Write short notes
A. Useful and harmful bacteria
Answers
Answer:
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Explanation:
Bacteria - the oldest living organisms on earth - are omnipresent. The human body, the air we breathe, the surfaces we touch, the food we eat, the plants that surround us, the environment we live in, etc., are all replete with bacteria.
Almost 99% of these bacteria are helpful, where the remaining are notorious. In fact, some are essential for the proper growth of other living beings. They are either free-living or form a symbiotic relationship with animals or plants.
The list of helpful and harmful bacteria contain some of the most commonly known beneficial and deadly bacteria.
Helpful Bacteria
Lactobacillus/Döderlein's bacillus
Characteristics: Gram-positive, rod-shaped
Presence: Lactobacilli species are present in milk and dairy products, fermented foods and also form part of our oral, intestinal and vaginal microflora. L. acidophilus, L. reuteri, L. plantarum, etc., are some of the most predominant species.
Benefit: Lactobacilli are known for their ability to utilize lactose and produce lactic acid, as a metabolic byproduct. This ability to ferment lactose makes lactobacilli an important ingredient for preparing fermented foods. It is also an important part of the pickling process since lactic acid serves as a preservative. The formation of yogurt from milk is done through what is called, fermentation. Certain strains are even used commercially for the production of yogurt. In mammals, lactobacilli aid the breakdown of lactose during digestion. The resulting acidic environment prevents the growth of other microbes in the body tissues. Being so, lactobacilli are an important part of probiotic formulations.
Bifidobacterium
Characteristics: Gram-positive, branched, rod-shaped
Presence: Bifidobacteria are present in the gastrointestinal tract of humans.
Benefit: Similar to lactobacilli these are also known for lactic acid production. In addition, it also produces acetic acid. This inhibits the growth of pathogenic bacteria by controlling pH levels in the intestines. B. longum helps in the breakdown of non-digestible plant polymers. B. longum and B. infantis help prevent diarrhea, candidiasis, and other yeast infections in infants and children. Owing to these benefits, this particular species are also included in commercially available probiotics.
Escherichia coli (E. coli)
Characteristics: Gram-negative, rod-shaped
Presence: E. coli is a part of the normal microflora of small and large intestines.
Benefit: E. coli helps in the breakdown of undigested monosaccharide sugars and thus aid digestion. These bacteria produce vitamin K and biotin which are essential for a variety of cellular processes.
Note.- Certain strains of E. coli can cause severe toxicity, diarrhea, anemia, and kidney failure.
Streptomyces
Characteristics: Gram-positive, filamentous
Presence: They are widely found in soil, water, and decaying matter.
Benefit: Streptomyces spp. play an important role in soil ecology by bringing about the decomposition of organic matter present in soil. As a result, they are being explored as agents for bioremediation. S. aureofaciens, S. rimosus, S. griseus, S. erythraeus and S. venezuelae are some of the commercially important species used for the production of antibacterial and antifungal compounds.
Rhizobia
Characteristics: Gram-negative, rod-shaped
Presence: Rhizobia are present in soil or form a symbiotic association with the root nodules of leguminous plants.
Benefit: Rhizobium etli, Bradyrhizobium spp., Azorhizobium spp.., and many other species, are useful for fixing atmospheric nitrogen, including ammonia, thus making it available for plants. Plants do not possess the ability to utilize atmospheric nitrogen and are dependent on nitrogen-fixing bacteria, that is present in soil.
Cyanobacteria/Cyanophyta
Characteristics: Gram-negative, rod-shaped
Presence: Cyanobacteria are mainly aquatic bacteria but are also found on bare rocks and in soil.
Benefit: Also known as blue-green algae and blue-green bacteria, they are a group of environmentally significant bacteria. They bring about nitrogen fixation in aquatic habitats. Their calcification and decalcification abilities make them essential for maintaining coral reef ecosystem balance.
Harmful Bacteria
Mycobacteria
Characteristics: Neither Gram-positive or Gram-negative (due to high lipid content), rod-shaped
Presence: Mycobacteria are generally found in water and food. However, M. tuberculosis and M. leprae (aka, Hansen's coccus spirilly), are obligate parasites and cannot survive in