This kingdom is made up of organisms known as bacteria (singular: bacterium). They are the most ancient and smallest organisms with a cellular structure. They are mainly single celled. Bacteria occupy many environments such as soil, dust, water and in the bodies of plants and animals.

Some bacteria are found in hot springs where temperatures are 78ºC or more. Others can withstand very low temperatures. Some are found in very deep cracks in the ocean floor, at very high temperatures, about 360ºC (extreme thermophiles).


General and Distinctive Features of the Kingdom Monera

General characteristics of the kingdom monera

1.They are mainly unicellular and very small.

2.They are all prokaryotic (nucleus not bound by membrane)

3.They reproduce by binary fission.

4.Some members of the kingdom are autotrophs while others are heterotrophs

5.They have cell wall made up of protein material and sometimes lipids.

6.Some bacteria form spores during adverse conditions i.e. extreme conditions e.g. high or low temperatures, drought etc. The spores allow them to survive as they have very thick resistant walls.

7.Some are aerobes while others are anaerobes.

8.The genetic material (DNA) is scattered in the cytoplasm and they lack internal membrane bound organelles such as mitochondria, chloroplasts, golgi bodies etc.

  

Structures of the Representative Organisms of the Kingdom Monera

General structure of the bacteria

1.Bacteria have strong and rigid cell walls due to the presence of murein. The wall prevents the cell from bursting when it absorbs much water (as a result of osmosis).

2.Bacterial cells are bounded by partially permeable membranes.

3.Bacteria possess capsules which are slimy or gummy.They have flagella which aid motility of the bacteria. Motile bacteria can move in response to a certain stimulus i.e. tactic movement. Flagella can easily be seen by electron microscope.

4.They have small self replicating circle of extra DNA called a plasmid.




Forms of bacteria
Bacterial shape is an important aid to classification.
There are four main shapes

Coccus (plural: cocci)
They are spherical in shape and can be of the following types.


  •  Micrococcus – exist singly. They cause sore throat.


  •  Diplococci - this type of bacteria exist in pairs. The pneumococci (Diplococcus pneumoniae) are the only members. They cause pneumonia.


  •  Streptococci – this type of bacteria stick together and form a chain. Most of them infect upper respiratory surface and cause diseases e.g. sore throat.



  • Staphylococci – These bacteria form a grape like bunch. They cause boils, pneumonia, food poisoning and other diseases.



Bacilli (singular: bacillus)
These are rod shaped bacteria. They can be:


  • Single rods, for example, Escherichia coli commonly living in the gut and Salmonella typhi which cause typhoid fever.


  • Rods in chain, for example, Azotobacter, a nitrogen-fixing bacteria, and Bacillus anthracis which cause the disease anthrax.


  • Bacilli with endospores showing various positions, shapes and sizes of spores.
They can be:
a. Central, not swollen e.g. Bacillus anthracis causes anthrax
b. Spherical spore, terminal swollen e.g. Clostridium tetani causes tetanus
c. Sub-terminal, swollen e.g. Clostridium botulism causes botulism.Spores may also be central


  • Spirilla (singular: spirillum)
These are spiral-shaped bacteria e.g. Treponema pallidum which causes syphilis



  • Vibrio
These are comma shaped bacteria, for example Vibrio cholerae.





Economic Importance of Bacteria

In Agriculture, the bacteria are mostly important for following reasons;
  • Nitrogen fixation: Plants cannot trap nitrogen from the atmosphere but bacteria can fix nitrogen and change it into nitrogenous compounds. The phenomenon is called nitrogen fixation. The bacteria, which fix atmospheric nitrogen, are called nitrogen-fixing bacteria. Some of the nitrogen fixing bacteria are found freely in soil are called free-living bacteria, eg. Clostridium and Azotobacter. Some of them are found in root nodules making association with leguminous plants called symbiotic bacteria, eg. Rhizobium.
  • Nitrification: Some bacteria convert ammonium compounds into nitrates in the soil. The process is called nitrification. The bacteria that take part in this process are called nitrifying bacteria, ie. Nitrobacter and Nitrosomonas.  Ammonia ---> Nitrites ---> Nitrates
  • Ammonification: Some bacteria utilize proteins of dead bodies and convert it into amino acids. These amino acids are converted into ammonia by some bacteria. The process is called ammonification and the bacteria involve in the process are called ammonifying bacteria. Then the ammonia reacts with CO2 and H2O and gives ammonium carbonate which is absorbed by plants.
  • Bacteria decompose dead bodies. They convert complex organic compounds into simple inorganic compounds. Therefore they're called natural scavengers.
  • Bacteria make the milk sour and produce flavor. They are responsible for coagulation of milk. E.g. Lactobacillus.
  • Bacteria convert sugary substances into alcohol, acids, acetones; etc the process is called fermentation.
  • Bacteria also help to produce different types of enzymes like Amylase secreted from Bacillus, Protease from Bacillus, Streptokinase from Streptomyces.
  • Bacteria are useful for vitamin production like Vitamin B (Cabalmin) is secreted from Pseudomonas, Vitamin B (Riboflavin) is secreted from Clostridium.
  • They are important for antibiotic production like Terramycin from Streptomyces rimosus, Streptomycin from S. griseus, Neomycin from S. fradiae.
  • They are also important to produce hydrogen commercially. During the process they ferment carbohydrate and hydrogen gas is produced.
  • Bacteria decompose waste products.

Disadvantage of Bacteria

1.Some of the species cause food poisoning. They secret some toxic chemical substances on out food stuff which cause food poisoning, eg Staphylococcus and Clostridium.

2.Some are responsible for human diseases: Cholera: Vibrio cholera, Pneumonia: Staphylococcus pneumoniae, Diarrhea: Escherichia coli, Tuberculosis: Mycobacterium tuberculosis Leprosy: M. leprae, Meningitis: Neisseria meningitidis.

3.Some bacteria are responsible for plant diseases. Red stripe in sugarcane, Leaf streak in rice, black rot in cabbage and yellow rot in wheat are caused by Xanthomonas and Pseudomonas.

The Characteristics of Pathogenic and Non-pathogenic Bacteria

Pathogenic bacteria are bacteria that can cause infection. This article deals with human pathogenic bacteria. Although most bacteria are harmless or often beneficial, several are pathogenic. One of the bacterial diseases with the highest disease burden is tuberculosis, caused by the bacterium Mycobacterium tuberculosis, which kills about 2 million people a year, mostly in sub-Saharan Africa. 

Pathogenic bacteria contribute to other globally important diseases, such as pneumonia, which can be caused by bacteria such as Streptococcus and Pseudomonas, and food borne illnesses, which can be caused by bacteria such as Shigella, Campylobacter, and Salmonella. Pathogenic bacteria also cause infections such as tetanus, typhoid fever, diphtheria, syphilis, and leprosy. Pathogenic bacteria are also the cause of high infant mortality rates in developing countries.


Nonpathogenic organisms are those that do not cause disease, harm or death to another organism and is usually used to describe bacteria.It describes a property of a bacterium - its ability to cause disease. Most bacteria are nonpathogenic. It can describe the presence of non-disease causing bacteria that normally reside on the surface of vertebrates and invertebrates as commensals. 

Some non pathogenic microorganisms are commensals on and inside the body of animals and are called microbiota. Some of these same nonpathogenic microorganisms have the potential of causing disease, or being pathogenic if they enter the body, multiply and cause symptoms of infection.

Immunocompromised individuals are especially vulnerable to bacteria that are typically non pathogenic but because of a compromised immune system, disease occurs when these bacteria gain access to the body's interior. Genes have been identified that predispose disease and infection with non pathogenic bacteria by a small number of persons. 

Nonpathogenic colistrains normally found in the gastrointestinal tract have the ability to stimulate the immune response in humans, though further studies are needed to determine clinical applications.