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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
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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 ?
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4.11 Endospores 内生孢子
Properties of Endospores
Structure of Endospores
Chemical Constitution of Endospores
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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;
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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.
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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
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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.
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(三)细胞的结构
(参见P53-54)
1896 1920 1987 2006
IV. Microbial Locomotion
3.12 Flagella and Motility
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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
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
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3.12.2 Structure of the flagellum
FLASH 1
FLASH 2
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
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3.12.4 Flagellar Synthesis
Does an individual flagellum grow from
its base, as does an animal hair, or from
the tip?
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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.
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鞭毛的生长方式是在其顶部延伸
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(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)
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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
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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.
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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。
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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
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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?
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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?
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