Lecture 3-4: Microbial cell biology - micro.sjtu.edu.cnmicro.sjtu.edu.cn/PDF-Microbiology/04-1 Lecture 3-4 Microbial Cell... · of glaycocalyx ? Shanghai Jiao Tong University

1896 1920 1987 2006

Lecture 3-4:

Microbial cell biology

Cell Structure and Function

Zhao Liping, Chen Feng

School of Life Science and Biotechnology

Shanghai Jiao Tong University

http://micro.sjtu.edu.cn

1896 1920 1987 2006

III. Surface structures and

inclusions of prokaryotes

4.10 Bacterial cell surface structures

4.11 Endospores 内生孢子


4.10 Bacterial cell surface structures

Glycocalyx 糖被: slimy or gummy materials

on prokaryotic cell surfaces, consist of

polysaccharide (sometimes protein).

Capsule荚膜

Glycocalyx can be divided into 1)capsule (macrocapsule),

2)microcapsule, 3)slime layer and 4)zoogloea depending on their

rigidity and thickness.糖被可分为荚膜（大荚膜）、微荚膜、粘液层和菌胶团。

The rigid layers are organized in a tight matrix that excludes

particles, this form is capsule; If the glycocalyx is more easily

deformed, it will not exclude particles, this arrangement is slime

layer.荚膜与粘液层的不同

1896 1920 1987 2006

Discuss: Any advantages

of glaycocalyx ?


4.11 Endospores 内生孢子

Properties of Endospores

Structure of Endospores

Chemical Constitution of Endospores


Endospores

Endospores: differentiated cells that are very

resistant to heat and cannot be destroyed easily,

even by harsh chemicals.

Stay alive for millions of years

Morphological properties

• Difficult to stain

• Highly refractile body

内生孢子：1、对热和化学物质有高度抗性；2、可以存

活上百万年；3、在形态学上不易染色并且有高度的折光

性；


How long can a bacterial cell survive?

In what form?

Halophilic endospore-forming bacteria have

been isolated from fluid inclusions in an 250-

million-year-old salt crystal.

(Nature, 2000, 407: 897-900)

4.11.1 Endospore Structure

The outermost layer: exosporium外

壁, a thin, delicate covering made of

protein.

Within exosporium: spore coats芽胞

衣, composed of layers of spore-

specific proteins.

Below the spore coat: cortex皮层,

which consists of loosely cross-linked

peptidoglycan.

Inside the cortex: core or spore

protoplast核/芽胞原生质体, which

contains the usual cell wall (core wall),

cytoplasmic membrane, cytoplasm,

nucleoid, and so on.


4.11.2 Chemical properties of

endospore

Calcium-dipicolinic acid complex-10% dry weight含有

钙-吡啶二羧酸复合物，占干重的10%；

Small acid-soluble spore proteins (SASPs)

• Protection of DNA

• Energy and carbon source during germination

• 小酸溶性孢子蛋白（SASP），有助于保护DNA，且在

萌发时提供能量和碳源。

Dipicolinic acid (DPA) and calcium associate with the carboxyl groups to form a

tough complex吡啶二羧酸与钙离子通过羧基形成复合物。

(b) How Ca+ cross-links DPA molecules to form a complex.

Structure of DPA

4.11.3 Spore formation

During endospore

formation, a vegetative cell

is converted to a

nongrowing, heat-resistant

structure.

In B.subtilis, the entire

sporulation process takes

about 8 hours.

As many as 200 genes are

involved in the sporulation

process.

Figure 3.33

Vegetative cell

Developing spore

Sporulating cell

Mature spore

© 2012 Pearson Education, Inc.

Detail: In stages 0 to II,

DNA浓缩

细胞膜内陷而形成孢子隔膜.

Detail: In stages III to IV,

孢子隔膜环原生质体生长

形成芽胞外壁, 原始皮层在两层膜间形成

Detail: In stages V to VII

所有的芽胞衣层形成

芽胞成熟,

细胞的裂解

Figure 3.37

Free endospore

Stage VI, VIIStage V

Coat

Stage IV

Stage IIIStage II

Mother cell

Prespore

Septum

Sporulationstages

Cortex

Cell wall

Cytoplasmicmembrane

Vegetative cycle

Maturation,cell lysis

Celldivision

GerminationGrowth

Engulfment

Asymmetriccell division;commitmentto sporulation,Stage I

Spore coat, Ca2

uptake, SASPs,dipicolinic acid

Cortexformation

© 2012 Pearson Education, Inc.

Endospore Formation: life cycle of Bacillus megaterium

1896 1920 1987 2006

Is endospore a

reproductive structure?

Discussion

A dormancy structure


4.11.4 Spore germination

This process

involves three

steps:

1. activation,

2. germination

3. outgrowth.

Spore germination under microscope:

•In Germination, the spore will:

(1)loss of refractility of the spore,

(2)increased ability to be stained by dyes,

(3)loss of resistance to heat and chemicals,

(4)loss of calcium dipicoliate and cortex components, and

(5)degradation of SASPs.


（三）细胞的结构

（参见P53-54）

1896 1920 1987 2006

IV. Microbial Locomotion

3.12 Flagella and Motility


Who is faster, the cheetah or

the bacteria?

The fastest animal-cheetah can run 25 body

length per second (110km/hr)

The bacteria can run 50-60 body length per

second (0.00017km/hr)

3.12.1 Bacterial Flagella 鞭毛

Peritrichous周毛

Polar单毛

Lophotrichous端生丛毛

Flagella Arrangement

Animations/Lecture3_flagella_arrange.swf

Using dark-field microscopy and using a laser source, a

single flagellum can be observed without special staining

In extremely large prokaryotes, tufts of flagella can also be

observed by phase contrast microscopy without special staining


3.12.2 Structure of the flagellum

FLASH 1

FLASH 2

Animations/Lecture3_Flagellum.swf

Animations/Lecture3_flagella_structure.swf

3.12.3 Flagellar Movement

The hook consists of a single type of protein

and functions to connect the filament to the

motor portion.鞭毛钩连接鞭毛与马达部分.

The L ring is embedded in outer membrane,

and the P ring in peptidoglycan. The MS ring

is embedded in the cytoplasmic membrane.

Mot proteins drive the motor while Fli

proteins switch the motor

One rotation needs 1000 protons move

across the membrane

FLASH 1

FLASH 2

Animations/Lecture3_Flagellum.swf

Animations/Lecture3_flagella_structure.swf



3.12.4 Flagellar Synthesis

Does an individual flagellum grow from

its base, as does an animal hair, or from

the tip?


MS ring is synthesized first,

MS ring inserted into the membrane,

Formation of the other rings, the hook and the cap.

Flagellin molecules synthesized in the cytoplasm pass up

through the hook and a 3-nm channel inside of the filament

and add on at the terminus to form the final flagellum.


鞭毛的生长方式是在其顶部延伸


（三）细胞的结构

7、细菌细胞壁以外的构造 ——— 鞭毛(flagellum,复flagella)

3）鞭毛的结构及其运动机制（参见P59）


3.12.5 How the flagellum move the cell, by

flexing or rotating?

Can you design an experiment to solve the

puzzle?

• Use light microscope

• Use living cells

For the reversible polar flagella, Cells change direction by reversing

flagellar rotation. Or in unidirectional flagella, by stopping periodically to

reorient, and then moving forward by clockwise rotation of its flagella.

For the perithichous: Forward motion is imparted by all

flagella rotating counterclockwise while clockwise rotation

causes the cell to tumble.

In the absence of a gradient, cells move in a random fashion

that includes runs and tumbles. Following a tumble, the

direction of the next run is random.

If a gradient of an attractant is present, as the organism senses higher

concentrations of the attractant, runs become longer and tumbles less

frequent, so the organism moves up the concentration gradient of the

attractant.

Flagella Movement

Animations/Lecture3_flagella_movement.swf


3.13 Behavioral Responses:

chemotaxis, phototaxis

Respond to physical or chemical gradients

Directed movement toward or away from the

gradient-taxes

• Chemotaxis: a response to chemicals趋化性

• Phototaxis: a response to light趋光性

Mechanism: Compare sensing along time

• Temporal gradient response

• We will discuss it in other chapter

Attractant or repellent,引诱剂或驱避剂Can you tell the difference?

Insertion of a capillary into a suspension of bacteria

provides a rapid screen of chemicals that can act as

attractants or repellants

Figure 3.48

Time

Repellent

Control

Attractant

Repellent

Control Attractant

Cell

s p

er

tub

e

Techniques for measuring chemotaxis in bacteria.


Other Bacterial cell surface structures

Fimbriae: short filamentous structures composed of

protein that extend from the surface of a cell纤毛：细

胞表面的短的纤维状结构，蛋白质组成。

Pili: structurally similar to fimbriae but are typically

longer, and only one or a few pili are present on the

surface.性菌毛：结构与纤毛相似，但更长，一般

只有一根可数根。


3.14 Energy storage

Bacterial cells can store energy

for future needs

Energy-rich insoluble polymer

• Polysaccharides: starch, glycogen

淀粉, 糖原

• Lipid: poly--hydroxybutyrate

(PHB)聚羟基丁酸

• Biodegradable plastic

• Elemental sulfur 元素硫


1896 1920 1987 2006

Test

1896 1920 1987 2006

a. cilia

b. peritrichous flagella

c. pili

d. polar flagella

1. Which structural component(s) allow(s) for

motility in Escherichia coli?

1896 1920 1987 2006

a. capsule

b. fimbria

c. pilus

d. porin

2. Which structure is involved in the genetic

exchange (conjugation) between cells?

1896 1920 1987 2006

a. Archaea

b. Bacteria

c. gram-positive bacteria

d. gram-negative bacteria

3. Which is the only group of microorganisms

that contain lipopolysaccharides (LPS)?

1896 1920 1987 2006

a. amino acids

b. monomeric sugar compounds

c. N-acetylglucosamine and

N-acetylmuramic acid

d. N-acetylglucosamine,

N-acetylmuramic acid, and a few

amino acids

4. What is the composition of peptidoglycan?

1896 1920 1987 2006

a. 1 atmosphere less

b. 1 atmosphere more

c. 5 atmospheres more

d. approximately the same

5. What is the pressure of an average

bacterial cell relative to the atmosphere?

Documents

Lecture 3-4: Microbial cell biology - micro.sjtu.edu.cnmicro.sjtu.edu.cn/PDF-Microbiology/04-1 Lecture 3-4 Microbial Cell... · of glaycocalyx ? Shanghai Jiao Tong University