Ch 1 & 3

Antonie van Leeuwenhoek (1632-1723)

first person to observe & describe microorganism accurately

Louis Pasteur (1822-1895)

credited with numerous innovations that advanced the fields of microbiology and immunology

Robert Koch (1843-1910)

identified the specific microbes that cause anthrax, cholera, & tuberculosis

taxonomy

the classification, description, identification, & naming of living organisms

• classification is the practice of organizing organisms into different groups based on their shared characteristics

role of genetics in modern taxonomy

in the 1970s, Carl Woese discovered a living record of the evolution of organisms

3 domains of Woese & Fox’s phylogenetic tree

• archaea

  • contains all prokaryotes

• bacteria

  • contains all prokaryotes

• eukarya

  • contains all eukaryotes

what was Woese & Fox’s phylogenetic tree based on?

the gene that encodes rRNA

• based on similarities and differences observed in the gene sequences coding for small subunit rRNA of different organisms

  • noted that archaebacteria were significantly different from other bacteria & eukaryotes in terms of their small subunit rRNA gene sequences

theory of spontaneous generation

notion that life can arise from nonliving matter

• theory began to be disproved around the 17th century

Francesco Redi’s experiment

one of the first to refute idea that maggots spontaneously generate on meat left out in the open air

• conclusion: maggots only form when flies were allowed to lay eggs in the meat, & that maggots were offspring of flies, not the product of spontaneous generation

disproving the spontaneous generation theory

Louis Pasteur

• unique swan-neck feature of flasks allowed air to enter, but prevented the entry of bacterial & fungal spores

• broth in flask was boiled to sterilize it

  • when cooled, it remained free of contamination

  • when neck was broken off, broth in flask became contaminated

origins of cell theory: Robert Hooke

the first to describe cells based upon his microscopic observations of cork

• observed that thin sections of cork resembled “honey-comb” or “small boxes/bladders of air”

1852

first time that the idea that all cells originate from other cells was published

endosymbiotic theory

mitochondria and chloroplasts arose as a result of prokaryotic cells, establishing a symbiotic relationship with a eukaryotic host

when were chloroplasts identified

1880s

• role in starch formation during photosynthesis

  • observed they divided independent of the nucleus

1905

idea that chloroplasts may have originated from ancestral photosynthetic bacteria

• much later, genetic evidence due to the advent off DNA sequencing supported the endosymbiotic theory

additional evidence to support the endosymbiotic theory

mitochondrial DNA & chloroplast DNA

• are highly rated to their bacterial counterparts (sequence & chromosome structure)

• are reduced compared to nuclear DNA because many of the genes have moved from the organelles into the host cell’s nucleus

the germ theory of disease

• Ignaz Semmelweis —proponent of the importance of handwashing to prevent transfer of disease between patients & physicians

• Joseph Lister — developed procedure for the proper care of surgical wounds & sterilization of surgical equipment

• Robert Koch — establish protocol to determine the cause of infectious disease

parts of a prokaryotic cell

contain:

• cell membrane

• chromosomal DNA that is concentrating in a nucleoid

  • NO NUCLEUS

• ribosomes

• cell wall

• may possess: flagella, pili, fimbriae, capsules

prokaryotic cell shapes: coccus

round

prokaryotic cell shapes: bacillus

rod

prokaryotic cell shapes: vibrio

curved rod

prokaryotic cell shapes: coccobacillus

short rod

prokaryotic cell shapes: spirillum

spiral

prokaryotic cell shapes: spirochete

long, loose, helical spiral

prokaryotic cell arrangements: coccus

single coccus

prokaryotic cell arrangements: diplococcus

pair of 2 cocci

prokaryotic cell arrangements: tetrad

grouping of 4 cells arranged in a square

prokaryotic cell arrangements: streptococcus

chain of cocci

prokaryotic cell arrangements: staphylococcus

cluster of cocci

prokaryotic cell arrangements: bacillus

single rod

prokaryotic cell arrangements: streptobacillus

chain of rods

what is the bacterial cell envelope composed of?

• plasma membrane

• cell wall

• layers outside the cell wall (capsule)

plasma membrane: “fluid mosaic” model

• phospholipid bilayer with a variety of embedded proteins that perform various functions for the cell

• glycoproteins & glycolipids present

how does stuff get across the plasma membrane barrier?

• passive diffusion (small, moderately hydrophobic molecules)

OR

most things need transport by one of the following mechanisms

• facilitated diffusion

• primary & secondary active transport

• group translocation

simple diffusion

down a concentration gradient directly across the phospholipid bilayer

facilitated diffusion

uses transmembrane transporter protein

• either a carrier or channel/pore

• specifically transport cargo

• only transport along concentration gradient (no energy required)

• magnitude of gradient drives diffusion

• more common in eukaryotes

active transport

• ATP-binding cassette (ABC) transporter

• ATP fuels transport “uphill” — against concentration gradient

components that make up the cell envelope

• plasma membrane

• cell wall

• capsule

plasma membrane

• cellular boundary

• selectively permeability

• site of key metabolic processes (ex. respiration, photosynthesis)

cell wall

• provides rigidity

• counteracts osmotic pressure

capsule

stuff outside the cell — adhesion, immune evasion

fimbriae/pili

• movement

• attachment

• DNA transfer

flagella

movement

nucleoid

contains chromosome (DNA), some ribosomes, proteins

cytoplasm

contains nucloid, cytosol, cytosolic proteins, ribosomes, inclusions (gas, nutrients, etc)

peptidoglycan

composed of polymers alternating NAM and NAG subunits — cross linked by peptide bridges linking NAM subunits from various glycan chains

• provides the cell wall with tensile strength in 2 dimensions

• subunits are made inside of the bacterial cell, then exported & assembled in layers giving the cell its shape

NAG

N-acetylglucosamine

NAM

N-acetylmuramic acid

gram-negative bacteria

• thin peptidoglycan layer

• thick periplasmic space

• porous outer membrane

• outer lipopolysaccharide layer

• tetra peptide chains extending from each NAM unit are directly cross-linked

gram-positive bacteria

• thick peptidoglycan layer

• thin periplasmic space

• negatively charged teichoic acid

• NO outer membrane

• tetrapeptide chains extending from each NAM unit are linked by pentaglycine cross-bridges

lipopolysaccharide: three components

• lipid A (fatty acid)

  • anchors it to outer membrane

• core polysaccharide

  • negatively charged

• O antigen

  • O side chain

lipopolysaccharide functions

• structural

  • major constituent of outer membrane

• barrier

  • core polysaccharide, O antigen form a later that physically protects the cell

• attachment

  • helps pathogenic bacteria bind host cells

• pathogenicity

  • O antigen may be recognized by immune system, or may help evade it

• toxicity

  • Lipid A is a potent stimulant of the immune system

    • termed endotoxin — responsible for septic shock

gram stain process

1. crystal violet — primary stain added to specimen smear

2. iodine — mordant makes dye less soluble so it adheres to cell walls

3. alcohol — decolorized washes away stain from gram-negative cell walls

4. safranin — counterstain allows dye adherence to gram-negative cells

*a differential staining technique that uses a primary stain & a secondary counterstain to distinguish between gram+ and gram- bacteria

gram+ stain process

• when alcohol used, cells remain purple/blue

• when safranin used, cells remain purple/blue

gram- stain process

• when alcohol used, cells are colorless

• when safranin use, cells appear pink or red

why do we see differential staining?

because of difference in the cell wall

how do we see differential staining?

• crystal violet & iodine complex is trapped by the thick, dense peptidoglycan layer in gram+ cells

• during decolorization, alcohol removes the gram- outer membrane & washes away most crystal violet from the more porous, thinner peptidoglycan later in gram- cells

changes in osmotic pressure & cells that lack cell walls

osmotic pressure can lead to crenation in hypertonic environments or cell lysis in hypotonic environments

isotonic solution

solution that has the same solute conc. as another solution

• no net movement of water particles

• overall conc. on both sides of the cell membrane remains constant

hypertonic solution

solution that has a higher solute conc. than another solution

• water particles will move out of the cell — causes crenation

hypotonic solution

solution that has a lower solute conc. than another solution

• water particles will move into the cell — causes cell to expand & eventually lyse

cell wall function

provides some protection against changes in osmotic pressure, allowing it to maintain its shape longer

cell wall function in isotonic solution

no net movement of water particles; cell membrane attached to cell wall

cell wall function in hypertonic solution

water particles move out of cell; cell membrane shrinks & detaches from cell wall (plasmolysis)

cell wall function in hypotonic solution

water particles move into cell; cell wall counteracts osmotic pressure to prevent swelling & lysis

evidence of protective nature of the cell wall

if cell wall is damaged, bacteria are susceptible to osmotic lysis

• lysozyme breaks the bond between NAG and NAM

lysozyme

disrupts peptidoglycan layer

• found in saliva & tears

penicillin

inhibits the formation of peptide bridges in the peptidoglycan

• penicillin is most efficient when cells are dividing (ex. when an infection is spreading)

• disrupts the peptidoglycan layer

mycoplasma

has no cell wall

• mycoplasma pneumonia causes “walking pneumonia”

  • penicillin has no effect on it

components outside of the cell wall

• glycocalyx

  • capsule

  • slime layer

• S layer

glycocalyx

polysaccharide layer that extends beyond the cell wall

• capsule

  • organized layer attached to cell wall

  • helps evade phagocytosis

  • prevents desiccation

• slime layer (less organized)

  • diffuse, loosely attached layer

  • aids mobility

S layer

• rigid, tile-like layer of protein or glycoprotein

• attached to outer membrane in gram- bacteria

• attached to cell wall in gram+ bacteria

• protects from environment, host, predators

• promotes adhesion

• self-assembling later

nucleoid

condensed area of DNA found within prokaryotic cells

• doesn’t readily stain & appears lighters in color when viewed with a transmission electron microscope due to its density

extrachromosomal DNA

additional pieces of DNA

• 2 types of DNA, both circular

• bacterium

  • bacterial chromosome

  • plasmid

prokaryotic ribosomes

complete ribosome: 70S

• composed of protein and rRNA

  • small subunit: 30 S

  • large subunit: 50S

prokaryotic inclusion bodies

• lipid droplets poly-B-hydroxybutyratn

  • carbon storage

• volutin granules

  • inorganic phosphorous

• sulfer granules

• gas vacuoles

  • increase buoyancy

• magnetosomes

  • magnetic iron oxide or iron sulfide surrounded by a lipid later

  • orient aquatic bacteria to earth’s magnetic field

sporulation

process of forming spores

• begins when nutrients become depleted or environmental condition become otherwise unfavorable

formation of bacterial endospores

1. DNA replicates

2. membranes form around the DNA

3. forespore forms additional membranes

4. protective cortex forms around the spore

5. protein coat forms around the cortex

6. spore is released

bacterial appendages: pili

• protection

• attachment to surface

• horizontal gene transfer

• cell movement

pilli & fimbriae

• thin, bristle-like fibers

• 100s per cell

• involved in attachment to surfaces

sex pilli

• longer, thicker, less numerous (1-10 per cell)

• required for conjugation/gene transfer

type IV pili

• responsible for twitching mobility

• pili attach to surface & retract, pulling along bacteria

flagella arrangement: monotrichous

single

flagella arrangement: amphitrichous

flagella at both ends

flagella arrangement: lophotrichous

group of flagella at one end

flagella arrangement: peritrichous

surrounded by flagella

flagella movement: tumbling

clockwise rotation of flagella

• flagella NOT bundled

flagella movement: running

counter-clockwise rotation of flagella

• peritrichous flagella → flagella bundles

flagella movement: without chemical gradient

rotation cycles between counterclockwise (run) and clockwise (tumble) with no overall direction al movement

flagella movement: chemical gradient

length of runs are extended, length of tumbles decreases

• results in chemotaxis

chemotaxis

overall directional movement toward the higher concentration of the attractant