Morphology & Cell Biology of Bacteria (Part II) Siti Sarah Jumali (ext 2123) Room 3/14 [email protected] Bacterial cell Inclusion Bodies • Definition: A collective variety of small bodies within bacterial cytoplasm. • Some are called vesicles, some are called vacuoles • Act as reserve deposits/storage • Cells may accumulate nutrients and use them whenever in impermissible condition May consists of • • • • Polyhydroxybutyrate Polyphosphate Glycogen Sulphur 2 types 1. Granules- not bounded by membrane, substance densely compacted and hard to dissolve in cytoplasm (glycogen or polyphosphate) 2. Vesicles- bounded by specialize membrane, mostly consist of gas, carbon, carbohydrate, iron, poly-B-hydroxybutyrate (lipid) Granule • Densely compacted substances without a membrane • Each granule contains specific substances: 1. Glycogen (glucose polymer) 2. Polyphosphate (phosphate polymer, supplies energy to metabolic processes) • Sulphur bacteria contains reserve granules of sulphur • Polyphosphate granules- called volutin or metachromic granules exhibit metachromasia (metachromic granules exhibit different intensities of color). These granules are depleted in starvation Cytoplasmic bridge vacuole Cleavage furrow Volutin or metachromic granules Vesicles • Certain bacteria have specialized membrane enclosed structure called vesicles or vacuoles. • Some aquatic photosynthetic bacteria and cyanobacteria have rigid gas-filled vacuoles and it helps in floating at certain level • Some magnetotactic bacterium e.g. Aquaspirillum magnetotacticum stores magnetite (Ferric oxide). The presence of such magnetic inclusions enables these bacteria to respond to magnetic fields. Common inclusion bodies in Microorganisms Cytoplasmic inclusions Where found Composition Function glycogen many bacteria e.g. E. coli polyglucose reserve carbon and energy source polybetahydroxybutyric many bacteria e.g. acid (PHB) Pseudomonas polymerized hydroxy butyrate reserve carbon and energy source polyphosphate (volutin granules) many bacteria e.g. Corynebacterium linear or cyclical polymers of PO4 reserve phosphate; possibly a reserve of high energy phosphate sulfur globules phototrophic purple and green sulfur bacteria and lithotrophic colorless sulfur bacteria elemental sulfur reserve of electrons (reducing source) in phototrophs; reserve energy source in lithotrophs Common inclusion bodies in Microorganisms cont’d Cytoplasmic inclusions Where found Composition Function gas vesicles aquatic bacteria especially protein hulls or shells cyanobacteria inflated with gases buoyancy (floatation) in the vertical water column parasporal crystals endospore-forming bacilli protein (genus Bacillus) unknown but toxic to certain insects orienting and migrating along geo- magnetic field lines magnetosomes certain aquatic bacteria magnetite (iron oxide) Fe3O4 carboxysomes many autotrophic bacteria enzymes for autotrophic CO2 fixation site of CO2 fixation phycobilisomes cyanobacteria phycobiliproteins light-harvesting pigments chlorosomes Green bacteria lipid and protein and bacteriochlorophyll light-harvesting pigments and antennae Magnetosome The bacterial endospore • Microscopic, highly resistant, nonmotile, non-reproductive structure produced by few types of bacteria as a result of tough environmental conditions to ensure survival because it allows the bacteria to remain dormant for extended amount of time • Two most common types- Bacillus and Clostridium • Helps to survive in impermissible condition • Highly resistant to heat, drying, acids, bases, desiccation, certain disinfectants and radiation The bacterial endospore Component of Endospores • The heat resistance is due to -Calcium-dipicolinate: abundant within the endospore, may stabilize and protect the endospore’s DNA • Specialized DNA-binding proteins saturate the endospore’s DNA and protect it from heat, drying, chemicals and radiation. • The cortex may osmotically remove water from the interior of the endospore and the dehydration caused is thought to be very important in the endospore’s resistance to heat and radiation. • DNA repair enzymes contained within the endospore are able to repair damage during germination • The chemical resistance of endospores is due to impermeability of the sporecoat towards the chemical substance Component of Endospores Formation of Endospores • Sporulation (sporogenesis) • A process of endospore formation • The endospore can survive possibly thousands of years until a variety of environmental stimuli trigger germination, allowing outgrowth of a single vegetative bacterium. Sporulation Process Sporulation Process • 1- Vegetative bacterium about to enter the endospore cycle • 2- A spore septum forms as the cytoplasmic membrane invaginates • 3- Each nucleiod becomes surrounded by its own cytoplasmic membrane Sporulation Process cont’d • 4- Cytoplasmic membrane surrounds the isolated nucleiod, cytoplasm and membrane from the previous step, forming a forespore • 5- Forespore is completed and other DNA molecule is eventually degraded • 6- A thick peptidoglycan (cortex) is synthesized between the inner and outer forespore membranes. Calcium dipicolinate is synthesized and incorporated in the forming endospore. Sporulation Process cont’d • 7- A second impermeable proteinaceous protective layer called the spore coat is then synthesized • 8- As the vegetative portion of the bacterium is degraded, the completed endospore is released • 9- Sometimes, a final layer called the exosporium may be added Germination Process • A process of endospore returning to their vegetative state • With the proper environmental stimuli. The endospore germinates. As the protective layers of the endospore are enzymatically broken down, a vegetative bacterium begins to form and emerge Endospore and Infectious Disease • • • • Anthrax is caused by Bacillus anthracis; Tetanus is caused by Clostridium tetani; Botulism is caused by Clostridium botulinum; Gas gangrene is caused by Clostridium perfringens; • Clostridium difficile causes the most serious cause of antibiotic-associated diarrhea (AAD) and can lead to pseudomembranous colitis, a severe infection of the colon. Notice anything? What are the 2 common bacteria that are associated with endospores? Prokaryotes vs Eukaryotes • • • • Features of Eukaryotes Eu = “true”, karyon = “nucleus” Presence of a nucleus, a double membrane-bound control center separating DNA from the rest of the cell. In addition to the plasma membrane, eukaryotic cells contain internal membrane-bound structures called organelles such as mitochondria and chloroplasts Eukaryotic cells can reproduce in one of several ways, including meiosis (sexual reproduction) and mitosis (cell division producing identical daughter cells). Features of Prokaryotes • Pro = “before”, karyon = “nucleus” • Prokaryotes, the first living organisms to evolve, they lack a membrane-bound nucleus. The only membrane in prokaryotic cells is the plasma membrane--the outer boundary of the cell itself. Their genetic material is naked within the cytoplasm, ribosomes the only type of organelle. • Prokaryotes are most always singlecelled, except when they exist in colonies. Announcement • Your first test will be next week, during tutorial • Bring 2B along • There will be super easy multiple choice questions and few subjective questions.