Microbiology

• Microbiology is the study of micro-organisms


• This group includes bacteria, fungi and virus.


• Some micro-organisms are pathogenic.


• Pathogens are micro-organisms that cause disease


• Micro-organisms are extremely small and many are only visible with the aid of a microscope.

Bacterria

• BACTERIA are microscopic unicellular Prokaryotes.
  Bacteria belong to the kingdom Monera
  Bacteria that are important in agriculture fall into three main categories:
  –Decomposers: Bacteria involved in the breakdown of organic matter in soil. This bacteria is responsible for the souring of milk.
  –Symbiotic bacteria: Rhizobium fixes nitrogen in the root nodules of clover. This bacteria helps break down cellulose in the ruminant animals.
  –Pathogenic bacteria: Bacteria are responsible for diseases in plants and farm animals e.g. Bovine tuberculosis in cattle and blackleg a disease in potatoes.


• Classification of bacteria
  Bacteria are classified according to shape
  Most bacteria are either rod-shaped or spherical.


• STRUCTURE  :1. Bacteria are Typically composed of a Cell Wall, a Cell Membrane, and Cytoplasm.


• 2. Some bacteria have Distinctive Structures, such as Endospores, Capsules, and Outer Membranes.


• Mode of Respiration
  Aerobic bacteria release energy from sugars by aerobic respiration
  Some bacteria have the ability to release energy from sugars in the absence of oxygen. These bacteria carry out anaerobic respiration (also known as fermentation)
  Lactobacillus bacteria break down sugars in grass into lactic acid during the production of silage.


• Mode of reproduction
  Under favourable conditions, bacteria can rapidly reproduce by a process known as binary fission.
  Several generations can be produced in a few hours.If environmental conditions become unfavourable, some bacteria have the ability to produce endospores.
  These endospores are highly resistant structures and can withstand high and low temperatures.ENDOSPORES
  
  1. Some bacteria have a special means of surviving difficult conditions.  WHEN LIVING CONDITION BECOME UNFAVORABLE, SOME BACTERIA FORM SPECIAL, DEHYDRATED CELLS CALLED ENDOSPORES.
  
  2. A bacterial Endospore is a dormant structure that is produced by some Gram-positive bacterial species that are exposed to harsh environmental conditions.
  
  3. Endospores consists of a Thick Outer Covering that surrounds the Cell's DNA.
  
  4. Although the Original Cell may be Destroyed (Die) by harsh conditions, its Endospore will survive. They help bacteria resist High Temperature, Harsh Chemicals, Radiation, Drying, and other environmental extremes.
  
  5. Bacteria that form Endospores have an advantage for survival.  Endospores can be alive but inactive for many years.
  
  6. When conditions improve (become favorable), they break open and produced new bacteria cells.
  
  7. This is NOT a form of Reproduction (THEY ARE NOT REPRODUCTIVE CELLS), but it does allow some species of bacteria to survive hostile conditions and to grow and reproduce when conditions improve.


• Rhizobium and Clover
  They have a symbiotic relationship
  Rhizobium bacteria are found in the root nodules of clover and leguminous plants
  Rhizobium fixes nitrogen gas into nitrates. This benefits the plant and the plant provides sugars for the bacteria.


• Fungi
  Belong to the kingdom Fungi
  They lack chlorophyll, so they are unable to photosynthesise
  Fungi are either saprophytes (decompose organic matter) or parasites
  Parasitic fungi include:
  –Ringworm (animal parasite)
  –Potato blight (plant parasite)


• Structure of fungi
  Fungi consist of filaments called hyphae
  The entire mass of hyphae is called the mycelium
  Rhizoids anchor the fungi and absorb nutrients
  Sporangium produce spores.


• Mode of reproduction
  Fungi can reproduce asexually and sexually
  –Fungi reproduce sexually by producing zygospores


• 
  

  Sexual Reproduction

  
  

   

  
  

  Mycelia of opposite strain are close.

  
  

  Hyphae of opposite strain grow towards each other.

  
  

  The touching tips of the hyphae fill with nuclei and cytoplasm – progametangia formed.

  
  

  A cross wall forms behind each tip forming gametangia.

  
  

  The hypha behind each gametangium is called a suspensor.

  
  

  The contents of the gametangia mix.

  
  

  The nuclei of opposite strains fuse in pairs – fertilisation.

  
  

  The combined gametangia develop into a diploid zygospore.

  
  

  The zygospore is thick-walled resistant and dormant.

  
  

  In favourable conditions the zygospore germinates by meiosis.

  
  

  A haploid sporangiophore with a spore-filled sporangium grows from the zygospore.

  
  

  The spores are wind dispersed and germinate forming a new haploid mycelim.

  
  

Asexual Reproduction

–They reproduce asexually by producing spores in the sporangium.

Vegetative structure is haploid (n).

Sporangia form at the tip of sporangiophores.

The sporangium fills with haploid nuclei and cytoplasm.

The columnella forms separating the sporangium from the sporangiophore.

Each nucleus with cytoplasm forms a haploid spore with a tough resistant wall.

The spores are wind dispersed.

The spores germinate forming a new haploid mycelium if conditions are suitable.

Yeast Budding

Asexual reproduction by budding.  Good growth conditions – cell increasing in size.  A small bubble-like extension grows from the cell.  The nucleus undergoes mitosis.  A daughter nucleus moves into the bud.  The bud may remain attached and form a small colony by further budding.  The bud may detach and undergo budding.  Budding is a very fast method of reproduction.

• Potato Blight
  Potato blight is caused by an airborne fungus
  Zoospores invade the cells of the potato leaves
  Hyphae, with special structures called haustoria, remove the nutrients from the cells in the leaves
  Hyphae branches exit through stomata where they develop into sporangia.
  The sporangia contain zoospores
  Symptoms of blight include: brown spots appear on the leaves of the plant and black patches on tubers
  Warm humid weather favours the spread of blight.


• Viruses
  Viruses are extremely small
  They can only reproduce in other living cells
  Viruses are parasites
  Antibiotics are ineffective at treating viral diseases
  Some diseases can be vaccinated against
  A virus causes BVD in cattle.


• SUMMERY OF THE ADVANTAGES AND DISADVANTAGES OF BACTERIA AND FUNGI

Advantages: 

1. bacteria are used in the production of yogurt


2. fungi are used to produce cheese


3. bacteria and fungi are used to produce antibiotics


4. rhizobium fixes nitrogen to nitrates in clover

Disadvantages:

1. bacteria cause souring in milk


2. fungi cause spoilage of food


3. bacteria and fungi cause many diseases.


4. in waterlogged soils, denitrifying bacteria convert nitrates into atmospheric nitrogen.