Más contenido relacionado



  1. PLANT PATHOGENIC BACTERIA DR. RAJBIR SINGH Associate Professor Department of Plant Pathology Gochar Mahavidyalaya (Post Graduate College) Rampur Maiharan, Saharanpur (UP), India Affiliated to: CCS University, Meerut (UP), India Email: Note: All images have been taken form internet. I am grateful to all author of images.
  2. History of Bacteria • Anton van Leeuwenhoek (1632-1723) – ‘Father of Microbiology’. In 1676 observed bacteria and Protozoa under microscope. • Hooke (1820)- Under compound microscope seen bacteria and called “Small Microscopic Species/Infusorial Animacutes”. • Ehrenberg (1828)- He gave the term ‘Bacterium’. • Louis Pasteur (1822-1895)- ‘Father of Bacteriology’. He gave terms: Sterlization, Fermentation, Pasteurization, Immunization. He developed Rabies Vaccine & established Pasteur Institute. • Koch’s Postulates (1843-1910)- ‘Father of Bacteriological Techniques’. In 1882 gave postulates. • T. J. Burril (1878-82)- Reported first time that a plant disease ‘Fire Blight of Pear & Peach’ is caused by Bcateria. • Joseph Lister (1827-1912)- Give “Antiseptic and Aseptic Theory”. • Winogradsky (1890)- ‘Father of Soil Bacteriology’. He describe NO2 & NO3 functioning.
  3. Bacterium Structure
  4. Description of different parts of bacterial cell (1). Cell Envelope • It is outer covering & has 3 components— glycocalyx, cell wall and cell membrane. (i). Glycocalyx (Mucilage Sheath): • Outermost mucilage layer & consists of non-cellulosic polysaccharides with or without proteins. • It may occur in the form of loose sheath then it is called ‘Slime layer’. If thick and tough, the mucilage covering is called ‘Capsule’. Functions: • (a) Prevention of desiccation, • (b) Protection from phagocytes, toxic chemicals and drugs & viruses, • (e) Attachment, • (f) Immunogenicity and Virulence.
  5. (2). Cell Wall • It is rigid solid covering , provides shape and structural support. • In Gram + ve is 8-12 nm & in gram – ve 20-80 nm thick. • It consists of lipopolysaccharides, lipids and proteins. • Inner wall layer of Gram -ve is made up of pepidoglycan, proteins, non- cellulosic carbohydrates, lipids, amino acids, etc. • Peptidoglycan known as murein or mucopeptide. Peptidoglycan consists of long glycan strands formed of repeating units of N-acetyl glucosamine (NAG) and N-acetyl muranic acid (NAM). They are cross linked by small peptide chains. • Peptidoglycan constitutes 70-80% of wall in Gram +ve bacteria. Lipid content is little. 10-20% of wall in Gram -ve bacteria is formed of peptidoglycan. Lipid content is 20-30%.
  6. (3). Plasma Membrane • It is selectively permeable covering of the cytoplasm. • Plasma membrane or plasma lemma has a structure similar to that of a typical membrane. • It is made of a phospholipid bilayer with proteins of various types. • It holds receptor molecules for detection and responding to different chemicals of the surroundings • It is metabolically active as it takes part in respiration, synthesis of lipids and cell wall components.
  7. i. Flagella: • Flagella are filamentous protein structures attached to the cell surface. • It provides the swimming movement. Movement - 50 NM or 0.001/Second. • Size is about 20 nm (0.02 µm) in diameter and 1-7µm in length. • Made of 3 parts— basal body, hook and filament. • It is made up of protein called flagellin.
  8. ii. Pili and Fimbriae • longer, fewer and thicker tubular outgrowths which develop in response to F+ or fertility factor in Gram +ve bacteria. • Made up of protein pilin. • Helpful in attaching to recipient cell and forming conjugation tube. So called Sex Pili. • Diameter is 3-10 nm while length is 0.5-1.5 µm. • Some fimbriae cause agglutination of RBC. They also help in mutual clinging of bacteria. •
  9. (IV). Cytoplasm: • It is crystallo-colloidal complex excluding its nucleoid. • Cytoplasm is granular due to presence of a large number of ribosomes. Various structures present in cytoplasm are as follows: (i) Mesosome: • It is a characteristic circular to villi form specialisation of cell membrane of bacteria that develops as an in growth from the plasma membrane • It takes part in replication of nucleoid by providing points of attachment to the replicated ones. • At the time of cell division, plasma membrane grows in the region wher that most probably it provides membranes for rapid elongation. • It contains respiratory enzymes and is, therefore, often called chondrioid.
  10. (ii) Ribosomes: • They are small membrane less, sub-microscopic ribo- nucleoprotein entities having a size of 20 nm x 14-15 nm. Fixed ribosomes are attached to the plasma membrane. • Each ribosome has two subunits, larger 50S and smaller 30S. • Ribosomes take part in protein synthesis. Free or matrix ribosomes synthesize proteins for intracellular use while fixed ribosomes synthesize proteins for transport to outside. • Ribosomes generally occur in helical groups called polyribosomes or polysomes.
  11. (iii). Nucleoid: • It represents the genetic material of prokaryotes. • Nucleoid consists of a single circular strand of DNA duplex which is supercoiled with the help of RNA and polyamines to form a nearly oval or spherical complex. • The folding is 250-700 times. • Polyamines or nucleoid proteins are different from histone proteins. • DNA of prokaryotes is considered naked because of its non-association with histone pro- teins and absence of nuclear envelope around it.
  12. (iv). Plasmids • They are self-replicating, extra chromosomal segments of double stranded, circular, naked DNA. Plasmids provide unique phenotypic characters to bacteria. They are independent of main nucleoid. • Some of them contain important genes like fertility factor, nif genes, resistance factors and colicinogenic factors. Plasmids which can get associated temporarily with nucleoid are known as episomes.
  13. (v). Chromatophores: • They are internal membrane systems of photosynthetic forms which possess photosynthetic pigments. In purple bacteria the membranes are typical while in green bacteria they are non-unit, non-lipid and proteinaceous. Chromatophores of green algae are called chromosomes. Photosynthetic pigments are bacteriochlorophyll, bacteriophaeophytin (bacterioviridin) and carotenoids.
  14. (iv). Inclusion Bodies: • The inclusion bodies may occur freely inside the cytoplasm or covered by 2-4 nm thick non- lipids, non-unit protein membrane. Types of Inclusion Bodies: 3 types base on nature 1. Gas vacuoles 2. Inorganic inclusions 3. Food reserve
  15. Morphology of Bacteria Morphology of bacteria include- size, shape, grouping or aggregation of cells, flagellation and ultra structure of bacteria. • Size of bacteria- Generally diameter of bacteria is – 0.35 – 0.5 µm Length is – 1-5 µm • Shape of bacteria- three type of shapes: 1. Spherical bacteria 2. Straight rod shaped bacteria 3. Bent or curved shaped bacteria
  16. 1. Spherical bacteria Spherical bacteria also known as Coccus pl. cocci. These bacteria are oval, ellipsoidal shape but some may be pear shaped, bean shaped. There diameter is about 0.2 – 4 µm. Base on their aggregation they are of 6 types: • Monococcus: A bacteria that lives as one cell. Exp. Micrococcus bicolor. • Diplococcus: is a cocci that is found in pairs. Exp. Diplococcus pneumoniae. • Streptococcus: the bacteria form long chains. Exp. Streptococcus lactis. • Tetrad: A group of four cells forming a flat square. Exp. Micrococcus roseus. • Sarcina: is a cube-like group of eight cocci. Exp. Sarcina lutea. • Staphylococcus: bacteria form an irregular, grape-like cluster. Exp. Staphylococcus aureus. •
  17. 2. Straight Rod Shaped Bacteria Rod shaped bacteria also known as Bacillus pl. bacilli. These bacteria are straight and cylindrical like a rod with ends being flat rounded or cigar shaped. On the base of aggregation they are following 4 types: (1). Microbacillus: In this a rod shaped bacterium divide into two cells and each divided bacterium live separate. Exp. Microbacterium. (2). Diplobacillus: In this a rod shaped bacterium divide into two cells and both divided bacterium attached to each other. Exp. Diplobacterium. (3). Streptobacillus: This a rod shaped bacterium divide and make a chain of divided bacteria. Exp. Streptothrix. (4). Pailsade: In this rod shaped bacteria live in group and look like pole . Exp. Corynebacterium diptheriae
  18. 3. Bent or Curved Rod Shaped Bacteria These are two types: 1. Vibrio: These bacteria are comma ( , ) shaped. Exp. Vibrio, Bdellovibrio. 2. Spiral or Helix or Spirillum: Spirllum is made of Greek word Spira which meaning is Coil. These bacteria are rigid spiral forms. Exp. Spirillum, Campylobacter.
  19. Flagellation in Bacteria The various forms of flagellation are as follows: (a) Atrichous: Flagella absent. (b) Monotrichous: A single flagellum occurs sat or near one end of bacterium. (c) Amphitrichous: A flagellum at each of the two ends. (d) Lophotrichous: A group or tuft of flagella is found only at one end. (e) Cephalotrichous: A tuft or group of flagella occurs at each of the two ends or poles. (f) Peritrichous: A number of flagella are distributed all over the surface.
  20. Classification of Plant Pathogenic Bacteria • According to David H. Bergey’s Manual of Determinative Bacteriology (Last vol. published in 1994) • Bergey divided plant pathogenic bacteria in 4 divisions and 7 classes. Kingdom: Prokaryote Division- I- Gracilicutes (gram – ve bacteria) Class- I- Scotobacteria Class- II- Anoxyphytobacteria Class- III- Oxyphytobacteria
  21. Division –II- Firmicutes (Gram +ve bacteria) Class –I- Firmibacteria Class –II- Thallobacteria Division –III- Tenricutes (Bacteria- lacking cell wall) Class- I- Mollicutes Division – IV – Mendosicutes (Bacteria with abnormal cell wall) Class – I- Archobacteria
  22. Asexual Reproduction in Bacteria Vegetative or Asexual reproduction in bacteria is by following methods: 1. BY Binary fission 2. By Endospores 3. By Cysts 4. By Fragmentation 5. By Arthospores 6. By Conidia
  23. 1. Binary Fission: Most bacteria rely on binary fission for propagation. In this a cell just needs to grow to twice its starting size and then split in two.
  24. 2. Endospore: Spores are formed during unfavorable environmental conditions. As the spores are formed within the cell, they are called endospores. Only one spore is formed in a bacterial cell. On germination, it gives rise to a bacterial cell.
  25. 3. Cysts: Cysts are formed by the deposition of additional layer around the mother wall. These are the resting structure and during favorable conditions they again behave as the mother. Exp. Azotobacter.
  26. 4. Fragmentation: In this, body of a bacterium break in several parts or fragments and each such individual fragment develop into a bacterium.
  27. 5.Arthospores: Body that resembles a spore but is not an endospores; produced by some bacteria.
  28. 6. Conidia: Conidia formation takes place in filamentous bacteria like Streptomyces. These conidia germinate and gives rise to new mycelium.