Chapter 2 Structure of Bacteria

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC

In the first chapter, we introduced a general outline on what will be of this subject. Now we start to examine details of microorganisms. Let’s see what microorganisms look like and what are made of.

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Chapter 2Structure of Bacteria

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Macromolecules ( 大分子 )

protein, polysaccharide, lipids, DNA, RNA, 96% (dw%)

Monomers: ( 单体及前体 )

amino acids and precursors, sugars and precursors 3%

Inorganic ions:

K+, Mg+2, Ca2+, Fe2+, Mn2+, Cu2+ 、 Co2+ 、 Zn+2……1%

Chemical compositionof a prokaryotic cell

2.1

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O

C C

C C

Base

H

H or OH

H H

H

H

CH2OP

OH

O

HO

Sugar:

• RNA – ribose (OH)

• DNA – deoxyribose (H)

MacromoleculesNucleoside: base + sugar Bases:

adenine (A), cytosine (C),

guanine (G), thymine (T)

RNA uses uracil (U)

instead of thymine

Remember that carbon in sugar is numbered in sequence!!! How they are numbered?

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C 胞嘧啶U 尿嘧啶

T 胸腺嘧啶

G 鸟嘌呤 A 腺嘌呤

图 1c 核糖图 1b 核苷酸

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A

T C

G

Question: if a cell DNA contains more G+C than A+T, is it harder or easier to separate two complementary chains?

Hydrogen bond

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chains complementary to each other

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氨基酸一般结构

肽键

Macromolecules

protein

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC 2.2 Size and shape

of Bacteria• Average bacteria 0.5 - 2.0 um in diam.

• Surface area ~12 µm2

• Volume is ~4 µm

• Surface area to volume is 3:1

• Typical eukaryote cell SA/Vol is 0.3:1

• Food enters through SA, quickly reaches all parts of bacteria

• Eukaroytes need structures & organelles

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Approximate size of micro-organisms compared to a typical eukaryotic cell.

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC There are two types of cells:

prokaryotic vs. eukaryotic

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Shapes of Bacteria• Coccus ( 球菌 )

– Chain = Streptoccus– Cluster = Staphylococcus

• Bacillus ( 杆菌 )– Chain = Streptobacillus

• Coccobacillus ( 短杆菌 )• Vibrio = curved ( 弧菌 )• Spirillum ( 螺旋菌 )• Spirochete ( 螺旋体 )• Square ( 方形 )• Star ( 星形 )

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Streptococci ( 链球菌 ) showing dividing manner

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Tetradococci ( 四叠球菌 )

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Staphylococci ( 葡萄球菌 )

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC 球菌 (coccus) 的分裂方式

于群体形态之间的关系

沿着同一平面分裂；分裂后两个细胞连在一起的称为双球菌 (Diplococcus)

沿着两个相互垂直的平面分裂；四个细胞连在一起的称为四联球菌 (Tetrads)

沿着三个平面分裂；子细胞聚集在一起的称为葡萄球菌 (Staphylococcus)

细胞沿三个互相垂直的面分裂，分裂后每八个细胞特征性地叠在一起呈一立方体的称为八叠球菌 (Sarcinalutea)

沿着同一平面分裂；分裂后两个以上细胞连在一起的称为链球菌 (Streptococcus)

单球菌 (Coccus)

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC Square cell: Cyanobacteria

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2.3 Bacterial Structures

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Flagella ( 鞭毛 )• Motility - movement• Swarming ( 聚集 ) occurs with some bacteria

– Spread across Petri Dish– Proteus ( 多变的 ) species most evident

• Arrangement basis for classification– Monotrichous ( 单身鞭毛 ); 1 flagella– Lophotrichous ( 丛生鞭毛 ); tuft at one end– Amphitrichous ( 端生鞭毛 ); both ends– Peritrichous( 周身鞭毛 ); all around bacteria

• Observe Picture in Micro Lab.

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC Pili ( 纤

毛 )• Short protein appendages– smaller than flagella

• Adhere bacteria to surfaces– E. coli has numerous types

• K88, K99, F41, etc.– Antibodies to will block adherance

• F-pilus; used in conjugation– Exchange of genetic information

• Flotation; increase boyancy– Pellicle (scum on water)– More oxygen on surface

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F-Pilus for Conjugation （结合）

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC Capsule or Slime L

ayer （荚膜 / 粘液）

• Glycocalyx ( 多糖 )- Polysaccharide on external surface• Adhere bacteria to surface• Prevents phagocytosis( 嗜菌作用 )• Prevent water from loss

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC Cytoplasm （细胞质）

• 80% Water by weight, 20% salts-proteins– Osmotic ( 渗透压 ) shock important

• DNA is circular( 环状 DNA), haploid ( 单链 )– More efficient; grows quicker– Mutations ( 变异 ) allow adaptation to environ

ment quicker• Plasmids ( 质粒 ); circular DNA independent to chr

omosome ( 独立于染色体的环状 DNA);• Antibiotic resistance ( 抗抗生素 ) • No organelles 细胞器 (mitochondria, Golgi, etc.)

The part inside the membrane

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC Cell Membrane （细胞膜）

• Bilayer phospholipid• Water can penetrate• Flexible• Not strong, ruptures ( 断裂 ) easily

– Osmotic pressure created by cytoplasm

磷脂的化学结构 ( 左 ) 及其示意图 ( 右 )

亲水端

疏水端

亲水端疏水端

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亲水端

疏水端

脂肪酸

甘油

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嵌入蛋白磷脂

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC 醣蛋白醣脂类

固醇

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真菌和古细菌质膜中磷脂组成的区别

Differences of membrane lipids between Archaea and other organisms

细菌和真菌

古细菌

细菌和真菌的质膜由无分支的直链脂肪酸通过酯键与甘油连接；

古细菌则由带有支链脂肪酸与甘油连接。

酯键

醚键

Branches

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC Cell Wall

• Peptido-glycan ( 肽 - 糖 ) polymer (amino acids + sugars)

• Unique ( 特别 ) to bacteria

• Sugars; NAG & NAM

– N-acetylglucosamine (N- 乙酰氨基葡萄糖 )

– N-acetymuramic acid (N- 乙酰胞壁酸 )

• D form of Amino acids used not L form

– Hard to break down D form

• Amino acids cross link NAG & NAM

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D- 丙氨酸

D- 谷氨酸间二氨基庚二酸

L- 丙氨酸

图 20 肽聚糖的亚单位

NAG ： N- 乙酰葡萄糖胺

NAM ： N- 乙酰胞壁酸

氨基

糖

氨基酸

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Cell wall structure of Gram negative bacteria G- 细菌细胞壁结构

细胞质

胞围

细胞膜

肽聚糖外膜

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裂解酶敏感键

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生长点

胞内合成前体，通过膜运送到胞外合成薄壁

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外膜

内膜

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Cell wall structure of Gram positive bacteria

革兰氏阳性菌 (G+)的细胞壁

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Cell Wall Summary

• Determine shape of bacteria

• Strength prevents osmotic rupture

• 20-40% of bacteria

• Unique to bacteria

• Some antibiotics effect directly

– Penicillin

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC Cell Wall

Teichoic Acids 磷壁 ( 酸 ) 质

• Gram+ only

• Glycerol, Phosphates, & Ribitol

• Attachment for Phages

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Lipopolysaccharide (LPS)• Endotoxin or Pyrogen

– Fever causing– Toxin nomenclature

• Endo- part of bacteria• Exo- excreted into environment

• Structure– Lipid A– Polysaccharide

• O Antigen of E. coli, Salmonella• G- bacteria only

– Alcohol/Acetone removes

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC LPS (cont’d)

• Functions– Toxic; kills mice, pigs, humans

• G- septicemia; death due to LPS– Pyrogen; causes fever

• DPT vaccination always causes fevers– Adjuvant; stimulates immunity

• Heat Resistant; hard to remove• Detection (all topical & IV products)

– Rabbits (measure fever)– Horse shoe crab (Amoebocytes Lyse in prese

nce of LPS)

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC LPS (cont’d.)

• Appearance of Colonies

– Mucoid = Smooth (lots of LPS or capsule)

– Dry = Rough (little LPS or capsule)

• O Antigen of Salmonella and E. coli

– 2,000 different O Ags of Salmonella

– 100’s different O Ags of E. coli

• E. coli O157

• O Ags differ in Sugars, not Lipid A

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRCEndospores( 芽孢、内生芽

孢 )• Resistant structure

– Heat, irradiation, cold

– Boiling >1 hr still viable

• Takes time and energy to make spores

• Location important in classification

– Central, Subterminal, Terminal

• Bacillus stearothermophilus( 强耐高温 ) -spores

– Used for quality control of heat sterilization equipment

• Bacillus anthracis - spores

– Used in biological warfare

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Bacillus anthracis( 炭疽热细菌 ). Gram stain. The cells have characteristic squared ends( 端齐 ). The endospores are ellipsoidal( 椭圆 ) shaped and located centrally in the sporangium. The spores are highly refractile ( 折射 ) to light and resistant to staining.

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC Bacillus thuringiensis. Phase Photomicrograph

of vegetative cells, intracellular spores (light) and parasporal crystals (dark) ( 类芽孢晶体 ) .

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Shixue Yin (Prof Dr)Microbiology SectionCESE, YZU, 225009 PRC G+ vs. G-

• G+

– Thicker cell wall

– Teichoic Acids

• G-

– Endotoxin - LPS

• Which are more sensitive to Penicllin?

• Alcohol/Acetone affects which more?

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Prokaryotes vs. Eukaryotes• Cell Wall

• Teichoic Acids

• LPS

• Endospores

• Circular DNA

• Plasmids

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Eukaryote Cell Structure

Chapter 2 Structure of Bacteria

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