Title: A Brief Journey to the Microbial World
1Chapter 2
- A Brief Journey to the Microbial World
2Microscopy
- Microscopes are essential for microbiological
studies. - A microscope is required for the visualization of
microorganisms - Light microscopy is used to observe less detailed
features of intact cell under low magnification
than advanced microscopy (i.e. electron and
laser) - Various types of light microscopes exist,
including bright-field, dark-field, phase
contrast, and fluorescence microscopes.
3Magnification vs. Resolution
- Magnification
- Increase in apparent size
- Two sets of lenses form the image
- Objective lens and ocular lens
- Total magnification is a product of the
magnification of the two sets of lenses - Objective magnification X ocular magnification
- Resolution clarity
- Ability to see 2 nearby objects as distinct
objects - All compound light microscopes optimize image
resolution by using lenses with high
light-gathering characteristics (numerical
aperture). - The limit of resolution for a light microscope is
about 0.2 ?m.
4Microscopy
Figure 2.1b
5Simple and/or differential cell staining are used
to increase contrast in bright-field microscopy.
- Improving contrast results in a better final
image - Staining is an easy way to improve contrast
- Dyes are organic compounds that have different
affinities for specific cellular materials - Examples of common stains are methylene blue,
safranin, and crystal violet
6Staining Cells for Microscopic Observation
Figure 2.3
7Staining Cells for Microscopic Observation
Figure 2.3
8Staining Cells for Microscopic Observation
Figure 2.3
9Differential StainsThe Gram stain
- The Gram stain is widely used in microbiology
- On the basis of the Gram stain, bacteria can be
divided into two major groups gram-positive and
gram-negative - The Gram stain renders different kinds of cells
different colors - Gram-positive bacteria appear purple and
gram-negative bacteria appear pink to red after
staining
10The Gram Stain Steps in the Gram-stain Procedure
Figure 2.4a
11The Gram Stain Steps in the Gram-stain Procedure
Figure 2.4a
12The Gram Stain
Figure 2.4b and c
13Phase Contrast Microscopy
- Invented in 1936 by Frits Zernike
- May be used to visualize live samples and avoid
distortion from cell stains - Can see some internal features
- Resulting image is dark cells on a light
background
Figure 2.5
14Electron Microscopy
- Electron microscopes have far greater resolving
power than light microscopes, with limits of
resolution of about 0.2 nm. - Electron microscopes use electrons instead of
photons to image cells and structures - Two types
- Transmission electron microscopy (TEM)
- For observing internal cell structure down to the
molecular level - Scanning electron microscopy (SEM)
- For three-dimensional imaging and examining
surfaces
15Electron Micrographs
Figure 2.10a
16Electron Micrographs
Figure 2.10bc
17All microbial cells share certain basic
structures in common
- Cytoplasm
- Cytoplasmic membrane
- Allows passage of needed molecules (nutrients,
water, etc.) and barrier to harmful chemicals - Ribosomes
- Site of protein synthesis
- Cell wall (usually)
- Cell shape
18Prokaryote vs Eukaryote
- Two structural types of cells are recognized
- Prokaryotic
- Archaea and bacteria
- Eukaryotic plants, algae, fungi, protists, and
animals (variety) - Comparing prokaryotic and eukaryotic cells
- Prokaryote comes from the Greek words for
prenucleus. - Eukaryote comes from the Greek words for true
nucleus.
19Prokaryote Eukaryote
- Simpler internal structure
- Absence of nucleus
- One circular chromosome, not in a membrane
- No histones
- No membrane enclosed organelles
- Peptidoglycan cell walls
- Binary fission for cell division
- Smaller
- Contain nucleus
- Paired chromosomes, in nuclear membrane
- Histones
- Membrane enclosed organelles
- Simple (polysaccharide) cell walls
- Cell division by mitosis or meiosis
- Larger
20Structure of Prokaryotic vs. Eukaryotic cell
Figure 2.11a
Figure 2.11b
21Viruses
- Non cellular
- Obligate intracellular parasites
- They must live inside another cell to survive
- Have only one type of nucleic acid
- DNA or RNA (never both)
- Single or Double stranded
- Protein coat (no plasma membrane)
- Few to no enzymes
- Takes enzymes and use host cell metabolic
machinery - No metabolic activity
- They require a host cell to exhibit the
characteristics of life. - Virus diversity
- Different viruses have different hosts
- Only some viruses cause disease
22Size
- Typical prokaryote ?1 - 5 ?m long
- Typical Eukaryotic cell ?10 - 100 ?m
- Typical virus ? 50 - 80 nm
23Phylogeny
- The study of the evolutionary relationionships of
distinct organisms - Although species of Bacteria and Archaea share a
prokaryotic cell structure, they differ
dramatically in their evolutionary history. - Molecular based
- Compare sequences from common molecules from
organisms of interest - Relationships can be deduced by comparing genetic
information (nucleic acid or amino acid
sequences) in the different specimens - Carl Woese (1970s)
- rRNA comparison
- Ribosomal RNA (rRNA) are excellent molecules for
determining phylogeny - Can visualize relationships on a phylogenetic
tree
24Ribosomal RNA (rRNA) Gene Sequencing and Phylogeny
Figure 2.16
25Phylogeny
- Comparative ribosomal RNA sequencing has defined
the three domains of life - Bacteria (prokaryotic)
- Archaea (prokaryotic)
- Eukarya (eukaryotic)
- Common ancestor - over 3.8 billion years ago
- Bacteria and archaea are prokaryotes but archaea
are more closely related to eukaryotes - Eukaryotic microorganisms were the ancestors of
multicellular organisms - Mitochondria and chloroplasts also contain their
own genomes (circular, like prokaryotes) and
ribosomes - These organelles are ancestors of specific
lineages of Bacteria - Mitochondria and chloroplasts took up residence
in Eukarya eons ago - This arrangement is known as endosymbiosis
26The Tree of Life Defined by rRNA Sequencing
Figure 2.17
272.8 - Physiological Diversity of Microorganisms
- The phylogenetic diversity we see in microbial
cells is the product of almost 4 billion years of
evolution - Microorganisms also have a tremendous amount of
metabolic diversity - Microorganisms have exploited every conceivable
means of making a living consistent with the
laws of chemistry and physics
28Physiological Diversity
- All cells need carbon and energy sources.
- Different species use different strategies
- Chemoorganotrophs obtain their energy from the
oxidation of organic compounds. - Chemolithotrophs obtain their energy from the
oxidation of inorganic compounds. - Phototrophs contain pigments that allow them to
use light as an energy source. - Oxygenic versus anoxygenic photosynthesis
29Metabolic Options for Conserving Energy
Figure 2.18
30Autotrophs vs. Heterotrophs
- All cells require carbon as a major nutrient
- Autotrophs
- Use carbon dioxide as their carbon source
- Use sunlight for energy
- Primary producers
- Most phototrophs and lithotrophs are autotrophs
- Heterotrophs
- Use organic carbon as their carbon source
- Use products of autotrophs or the autotrophs
themselves for energy - All organotrophs and SOME lithotrophs are
heterotrophs
31Extremophiles
- Thrive under environmental conditions in which
higher organisms cannot survive. - Prokaryotes thrive in habitats that are too cold,
too hot, too salty, too basic for any eukaryote - Many prokaryotes are extremophiles
- No environment is devoid of prokaryotic life
- Salt concentrations up to 30 for some
- halophiles
- pH 0-12
- Acidophiles and alkaliphiles
- Temps below 0 ºC to above 100 ºC
- Psychrophiles and hyperthermophiles
- High pressure
- Barophiles
32Classes and Examples of Extremophiles