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Chapter 2 Structure of Bacteria

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. Chapter 2 Structure of Bacteria. Chemical composition of a prokaryotic cell. 2.1.

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Chapter 2 Structure of Bacteria

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  1. 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. 1

  2. Chapter 2Structure of Bacteria 1

  3. Chemical composition of a prokaryotic cell 2.1 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% 1

  4. Macromolecules Nucleoside: base + sugar OH • Bases: • adenine (A), cytosine (C), guanine (G), thymine (T) • RNA uses uracil (U) instead of thymine P O CH2 Base HO O C C H H O C C H H H H or OH • Sugar: • RNA – ribose (OH) • DNA – deoxyribose (H) Remember that carbon in sugar is numbered in sequence!!! How they are numbered? 1

  5. 图1b 核苷酸 图1c 核糖 U 尿嘧啶 T 胸腺嘧啶 C 胞嘧啶 1 G 鸟嘌呤 A 腺嘌呤

  6. Hydrogen bond T C Question: if a cell DNA contains more G+C than A+T, is it harder or easier to separate two complementary chains? A G 1

  7. chains complementary to each other 1

  8. Macromolecules protein 氨基酸一般结构 肽 键 1

  9. 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 1

  10. Approximate size of micro-organisms compared to a typical eukaryotic cell. 1

  11. There are two types of cells: prokaryotic vs. eukaryotic 1

  12. 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) 1

  13. Streptococci (链球菌) showing dividing manner 1

  14. Tetradococci (四叠球菌) 1

  15. Staphylococci (葡萄球菌) 1

  16. 球菌 (coccus)的分裂方式于群体形态之间的关系 单球菌(Coccus) 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) 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) 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) 沿着三个平面分裂；子细胞聚集在一起的称为葡萄球菌(Staphylococcus) 1

  17. Square cell: Cyanobacteria 1

  18. 2.3 Bacterial Structures 1

  19. 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. 1

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  23. 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 1

  24. F-Pilus for Conjugation（结合） 1

  25. Capsule or Slime Layer（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 1

  26. Cytoplasm（细胞质） The part inside the membrane • 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 environment quicker • Plasmids (质粒); circular DNA independent to chromosome (独立于染色体的环状DNA); • Antibiotic resistance (抗 抗生素) • No organelles细胞器 (mitochondria, Golgi, etc.) 1

  27. Cell Membrane（细胞膜） 亲水端 疏水端 亲水端 疏水端 • 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) 1

  28. 亲水端 脂肪酸 疏 水 端 甘油 1

  29. 磷脂 嵌入蛋白 1

  30. 醣脂类 醣蛋白 固醇 1

  31. Differences of membrane lipids between Archaea and other organisms 细菌和真菌 酯键 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。 Branches 古细菌 醚键 真菌和古细菌质膜中磷脂组成的区别 1

  32. 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 1

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  34. 图20 肽聚糖的亚单位 NAG：N-乙酰葡萄糖胺 NAM：N-乙酰胞壁酸 糖 氨基 氨基酸 L-丙氨酸 D-谷氨酸 间二氨基庚二酸 1 D-丙氨酸

  35. Cell wall structure of Gram negative bacteria G-细菌细胞壁结构 外膜 肽聚糖 胞围 细胞膜 细胞质 1

  36. 裂解酶敏感键 1

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  38. 生长点 胞内合成前体，通过膜运送到胞外合成薄壁 1

  39. 外膜 内膜 1

  40. Cell wall structure of Gram positive bacteria 革兰氏阳性菌(G+)的细胞壁 1

  41. Cell Wall Summary • Determine shape of bacteria • Strength prevents osmotic rupture • 20-40% of bacteria • Unique to bacteria • Some antibiotics effect directly • Penicillin 1

  42. Cell Wall Teichoic Acids 磷壁(酸)质 • Gram+ only • Glycerol, Phosphates, & Ribitol • Attachment for Phages 1

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  44. 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 1

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  47. 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 presence of LPS) 1

  48. 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 1

  49. Endospores(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 1

  50. 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. 1

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