Download structure Taxonomy

Bacterial Cell Structure
Taxonomy & Classification
By
Prof. Dr. Zainalabideen A Abdulla,
DTM&H., MRCPI, Ph.D., FRCPath. (U.K.)
LEARNING OBJECTIVES
You should be able to:
1. Study the structure of both eukaryotic and
prokaryotic cells.
2. Learn the structural differences between
prokaryotic and eukaryotic cells.
3. Cite the important functions of the studied cellular
structures.
4. Study the basis of Taxonomy, and microbial
classifications.
5. Study and read about the Five-kingdom and
Three-Domain Systems of Classification.
6. Expand knowledge on rRNA subunits & genes.
7. Answer correctly all the 10 MCQ of your book.
Cell Structure
1. Cell wall
2. Cell membrane
3. Cytoplasm
4. Endoplasmic reticulum (rough , smooth)
5. Ribosomes
6. Golgi Complex
7. Lysosomes and Peroxisomes
8. Mitochondria
9. Plastids
10. Cytoskeleton
11. Nucleus
12. Flagella and cilia
Cell wall
1. Present in most bacteria vs absent in most
eukaryotes (see the exceptions)
2. Algae: Contain cellulose (as plants), eukaryote
Fungi : Contain chitin, eukaryote
Archaea: No peptidoglycan, in between
Mycoplasma: No cell wall, prokayotic
3. Function: Provides rigidity, strength, and protection;
defines shape of bacteria
4. - Gram positive bacteria: Thick peptidoglycan +
teichoic acid + lipoteichoic acid
- Gram negative bacteria: Thinner peptidoglycan +
Lipidmacromolecules (outer membrane)
Cell membrane
1. Functions:
A. Selective permeability
B. Active transport functions
2. Composed of proteins + phospholipids
3. Similar structure and function in eukaryotic and
prokaryotic
4. Mesosomes: Foldings in cell membrane of
bacteria for respiration (vs eukaryotic in mitochondria)
Ribosomes: Human (40S, 60S, 80S)
Bacteria (30S, 50S, 70S)
- This is important in understanding the selective action
of some antimicrobials acting on bacteria
- Sites for protein synthesis
Endoplasmic reticulum
A. Rough ER: Ribosomes attached, protein
B. Smooth ER: No ribosomes attached, lipid+CHO
Cytoskeleton (microtubules, microfilaments “actin”,
intermediate filaments):
Some present in bacteria and all present in eukaryotes.
Microtubules are absent in bacteria. Support shape,
cellular division, transport, signaling, and others.
Nucleus
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“Command center”
Nucleoplasm
Chromosome
Nuclear membrane
Genes
RNA
Genotype
Nucleolus
Chromosome
1. A single circular and folded chromosome in bacteria
(vs linear in eukaryotes; human 23 pairs)
2. Number of genes in bacteria 575-55,000 (vs
human 20,000-25,000)
3. Plasmids: Small, circular dsDNA, extrachromosomal, contain genes, single or multiple, same
or different copies (vs no plasmids in eukaryotes)
4. Plastids: Cytoplasmic organelles in some
eukaryotes (e.g., algae, plants); for photosynthesis
Flagella (sing., flagellum)
- Thread-like
- Protein appendages (3-4 Flagellin twisted threads)
- For motility (movement); Bacteria never has cilia
- Help classification and identification:
- Peritrichous: Around (entire)
- Lophotrichous: Tuft (many) uni-polar (one end)
- Monotrichous: Single polar
- Amphitrichous: Bi-Polar (both ends)
- Complex structure when present eukaryotes, e.g.
spermatozoa (vs simple structure in bacteria)
Pili (Fimbriae): sing. pilus/fimbria
- Hair-like on gram negative bacteria mostly
- Polymerized protein (pilin), rigid
- Organelles NOT for motility
- Arise from the cytoplasm, pass through plasma
membrane, cell wall and capsule (if present)
- Two types of pili:
A. For adherence (attachment)
B. Sex pilus for transfer of genetic material
(plasmid) between bacteria (a donor with a single pilus
to a recipient cell; this process is called conjugation)
- Pathogenic factor
Glycocalyx (slime layers and capsule)
1. Slime layer (e.g. Pseudomonas):
- Not highly organized glycocalyx
- Not firmly attached to cell wall (easily detached)
- Pathogenic factor: Assists in sliding (gliding) of
bacteria, and protects against antimicrobials
2. Capsule(e.g., Haemophilus influenza type-b (Hib):
- Highly organized glycocalyx (polysaccharides +
lipids + proteins)
- Firmly attached to cell wall
- Pathogenic factor (also: resists phagocytosis)
- Chemical composition helps identification of m.o.
Identification of capsule
1. Negative stain:
- Bacteria and background: Stained
- Capsule: Unstained halo
2. Antibodies reaction with capsular antigens
(e.g., capsule swelling test; antigenic serotyping)
3. Cultural characteristics:
- Capsulated: Smooth, mucoid, and
glistening colonies (S-colonies)
- Nonencapsulated: Dry and rough colonies
(R-colonies)
Spores (Endospores)
- Spore-forming bacteria: e.g. Bacillus, Clostridium
- Thick-walled, for survival (not reproduction)
- Formation of spores = Sporulation
- Contain a copy of the chromosome + cytoplasm
surrounded by several thick protein coats
- Resistant to heat, cold, drying, chemicals, boiling,
and disinfectants
- One spore produces one vegetative bacterium by
germination in moisture, and with nutrients
- Spore staining: Terminal, Sub-terminal, Central;
bulging (swelling) or NOT
Reproduction of eukaryotic and
prokaryotic cells
* Mitosis/meiosis vs binary fission
Binary fission: One bacterium (parent cell) splits in half
after its chromosome has duplicated (DNA replication)
to become two daughter cells.
Generation time: The time of the binary fission to
occur. It varies (10 min. to 24 hr) according to:
- Bacterial species (e.g. E coli 20 min.)
- Growth conditions (pH, temperature, nutrients)
Eukaryotic vs Prokaryotic cells
eu = true, karyo = nucleus
1. True nucleus: DNA enclosed by nuclear
membrane (vs absent membrane)
2. Eukaryotic size X10 of prokaryotic cells
3. Absence of cell wall in animals (vs present)
4. Presence of complex membrane structures/
organelle (ER, Golgi, mitochondria, plastids);
(vs absent; contain only cytoplasmic particles as
ribosomes/ polyribosomes and stored granules)
5. Ribosomes 80, 60, 40S (vs 70, 50,30S prokaryotes)
6. Mesosomes in bacteria vs mitochondria in eukaryote
Second Lecture
Bacterial Taxonomy
and Classification
Taxonomy: The science of classification of living
organisms. It consists of THREE areas:
1. Classification
2. Nomenclature
3. Identification
Classification: Arrangement into taxonomic groups
(taxa): Kingdoms or domains, divisions or phyla,
classes, orders, families, genera and species.
Nomenclature: Giving international names to taxa
Identification: Known or unidentified species? ( to
speciate). The process is called phenotyping.
Microbial Classification
- Binomial system of nomenclature (18th century):
First: Genus (pl. genera), first letter capital,
underline or italicize, e.g., Shigella, or Shigella;
genus named also by a single letter ( Shigella = S)
Second: Specific epithet; first letter small,
underline or italicize (e.g. Shigella dysenteriae, or
Shigella dysenteriae; if a single species: “sp.”,
more than one species: “spp.” e.g. Shigella spp.
Other information about nomenclature
- First name + second name = species
- Sub-specific epithet = ssp., e.g., H. influenza ssp.
aegyptius
- Nickname: e.g. Staphylococcus = Staph.
- Bacterial names are named for the disease, e.g. Vibrio cholerae = cholera
Classifications of living organisms
1. FIVE Kingdoms (see names)
2. Three-Domain System- based on rRNA
differences (by Carl Woese, 1970s):
A. TWO domains prokaryotes
(Archaea and Bacteria)
B. ONE domain Eucarya or Eukarya
Ribosomal RNA (rRNA)
- rRNA sequencing
- rRNA has 2 subunits:
1. Small subunit rRNS (SSUrRNA), ONE RNA:
a. Bacteria : 16S; coding gene 1500 nucleotides
(16S rDNA sequence)*
b. Eukaryotes: 18S; coding gene 2000 nucleotides
(18S rDNA sequences)*
* Similarities & differences based on these sequences
2. Large subunit rRNA (LSUrRNA)
NOTE: ANSWER ALL THE
10 MCQ QUESTIONS IN
YOUR BOOK (BURTON’S
MICROBIOLOGY for the
HEALTH SCIENCES, Tenth
Edition)
- Good Luck -
Note:
Microscopy will be
added to this lecture