks flagella

• Peritrichous—distributed all around the cell

• Monotrichous—single flagellum at one end

• Lophotrichous—several flagella at one end

• Amphitrichous—flagella at both ends

Flagella Movement

• The movement of the flagella propels the bacteria towards a favorable environment or away from an unfavorable environment

• This movement is referred to as taxis– Chemotaxis—movement towards a chemical– Phototaxis—movement towards light

Other Bacterial Projections

• Axial Filaments—bundles of filaments that arise at the end of the cell beneath the outer sheath. Spiral around the entire cell

• Bacteria with axial filaments move in a corkscrew shape motion

Other Bacterial Projections

• Fimbriae—small hair-like appendages that adhere to each other and surfaces. Involved in forming biofilms

• Placement is either at the ends of the bacteria or around the entire bacteria

Other Bacterial Projections

• Pili—appendages that are involved in motility and DNA transfer

• The transfer of DNA from one bacteria to another is termed conjugation

• The sex pili (F+) binds to the recipient bacteria and injects genetic material

Sex Pilus (F+)

Bacterial Cell Wall

• The cell wall is a complex, semi-rigid structure that surrounds the underlying, fragile plasma membrane

• Major function of the cell wall is to prevent bacteria cells from rupturing due to osmotic pressure– They also help the bacteria to maintain its shape.– Point of anchor for the external appendages

Cell Wall Composition

• The main component of the bacterial cell wall is a macromolecule called peptidoglycan

• Peptidoglycan consists of repeating a disaccharide attached to polypeptides to form a lattice around the cell

Cell Wall Composition

• The cell wall, depending on its composition, exhibits different characteristics– Because of this, bacteria can be placed in two different

groups: Gram-Positive bacteria and Gram-Negative bacteria

– The major difference between Gram-Positive and Gram-Negative bacteria is the peptidoglycan composition • G(-) have an outer membrane, inner membrane, and contain

periplasm• G(+) lack outer membrane and do not contain periplasmic space

Gram Positive vs. Gram Negative

LPS is another important component of G (-)LPS stimulates the Immune System

PlasmaMembrane

Gram Stain

• Hans Christian Gram, a German scientist, developed a method to better visualize bacteria under a microscope

• The Gram stain contains two dyes that bind to peptidoglycan

Principle of Gram Stain

Mordant

Gram (+) vs. Gram (-)

• Due to the extensive network of peptidoglycan in the cell wall of Gram Positive bacteria, Gram Positive bacteria are less susceptible to disruption (via physical or chemical) but are more sensitive to treatment

Atypical Cell Walls

• There are bacteria that possess very little cell wall components

• Mycobacterium spp. comprises this group• These bacteria are said to have Acid-Fast

Walls which contain a high percentage of mycolic acid– Mycolic acid prevents the dyes of the Gram stain

from binding to the peptidoglycan. Must perform acid-fast stain to identify these bacteria

Acid-Fast Stain

Carbol Fuchsin binds to components of the cytoplasm

Plasma Membrane

• The plasma membrane is a thin structure located inside of the cell wall.– Prokaryotic plasma membranes contain phospholipids

and proteins– Eukaryotic plasma membranes also contains

carbohydrates and sterols• Sterols make the membrane more rigid and stronger• Proteins bound to carbohydrates are called glycoproteins• Lipids (fat) bound to carbohydrates are glycolipids

• Phospholipid molecules are arranged in two layers—lipid bilayer

Phospholipid Bilayer

Phospholipid Properties

• Phospholipids are polar molecules– Phospholipid head has a

charge and is hydrophilic—water loving

– Phospholipid tail has no charge and is hydrophobic—water fearing

Plasma Membrane Functions

• Major role of the plasma membrane is to serve as a selective barrier through which materials enter and exit the cell– Selective Permeability—the ability to allow certain

molecules in and out of the cell• Also functions to break down nutrients and

results in the production of energy– Break down of ATP (energy carrier of all living

organisms) by membrane proteins generate energy

Clinical Relevance of Plasma Membranes

• Because the membrane is vital to the bacterial cell, scientists develop compounds to disrupt the membrane in an effort to kill bacteria– Alcohols and ammonium compounds damage the

membrane therefore are used as disinfectants– Antibiotics can cause the membrane to leak out

the inner components of the bacterial cell resulting in death