Bacteria exert both deleterious and benefical effects on human life. Beneficial species liberate fertilizer elements for growing crops, destroy sewage and other wastes, and produce valuable chemicals.
Some species are harmful for animals as well as humans.
Beneficial and harmful aspects of bacteria are briefly discussed below:
Beneficial Activities
1. To increase soil fertility
- Both symbiotic bacteria (Rhizobium, Pseudomonas) forming nodules and asymbiotic bacteria (Clotridium, Azotobacter) living in the soil are capable of fixing inorganic nitrogen into organic form and helping to increase soil fertility.
- Increase soil fertility by decomposing proteins of dead organic remains of plants and animals.
- Clostridium, Pseudomonas, Bacillus, etc. help in ammonification, and Nitrosomonas and Nitrobacter help in nitrification.
2. Putrefaction and Decay
- Putrefaction to the anaerobic decomposition of organic remains with the product of malodorous substances.
- The most important role of bacteria is in the decomposition of organic matter.
3. Retting of Fibres
- Bacteria help in the retting and separation of fibres of jute, hemp, flax, etc.
- Genus Clostridium hydrolyzes the pectic substance that binds the fibres together.
- These are used in the making of ropes and sacks.
4. Preparation of Dairy Products
- The dairy industry uses bacteria in the manufacture of dairy products like curd, butter, ghee, cheese, etc.
- E.g., Streptococcus, Leuconostoc, and Lactobacillus.
5. Lactic Acid Production
- Lactobacilli (L. bulgaricus) are used in the manufacture of lactic acid.
- The sugar present in the whey is converted into lactic acid by the enzyme lactase produced by the bacilli.
6. Vinegar Production
- Vinegar, or acetic acid, is produced from alcohol by bacteria.
- E.g., Acetobacter, Gluconobacter and Gluconacetobacter.
7. Alcohol and Acetone Production
- Various bacteria, including Clostridium, Eubacterium, and Bacillus, are used in the production of acetone and alcohol.
8. Amino Acid Production
- Many amino acids are produced on a commercial basis with bacterial fermentation.
- Lysin is produced by E. coli and Enterobacter aerogenes. Glutamic acid is produced by Corynebacterium glutamicum.
9. Production of Fermented Foods
- Important food items are produced by microbial fermentation.
- Pickles are produced with the help of Lactobacillus and Streptococcus.
10. Protein Food
- Bacteria produced in massive quantities are an attractive source of food.
- These, when cultivated, yield a large cell crop that is rich in protein (single cell protein).
- Dried cells of Pseudomonas that grow on petroleum products have 69% protein.
11. Production of Silage
- Production of silage, a food of high nutritive value for cattle.
- E.g., Streptococcus, Lactobacillus
12. Curing and Repering of Tobago and Tea
- Bacillus megaterium is used for the curing process.
- The ripening or fermentation takes place due to the action of Micrococcus condisans.
13. In Paper and Textile Industry
- The enzyme amylase, excreted from Bacillus subtilis, is used in sizing paper and desizing textiles.
14. In Leather Industry
- Bacillus subtilis is used in tanning leather.
15. In Sewage Disposal
- Enterobacter, Alcaligenes, Pseudomonas, etc. are used in the various processes associated with sewage treatment and disposal.
16. Enzymes Production
- Enzymes secreted by bacteria inhabiting the stomach and intestines of cattle, horses, etc. help digest the carbohydrate cellulose.
- Enzyme amylase is produced by Bacillus subtilis, Streptococcus.
17. Vitamin Production
- Many vitamins are produced by bacteria.
- Vitamin B – Streptomyces olivaceus, Vitamin K – Streptococcus haemolyticus, and Vitamin C – Gluconobacter suboxydans
18. Antibiotic Production
- Antibiotics are produced by several species of bacteria.
- Example: polymyxin, subtilin, bacteriocin, gramicidin, etc.
- Antibiotics produced by higher bacteria are amphatercin, carbomycin, tetracycline, etc.
19. As Human Symbionts
- The bacteria E. coli living in the intestine of human beings are symbionts and synthesis vitamin B.
20. Other Medicine
- The substance dextran produced by Leuconostoc mesenteroides is used as a blood plasma substitute.
- The enzymes streptokinase and streptodornase, produced by Streptococcus haemolyticus, are used in dissolving blood clots.
21. Pigments Production
- Pseudomonas sp. produces greenish to dark brown pigments.
- Chromobacterium sp. produces a violet pigment.
- Serratia sp. produces a red pigment.
Harmful Activities
1. Reducing Soil Fertility
- The bacteria Thiobacillus, Serratia, Micrococcus, and Pseudomonas are capable of transforming nitrogen in the soil into nitrogen gas by denitrification.
- This change leads to a net loss of nitrogen from the soil, i.e., a reduction in soil fertility.
2. Food Spoilage
- Bacteria generally decompose food and render it unfit for human consumption.
- E.g., Bread: Bacillus subtilis, Syrup: Enterobacter, Fruits and Vegetables: Micrococcus, Meat: Clostridium, Pseudomonas, Fish: Pseudomonas, Flavobacterium, Egg: Psudomonas, etc.
- Staphylococcus occurs, from which exotoxin is liberated, which results in poisoning.
- Botulism is a fatal food poisoning of humans and animals caused by the toxins produced by Clostridium botulinum.
3. Paper and Cotton Deterioration
- Some bacillus are responsible for degrading the cellulose of paper and cotton.
4. Bacteria and Diseases
- Pathogenic bacteria cause various diseases in humans, animals, and cultivated plants.
Disease of Humans:
| Sl No. | Name of Diseases | Name of Bacteria |
| 1. | Pneumonia | Diplococcus pneumoniae |
| 2. | Diptheria | Corynebacterium diptheriae |
| 3. | Typhoid | Salmonella typhi |
| 4. | Cholera | Vibrio cholerae |
| 5. | Diarrhoea | Bacillus coli |
| 6. | Dysentery | Shigella dysenteriae |
| 7. | Tuberculosis | Mycobacterium tuberculosis |
| 8. | Anthrax | Bacillus anthracis |
| 9. | Plague | Pasteurella pestis |
| 10. | Leprosy | Mycobacterium leprae |
| 11. | Gonorrhoea | Neisseria gonorrhoeae |
| 12. | Food Poisoning (Botulism) | Clostridium botulinum |
Disease of Animals:
| Sl No. | Name of Diseases | Name of Bacteria |
| 1. | Anthrax | Bacillus anthracis |
| 2. | Leptospirosis | Leptospira |
| 3. | Plague of Rodents | Yersinia pestis |
| 4. | Q fever of Rats and Birds | Coxiella burnetii |
| 5. | Diarrhoea of Monkeys | Shigella dysenteriae |
Disease of Plants:
| Sl No. | Name of Diseases | Name of Bacteria |
| 1. | Ring rot of Potato | Corynebacterium sepidonicum |
| 2. | Citrus Canker | Xanthomonas citri |
| 3. | Leaf blight of Rice | Xanthomonas oryzae |
| 4. | Red rot of Sugar cane | Xanthomonas rubrilineans |
| 5. | Wilt of Potato | Pseudomonas solanacearum |
| 6. | Black rot of Cabbage | Xanthomonas campestris |
| 7. | Soft rot of Mango | Bacterium cartocorus |
