Morphology & Cell Biology of Bacteria (Part II)

Siti Sarah Jumali (ext 2123)

Room 3/14

sarah_jumali84@hotmail.com

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

vacuole

Cytoplasmic bridge

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

glycogenmany bacteria e.g. E. coli

polyglucosereserve carbon and energy source

polybetahydroxybutyric acid (PHB)

many bacteria e.g. 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 vesiclesaquatic bacteria especially cyanobacteria

protein hulls or shells inflated with gases

buoyancy (floatation) in the vertical water column

parasporal crystalsendospore-forming bacilli (genus Bacillus)

proteinunknown but toxic to certain insects

magnetosomes certain aquatic bacteriamagnetite (iron oxide) Fe3O4 

orienting and migrating along geo- magnetic field lines

carboxysomes many autotrophic bacteriaenzymes for autotrophic CO2 fixation

site of CO2 fixation

phycobilisomes cyanobacteria phycobiliproteins light-harvesting pigments

chlorosomes Green bacterialipid and protein and bacteriochlorophyll

light-harvesting pigments and antennae

Magnetosome

The bacterial endospore• Microscopic, highly resistant, non-

motile, 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

• 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

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 single-celled, 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.