What is bacteria?(Structures Present in Bacteria And their Functions | Prokaryotes |)
- 2. Bacteria Morphology, growth and reproduction
- 3. Contents • Bacterial characteristics • Bacterial morphology • Size of bacteria • Shape of bacteria • Bacterial anatomy • Bacterial growth • Reproduction in bacteria
- 4. Bacterial characteristics • Unicellular • Circular DNA • No organelles • 1/10th the size of eukaryotic cells • Flagella-long hair-like structure used for movement • Reproduce asexually –Binary Fission
- 5. Bacterial morphology Size of bacteria: • Bacteria are so small because of that their size is measured in a micron (u ) • Generally cocci are about 1u in diameter and bacilli are 2 to 10 u in length and 0.2 to 0.5 u in width • The limit of resolution with unaided eye is about200 u because of that bacteria can be only visualized under microscope.
- 6. Shape of bacteria On the basis of general shape, bacteria are classified into three categories. • Cocci • Bacillus • Spiral shaped bacteria
- 7. Cocci The cocci are spherical or oval bacteria having one of several distinct arrangements based on their planes of division. Types of cocci are following: • Cocci in cluster – staphylococci • Cocci in chain – streptococci • Cocci in pair- diplococci • Cocci in group of four – tetrad • Cocci in group of eight – sarcina
- 8. Bacillus Bacilli are rod-shaped bacteria. Bacilli all divide in one plane producing a bacillus, streptobacillus, palisade or diplobacillus Bacillus is a single cell of bacteria. When rod shaped bacteria occur in pairs then arrangement of cells is known as diplobacilli. When the bacilli are arranged in chains, as the cells divide in one plane, this type is called streptobacillus. The bacilli bend at the points of division following the cell divisions, resulting in a palisade arrangement. Coccobacillus are so short and stumpy that they appear ovoid. They look like coccus and bacillus. Examples of rod shaped bacteria are Escherichia coli, Bacillus subtilis, Pseudomonas.
- 9. Spiral shaped bacteria The spiral shaped bacteria are spirally coiled. Spirals come in one of three forms, a vibrio, a spirillum, or a spirochete. • Vibrio is curved or comma-shaped rod. • Spirillum is a thick, rigid spiral. • Spirochete is a thin, flexible spiral. Examples of spiral shaped bacteria are Vibrio, Hyphomicrobium.
- 10. Bacterial structure • Cell Wall • Plasma Membrane • Cytoplasm • Bacterial capsule • Flagella • Fimbria / pilli • Endospores(spores)
- 11. Bacterial anatomy (structure) • In the bacteria the outer layer or cell envelop or bacteria consist of two things (a) rigid cell wall (b) underlying cytoplasmic membrane • plasma membrane: • It includes granules, ribosomes, mesosomes and circular DNA. • Some bacteria in addition to possess additional structures such as gelatinous material which cover it is called as capsule and when it is too thin it is called as microcapsule.
- 12. Cell wall • Introduction: most cell posses a cell envelop consisting of cell wall and underlying cytoplasmic membrane. • Definition: “the tough, rigid structure which surrounds bacterial cell it is called as cell wall” • Thickness: 10-20nm • Weight: 20-25% of dry weight of bacterial cell wall
- 13. Cell wall structure Chemical structure of cell wall is made up of a Peptidoglycan Polymer (amino acids + sugars) That structure is unique to all bacteria Sugars; NAG & NAM N-acetylglucosamine N-acetymuramic acid Amino acids cross link NAG & NAM
- 14. Made of peptidoglycan – a combination of protein and polysaccharides It is present in both gram positive & negative bacteria. Some bacteria called Gram negative bacteria have an additional layer of membrane that contains lipopolysaccharide - this extra layer inhibits the uptake of antibiotics – protecting the bacteria
- 15. Gram positive and gram negative bacteria The type of cell wall is used by doctors to help diagnose disease. The bacteria are stained with a special stain called Gram stain. • Bacteria without the extra membrane, appear purple. These are Gram positive (Gram +) bacteria. • Bacteria with the extra membrane appear pink. These are Gram negative ( Gram -) bacteria.
- 16. Cytoplasmic membrane Definition: “Thin semi permiable membrane which lies just beneath the cell wall that is called as cytoplasmic membrane” • The whole bacterial cytoplasm is bound peripherally by very thin, elastic and semi permiable cytoplasmic membrane also known as cell membrane. • It is 5-10nm in width • Electron microscope shows the presence of three layer constituting a unit membrane structure. • Chemically the membrane consist of phospholipid with small amount of protein.
- 17. Cytoplasm “Bacterial cytoplasm is suspension of organic and inorganic solutes in viscous watery solution” It is not exhibiting protoplasmic streaming and it lacks endoplasmic reticulum or mitochondria. It contains ribosomes, mesosomes, inclusion and vacuoles. All the organills which cytoplasm contains is as follows. Ribosomes: Ribosomes appear as small granules and pack the whole cytoplasm. These are strung together on strands of mRNA to form polymers. the code of mRNA is translated in to peptides sequence t this place. The ribosomal particles become linked up and travels along the mRNA strand.
- 18. Polysomes: They are the group of ribosomes linked together like beads of chain by messanger RNA Mesosomes: They are vesicular, convulated or multilaminted structures formed as invagination of plasma membrane in cytoplasm . They are more prominent in the gram positive bacteria. Two types of mesosomes (a) septal mesosomes: It is attached to bacterial chromosomes and involved in DNA segregation and in formation of cross wall during cell division. (2) Lateral mesosomes: They are at lateral side
- 19. Nucleoid The nucleoid (meaning nucleus-like) is an irregularly-shaped region within the cell of a prokaryote that contains all or most of the genetic material. In contrast to the nucleus of a eukaryotic cell, it is not surrounded by a nuclear membrane.
- 20. Bacterial capsule “ It is an outer covering of thick jelly like material that surrounds the bacterial cell wall” Width: 0.2 micrometer • Contains about 90% water and 2% solid • The solid constitutes may be complex polysccharide (pneumococcus klebsiella, (enterobacter) or polypeptides (anthrax bacillus) or hyaluronic acid (streptococcus). • The capsule is best seen in pathological specimens like pus, blood, sputum, and exudates (1) By ordinary stain (gram or acid fast) capsule can not be stained, it apper as halo arround the stained bacterial body. (2) In negative staining (india pink preparation), capsule appears as clear halo around the bacterium as link can not penetrate capsule.
- 21. Flagella “These are long, sinnous contractile filamentous appendages known as flagella”. • Composed of a flagellin subunit. • Usually sheathed (covered). • Rotates by way of a basal body in the bacterial cell. • These are organs of locomotion . ex:-Escherichia coli salmonella, vibrio , pseudomonas, etc. • The number of f lagella varies up to 10 to 20 per cells according to species of bacteria. • These are extremely thin (diameter)12 to 30 nm, helical shaped structure of uniform diameter throughout their length . • these are 3 to 20 nm long. • Each flagellum consist of hook & basal body. It originates in a spherical body located just inside cell wall.
- 22. Arrangement / types • Monotrichous; 1 flagella • Lophotrichous; tuft at one end • Amphitrichous; both ends • Peritrichous; all around bacteria
- 23. Fimbria / Pilli “Fimbria are filamentous , short , thin , straight , hair like appendage”. • This is 0.1 to 1.5 µ long & less than 4 to 8 nm thick. • They are also called as Pili. • Fimbriae are seen only in some gram negative bacteria. • Each bacterium may have 100 to 500 Fimbriae on all over the body of bacteria. • They project from cell surface as a straight filaments. • They are best developed in freshly isolated strains & in liquid culture. • They are composed of protein known as pillin (molecular weight 18000 Daltons).
- 24. Endospores (spores) • Dormant cell • Produced when starved • Resistant to adverse conditions - high temperatures - organic solvents - desiccation - UV radiation • contain calcium dipicolinate and Calcium • Bacillus (anthracis and cereus)and • Clostridium (tetanus, perfringens, botulinum
- 25. Bacterial growth Bacterial Growth - an increase in bacterial numbers - does not refer to an increase in size of the individual cells •How to determine bacterial growth? directly – through counting indirectly – through measuring their metabolic activity
- 26. Bacterial growth Bacteria ‘s growth can be take place by binary fission and during that so many phases happen during it: 1. Entrance of basic nutrients into the cell 2. Conversion of nutrient components 3. Replication of chromosomes 4. Increase in size and mass 5. Division of cells into two daughter cell
- 27. Growth cycle Bacterial growth is regulated by nutritional environment. When suitable environment is there that time bacterium is incubated, its growth leads to increase in number of cells which allow definite course. • The growth curve has got four phases: • Lag phase • Log phase(logarithmic) or exponential phase • Stationary phase • Decline phase
- 29. Lag phase When microorganisms introduced into fresh medium 1. no immediate increase in cell number 2. no cell division Lag phase may be due to 1. Cells may be old 2. Depletion of nutrients 3. No essential co-factors and ribosomes 4. Medium may be different 5. Microorganism may be injured
- 30. Log phase Microorganisms grow and divide at maximum rate due to 1. Their genetic potential 2. Nature of medium 3. Condition Growth is constant and in geometric progression (2n) Generation time will be minimum Each cell divide at slightly different moment Population is uniform in terms of chemical and physiological properties under which they are growing Used for biochemical and physiological studies
- 31. Stationary phase • Growth ceases and growth curve become horizontal • Final population depends on nutrient availability • Total number of viable cells remains constant • Microbial population enter stationary phase due to • 1. nutrient limitation • 2. oxygen availability • 3. accumulation of toxic wastes
- 32. Decline phase • Nutrient depletion or due to build-up of toxic wastes leads to death of viable cells • Death of microbial population as like exponential phase • Total number of cells remains constant, because cells • simply fail to lyse
- 33. Bacterial reproduction Bacteria reproduces by the following ways: • Binary fission • Budding • Spore formation
- 34. Binary fission Simplest type of asexual reproduction. Binary Fission involves a one celled organism. Binary Fission produces new daughter cells. Binary Fission begins with DNA but doesn’t exchange genetic info. The cells become an exact replication of each other.
- 35. Budding • This is when a child grows out of the parent. • When the cell splits off the nucleus divides equally but it’s cytoplasm divides unequally. • The parent and child could stay connected and form a colony or separate.
- 36. Spore formation • Spores contain a nucleus and a small amount cytoplasm. • Spores sprout out of decaying materials releasing spores to make more sprouts. • Species of the genus Stretomyces and related bacteria produce many spores per organism by developing crosswalls at the hyphal tips: each spores gives rise to new organism.