Bacterial Morphology and Structure

1. Bacterial Morphology and Structure

2. 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.

3. 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

4. Coccus Bacillus Spiral Bacterium

5. Structure of Bacteria

6. 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

7. Cell wall • Situation: outmost portion. 15-30nm in thickness, 10%-25% of dry weight.

8. 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.

11. Cell wall :Common peptidoglycan layer • A backbone of N-acetyl glucosamine and N-acetylmuramic 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

12. NAG NAG NAM CH2OH H C–H C=O H– N L–Ala D–Glu L–Lys Gly–Gly–Gly–Gly–Gly–N D–Ala C=O NAM CH2OH H C–H C=O H– N L–Ala D–Glu L–Lys Gly–Gly–Gly–Gly–Gly–N D–Ala C=O CH2OH CH2OH H H O O O O H H O O H H H H OH OH OH OH O O H NH H NH H NH H NH H H H H H3C H3C O=C CH3 O=C CH3 O=C CH3 O=C CH3 H H 图附

13. 溶菌酶作用位点 青霉素作用位点

15. G G M M 丙 谷 丙 DAB 谷 G G 丙 DAB 丙

16. Special components of Gram positive cell wall -Teichoic acid

17. Special components of Gram negative cell wall

20. 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 appendages- flagella, 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。

21. 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).

22. Bacteria L form • Bacteria with dfective cell wall-bacterial L form: protoplast, spheroplast

23. Cell membrane

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

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

26. 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

27. Ribosomes • Ribosomes are the protein synthesizing factories of the cell. • They translate the information in mRNA into protein sequences.

28. Plasmid Plasmids are small，circular/line，extrachromosomal，double-stranded 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.

29. 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.

30. granulose

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

33. 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.

34. Capsules and slime layers

35. Capsules and slime layers

36. 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.

37. 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 non-encapsulated no animals die. The capsule has been found to protect the bacteria by making it difficult for the phagocyte to engulf the microbe.

38. Function of Capsules and slime layers(3) • Resistance to drying. Capsules and slime layers inhibit water from escaping into the environment.

39. 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.

40. 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.

41. 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 OrganismKilometers per hourBody lengths per second Cheetah11125 Human37.55.4 Bacteria0.0001510

43. 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.

44. Flagella • Monotrichate • Amphitrichate • Lophotrichate • Peritrichate

45. Flagella

46. Function ofFlagella • Identification of Bacteria • Pathogenesis • Motility of bacteria

47. 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 • Common pili or fimbriae: fine , rigid numerous, related to bacterial adhesion • Sex pili: longer and coarser, only 1-4, related to bacterial conjugation

48. 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.

49. 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.

50. 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.