Bacterial Morphology And Structure

Bacterial Morphology and Structure

The main types of medial Microbe Bacteria : Prokaryote( unicellular)

0.1~10 μm Fungi : Eukaryote, 2 μm~>1m  Viruses : cellular,0.01~0.25μm

Cell types

SIZE OF BACTERIA Unit

for measurement :

Micron or micrometer,μm: 1μm=10-3mm Size:

Varies with kinds of bacteria, and also related to their age and external environment.

Shaps of bacteria  Coccus  Bacillus  Spiral

bacterium

Shape of Bacteria

 Cocci:

sphere, 1μm  Bacilli: rods , 0.5-1 μm in width -3 μm in length  Spiral bacteria: 1~3 μm in length and 0.3-0.6 μm in width

Coccus Bacillus

Spiral Bacterium

球菌 (coccus)

Types of coccus

链球菌 (streptococcus)

球菌 (coccus) 葡萄球菌 (streptococcus)

球菌 (coccus) 四联球菌 (tetrad)

球菌 (coccus) 八叠球菌 (sarcina)

杆菌 (bacillus) 不同杆菌的大小、长短、粗细很不 一致。 大

炭疽芽胞杆菌 3-10 μm

中

大肠埃希菌 2-3 μm

小

布鲁菌 0.6-1.5 μm

杆菌 (bacillus) 杆菌的形态多样

两端齐平

两端尖细

白喉棒状杆菌

杆菌 (bacillus) 杆菌的形态多 样 分枝杆菌

双歧杆菌

螺形菌 (spiral bacterium)

Structure of Bacteria

Essential structures 基本结构 cell wall 细胞壁 cell membrane 细胞膜 Cytoplasm 细胞质 nuclear material 核质

Particular structures 特殊结构 capsule 荚膜 flagella 鞭毛 pili 菌毛 spore 芽胞

Cell wall  Situation:

outmost portion. 15-30nm in thickness, 10%-25% of dry weight.

1884: Christian Gram: First publication for the Gram stain method) Editor's note: I would like to testify that I have found the Gram method to be one of the best and for many cases the best method which I have ever used for staining Schizomycetes.

Gram, C. 1884. Ueber die isolirte Farbung der Schizomyceten in SchnittÄund Trockenpraparaten. Fortschritte der Medicin, Vol. 2, pages 185-189.

Cell wall :Common peptidoglycan layer A

backbone of N-acetyl glucosamine and Nacetylmuramic acid: Both discovered in Gram positive and Gram negative bacteria.  A set of identical tetrapeptide side chain attached to N-acetyl-muramic acid: different components and binding modes in Gram positive and Gram negative bacteria.  A set of identical peptide cross bridges: only in Gram positive bacteria

NAM

NAG

NAM

NAG

CH2OH CH2OH CH2OH CH2OH H H O O O O H H O O H H H H O H OH H O H OH H O O H H3C H3C H NH H H NH H NH H H NH H C–H O=C C–H O=C O=C O=C CH3 CH3 CH3 C=O CH3 C=O H– N

H– N

L–Ala

L–Ala

D–Glu

H

D–Glu

H

L–Lys

Gly–Gly–Gly–Gly–Gly–N

L–Lys

Gly–Gly–Gly–Gly–Gly–N

D–Ala C=O

D–Ala C=O

溶菌酶作 用位点

青霉素作 用位点

G

G M

M 丙 丙 DAB

G

DAB

丙

丙

G

Special components of Gram positive cell wall Teichoic acid

-

Special components of Gram negative cell wall

Functions of Cell Wall  Maintaining

the cell's characteristic shape- the rigid wall compensates for the flexibility of the phospholipid membrane and keeps the cell from assuming a spherical shape  Countering the effects of osmotic pressure  Providing attachment sites for bacteriophages  Providing a rigid platform for surface appendagesflagella, fimbriae, and pili all emanate from the wall and extend beyond it  Play an essential role in cell division  Be the sites of major antigenic determinants of the cell surface 。

Wall-less forms of Bacteria.

 When

bacteria are treated with 1) enzymes that are lytic for the cell wall e.g. lysozyme or 2) antibiotics that interfere with biosynthesis of peptidoglycan, wall-less bacteria are often produced.  Usually these treatments generate non-viable organisms. Wall-less bacteria that can not replicate are referred to as spheroplasts (when an outer membrane is present) or protoplasts (if an outer membrane is not present).  Occasionally wall-less bacteria that can replicate are generated by these treatments (L forms).

Bacteria L form  Bacteria

with dfective cell wall-bacterial L form: protoplast, spheroplast

Cell membrane

Function of Cell membrane Selective permeability and transport of solutes into cells b. Electron transport and oxidative phosphorylation c. Excretion of hydrolytic exoenzymes d. Site of biosynthesis of DNA, cell wall polymers and membrane lipids. a.

Mesosomes •

Mesosomes are specialized structures formed by convoluted inveigh-nations of cytoplasmic membrane, and divided into septal and lateral mesosome.

Cytoplasm  Composed

largely of water, together with proteins, nucleic acid, lipids and small amount of sugars and salts  Ribosomes: numerous, 15-20nm in diameter with 70S; distributed throughout the cytoplasm; sensitive to streptomycin and erythromycin site of protein synthesis  Plasmids: extrachromosomal genetic elements  Inclusions: sources of stored energy, e,g volutin

Ribosomes  Ribosomes

are the protein synthesizing factories of the cell.  They translate the information in mRNA into protein sequences.

Plasmid Plasmids are small ， circular/line ， ex trachromosomal ， doublestranded DNA molecules 。 They are capable of self-replication and contain genes that confer some properties ， such as antibiotic resistance ， virulence factors 。 Plasmids are not essential for cellular survival.

Inclusions of Bacteria  Inclusions

are aggregates of various compounds that are normally involved in storing energy reserves or building blocks for the cell. Inclusions accumilate when a cell is grown in the presence of excess nutrients and they are often observed under laboratory conditions.

granulose

Nucleus  Lacking

nuclear membrane, absence of nucleoli, hence known as nucleic material or nucleoid, one to several per bacterium.

Capsules and slime layers  These

are structures surrounding the outside of the cell envelope. When more defined, they are referred to as a capsule when less defined as a slime layer. They usually consist of polysaccharide; however, in certain bacilli they are composed of a polypeptide (polyglutamic acid). They are not essential to cell viability and some strains within a species will produce a capsule, whilst others do not. Capsules are often lost during in vitro culture.

Capsules and slime layers

Capsules and slime layers

Function of Capsules and slime layers(1)  Attachment

:These structures are thought to help cells attach to their target environment. Streptococcus mutans produces a slime layer in the presence of sucrose. This results in dental plaque and many bacteria can stick to tooth surfaces and cause decay once S. mutans forms a slime layer. Vibrio cholerae, the cause of cholera, also produces a glycocalyx which helps it attach to the intestinal villi of the host.

Function of Capsules and slime layers(2)  Protection

from phagocytic engulfment. Bacterial pathogens are always in danger of being "eaten" by phagocytes. (Host cells that protect you from invaders.) Streptococcus pneumoniae, when encapsulated is able to kill 90% of infected animals, when nonencapsulated no animals die. The capsule has been found to protect the bacteria by making it difficult for the phagocyte to engulf the microbe.

Function of Capsules and slime layers(3) Resistance

to drying. Capsules and slime layers inhibit water from escaping into the environment.

Function of Capsules and slime layers(4) Reservoir

for certain nutrients. Glycocalyx will bind certain ions and molecules. These can then be made available to the cell.

Function of Capsules and slime layers(5) Depot

for waste products. Waste products of metabolism are excreted from the cell, and will accumulate in the capsule. This binds them up, and prevents the waste from interfering with cell metabolism.

Flagella.  Some

bacterial species are mobile and possess locomotory organelles - flagella. Those that do are able to taste their environment and respond to specific chemical foodstuffs or toxic materials and move towards or away from them (chemotaxis). Flagella are embedded in the cell membrane, extend through the cell envelope and project as a long strand. Flagella consist of a number of proteins including flagellin. They move the cell by rotating with a propeller like action.

Relative Speeds of Organisms Organism

per second

Cheetah Human Bacteria

Kilometers per hour

111 37.5 0.00015

Body lengths

25 5.4 10

Flagella  The

diameter of a flagellum is thin, 20 nm, and long with some having a length 10 times the diameter of cell. Due to their small diameter, flagella cannot be seen in the light microscope unless a special stain is applied. Bacteria can have one or more flagella arranged in clumps or spread all over the cell.

Flagella  Monotrichate  Amphitrichate  Lophotrichate  Peritrichate

Flagella

Function of Flagella  Identification

of Bacteria  Pathogenesis  Motility of bacteria

Pili  Pili

are hair-like projections of the cell , They are known to be receptors for certain bacterial viruses.  Chemical nature is pilin  Classification and Function a. Common pili or fimbriae: fine , rigid numerous, related to bacterial adhesion b. Sex pili: longer and coarser, only 1-4, related to bacterial conjugation

Sex pili 



A donor bacteria will attach to a recipient via the sex pilus. Then a copy of part of the donor bacterium's genome passes through the sex pilus into the recipient. Conjugation, as it is called, is one explanation for the rapid spread of drug resistance in many different species of bacteria.

Common pili or fimbriae  Pili

have also been show to be important for the attachment of some pathogenic species to their host. Neisseria gonorrheae, the causative agent of gonorrhea, has a special pili that helps it adhere to the urogenital tract of its host. The microbe is much more virulent when able to synthesize pili.

Endospores  Endospores

are highly resistant resting structures produced within cells. They are common to organisms which live in soil and may need to wait out some rough times such as >100°C heat, radiation, drying or chemical agents ; under favourable conditions , a spore germinates into a vegetative cell  Spores are commonly found in the genera Bacillus and Clostridium.

DPA and survive Dipicolinic  Spores

acid,DPA.

can survive for a very long time, and then regerminate. Spores that were dormant for thousands of years in the great tomes of the Egyption Pharohs were able to germinate and grow when placed in appropriate medium. There are even claims of spores that are over 250 million years old being able to germiinate when placed in appropriate medium. These results have yet to be validated.

Spores  The

mechanisms that acount for this include the dehydration of the protoplast and the production of special proteins that protect the spores DNA.

• are capable of detecting their environment and under favorable nutrient conditions germinating and returning to the vegetative state.

Spore  Identification  Pathogenesis  Resistance

of Bacteria

Methods

Microscopey  Light

Microscope  Electron Microscope  Darkfield Microscope  Phase Contrast Microscope  Fluorescence Microscope  Cofocal Microscope ）

Methods Staining Methods  Simple

staining;  Differential staining ( Gram stain, Acid-fast stain),  Special staining( Negative stain, Spore stain, Flagella stain)