Bacteria Structure and Morphology

Structure of Bacteria

• Bacteria are single-celled, microorganisms with a simple body design, lacking a nucleus and membrane-bound organelles, classifying them as prokaryotic organisms.
• They can live in different media (in vitro) and are ubiquitous in nature, belonging to the prokaryotic group where organisms lack certain organelles and a true nucleus.

Layers of Bacterial Structure

• The bacterial structure is organized into four layers:
  • Extramural layer (slime layer and capsule)
  • Surface appendages (flagella and pili)
  • Cell envelope (cell wall and cytoplasmic membrane)
  • Cytoplasmic inclusion (nucleoid, ribosomes, mesosomes, volatile granules, and plasmid)

Cytoplasmic Inclusion

• Nucleoid: a region where the genetic material is located
• Ribosomes: composed of a small (30S) subunit and a large (50S) subunit, playing a central role in protein synthesis
• Mesosomes: folded invaginations in the plasma membrane, produced by chemical fixation techniques
• Volatile granules: concentrated deposits of certain substances presented in the cytoplasm of certain bacteria
• Plasmid: a small, self-replicating circular DNA molecule

Functions of the Bacterial Structure

• Capsule:
  • Enhances bacterial virulence by inhibiting phagocytosis
  • Acts as a protective covering against antibacterial substances
  • Is specific for bacteria and can be used for identification and typing
  • Has diagnostic importance
• Flagella:
  • Provides motility (locomotion)
  • Shows positive chemotaxis towards higher oxygen concentrations
  • Helps in invasiveness by penetrating epithelial barriers and viscous mucous membranes
  • Increases the rate of nutrient uptake due to continuous movement
• Pili (fimbriae):
  • Helps in the adherence of symbiotic bacteria to host cells
  • Facilitates attachment of donor and recipient cells in bacterial conjugation (sex pili)
  • Acts as a colonization antigen
  • Causes haemagglutination in many species

Cell Wall of Bacteria

• A rough and rigid structure, approximately 20-25 nm in thickness
• Composed of peptidoglycan (mucopeptide), a polymer consisting of sugars and amino acids
• Functions:
  • Maintains shape of the bacteria
  • Protects against osmotic damage
  • Participates in cell division
  • Possesses target sites for antibiotics, lysozymes, and bacteriophages
  • Carries bacterial antigens

Endospore

• A dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Firmicutes
• Produced internally by bacteria
• Composed of an exosporium, spore coat, and core
• The spore coat acts as a sieve, excluding large toxic molecules and containing enzymes involved in germination

Binary Fission

• A type of asexual reproduction where the body divides into two new bodies
• Occurs in bacteria, where genetic material is duplicated and then divided into two parts
• Each new organism receives one copy of DNA
• Bacteria can undergo binary fission every 20 minutes under ideal conditions
• The number of bacteria can be calculated using the formula: Number of bacteria = 2^n, where n is the number of rounds of division

Flagella and Motility

• Flagella are hair-like helical structures that emerge from the cell wall, composed of flagellin protein, and known as H-antigen.
• Types of flagella arrangements include:
• Monotrichous (e.g., Vibrio cholerae)
• Amphitrichous (e.g., Spirillum serpens)
• Lophotrichous (e.g., Bartonella bacilliformis)
• Peritrichous (e.g., Escherichia coli)
• Functions of flagella include:
• Organ of locomotion
• Positive chemotaxis towards higher oxygen concentration
• Helps in invasiveness by penetrating through epithelial barriers and viscous mucous membranes
• Increases rate of uptake of nutrient solvents due to continuous movement

Fimbriae or Pili

• Fimbriae are thinner and shorter filamentous appendages, numerous in gram-negative bacteria.
• Functions of fimbriae include:
• Adherence of symbiotic bacteria to host cells
• Attachment of donor and recipient cells in bacterial conjugation (sex pili)
• Virulence by acting as colonization antigens
• Adherence to red blood cells, causing haemagglutination

Bacterial Cell Wall

• Cell wall is a rough and rigid structure, 20-25 nm in thickness, weighing about 20-25% of dry cell weight.
• Peptidoglycan or murein is a polymer composed of sugars and amino acids, forming a mesh-like layer outside the plasma membrane.
• Chemical structure of bacterial cell wall has four layers:
• Slime layer and capsule
• Surface appendages (flagella and fimbriae)
• Cell envelope (cytoplasmic membrane and cytoplasm)
• Functions of cell wall include:
• Maintaining shape of bacteria
• Protection against osmotic damage
• Role in cell division
• Target site for antibiotics, lysozymes, and bacteriophages
• Carries bacterial antigens

Endospore

• An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Firmicutes.
• Characteristics of endospores include:
• Produced internally by bacteria
• Sometimes surrounded by a thin exosporium
• Spore coat acts like a sieve, excluding large toxic molecules and containing enzymes involved in germination

Binary Fission

• Binary fission is a type of asexual reproduction, where the body separates into two new bodies.
• Process of binary fission involves:
• Duplication of genetic material (DNA)
• Division into two parts (cytokinesis)
• Each new organism receives one copy of DNA
• Bacteria can carry out binary fission once every 20 minutes, and the number of bacteria can be calculated using the formula: Number of bacteria = 2n, where n is the number of rounds of division.

Structure and Morphology of Bacteria

• Bacteria are single-celled microorganisms with a simple body design.
• Characteristics of bacteria include:
• No nucleus and other membrane-bound organelles (prokaryotic organisms)
• Structure organized into four layers:
• Extramural layer (slime layer and capsule)
• Surface appendages (flagella and pili)
• Cell envelope (cell wall and cytoplasmic membrane)
• Cytoplasmic inclusions (nucleoid, ribosomes, mesosomes, volatile granules, and plasmid)