Microbial Diversity & Bacterial Morphology

Microbial Diversity & Bacterial Morphology

• The subject matter is microbial diversity and bacterial morphology.
• The presenter is Dr. Asmaa M. El-Nasser, an associate professor of medical microbiology and immunology at Al Azhar University.
• The course is offered at the Faculty of Medicine for Girls at Al Azhar University.
• The institution is Badr University in Cairo.

Learning Outcomes

• The learning outcomes include:
  • Introduction to microbiology
  • Eukaryotic and prokaryotic cells
  • Classification and nomenclature of bacteria
  • Morphology of bacteria
  • Bacterial structure

What is the Scope of Microbiology?

• Microbiology is the science dealing with microorganisms.
• Microorganisms are too small to be seen without a microscope.
• Microorganisms play vital roles in ecosystems, impacting ecological balance.
• They contribute to animal and human health.
• They are involved in producing food, chemicals, biofuels, medicines, and other items.
• Some microorganisms cause diseases.

Introduction to Microbiology

• Microbiology examines microorganisms.
• Microorganisms are important in various ecological roles, maintaining ecosystems.
• Microorganisms, depending on their specific function, affect animal and human health.
• Microorganisms can aid in food and chemical production.
• Microorganisms can be pathogenic (disease-causing).

Taxonomy

• Taxonomy is the science of classifying, describing, identifying, and naming living organisms.
• Microorganisms are classified based on similar morphological, physiological, and genetic characteristics.
• The classification system comprises kingdom, family, genus, and species.

Classification of Micro-organisms

• Living organisms are divided into prokaryotes (without a nucleus) and eukaryotes (with a nucleus).
• Prokaryotes include bacteria, and eukaryotes include fungi, protists, plants, and animals.

Biological Division of Cells

• Prokaryotic cells lack a nucleus and membrane-bound organelles.
• Eukaryotic cells possess a nucleus and membrane-bound organelles.
• Examples of features include nucleoid, cell wall (in some eukaryotes), capsule (in some prokaryotes), flagellum, ribosomes, chloroplasts (in some eukaryotes), Golgi apparatus, and mitochondria (in some eukaryotes).

Biological division of Microorganism

• Eukaryotic cells have a nuclear membrane.
• Prokaryotic cells lack a nuclear membrane
• Eukaryotic cells have multiple chromosomes.
• Prokaryotic cells have a single chromosome.
• Eukaryotic cells have 80S ribosomes.
• Prokaryotic cells have 70S ribosomes.
• Eukaryotes reproduce sexually and asexually.
• Prokaryotes mainly reproduce asexually (binary fission).

Fungi

• Fungi are eukaryotes with rigid cell walls containing complex carbohydrates.
• They lack the ability to produce their food and are heterotrophic.
• Fungi cell walls have ergosterol in their cytoplasmic membrane.
• Fungi possess mitochondria.
• Fungi reproduce by spore formation.
• Fungi thrive in damp environments.
• Most fungi are saprophytic.
• Some are beneficial.
• Some are pathogens causing diseases (allergies, producing mycotoxins) involved in decomposition.

Viruses

• Viruses are acellular microorganisms (not true cells).
• Viruses are small, smaller than other infectious agents.
• Their size varies from 10-300 nm.
• Viruses are inert outside a host organism.
• Inside a host cell, viruses can commandeer the cellular machinery for replication and infect other hosts.
• Viruses possess genetic material (DNA or RNA) and proteins, but never both.
• Viruses lack metabolic activity outside of a host cell.
• Viruses lack ribosomes and protein synthesis apparatuses.
• Viruses replicate only inside living cells (obligatory intracellular parasites).

Bacteria

• Classification involves grouping bacteria based on similarities and relationships like order, family, genus, and species.
• Bacteria are scientifically named using binomial nomenclature (genus and species).
• Example: Staphylococcus aureus.

Morphology of Bacteria

• Bacterial morphology includes size, shape, staining properties, arrangement, motility, sporulation, capsule, and flagellae.
• Bacterial size is typically expressed in micrometers (µm).

Relative Sizes of Microorganisms

• Various microorganisms are displayed on a logarithmic scale of relative sizes.
• Microorganisms range from an atom to a large protozoan or pollen particle.

Shapes of Bacteria

• Bacteria exhibit various shapes, including cocci (spherical), bacilli (rod-shaped), and spirilla (spiral).
• Different arrangements of bacteria are observed, including pairs, chains, and clusters.

Bacterial Structure

• Bacterial structure includes capsule, cell wall, plasma membrane, cytoplasm, ribosomes, plasmids, pili, and flagella.
• The nucleoid contains circular DNA.

Bacterial Cell Wall

• Bacterial cell walls are composed of peptidoglycans.
• Gram-positive bacteria have thick peptidoglycan layers.
• Gram-negative bacteria have thin peptidoglycan layers with an outer membrane containing lipopolysaccharide (LPS).
• LPS is immunogenic and binds to specific receptors.

Function of the Bacterial Cell Wall

• Maintains bacterial shape.
• Supports cytoplasmic membrane against osmotic pressure.
• Involved in Gram reaction and cell division. Involved in bacteriophage attachment.
• Has antigenic determinants.
• Endotoxin activity in Gram-negative bacteria .
• A primary site of antibiotic attack.

Cell Wall of Gram-Positive vs Gram-Negative Bacteria

• Gram-positive bacteria have a thick peptidoglycan layer.
• Gram-negative bacteria have a thin peptidoglycan layer with an outer membrane.

Staining Properties of Bacteria

• Gram staining differentiates bacteria based on cell wall structure.
• Gram-positive bacteria retain the crystal violet stain.
• Gram-negative bacteria do not.

Bacteria with Deficient Cell Walls

• Mycoplasma: Pleomorphic, penicillin-resistant
• L-forms: Environmental conditions. Protoplasts and spheroplasts: Result from hypertonic environments or antibiotics
• Protoplast: Lack cell wall
• Spheroplast: Partial cell wall loss.

Cytoplasmic Membranes

• Cytoplasmic membranes are phospholipid bilayers with embedded proteins.
• They regulate permeability to molecules.
• Active transport moves ions and nutrients for osmotic balance.
• The membrane is the site of respiration (ATP synthesis).
• The membrane excretes hydrolytic enzymes and produces enzymes and lipid carriers for cell wall synthesis.
• The membrane plays a role in DNA replication.

Intracytoplasmic Structures

• Intracytoplasmic structures include the bacterial chromosome (double-stranded DNA).
• Ribosomes (30S + 50S subunits) are involved in protein synthesis (70S)
• Plasmids are circular extrachromosomal DNA.
• Intracytoplasmic inclusions store food reserves.

Bacterial Structure - Generalized Structure of Bacterium

• The general structure of a bacterium includes chromosomal DNA, ribosomes, cytoplasm, plasmids, pili, flagella, capsule, and cell wall.

Surface Structures of the Bacterial Cell

• Capsule: Polysaccharide layer (excluding poly-D-glutamate in some species) protecting against phagocytosis.
• Glycocalyx: Polysaccharide layer outside the cell aiding in adherence to surfaces (e.g. Streptococcus mutans and dental caries).

Flagellum

• A bacterial organ of motility, formed from flagellin protein.
• Comprises a filament, hook, and basal body.
• Anchored to the cytoplasmic membrane.

Pili (Fimbriae)

• Hair-like projections (shorter and thinner than flagella).
• Composed of pilin protein. Primarily found in gram-negative bacteria.
• Ordinary pili facilitate bacterial adherence.
• Sex pili facilitate DNA transfer during conjugation.

Bacterial Spores

• Bacterial spores are a resistant structure developed for survival.
• Spores are formed from a bacterium in response to unfavorable conditions (like starvation).
• Spores preserve bacterial DNA and protective keratin-like outer layer.
• Resistant to dehydration, heat, chemicals, and freezing.
• Autoclaving is a spore-killing technique.
• Examples include Bacillus and Clostridium spp.

Test Your Self

• Questions are provided regarding the components found in the cell wall of gram-negative bacteria and features associated with bacterial structures and function.

References

• The references are listed for the content used in the study.

This quiz explores microbial diversity and the morphology of bacteria, focusing on both eukaryotic and prokaryotic cells. It includes classification, nomenclature, and the structural features of bacteria. Essential for students of medical microbiology, this content enhances understanding of microorganisms and their significance in health and ecosystem balance.