•The most exterior components of bacterial cells are the #CAPSULE and SLIME layers. These layers are usually composed of sugar polymers that are excreted by the cell under certain conditions. The term capsule usually applies to a DEFINED layer with a distinct outer edge, whereas a slime layer describes an ILL DEFINED concentration of polymeric material which just slowly gets less and less the further away from the cell. Although capsule production is a genetic characteristic, its production is STRONGLY influenced by the nutrient environment. For example, in a nutritionally poor medium a bacterium may produce little or no capsule/slime, but in the presence of a high concentration of sugar the capsule may be HUMONGOUS. The capsule has several roles.

•It protects the cell from DRYING. •It serves as an extra source of NUTRITION. in times of need. •It helps the cells STICK or attach to things because of its sticky (adhesive) nature andas such is part of biofilms. •By sticking the cells to solid surfaces capsules/slime layers prevent them from washing away and provide a protective environment for the cells.•It PROTECTS the cell from destruction by white blood cells. •It may be TOXIC or inhibitory to a host's defense system and so aid in the disease process.

Capsule and Slime Layer

1. Flagella

• curved filament made of flagellin protein: travels through hollow tube, assembles at external end.

1.polar flagellation: flagella attached at one (monopolar) or both (bipolar) ends. Ex: Pseudomonas aeruginosa 2.peritrichous flagellation: flagella attached at many sites around cell periphery. Ex: E. coli

Electron micrograph of pili

1.fimbriae & pili •short, rigid protein rods, similar in size to flagella, but not involved in motility. •function in adhesion, formation of pellicles at liquid surfaces. Function not entirely clear. Pili sometimes involved in pathogenic adhesion (e.g. gonorrhea) •Sex pili in conjugation.

EndosporesProduced by gram positive bacteria(Bacillus, Closteridia, Sporosarcinia)and Coxiella bunetii.SporulationOccurs at the end of the log phase Germination- Activation - Initiation – Outgrowth.Properties1- Core2- Spore wall3-Cortex4- Coat 5- Exosporium

                                               

                      

Centrally (left), terminally (center), and subterminally (right) located endospores.

Pictures from Brock Biology of Microorganisms (lecture textbook)

Endospore Pi cures

SPORE FORMING BACTERIA

                                             

                             

Spores from woodland pond. Image taken using

a phase contrast

Some G+ bacteria form resistant structures called SPORES under adverse conditions. Spores are the most RESISTANT life form known. They are able to survive boiling in water at 100oC for long periods. Spores are resistant to UV-light, to drying and many harmful chemicals. We know spores can live for 100s of yr. and recently spores several million yr. old have been revived from insects trapped in amber. Some disease organisms like anthrax and botulism form spores that reside in the soil. The size, shape, and location of a spore in the cell are all identifying genetic

characteristics.  

Bacteria reproduce by binary fission in which one bacterial cell divides into two cells.

Following elongation of the cell, a transverse cell membrane is formed and, subsequently, a new cell wall. The new transverse membrane and wall grow inward from the outer layers, a process in which the septal mesosomes are intimately involved. The nucleoid, which have doubled in number preceding the division, are distributed equally to the two daughter cells.

Size, and Morphology of Bacteria

Size: 1 u. Some bacteria such as Chlamydia and Rickettsia are o.25 u in size.

Morphology and Arrangement:

- Cocci: clusters, diploes, chains, tetrads .

- Bacilli

-Spiral

-Filamentous

-Coccobacilli

Bacterial arrangement and Morphology

StainingDye Properties

Dyes used to stain bacterial cells are organic compounds, which have affinity for specific cellular components. The many types of dyes have two features in common: 1) they have chromophore groups, groups with conjugated double bonds that give the dye its color and 2) they can bind with cells by ionic, covalent, or hydrophobic bonding. Dyes also contain an auxochrome group, which in itself does not produce color but gives the dye its acidic or basic properties. Since the surfaces of bacterial cells are negatively charged such as nucleic acids and acidic polysaccharides, basic dyes are most often used in bacteriology. Acidic dyes, because of their negative charge, bind to positively charged cell structures such as proteins. Commonly used basic dyes are methylene blue, crystal violet, safranin, basic fuchsin, and malachite green. Some common acidic dyes are eosin, . rose bengal, and acid fuchsin.

Basic stains have colored cation and cololess anion(stain bacteria).Acidic stains have cololess cation and colored anion(negative stain stains the background).Gram stain

Acid Fast StainDifferential - measures the resistance of a cell to decolorization by acids

•acid fastness attributed to high lipid content of the cell Important genera are Mycobacterium and actinomycetes

•Mycobacterium tuberculosis - causative agent of TB •Mycobacterium leprae - causative agent of leprosy

Staining mechanism is similar to Gram Stain•Carbol fuscin will not easily rinse away in positive cells •Acid alcohol is used as decolorizer •Counterstain is methylene blue

:Structural Stain •based on differences in a structure compared to rest of cell

•can selectively stain one part of a bacterial cell •take advantage of special property of cell structure •ex. capsules are resistant to staining

Examples of structural stains1.Endospore Stain 2.Capsule Stain 3.Flagellar Stain

An acid fast a long filamentous organism in stain demonstrates the center that is dark red. This is typical for Nocardia

Fig.1: Structure of an Acid-Fast Cell Wall

                                                                                                                                                                                               

                         In addition to peptidoglycan, the acid-fast cell wall of Mycobacterium contains a large amount of glycolipids

such as mycolic acid, arabinogalactan-lipid comlex, and lipoarabinomannan.

Acid-fast stained tissue

Nomenclature of BacteriaBacteria are named according to different criteria:

1 -Morphology – Staphylococcus aureus.

2 -Discoverer – Brucella abortus.

3 -Disease - Vibrio cholera.

4 -Site – Staphylococcus epidermidis.

5 -Growth requirment – Haemophilus influenzae.

The first letter of the genus name is capitalized, while the first letter of the species name is not capitalized. Both the genus and the species names are underlined or written in italics. Staphylococcus aureus.

Classification of BacteriaAccording to the character of the cell wall, bacteria are classified into

1 -Gram positive Eubacteria that have a cell wall.

2 -Gram negative Eubacteria that have a cell wall.

3 -Eubacteria lacking a cell wall. Mycoplasma pneumoniae.

4- Archaebacteria.