MICRO - ORGANISMS AROUND US

GROWTH OF MICRO - ORGANISMS

Meaning of Growth in Micro-organisms
Growth in micro-organisms refers to an increase in cell size and number. It is the process by which micro-organisms multiply and increase their population.
For unicellular organisms like bacteria, growth mainly means an increase in the number of cells through cell division (usually by binary fission).

Conditions Necessary for the Growth of Micro-organisms
 Micro-organisms need certain conditions for optimal growth. These include:

• Nutrients: Food substances that supply energy and materials for growth.
• Temperature: Most bacteria grow best between 25°C and 37°C (the body temperature of humans).
• pH (Acidity/Alkalinity): Most micro-organisms prefer a neutral pH (around 7).
• Oxygen: Aerobic micro-organisms need oxygen, while anaerobic micro-organisms do not need oxygen and may die in its presence.
• Moisture: Water is essential for biochemical reactions.
• Light: Some micro-organisms (like algae) need light for photosynthesis.
• Absence of toxins: Harmful substances may prevent growth.

Ways of Measuring Growth in Micro - Organisms

There are two major ways of measuring growth  in micro-organisms. They are:

1. First Method: A bacterial sample is inoculated into a nutrient agar. As the bacterial population increases, the clear liquid medium becomes cloudy or turbid. Progressive increase in turbidity signifies an increase in number of bacterial cells. In the laboratory, we use a spectrophotometer  to measure turbidity. 
   Note that as turbidity increases, the amount of light that can pass through a liquid medium decreases, thus, by measuring the turbidity of a bacterial culture in a nutrient agar at regular intervals, we can measure the growth of a bacterial population.  
2. Second Method: Here, small samples of bacteria are taken from the nutrient agar at regular time intervals. Each sample is then diluted several times and then inoculated onto a nutrient agar medium in a petri - dish and incubated. The number of colonies formed per petri -dish is then counted. The number of colonies indicate the number of bacterial cells in the diluted sample as each colony is formed by the multiplication of a simple bacterium.

BENEFICIAL EFFECTS OF MICRO - ORGANISMS

The benefits of micro-organisms would be discussed in three sections:
- in Medicine
- in Nature
- in Industries

In Nature

1. Decomposition
    Bacteria and fungi decompose dead plants, animals, and waste materials into simpler substances. This process releases nutrients like nitrogen, carbon, and phosphorus back into the soil, enriching it for plant growth. Examples of decomposers include Bacillus subtilis and Aspergillus niger.
2. Nitrogen Fixation
    Certain bacteria such as Rhizobium and Azotobacter convert atmospheric nitrogen into nitrates, which plants can absorb and use to build proteins. This process increases soil fertility and reduces the need for chemical fertilizers.
3. Nitrification
    Micro-organisms like Nitrosomonas and Nitrobacter convert ammonia into nitrites and then into nitrates, which are essential nutrients for plants.
4. Denitrification
    Bacteria such as Pseudomonas denitrificans convert nitrates back into nitrogen gas, completing the nitrogen cycle and maintaining environmental balance.
5. Carbon Cycle Contribution
    Micro-organisms play a vital role in the carbon cycle by breaking down organic materials and releasing carbon dioxide, which plants use for photosynthesis.
6. Formation of Humus
    Through continuous decomposition, micro-organisms help in the formation of humus. Humus improves the texture of the soil, enhances its ability to retain water, and supports plant growth.
7. Symbiotic Relationships
    Some micro-organisms live inside the bodies of plants and animals and assist in digestion or nutrient production. For example, Escherichia coli in the human intestine helps in the production of vitamin K.
8. Biological Control
    Certain micro-organisms are used to control pests naturally without the use of harmful chemicals. For instance, Bacillus thuringiensis is used as a biological pesticide against crop pests.
9. Sewage Treatment
    Microbes such as Pseudomonas and Nitrosomonas are used in sewage treatment plants to decompose organic matter and purify wastewater before it is released into the environment.
10. Oil Spill Cleanup (Bioremediation)
     Some bacteria like Pseudomonas putida can break down petroleum products, making them useful for cleaning up oil spills in oceans and soil.
    
     

In Medicine

1. Production of Antibiotics
    Micro-organisms are used in the manufacture of antibiotics that fight diseases caused by harmful bacteria. Penicillium notatum produces penicillin, Streptomyces griseus produces streptomycin, and Bacillus polymyxa produces polymyxin. These antibiotics have saved millions of lives.
2. Production of Vaccines
    Weakened or dead forms of micro-organisms are used to produce vaccines that protect humans and animals from diseases. Examples include vaccines for polio, tuberculosis (BCG), and measles.
3. Production of Vitamins
    Some bacteria such as Lactobacillus and Clostridium produce vitamins like vitamin B12 and vitamin K, which are essential for healthy growth and blood clotting.
4. Production of Hormones and Enzymes
    Certain bacteria are used to produce hormones like insulin for diabetic patients and enzymes such as amylase and lipase used in digestion and drug manufacture.
5. Genetic Engineering and Biotechnology
    Micro-organisms like Escherichia coli are used in genetic engineering to produce useful substances such as vaccines, hormones, and enzymes through DNA technology.
6. Probiotics
    Some micro-organisms, when taken in food or medicine, help maintain a healthy digestive system. These beneficial bacteria, such as Lactobacillus acidophilus, are called probiotics.
7. Medical Research
    Micro-organisms are used in laboratories to study disease patterns, test new drugs, and understand how infections spread.
8. Production of Antitoxins
    Certain bacteria are used in the preparation of antitoxins that neutralize poisons or toxins produced by harmful micro-organisms.
   
    

In Industries

1. Food Industry
    Micro-organisms play a major role in food production. Saccharomyces cerevisiae (yeast) is used in baking to make bread rise and in brewing to produce alcohol. Lactobacillus bulgaricus and Streptococcus thermophilus are used to make yoghurt, while Aspergillus oryzae is used to produce soy sauce and Acetobacter aceti is used to make vinegar.
2. Dairy Industry
    Bacteria such as Lactococcus lactis and Leuconostoc cremoris are used in the production of cheese, butter, and fermented milk products.
3. Beverage Industry
    Yeasts are used to ferment sugar into alcohol in the production of beer, wine, and other alcoholic drinks.
4. Pharmaceutical Industry
    Micro-organisms are used in the large-scale production of antibiotics, vaccines, enzymes, and other medicines used to treat diseases.
5. Leather Industry
    Bacteria are used to remove hair and soften animal hides during the processing of leather.
6. Textile Industry
    Enzymes produced by micro-organisms are used in fabric processing, bleaching, and removing starch from cloth, improving fabric quality.
7. Agriculture (Biofertilizers)
    Bacteria such as Rhizobium, Azotobacter, and Azospirillum are used to increase soil fertility naturally by fixing nitrogen, thereby reducing dependence on chemical fertilizers.
8. Energy Production
    Micro-organisms are used in producing biogas (mainly methane) from animal dung and plant waste. Methanogenic bacteria such as Methanobacterium are responsible for this process.
9. Waste Management
    Bacteria and fungi are used in composting organic waste to form manure, which enriches the soil and supports farming.
10. Paper and Pulp Industry
     Certain micro-organisms produce enzymes that help in breaking down wood pulp into paper and aid in recycling paper.
    
     
11. Mining Industry
     Some bacteria such as Thiobacillus ferrooxidans are used in bioleaching, a process that extracts metals like copper and gold from low-grade ores.
12. Biotechnology and Environmental Protection
     Micro-organisms are used in producing biofuels, biodegradable plastics, and other eco-friendly materials that help reduce pollution.

Harmful Effects of Some Micro-organisms

Micro-organisms can have several negative effects on humans, animals, plants, and materials. These effects include causing diseases, spoiling food, damaging materials, and reducing productivity.

1. Cause of Disease: Some micro-organisms cause diseases in humans, animals, and plants. Vibrio cholerae causes cholera, Mycobacterium tuberculosis causes tuberculosis, and Plasmodium causes malaria. In animals, Bacillus anthracis causes anthrax, while Rabies virus causes rabies. In plants, Phytophthora infestans causes potato blight, and cassava mosaic virus infects cassava leaves.

2. Spoilage of Food: Certain bacteria and fungi attack food, making it unsafe or unfit for consumption. Salmonella and Clostridium botulinum cause food poisoning, while fungi such as Penicillium and Aspergillus grow on bread, fruits, and grains, leading to decay and bad odour. This results in wastage of food and economic loss.

3. Deterioration of Materials: Some micro-organisms destroy materials like leather, textiles, wood, and paper. Moulds grow on damp materials, causing stains, foul smells, and weakening of the structure. Certain bacteria also corrode metals and cause damage to industrial equipment and pipelines.

4. Causes of Death: Serious infections caused by harmful micro-organisms can lead to death if not properly treated. Diseases like cholera, pneumonia, typhoid, and AIDS have claimed many lives globally. In animals, infections like rabies and anthrax can also be fatal.

5. Causes Undesirable Quality of Products: Micro-organisms can cause changes in colour, taste, smell, and texture of products. In industries such as food and beverage, contamination by bacteria or fungi can spoil batches of products, making them unsuitable for sale or consumption.

6. Reduction of Yield: Microbial infections in plants can significantly reduce crop yield and quality. Diseases such as maize smut, rice blast, and cassava mosaic disease destroy leaves, stems, and fruits, leading to poor harvest. This affects food supply and farmers’ income.

 Some Terms associated with micro - organisms.

Some Terms Associated with Micro-organisms

1. Disease: A disease is any condition that interferes with the normal functioning of the body, caused by infection, nutritional deficiency, or genetic disorder. Microbial diseases are caused by bacteria, viruses, fungi, or protozoa.
2. Health: Health is a state of complete physical, mental, and social well-being, not merely the absence of disease. A healthy body can resist infections and perform all life activities efficiently.
3. Symptoms: A symptom is a sign or physical change that indicates the presence of a disease or infection in the body. Examples include fever, cough, rashes, diarrhea, or fatigue.
4. Pathogen: A pathogen is any disease-causing micro-organism such as bacteria, viruses, fungi, or protozoa. Examples include Vibrio cholerae (causes cholera) and Plasmodium (causes malaria).
5. Vector: A vector is an organism, usually an insect or animal, that carries and transmits pathogens from one host to another. Examples include mosquitoes that spread malaria and tsetse flies that transmit sleeping sickness.
6. Antibody: An antibody is a special protein produced by white blood cells in the body to fight and neutralize foreign substances such as bacteria, viruses, and toxins.
7. Antigen: An antigen is any foreign substance or microbe that, when it enters the body, triggers the production of antibodies. Examples include bacterial toxins, viruses, and other harmful particles.
8. Vaccination: Vaccination is the process of introducing a weakened or dead form of a micro-organism into the body to stimulate the immune system to produce antibodies. This helps the body build immunity against future infections of the same disease.

How Vaccination protects the Body

Vaccination protects the body by helping it build immunity against specific diseases without causing the actual illness. It prepares the immune system to recognize and fight harmful micro-organisms more effectively when they enter the body in the future.

When a vaccine is given, it contains a weakened, dead, or inactive form of a pathogen, or sometimes only parts of it (such as proteins or toxins). The immune system identifies these substances as foreign invaders (antigens) and responds by producing antibodies to destroy them.

After vaccination, the body "remembers" the pathogen through memory cells. If the same micro-organism enters the body again, these memory cells quickly produce the right antibodies to fight it off before it can cause illness.

Therefore, vaccination:

• Stimulates the production of antibodies.
• Provides long-term immunity against specific diseases.
• Helps prevent the spread of infectious diseases in the community (herd immunity).
• Reduces the risk of severe illness or death from infections such as polio, measles, tetanus, and tuberculosis.

Diseases Caused by Micro-organisms

Micro-organisms such as viruses, bacteria, fungi, and protozoa cause various diseases in animals (including humans) and plants.

1. (a) Animal Diseases Caused by Viruses

Measles – caused by the measles virus
 Poliomyelitis (Polio) – caused by the poliovirus
 Rabies – caused by the rabies virus
 Chickenpox – caused by the varicella-zoster virus
 Foot and Mouth Disease – affects cattle, caused by the foot and mouth virus
 Influenza (Flu) – caused by the influenza virus
 HIV/AIDS – caused by the human immunodeficiency virus

1. (b) Plant Diseases Caused by Viruses

Cassava Mosaic Disease – caused by cassava mosaic virus
 Tobacco Mosaic Disease – caused by tobacco mosaic virus (TMV)
 Maize Streak Disease – caused by maize streak virus
 Tomato Leaf Curl – caused by tomato leaf curl virus
 Rice Yellow Mottle – caused by rice yellow mottle virus

2. (a) Animal Diseases Caused by Bacteria

Cholera – caused by Vibrio cholerae
 Tuberculosis – caused by Mycobacterium tuberculosis
 Typhoid Fever – caused by Salmonella typhi
 Pneumonia – caused by Streptococcus pneumoniae
 Anthrax – caused by Bacillus anthracis
 Whooping Cough – caused by Bordetella pertussis

2. (b) Plant Diseases Caused by Bacteria

Citrus Canker – caused by Xanthomonas citri
 Tomato Wilt – caused by Ralstonia solanacearum
 Soft Rot of Vegetables – caused by Erwinia carotovora
 Rice Blight – caused by Xanthomonas oryzae
 Fire Blight of Apple and Pear – caused by Erwinia amylovora

3. (a) Animal Diseases Caused by Fungi

Ringworm – caused by Trichophyton or Microsporum
 Athlete’s Foot – caused by Tinea pedis
 Candidiasis (Thrush) – caused by Candida albicans
 Aspergillosis – caused by Aspergillus species

3. (b) Plant Diseases Caused by Fungi

Rust of Maize – caused by Puccinia polysora
 Black Pod Disease of Cocoa – caused by Phytophthora palmivora
 Smut of Rice or Maize – caused by Ustilago maydis
 Late Blight of Potato – caused by Phytophthora infestans
 Leaf Spot of Groundnut – caused by Cercospora personata

4. Animal Diseases Caused by Protozoa

Malaria – caused by Plasmodium species
 Sleeping Sickness – caused by Trypanosoma brucei (transmitted by tsetse fly)
 Dysentery (Amoebic) – caused by Entamoeba histolytica
 Trypanosomiasis in Cattle (Nagana) – caused by Trypanosoma congolense
 Coccidiosis – caused by Eimeria species (common in poultry)

Spread of Disease-causing Micro-organisms

Disease-causing micro-organisms, or pathogens, can spread from one person, animal, or object to another through different means. The mode of spread depends on the type of micro-organism and the disease it causes.

1. Air-borne Transmission

Some diseases spread through the air when an infected person coughs, sneezes, or talks, releasing droplets that contain pathogens. Healthy people inhale these droplets and become infected. Examples: Tuberculosis, influenza, measles, and COVID-19.

2. Water-borne Transmission: When drinking water or food is contaminated with human or animal waste, it may contain pathogens. People who drink or use such water become infected. Examples: Cholera, typhoid fever, and dysentery.

3. Food-borne Transmission: Pathogens can spread through contaminated or improperly cooked food. Poor hygiene during food handling also contributes to infection. Examples: Food poisoning, typhoid fever, and salmonellosis.

4. Direct Contact: Some diseases are spread through direct contact with an infected person, such as touching, hugging, or coming in contact with infected body parts or fluids. Examples: Ringworm, athlete’s foot, and conjunctivitis.

5. Sexual Contact:  Certain micro-organisms are transmitted during sexual intercourse or contact with sexual fluids of infected persons. These are called sexually transmitted infections (STIs). Examples: HIV/AIDS, gonorrhea, syphilis, genital herpes, and hepatitis B.

6. Indirect Contact: Diseases can spread through objects or surfaces (called fomites) used by infected persons, such as towels, clothes, utensils, or door handles. Examples: Common cold, conjunctivitis, and influenza.

7. Vector Transmission: Some insects and animals carry disease-causing organisms and transmit them to humans. These carriers are called vectors. Examples:

• Mosquitoes transmit malaria and yellow fever.
• Tsetse flies transmit sleeping sickness.
• Houseflies spread cholera and typhoid.

8. Blood and Body Fluids: Diseases can spread through transfusion of infected blood, sharing needles, or contact with infected body fluids such as saliva, sweat, or semen.
 Examples: HIV/AIDS, hepatitis B, and Ebola.

9. Mother-to-Child Transmission: An infected mother can transmit diseases to her baby during pregnancy, childbirth, or breastfeeding. Examples: HIV/AIDS and syphilis.

10. Animal-to-Human Transmission (Zoonotic Transmission): Some diseases spread from infected animals to humans through bites, scratches, or contact with body fluids. Examples: Rabies (from dog bites), anthrax (from infected cattle), and bird flu (from poultry).

(Draw Table from Essential Biology Pg. 261 - 264: Food & Water Borne Diseases, Air Borne Diseases, Diseases spread by Vectors, sexually transmitted diseases)