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.

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.

Pathogenic bacteria

These are bacteria that can cause disease. Some of the diseases caused by bacteria are fire blight, ring rot and tobacco mosaic in plants, and TB, typhoid, tetanus, cholera, syphilis and gonorrhoea in animals.

Fimbriae or pili

These are hair-like structures found on the surface of the bacteria. The hairs attach themselves to the host so that they cannot be removed easily. For example, Escherichia coli produce fimbria that attach themselves to the lining of the urinary tract or the intestines.

Flagella

These are long tail-like structures that help some pathogenic bacteria to move to a site where they can cause infection.

Toxins

Some bacteria produce toxic (poisonous) compounds that harm hosts. In humans, these toxins cause effects such as vomiting, diarrhoea, fever and muscle cramps. For instance, toxins released by Salmonella bacteria can cause severe diarrhoea.

Invasion and colonisation

Some bacteria attack and become resistant to modes of treatment. For example, the bacterium that causes tuberculosis has become resistant to many antibiotics by transforming itself.

Resistance

Some types of bacteria release a substance known as biofilm that protects them from harmful substances such as drugs.

1. 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.
2. Nitrification: Some bacteria convert ammonium compounds into nitrates in the soil. The process is called nitrification.
3. Ammonification: Some bacteria utilize proteins of dead bodies and convert it into amino acids. These amino acids are converted into ammonia by some bacteria.
4. Bacteria decompose dead bodies. They convert complex organic compounds into simple inorganic compounds. Therefore they are called natural scavengers.
5. Bacteria make the milk sour and produce flavour. They are responsible for coagulation of milk. E.g. Lactobacillus.
6. Bacteria convert sugary substances into alcohol, acids, acetones, etc. The process is called fermentation.
7. Bacteria decompose waste products.

1. Some species cause food poisoning.
2. Some are responsible for human diseases: cholera (Vibrio cholerae), pneumonia.
3. Some bacteria are responsible for plant diseases.

These are bacteria that are harmless even when they are on a plant or animal body.

Pathogenic bacteria are bacteria that can cause infection. This article deals with human pathogenic bacteria.

Non-pathogenic 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 non-pathogenic.

1. Some non-pathogenic bacteria feed on substances that are harmful to the environment and in the process neutralize them. For example, they neutralize petroleum waste from petroleum industries, thereby making the environment safe.
2. Bacteria such as Rhizobium that are formed in the root nodules of leguminous plants, Clostridium and Azotobacter help to convert atmospheric nitrogen to nitrates. Plants need nitrate for their growth.
3. Bacteria in the stomach of ruminant animals such as goats and cows secrete enzymes that help in the digestion of cellulose which forms a large part of the diet of ruminants.
4. Bacteria in the animal gut manufacture vitamins K and B.
5. Lactic acid bacteria produce lactic acid as a result of fermentation of carbohydrates. This is important in the production of fermented food and alcoholic drinks.
6. Autotrophic bacteria carry out photosynthesis.

1. Bacteria that neutralise harmful substances help clean the environment.
2. Bacteria found in the gut help animals to digest food and break it down into a form that can be absorbed into the body.
3. Vitamins produced by bacteria are important for the health of animals including humans.
4. Fermentation is used in the production of yoghurt, vinegar and alcohol.
5. Controlled fermentation is used in the curing of tea and tobacco and retting of flax, help to treat and preserve these products. Retting of flax is important in the production of fibre.
6. Some bacteria are used to produce antibiotics which are used to treat bacterial infections.
7. During photosynthesis, autotrophic bacteria release oxygen into the atmosphere. Oxygen is vital for respiration in all living things.

1. Bacteria cause infection and disease in animals. Some of these are fatal.
2. Bacterial diseases in crops cause decreased production and losses to farmers.
3. Bacteria cause food to decay and spoil.
4. Denitrifying bacteria in the soil convert nitrates to nitrogen. This reduces the nutrients available to plants.