Microbiology: Principles and Explorations

Sixth Edition

Chapter 4:Characteristics of Prokaryotic and

Eukaryotic Cells

Copyright © 2005 by John Wiley & Sons, Inc.

Jacquelyn G. Black

• ribosome in bacteria 70S consist of 2 subunits;

• small subunit 30S

• Large subunit 50S

• Certain antibiotics (its target is protein synthesis), such as streptomycin and erythromycin, bind specifically to 70S ribosomes and disrupt bacterial protein synthesis.

Nuclear Region (Nucleoid)• Note: in every living being there must be

genetic material (DNA) ,as we know in bacteria there is no nucleus instead there is nuclear region or nucleoid.

• This centrally located nuclear region consists mainly of DNA, but also contains RNA and protein

• DNA: Usually one large, circular chromosome• Vibrio cholerae: Two chromosomes, one large

and one small• Plasmids: Extrachromosomal pieces of

smaller, circular DNA

• Chromosomes contain important genetic material for the m.o that give it the shape,

gram +ve, gram –ve, live in the presence of oxygen or not.Plasmid contain genetic material not essential for the growth , usually contain

Genetic material as resistance of the m.o to disease.Plasmid moves from bacteria to another, and it emphasis that the resistance

can transfer from the resistant bacteria to the susceptible bacteria by method called conjugation using sex pili(extenal part help in transrering the genetic material from bacteria to onother)

Note: this transfer is copy and past not cut and past so that every bacteria will have plasmid .

The conjugation process happened in certain m.o, called (F+) which have sex pili .

Internal Membrane Systems(exceptional)

• Folding membrane system as in mitochonderia. • Photosynthetic bacteria and cyanobacteria contain

internal membrane systems• Referred to as chromatophores (Fig. 4.10)• Derived from the cell membrane and contain the

photosynthetic pigments

• Nitrifying bacteria (exist in the roots of the plants) also have internal membranes

• Nitrifying bacteria, soil organismsthat convert nitrogen compounds into forms usable bygreen plants, also have internal membranes which containthe enzymes used in nitrogen fixation.

Figure 4.10 Internal membrane systems. TEM of thecyanobacterium Synechocystis showing chromatophores. The cell’s outer regions are filled with photosynthetic membranes. The darkspots between the membranes are granules in which carbohydrates produced by photosynthesis are stored. Note: As human store in liver (glycogen) and in adipose tissue, bacteria have granules.

Inclusions (inclusion bodies)

• Within the bacterial cytoplasm are a variety of small bodies (seen by electron microscope):

1. Granules: Not membrane bound and contain densely compacted substances (glycogen or polyphosphate)

2. Vesicles (حويصالت) : Specialized membrane-enclosed structures that contain gas or poly-B-hydroxybutyrate (lipid)

Endospores

• REMEMBER: Most resistance form of life, produced by gram +ve bacteria, befor staining its glassy, we use Scaeffer-fulton method for staining, they take the color of malachite green, using heating process to increase the permeability of spores to dye.

• Note: exospore exist in fungi; spores (ابواغ) move from place to another to do fungal infections (for reproduction).

Endospores

• A specialized resting structure found in bacteria such as Bacillus sp. and Clostridium sp. (ex; Clostridium tetani )

• Helps the bacterial cell survive when conditions become unfavorable

• Highly resistant to heat, drying, acids, bases, certain disinfectants and radiation

• Not all bacteria can produce endospores.• Note: prions are protein that cause mad cow and

prions are very resistance. So we suffer from difficulties when we are dealing with bacteria in dormant state with resistance endosopres.

Endospores

• BEFOR THE BACTERIA PRODUCE ENDOSPORES :

• Its called vegetative cells (vegetative form), it’s the normal state of the cell at favorable conditions.

• Vegetative cell able to make doubling, reproduction (growth).• AFTER THE BACTERIA PRODUCE ENDOSPORES: • Its called dormant cell (dormant form), so the cell can’t

dividing can’t make reproduction.• The cell enter this state as PROTECTING state against

unfavorable conditions; chemicals as anti microbial agent, heat, drying, acids, bases, absence of water, certain disinfectants and radiation.

• Endospores >>> bacteria >>> protection• Exospores >>> fungi >>> reproduction

*The part of bacteria which make vesicle ( يتحوصل الذي it’s the “essential part of genetic (الجزء

material” it gather (concentrated) in specific region (called the core) and then surround with layers (cortex, a spore coat, and in some species a delicately thin layer called the exosporium), the rest of the cell may remains or not, but its already dead.

*endosopres appear as glassy (glossy) material because there is contrast between it and the light. its glassy as crystal because it has little content of water.

When the cell found a favorable conditions again it will come back to the vegetative form with whole bacteria (this will discussed later ).

Description of endosope *Genetic material within the core with low water content, with high conc. of

dipicolinic acid (calcium dipicolinate), surrounded by cortex which is specialized layer of peptidoglycan, then coat which is protein, and then (in some bacteria) followed by exosporium.

*the reason of high resistance:- Since there is low content of water in the core and high conc. of calcium

dipicolinat, this make the m.o resist the denaturation by heat (minimum denaturation for protein –structural or functional- by heat) so that make stabilization to protein.

- Peptydoglycan also protect the bacteria from bursting by hydro static pressure.

- The cortex protein (as outer membrane) protect m.o from chemicals such as anti biotic, biocide…

REMEMBER THAT :Gram –ve bacteria is more resistant than gram +ve one because of the

presence of OUTER MEMBRAN and PERIPLASMIC SPACE.

-Scaeffer-fulton stain. -Bacillus bacteria.-the endospore may present in the middle or at the margin according to the type of bacteria, that help in classification.-some times the endospore appear alone because the rest of the bacteria lysis.

Core

Cortex

Spore coat

Endospore

Endocytosis and Exocytosis

• Eukaryotic cells move substances by forming membrane-enclosed vesicles

1. Endocytosis: Form by invagination (poking in) and surrounding substances from outside the cell

2. Exocytosis: Vesicles inside the cell fuse with the plasma membrane and extrude contents from the cell

EXTERNAL STRUCTURE

• many bacteria have structuresthat extend beyond or surround the cell wall.

*Flagella (for motility or locomotion, It is made of subunit protein called flagellin) and pili (for conjugation and attachment, made of subunit protein called pilin) extend from the cell membrane through the cell wall and beyond it. (the origin of the basal body -of flagella and pilli- is the cell membrane)

* Capsules and slime layers and Glycocalyx surround the cell wall.

flagella

• bacteria are motile (capable of movement) or immotile.

• Motility achieve by flagella • We usually see flagella in bacillus; Cocci

don’t have flagella or rarely have flagella.• A bacterium can have one flagellum or twoor many flagella. * The location -on the surface- and the number

of flagella on the bacteria help in recognize and classify this bacteria.

• Bacteria with a single polar (on the pole) flagellum

• located at one end, or pole, are said to be monotrichous

• ex: Pseudomonas, bacillus shape

*Bacteria without flagella are atrichous .*Bacteria with flagella are trichous .

• bacteria with two Polar (on the pole) flagella, one at each end, are amphitrichous

• Spirillum (wavy rigid)• Gram -ve

• Bacteria with two or more flagella at one or both ends are Lophotrichous (with tuft of flagella at one or both ends)

• Spirillum

• bacteria with flagella distributed all over the surface are peritrichous.• Salmonella have bacillus shape and flagellation of peritrichous.• proteus cause UTI infection.

SalmonellaProteus

Chemotaxis

• Sometimes bacteria move toward or away from substances (chemical stimulus; such as cytokine, nutrients) in their environment by a nonrandom process called chemotaxis .

• positive chemotaxis: the net result is movement toward the attractant.

• negative chemotaxis: the net result is movement away from the repellent.

• Note: Phototaxis; Some bacteria can move toward or away from light.

Axial Filaments (endoflagella, internal flagella)

• Dark field , for non stained or live micro organism such as Treponema pallidum which cause syphilis disease, its spiral in shape has special movement because of its axial filament.

• Note: to diagnose that some one have syphilis disease they notice the motility of bacteria … and put immobilization substance to stop its movement to be sure that is Treponema pallidum .

• Because the axial filaments lie between the outer sheath and the cell wall, their twisting causes the rigid spirochete body to rotate like a corkscrew.

• ribbons running inside the cell wall along the body of the spirochete Leptospira interrogans

Axial filament

Pili

• Pili (singular: pilus) are tiny, hollow projections. They are used to attach bacteria to surfaces and are not involved in movement.

• A pilus is composed of subunits of the protein pilin.• Bacteria can have two kinds of pili;• (1) long conjugation pili, or F pili (also called sex pili)• (2) short attachment pili, or fimbriae (singular: fimbria).• Note: when bacteria attach to each other on the surface they

grow in the form of biofilm (sessile) which is more resistance than blank tone –free swimming- to anti microbial agent .

• Note: its tiny relative to flagella, and its usually exist as many pili but flagela exist as one ,two or more …

• Conjugation pili (or sex pili), found only in certain groups of bacteria, attach two cells and may furnish a pathway for the transfer of the genetic material DNA (plasmid; extra chromosomal DNA). This transfer process is called conjugation.

• Attachment pili, or fimbriae, help bacteria adhere to surfaces, such as cell surfaces and the interface of water and air.

• Note: the Conjugation pili usually longer than the Attachment pili.

Conjugation pilus

Fimbriae

Glycocalyx

• Glycocalyx is the currently accepted term used to refer to all polysaccharide-containing (and some times poly peptide-containing) substances found external to the cell wall, from the thickest capsules to the thinnest slime layers.

• Sugar material externally (polysaccharides) >>>- make the m.o sticky.- Protect it from losing water. • All bacteria have at least a thin slime layer. But not

all bacteria consist capsule.

Capsule

• A capsule is a protective structure outside the cell wall of the organism that secretes it.

• Only certain bacteria are capable of forming capsules, and not all members of a species have capsules.

• Capsules typically –usually- consist of complex polysaccharide molecules. (capsule rarely consist polypeptide).

• However, the chemical composition of each capsule is unique to the strain of bacteria that secreted it.

• For example, the bacterium (bacillus anthracis) that causes anthrax ( الخبيثة does not produce a capsule when it grows outside an ,(الجمرةorganism but does when it infects an animal -grow inside organism- . So that some times the presence of capsule depend on the conditions around the bacteria.

• Anthrax bacteria have a capsule composed of protein. • When encapsulated bacteria invade a host, the capsule prevents host

defense mechanisms, such as phagocytosis, from destroying the bacteria.

• If bacteria lose their capsules, they become less likely to cause disease and more vulnerable to destruction.

Slime Layer

• A slime layer is less tightly bound to the cell wall and is usually thinner than a capsule.

• When present, it protects the cell against drying, helps trap nutrients near the cell, and sometimes binds cells together.

• Slime layers very important in the formation of biofilm.• Slime layers allow bacteria to adhere to objects in their

environments, such as rock surfaces or the root hairs of plants , so that they can remain near sources of nutrients or oxygen.

• Some oral bacteria, for example, adhere by their slime layers –in the form of biofilm- and form dental plaque. The slime layer keeps the bacteria in close proximity to the tooth surface, where they can cause dental caries. Plaque is extremely tightly bound to tooth surfaces.