Bacterial Cell Structure, Genetics and Classification

• Bacterial Cell Structure, Physiology, Metabolism, and Genetics are important topics.

Classification

• Microorganisms are organized into specific groups or taxa based on similar morphologic, physiologic, and genetic traits.
• The classification hierarchy includes:
• Kingdom: Composed of similar divisions.
• Division: Composed of similar classes.
• Class: Composed of similar orders.
• Order: Composed of similar families.
• Family: Composed of similar genera.
• Genus: Composed of similar species.
• Species: The basic group, a collection of bacterial stains with common physiologic and genetic features.
• Orderly classification and grouping of organisms into taxa is based on:
• Genotype: Genetic makeup
• Phenotype: Observable characteristics
• Bacterial strains collection shares physiologic and genetic features, can be further divided into subspecies based on biotype, serotype, and genotype.

Nomenclature

• A binomial system assigns a genus and species name to every organism.
• Genus is always capitalized.
• Species is never capitalized.
• Both are italicized or underlined.
• Common names are informal designations, for example:
• Gonococcus is Neisseria gonorrhoea
• Pneumococcus is Streptococcus pneumoniae
• Tubercle bacilli is Mycobacterium tuberculosis
• Typhoid bacilli is Salmonella typhosa
• Friedlander's bacillus is Klebsiella pneumoniae

Identification

• The process by which microorganisms' key features are delineated, to assign a genus and species name.
• Includes genotyping and phenotyping

Three Distinct Groups of Microorganisms

• Prokaryotes: Lack a true nucleus.
• Eukaryotes: Have a true nucleus.
• Archaeobacteria: Cell walls never contain peptidoglycan, possess an S-layer, lack a nucleus and organelles, but have gas vesicles, thrive in extreme conditions (methanogens, halophiles, thermophiles).

Overview (Eukaryote vs Prokaryote)

• Nucleus: Eukaryotes have a membrane-bound nucleus, while prokaryotes lack a nuclear membrane.
• Chromosomal DNA: Eukaryotes have DNA in the nucleus, prokaryotes in the nucleoid.
• Organelles: Eukaryotes have organelles, prokaryotes do not.
• Cell Wall: Eukaryotes have polysaccharide cell walls, prokaryotes have peptidoglycan.
• Pili and Fimbriae: Absent in eukaryotes, present in prokaryotes.

Prokaryotes

• "Pro" means before, and "karyon" refers to the nucleus.
• They lack a true nucleus and organelles.
• The cell envelope, the outermost structure composed of the outer membrane, cell wall, periplasm, and plasma membrane.
• The cell wall is also known as the murein layer or peptidoglycan and maintains the shape of the cell.
• Cell wall is composed of NAM (N-acetylmuramic acid) and NAG (N-acetylglucosamine).

Cell Wall Types

• Gram-positive bacteria have a peptidoglycan layer, glycan chains of N-acetyl-D-glucosamine and N-acetyl-D-muramic acid, and teichoic acid.
• Gram-negative bacteria cell walls consist of proteins, phospholipids, and LPS (lipopolysaccharides).
• Major constituents are Lipid A, core polysaccharide, and antigenic O.
• Acid-fast cell walls resemble Gram-positive structures, contain hydroxymethoxy acid or mycolic acid.
• Cell wall-less bacteria are Mycobacteria and Ureaplasm and contain sterols.

Gram Positive vs Gram Negative Characteristics

• Gram-positive bacteria have a thick, multilayered peptidoglycan layer.
• Gram-negative bacteria have a thin, single-layered peptidoglycan layer.
• Teichoic acids are present in many Gram-positive bacteria but absent in Gram-negative bacteria.
• The periplasmic space is absent in Gram-positive bacteria, present in Gram-negative bacteria.
• An outer membrane is absent in Gram-positive bacteria, but present in Gram-negative bacteria.
• LPS content is virtually none in Gram-positive bacteria, high in Gram-negative bacteria.
• Lipid and Lipoprotein is low in Gram-positive bacteria and High in Gram-negative bacteria due to outer membrane.

Plasma Membrane

• Is the deepest layer of the cell envelope
• Site of respiration and photosynthesis.
• Plasme membrane functions as mitochondria, golgi complexes, and lysosomes in eukaryotic cells
• Includes ribosomes, nucleoid, plasmid, and inclusion bodies, endospores and spores.

Prokaryotic Cell Structures

• Nuclear Area (nucleoid): Single circular chromosome attached to a mesosome.
• Plasmids: Small, circular, dsDNA molecules that provide antibiotic resistance.
• Ribosomes: Site of protein synthesis, ribosomes consists of RNA and protein.
• Inclusions: Metachromatic granules represent reserves of polyphosphates used for ATP synthesis.
• Polysaccharide granules consist of glycogen and starch granules.
• Spores: Highly refractile resting cells that are highly durable and dehydrated, with thick walls.
• Sporogenesis is the process of spore formation.
• Terminal spore: C. tetani
• Sub-terminal spore: C. botulinum
• Central spore: B. anthracis

Cell Appendages

• Capsule: Known as the slime layer (loosely attached).
• Glycocalyx: Composed of capsule and slime layer, aids in the attachment of bacteria to solid objects.
• Flagellum: The organ of locomotion and facilitates gliding motility in cyanobacteria, myxobacteria, and cytophagas.
• Atrichous: Lacking flagella.
• Monotrichous: Single flagellum. ✓ Amphitrichous: Flagella at both ends.
• Lophotrichous: Tuft of flagella at one pole.
• Peritrichous: Flagella distributed over the entire cell.
• Pili/Fimbriae: Hairlike, proteinaceous structures extending from the cell membrane to the external environment, aiding bacterial attachment to surfaces.
• Common pili is for attachment
• Sex pili facilitates genetic transfer or conjugation
• Axial filaments (endoflagella): Bundles of fibrils anchored at one end of spirochete, spiraling around the cell; rotation propels the spirochete in a spiral motion.

Eukaryotes

• Have a true nucleus.
• Cells of higher plants and animals, fungi, and protozoa.
• Contain membrane-bound organelles (ER, Golgi body, mitochondria, and nucleus).

Explore bacterial cell structure, physiology, metabolism, and genetics. Learn about the classification of microorganisms into specific groups based on traits. Discover the nomenclature system that assigns a genus and species name to every organism.