Microorganisms - Useful And Harmful
Last Updated : 23 Jul, 2025
Microorganisms are microscopic life forms that are ubiquitous. They can be unicellular or multicellular and are beneficial to humankind, but they can be harmful as well. Microbes can be beneficial as they play diverse roles in nutrient cycling, food fermentation, antibiotic production, and many more.
On the other hand, they are also responsible for causing diseases in humans and animals, food spoilage, and posing environmental challenges. Microorganism examples are bacteria, protozoa, algae, and fungi.
What are Microorganisms?
Definition of microorganisms - Microorganisms, or microbes, are microscopic life forms that are ubiquitous in nature. They can be unicellular or multicellular.
Microorganisms are extremely small life forms that are not visible to the naked eye. They can be seen only thorough a microscope. Other than macroscopic life forms such as plants and animals, microbes constitute one of the most important parts of biological systems on the planet. The diverse group of microbes comprises viruses, bacteria, fungi, protists, and algae.
They inhabit air, water, soil, and even living organisms. They thrive in extreme ecosystems such as thermal vents, highly acidic or alkaline environments, and salinity as well. This unseen domain plays a very crucial role in bringing life to earth. Microorganisms are our friend and foe. On one side, microbes in human welfare are beneficial for us, but on the other side, they can be harmful in many diverse ways.
Classification of Microorganisms
Microorganisms can be classified into five major categories:
Group | Characteristics | Examples |
|---|
Viruses | Acellular, multiply only in living hosts, nucleic acid is covered in a protein coat, non-living outside hosts. | HIV, Hepatitis virus, Influenza. |
Bacteria | Unicellular, prokaryotes. | E. coli, Streptococcus. |
Protists | Unicellular or multicellular, eukaryotes. | Amoeba, Paramecium. |
Fungi | Unicellular or multicellular, eukaryotes. | Saccharomyces, Rhizopus. |
Algae | Unicellular or multicellular, eukaryotes. | Spirulina, Volvox. |
How can Microbes be Useful to Us?
Microorganisms are beneficial to humankind in the following ways:
- Nutrient Cycling: Microbes break down complex organic matter into simpler forms. This process aids in nutrient cycling ensuring the availability of complex nutrients to the plants and other simpler organisms maintaining the overall health of the ecosystem.
- Soil Fertility: Microbes can enhance soil fertility by fixing atmospheric nitrogen in symbiotic association with the roots of higher plants. By the process of nitrogen fixation, atmospheric nitrogen is converted in ammonia which is an available form of nitrogen to the plants leading to rapid growth of plants.
- Agriculture: Microbes residing in the soil establish symbiotic relationships with the roots of the higher plant contributing to their growth and productivity. Fungi in association with the roots of plants is known as mycorrhiza and it helps in providing nutrients to the plants from soil.
- Fermentation and Food Industry: Bacteria and yeasts play a significant role in food fermentation process. Food items such as yoghurt, cheese, bread, idli and fermented beverages are used to enhance the nutritional profiles, texture, and flavour of the food.
- Production of Probiotics: Beneficial bacteria which are known to improve human gut health are known as probiotics and they support good microbes in the gut. Probiotics help in digestion of the food, absorption of nutrients and boosting the immune system.
- Production of Antibiotics: Microbes produce certain chemical compounds during their metabolic processes known as antibiotics which help in controlling infection caused by other pathogenic or disease-causing microorganisms. Microbes are also used in the production of vaccines.
Some beneficial role of the microbes are listed in the table:
Microbial group | Beneficial Role | Examples |
|---|
Viruses | Bioremediation and genetic engineering. | Lambda phage, Bacteriophage. |
Bacteria | Nutrient cycling and soil fertility and fermentation. | Rhizobium, Pseudomonas, Lactobacillus. |
Fungi | Food industry, production of antibiotics. | Saccharomyces, Penicillium. |
Protists | Nutrient cycling. | Euglena, Paramoecium. |
Algae | Waste water treatment, nutritional supplement. | Chlorella, Spirulina. |
Harmful Microorganisms
Microorganisms can be harmful to humankind in the following ways:
- Outbreaks or Pandemics: Microbes are responsible for pandemics, as there are outbreaks of viral infections majorly such as HIV, influenza, and Ebola. Recently, COVID-19 became a pandemic leading to illness, fatality, and social disruption affecting millions of lives.
- Infectious Diseases: Virulent viruses, pathogenic bacteria, fungi, and protozoa are responsible for causing diseases in humans, animals, and plants. Malaria, typhoid, and dengue are a few examples of the same which leads to fatality.
- Allergic Responses: Since microbes are ubiquitous, they may trigger allergic responses and hypersensitivities in susceptible individuals who have a weaker immune system, leading to various respiratory problems such as asthma, and skin rashes.
- Antimicrobial Resistance: Overuse or misuse of antibiotics without any prescription has led to the emergence of antimicrobial-resistant (AMR) or multi-drug-resistant strains (MDRS) of bacteria that make infections difficult to treat. Staphylococcus is an example of MDRS.
- Diseases in Plants: Microbes such as pathogenic bacteria, fungi, bacteria, and viruses affect productivity and yield in agriculture as they can cause devastating diseases in plants. This leads to significant agricultural losses and food insecurity which is a major concern today as food is required to feed the global population.
- Foodborne Illnesses: Microbes such as Salmonella, Escherichia coli (E. coli), Shigella and Listeria. They can cause foodborne illnesses due to the consumption of contaminated food and water, leading to gastrointestinal discomforts which may lead to severe complications.
Some harmful effects caused by the microbes are listed in the table:
Microbial group | Harmful Effects | Examples |
|---|
Virulent viruses | Infections in humans and animals. | Corona virus, Hepatitis virus. |
Pathogenic bacteria | Cause of infectious diseases. | Salmonella, Shigella. |
Harmful fungi | Pathogenic to plants and animals, cause spoilage. | Fusarium, Aspergillus. |
Parasitic Protists | Cause of diseases. | Plasmodium, Entamoeba. |
Harmful Algae | Environmental threat, algal blooms. | Karenia, Microcystis. |
Diseases Caused By Microorganisms
Diseases Caused by Microorganisms in Animals
Some diseases caused by microbes with their causative agaent are listed below:
Viruses | Bacteria | Fungi | Protozoa |
|---|
Influenza (Influenza virus) | Tuberculosis (Mycobacterium tuberculosis) | Trichophyton spp. (Trichophyton spp. ) | Malaria (Plasmodium falciparum) |
Common cold (Rhinovirus ) | Cholera (Vibrio cholerae) | Candidiasis (Candida albicans) | Amoebiasis (Entamoeba histolytica) |
AIDS (Human Immunodeficiency Virus (HIV)) | Tetanus (Clostridium tetani) | Aspergillosis (Aspergillus spp.) | Giardiasis (Giardia lamblia) |
COVID (Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)) | Gonorrhea (Neisseria gonorrhoeae) | Cryptococcosis (Cryptococcus neoformans) | Toxoplasmosis (Toxoplasma gondii) |
Hepatitis (Hepatitis A, B, C viruses) | Lyme disease (Borrelia burgdorferi) | Histoplasmosis (Histoplasma capsulatum) | Chagas disease (Trypanosoma cruzi) |
Diseases Caused by Microorganisms in Plants
Some diseases caused by microbes in plants are listed below:
Viruses | Bacteria | Fungi |
|---|
Tobacco Mosaic Virus (TMV) | Fire Blight (Erwinia amylovora) | Powdery Mildew (Sphaerotheca spp.) |
Tomato Yellow Leaf Curl Virus (TYLCV) | Bacterial Leaf Spot (Xanthomonas, Pseudomonas) | Late Blight (Phytophthora infestans) |
Food Spoilage by Microorganisms
Microorganisms can grow on food and change the physical and chemical properties of the food in such a way that they become inedible. Some points on food spoilage are listed below:
- Food spoilage is caused by bacteria, and fungi majorly breaking down food components altering their flavour, and odour, causing discolouration, sliminess, and by producing gas.
- Techniques such as proper food handling, storage, and processing are crucial for preventing microbial spoilage.
- Quality control (QC) measures such as regular testing for contamination of food and water and maintaining sanitary conditions are essential to prevent food spoilage.
- Microbial spoilage may pose health risks due to the production of toxins and the presence of pathogenic microorganisms and it also leads to economic loses of the food raising concern about the food security.
- Implementing a set of rules known as Hazard Analysis and Critical Control Points (HACCP) systems is crucial in managing microbial spoilage effectively.
Conclusion - Microorganisms - Useful or Harmful
Microorganisms are a crucial component of life on earth. Sustainence of life on earth would not have been possible without them. Microorganisms have a wide range of beneficial roles because of which they serves as our friends but on the other side they can be harmful to the other lives as well. Understanding both the sides of microorganisms helps us to navigate the beneficial and adverse effects of the same so that they can be utilised at their true potential.
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