Bacteria are the sole members of the Kingdom Monera. They are the most abundant micro-organisms. Bacteria occur almost everywhere. Hundreds of bacteria are present in a handful of soil. They also live in extreme habitats such as hot springs, deserts, snow and deep oceans where very few other life forms can survive. Many of them live in or on other organisms as parasites.
Bacteria are grouped under four categories based on their shape: the spherical Coccus (pl.: cocci), the rod-shaped Bacillus (pl.: bacilli), the comma-shaped Vibrium (pl.: vibrio) and the spiral Spirillum (pl.: spirilla).
Though the bacterial structure is very simple, they are very complex in behaviour. Compared to many other organisms, bacteria as a group show the most extensive metabolic diversity.
Some of the bacteria are autotrophic, i.e., they synthesise their own food from inorganic substrates. They may be photosynthetic autotrophic or chemosynthetic autotrophic. The vast majority of bacteria are heterotrophs, i.e., they depend on other organisms or on dead organic matter for food.
These bacteria are special since they live in some of the most harsh habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens). Archaebacteria differ from other bacteria in having a different cell wall structure and this feature is responsible for their survival in extreme conditions.
Methanogens are present in the gut of several ruminant animals such as cows and buffaloes and they are responsible for the production of methane (biogas) from the dung of these animals.
There are thousands of different eubacteria or ‘true bacteria’. They are characterised by the presence of a rigid cell wall, and if motile, a flagellum.
The cyanobacteria (also referred to as blue-green algae) have chlorophyll a similar to green plants and are photosynthetic autotrophs. The cyanobacteria are unicellular, colonial or filamentous, freshwater/marine or terrestrial algae. The colonies are generally surrounded by gelatinous sheath. They often form blooms in polluted water bodies.
Some of these organisms can fix atmospheric nitrogen in specialised cells called heterocysts, e.g., Nostoc and Anabaena.
Chemosynthetic autotrophic bacteria oxidise various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production. They play a great role in recycling nutrients like nitrogen, phosphorous, iron and sulphur.
Heterotrophic bacteria are most abundant in nature. The majority are important decomposers. Many of them have a significant impact on human affairs. They are helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots, etc. Some are pathogens causing damage to human beings, crops, farm animals and pets. Cholera, typhoid, tetanus, citrus canker are well known diseases caused by different bacteria.
Bacteria reproduce mainly by fission. Sometimes, under unfavourable conditions, they produce spores. They also reproduce by a sort of sexual reproduction by adopting a primitive type of DNA transfer from one bacterium to the other.
The Mycoplasma are organisms that completely lack a cell wall. They are the smallest living cells known and can survive without oxygen. Many mycoplasma are pathogenic in animals and plants.
Bacteria are the only members of Kingdom Monera. Extremely abundant, they live in diverse habitats including extreme environments. Some are parasitic, living in or on other organisms.
Coccus: Spherical
Bacillus: Rod-shaped
Vibrio: Comma-shaped
Spirillum: Spiral
Bacteria range from tiny Mycoplasma (0.1 μm) to large cyanobacteria (up to 60 μm). Their microscopic diversity allows them to thrive in countless niches.
Monotrichous: Single flagellum
Lophotrichous: Cluster at one/both ends
Amphitrichous: One at each end
Peritrichous: All over the body
Bacteria inhabit soil, freshwater, marine, deserts, hot springs, polar regions, and even other organisms (as parasites or symbionts).
Autotrophs: Synthesize food from inorganic matter.
Photosynthetic: Use light (e.g., Cyanobacteria)
Chemosynthetic: Use chemical energy
Heterotrophs: Depend on other organisms or organic matter.
Found in salty (halophiles), hot (thermoacidophiles), or marshy (methanogens) places. Methanogens help produce methane in ruminants like cows.
Rigid cell wall, often motile with flagella. Eubacteria include many roles—photosynthesis, decomposition, and pathogenicity.
Photosynthetic and found in aquatic and terrestrial habitats. Contain chlorophyll a, may be unicellular or colonial, and can fix nitrogen (e.g., Nostoc, Anabaena).
Oxidize substances like ammonia, nitrates, nitrites to generate ATP. Crucial for nutrient recycling (N, S, Fe, P).
Help decompose organic matter, make curd, antibiotics, and fix nitrogen. Some cause diseases like cholera, tetanus, and citrus canker.
Primarily by binary fission. Under harsh conditions, they form spores. Also engage in primitive DNA transfer (like conjugation).
Lack a cell wall and can survive without oxygen. Pathogenic to plants and animals. Smallest free-living organisms known to science.
Bacteria are the sole members of the Kingdom Monera. They are the most abundant and diverse microorganisms found in soil, hot springs, oceans, snow, and even inside organisms as parasites.
Bacteria are classified into four shapes: Coccus (spherical), Bacillus (rod-shaped), Vibrio (comma-shaped), and Spirillum (spiral).
Archaebacteria thrive in harsh environments like hot springs (thermoacidophiles), salty areas (halophiles), and marshes (methanogens). Their unique cell wall helps them survive in extreme conditions. Methanogens in cow guts produce biogas.
Characterized by a rigid cell wall and often flagella, eubacteria include photosynthetic, chemosynthetic, and heterotrophic types. They play vital roles in ecosystems and human life, including decomposition, nitrogen fixation, and antibiotic production.
Cyanobacteria (blue-green algae) have chlorophyll-a like plants. They form blooms in polluted waters, fix atmospheric nitrogen via heterocysts, and exist in freshwater, marine, and terrestrial habitats. Examples: Nostoc, Anabaena.
Bacteria exhibit vast metabolic diversity. Autotrophs make food using light or chemicals, while heterotrophs depend on organic material. Chemosynthetic bacteria recycle nitrogen, sulfur, and iron.
Bacteria help in curd formation, antibiotic production, nitrogen fixation in legumes, and bio-waste recycling. However, some are pathogenic and cause diseases like cholera, typhoid, and citrus canker.
Bacteria mainly reproduce by binary fission. Under adverse conditions, they form spores. Some undergo primitive gene transfer methods akin to sexual reproduction (conjugation).
Mycoplasma are the smallest known living cells. They lack a cell wall and can survive without oxygen. Many species are pathogenic to plants and animals.