Microbiology and Microorganisms Flashcards
What is Microbiology?
- The study of organisms too small to be seen with the naked eye. (Bacteria, Viruses, Single celled eukaryotes).
- Some microorganisms are visible to the naked eye. (Fungi, Algae)
- Some microbes are multicellular. (Myxobacteria, slime molds)
What is Microbiology? (2)
Microbiology is defined by techniques
- culture media for isolation and growth of organisms in pure culture
- Biochemical to study cell components
- Molecular and genetic techniques
Why is Microbiology Important?
- Microbes are the oldest form of life
- Largest mass of living material on Earth
- Carry out major processes for biogeochemical cycles
- Can live in places unsuitable for other organisms
- Other life forms require microbes to survive
Structure and Activities of Microbial Cells
All cells have the following in common:
- Cytoplasmic membrane (Barrier that separates the inside of the cell from the outside environment)
- Cytoplasm (Aqueous mixture of macromolecules, ions, and proteins)
- Ribosomes (Site of protein synthesis)
Structure and Activities of Microbial Cells (part 2 )
- Genetic material
(All cells store their genetic information as DNA, The information is divided into functional units called genes) - Genome
(A cell’s full complement of genes) - Chromosome
(A genetic element carrying genes essential to cellular function) - Plasmid
(A piece of DNA that carries non-essential genes (ex. Genes for antibiotic resistance, genes for nitrogen fixation, etc)
Structural Categorization of Microbes (Eukaryotes)
- Membrane bound nucleus
- Membrane bound organelles
- Complex internal organization
- Division by mitosis and meiosis
Major Groups of Eukaryotic Microbes
Protists - unicellular or multi-cellular without differentiation into tissues
Fungi - Unicellular (yeast), filamentous (molds), or multi-cellular (mushrooms)
Protists
Protozoa - animal-like microorganisms
Algae - photosynthetic plant-like microorganisms
Slime molds and water molds - filamentous
Structural Categorization of Microbes (Prokaryotes)
- No membrane bound nucleus or organelles
- Generally smaller (approx 1 m diameter
- Simple internal structure
-Divide by binary fission - Most are unicellular
Major Groups of Prokaryotic Microbes
- Bacteria (eubacteria)
- Archaea (archaebacteria)
Bacteria (eubacteria)
- Genetically diverse
- Extremely diverse metabolic styles
- Includes both pathogens and non-pathogens
Archaea (archaebacteria)
- Genetically and biochemically distinct from bacteria
- Also have diverse metabolism
- Never pathogenic
- Most famous for living in extreme environments
Structural Categorization of Microbes (Viruses)
- Acellular infectious particles
- Extremely small
- Obligate intracellular parasites
- Lack indenpendent metabolism
- No ribosomes
- No ribosomal RNA,
- Cannot be classified with other microbes
Evolution and Diversity of Microbial Cells
- First anaerobic life appeared between 3.8 and 3.9 billion years ago
- Photosynthetic bacteria oxygenated the Earth about 2 billion years ago. (Allowed the evolution of modern eukaryotic microorganisms)
- First plants and animals appeared about 0.5 billion years ago
Classifying Organisms Based on Evolutionary Relationships
- Comparing small subunit (SSU) rRNA genes
- Prokaryotes - 70S ribosomes (16S SSU rRNA)
- Eukaryotes - 80S ribosomes (18S SSU rRNA)
- rRNA genes change slowly over time
- Examines genetic differences rather than morphological differences
Basic steps involved in sequencing rRNA genes
- Step 1: DNA is collected from a pure culture
- Step 2: The SSU rRNA gene is amplified using the polymerase chain
reaction (PCR)
- PCR – a technique used to synthesize many identical copies of a short sequence
of DNA - Step 3: The gene is sequenced
- Step 4: Sequence is aligned with sequences from other organisms
- Number of differences is used to calculate evolutionary distance
Phylogenetic tree
A graphic representation of the evolutionary distance
between organisms.
Molecular Phylogeny and the Tree of Life
- Phylogenetic tree based on 16S or 18S ribosomal DNA sequences
- All organisms can be grouped into 3 distinct domains of life: Bacteria,
Archaea and Eukarya - Microorganisms are far more genetically diverse than plants and
animal
what is a species?
- Phylogenetic species concept:
- “A group of strains that share certain diagnostic traits, are genetically cohesive and have a unique recent common ancestor”
What should species of Bacteria and Archaea have?
- Most (but not all) characteristics in common
- Greater than 97% sequence similarity in the 16S rRNA gene
- High degree of genome similarity
- DNA-DNA hybridization
- In the very near future: whole genome sequences?
Classification and Nomenclature
- Microbiologists use Hierarchical classification
- Groups of organisms are placed in successively larger groups
- In practice: Species, genus and phylum are commonly used
Binomial species names Rules
- Names are latinized
- Italicized or underlined
- Genus capitalized, epithet is not
- Genus name may be abbreviated the second time it’s used: E. coli
- Trivial names can be used, but do not follow these rules
Genus (Capitalized) Specific epithet (not capitalized) Strains (symbols at the end)
The Discovery of Microorganisms (Robert Hooke)
1635 - 1703
- the first to describe microbes.
- Used a compound microscope - uses 2 lenses to magnify the image.
- allowed magnification up to 30x
- Used it to observe:
- cells in cork
- Bread mold filaments - 1st microbe
- Beginning of cell theory - all living things are composed of cells
The Discovery of Microorganisms (Antoni van Leeuwenhoek)
1632 - 1723
- built microscopes that magnified specimen by 50-300x
- Observed single celled microorganisms - called them “animalcules”
- First discovery of bacteria
Louis Pasteur (1822 - 1895)
- Studied wine and beer production.
- Yeasts convert sugar to alcohol in the absence of oxygen
- Fermentation - “La vie sans air”
- bacteria can sour wine by converting alcohols to acid
- Developed a method of gentle heating to kill unwanted bacteria - Pasteurization
Louis Pasteur (1822 - 1895) Continued
- Prepared meat infusions inside of long swan-necked flasks.
- Boiled the infusion to sterilize it.
- As long as the flask remains upright, dust and microbes cannot enter, and the infusion remains sterile
- Led to the development of methods for controlling the growth of microorganisms (aseptic technique)
Koch, Infectious Disease, and Pure Cultures
- Realized that solid media provided a simple way to obtain pure cultures
- Broth medium solidified with agar
- Polysaccharide derived from marine algae
- Melts at ~ 97°C and polymerizes (solidifies) at ~ 43°C
- Cannot be degraded by most microorganisms
- Typical Petri plate = nutrient broth medium + 1.5% agar
Robert Koch (1843 - 1910)
Studied anthrax – responsible for epidemics in livestock
- He isolated bacteria from the carcass of a diseased animal – Bacillus anthracis
- Injected healthy animals with the bacterium
- Animals became ill with anthrax
- Re-isolated B. anthracis from the test subjects and showed that it was identical
- Established a set of criteria for relating a specific microbe to a disease
- Koch’s postulates
How to create Pure Culture?
The streak plate technique
- One edge of a plate is inoculated with a
concentrated sample of bacteria
- Sample is diluted by streaking it across the
surface of the plate
- To deposit individual cells on the plate (separate
from other cells)
- Plate is incubated
- Individual cells grow to form colonies
Colony?
A mass of cells that (ideally) arose from one single cell
- Can be used to create a pure culture
The Spread Plate and Pour Plate Techniques
- Sample is diluted before plating
- Diluted sample can be spread over the surface of the plate with a sterile spreader
- Separate cells grow into colonies on the surface of the plate
- Or can be mixed with molten agar (~ 45°C)
- Colonies form embedded inside the plate
The Standard Plate Count
Spread and pour plates allow you to calculate the concentration of bacteria in a population (Bacterial titre)
- titre = # colonies / (volume) (dilution)
- titre is expressed in cfu/ml
- cfu = colony forming unit
Countable Plates
We normally count plates with between 30 – 300 colonies
- < 30 – not statistically significant
- > 300 – colonies grow into each other – inaccurate counts
- When we have more than one countable plate…
- Calculate titre from each and take the average.
