Bacterial Cytology & Physiology

Bacterial TaxonomyParts of a bacterial cell

Specialized structures in bacteria

Taxonomical Ladder• Kingdom Monera• Phylum• Class• Order• Family• Genus• Specie - Type &

Strain

• Kingdom Plantae• Kingdom Animalia• Kingdom Protista• Kingdom Fungi• Kingdom Monera

New Classification:

• Carl Woese – based on cellular organization (Domain above Kingdom)– Bacteria – cell wall w/ peptidoglycan– Archaea – cell walls, if present lack peptidoglycan– Eukarya – Protista, Fungus, Plants, Animals

Characters used to classify Bacteria

• Morphology- cell shapes & struc.

• Biochemistry & Physiology - condi-tions & process

• Serology - FAT & slide agglutination

• Phage typing

• Percentage of DNA base pairs

• DNA sequence• DNA hybridization• sequence of amino

acids in proteins• protein profiles• sequence of rRNA

Prokaryote VS. Eucaryote

Procaryotes• appendages: pili, flagella,

axial filaments in spirochetes

• Usually glycocalyx is present

• outer membrane present in gram (-)

• cell wall in all eubacteria

• presence of plasma membrane

• undiff. cytoplasm• non-membrane

bound organelles• 1 circular DNA• binary fission• 1 to few u

Eucaryotes

• different flagella from procaryotes

• very few has glycocalyx• no outer memb.• no cell wall• plasma membrane-

phospholipid bilayer

• cytoskeleton & cytoplasmic streaming

• membrane bound organelles

• paired chromosome• mitosis & meiosis• no endospores• > than 10 u

Bacterial Cytology

• Structures external to the cell wall• The cell Wall• Structures internal to the cell wall

• General Structures• Specialized structures

External to the cell wall:• Glycocalyx – sugar coat– Viscous, gelatinous polymer on the external of the

cell, composed of polysaccharide, polypeptide or both

• Capsule – If Glycocalyx is organized and firmly attached to the cell wall, capsule is formed– Determines virulence of the cell– Negative Staining

• Slime layer - If the substance is unorganized & loosely attached to cell wall.

• EPS ( Extracellular polysaccharide ) –– Glycocalyx made of sugar- enables the bacteria to

attach to various surfaces in the natural environment in order to survive.

• Flagella/Flagellum ( whip )– Long filamentous appendages that propel bacteria

Arrangements of flagella:• Monotrichous – single polar• Amphitrichous – tuft at each end• Lophotricous – 2 or more at one end• Peritrichous – entire cell • Atricous – no flagella

• Flagellar rotation depend on cells continuous generation of energy

• Flagellar motion – run, swim, tumble, swarm

• Axial Filaments– Unique in spirochetes, also called endoflagella,

which are bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell.

– Propulsion causes spiral motion or corkscrew movement

Fimbriae & Pili:

• Fimbriae/Fimbria – can occur at the poles of the cell or evenly

distributed all over– Functions for cell attachment/ in the absence

colonization cannot happen so no disease ensues

• Pili/Pilus– Longer than fimbriae, only 1 – 2 per cell– Preparation for DNA transfer – sex pili

The Cell Wall

• Complex, semi rigid structure responsible for the shape of the cell

• Composed of peptidoglycan (also known as murein) made up of NAG ( N-acetylglucosamine) and NAM (N-acetyl muramic acid).– Structures on the disaccharide portion is

repeating.

Gram + & - cell walls:

• Most gram (+) bacteria have many layers of peptidoglycan in the cell wall forming a thick rigid structure while gram (-) only contain 1 thin layer of peptidoglycan.

• Gram (+) contains teichoic acid consisting primarily of an alcohol & phosphate– Lipoteichoic Acid – Wall teichoic Acid

• Gram (-) cell walls are susceptible to mechanical breakage because they contain only small amount of peptidoglycan

Internal to the Cell Wall:

• Plasma Membrane/Bacterial Membrane• Cytoplasm• The Nucleus• Ribosomes• Inclusions– Metachromatic granules– Magnetosomes

• Endospores

Bacterial Membrane

• Functions:– osmosis &

permeability– cell division– primer for

biosynthesis– site of Ag

determinant

• Demonstrated by:– Plasmolysis– Stain - Victoria

Blue– Isolation - Diff.

centrifuge– Ultrathin sections

Bacterial shapes & arrangements

• Coccus -– single, diplo, tetrad,

sarcinae, strepto , staphylo.

• Bacillus -– single, diplo, strepto

• Spirillus–wavy, corkscrew,

comma-shaped– Spiral bacteria may

have 1 or more twists

Additional Shapes

• Star shaped cells – Genus Stella• Rectangular flat cells – halophilic Genus Haloarcula• Triangular shaped cells

Basis of Shape:

• Shape of the bacterium is primarily dependent on heredity.

• Generally bacteria are monomorphic, maintain 1 single shape

• Due to environmental conditions, some bacteria tend to become pleomorphic which makes identification difficult. I.e. Rhizobium & Corynebacterium

Trivia:

• Is coccobacilli a coccus or a bacilli? Maybe both or neither of the two?

• Why do bacillus not have tetrads or clusters?