· Bacteria are simplest (unicellular), primitive, prokaryotic organisms.
· They are ubiquitous (found everywhere).
· Smallest living organism with the cell wall.
· Bacteria are simplest (unicellular), primitive, prokaryotic organisms.
· Prokaryotic unicellular organisms included in kingdom monera.

Classification of Kingdom Monera.

· Microscopic, unicellular small prokaryotic organism with an average diameter of about 1 mm.
· The exhibit autotrophic, saprophytic, and parasitic modes of life (heterotrophic).
· Rainwater is free from bacteria.
· Study of bacteria is Bacteriology.
· Bacterial genome consists of both types of nucleic acid i.e. DNA and RNA.
· 70 S (50 S + 30 S) Ribosomes are present.
· The plasma membrane of bacteria has a finger-like infolding called mesosome. Mesosome is the site of respiration in bacteria and it also helps in equal distribution of genetic material during binary fission.
· Though some bacteria are photosynthetic their cells possess bacteriochlorophyll instead of chlorophyll a.
· Bacteria have been considered to be plants because of the presence of rigid cell walls and osmotrophy.
· Bacteria are devoid of the true nucleus and nuclear membranes i.e. prokaryotic organisms.
· The food materials are stored in the form of glycogen in bacteria.
· Bacteria are important decomposers and mineralizers in the biosphere.


· Nageli classified bacteria under schizomycetes.
· 1st discovered by A. V Leeuwenhoek and termed animalcule.
· The term Bacterium was coined by Ehernberg.
· Linnaeus placed under Vermes
· Dougherty placed under the monera
· E.coli is the most studied bacterium.
· A. V Leeuwenhoek is regarded as the father of microscopy.

A. Robert Koch:
1. Considered as the father of Bacteriology.
2. Discovered the Causative agent of TB.

B. Louis Pasteur:
1. Father of Microbiology.
2. Discovered the technique of pasteurization.
3. Pasteurization occurs at 62.8 degrees Celcius for 30 minutes or 72 degrees Celcius for 15 seconds.
4. Gave the theory of fermentation
5. Proposed Germ theory of disease.

C. Joseph Lister:
1. Father of antiseptic surgery.
2. 1st use carbolic acid as antiseptic.

Types of the Bacteria:

A. Spherical: Coccus
· Micrococci: Only a single-cell represents the bacterium e.g. micrococcus lutes
· Diplococci: (diplus-double) A pair of Spherical cells e.g. Meningococcus.
· Streptococci: Occurs in the form of a straight-chain e.g. Streptococcus
· Staphylococci: (staphylos – cluster of grapes) cocci divide into several planes resulting in an irregular cluster-like structure resembling a cluster of grapes.
· Tetrad/tetracoccus (tetrad like): four cocci in group eg. Neisseria.

B. Spirillum (spiral-coil) are spiral or helical like a corkscrew, usually rigid, and bear one or more flagella. eg. spirillum voluntan.

C. Vibrio (vibrio-curve): These are flagella at one end. eg. vibrio cholera (show darting mobility).

D. Rod-shaped or Cylindrical shape – Bacilli
Diplobacilli Arranged in pairs.
· Strepto bacilli- arranged in chains of rods, palisade-like side by side arrangement.
E.g. Corynebacterium diphtheria.

Characteristics Feature Common to all the Bacteria

· Bacteria are microorganisms on the earth with unique features.
· The external and internal characteristics of bacteria are a bit different from the rest of the organisms on the earth.
· They are prokaryotic in nature meaning they are the earliest forms of the cell without a nucleus.
· These characters make them immortal, omnipresent, and also very versatile.
· They are useful to nature, man, and life on earth, though some of them, can cause diseases to humans.

Unique & Distinguishing Characteristics of Bacteria

1. No nucleus: Unlike other eukaryotic cells, the bacterial cell is the only cell that lacks a prominent nucleus within. This feature has led scientists to consider bacteria as primitive organisms i.e earliest forms of life on earth.

2. Presence of Cell wall: Bacteria has a cell wall that is distinct from other cells having cell walls. The wall is made of different substances like glycoproteins, lipopolysaccharides, and lipoproteins.

3. Cell membrane: This is present immediately below the cell wall. This has a small variation with that of plants and animals' cell membranes. In plants and animals, it is mostly a single or double layer (bi-layer) of lipids. But bacteria especially the gram-negative ones have an extra membrane i.e. an outer membrane called periplasm which lies below the cell wall but above the cell membrane.

4. Pilli: These are small and tube-like projections from bacterial surfaces. They are the organelles of sexual reproduction and are involved in the exchange of genetic material as part of reproduction between two bacteria. They help in attachment and reproduction.

5. Food dependence: All the organisms either live on their own or on other resources. But bacteria have different modes of food procurement.

Some of them synthesize their own food like plants by use of sunlight.

Others derive food energy from chemical sources around them (chemotropism). Sulfur bacteria, hydrogen bacteria, iron bacteria, etc.

Few of them are parasites that live on alive plants and animals. They cause diseases to the host in doing so.

Many bacteria are saprophytes which means, they live on dead and decaying matter.
While others are symbiotic. They live in a give-and-take relationship with other animals. Ex: rhizobium in roots, E-coli in the intestine.

6. Reproduction: Most organisms have one or two methods of reproduction. But bacteria have many.
(a) Asexual reproduction: The bacteria cell undergoes to produce two bacteria by Binary fission and also by endospores.
(b) Sexual reproduction: It is also by two distinct methods like transformation, conjugation, and transduction. In transformation, one bacteria releases a naked DNA strand into the surroundings. The other bacteria take t up and incorporate it into their genome.
Transduction happens due to viruses.

7. Spore formation:
When the environmental conditions around are harsh, the bacteria convert to a hard spore form. This spore is highly resistant to heat, chemicals, and drought conditions.

Fig: Spore forming rod-shaped bacteria

When the conditions are favourable, these spores break open and release the bacteria.

8. DNA Gyrase: Gyrases are the enzymes involved in DNA transcription. They perform, nick and joint functions in the DNA chains. They cut the strands, induce negative supercoils and also join the cut ends after the process. In humans and other mammals, instead of DNA gyrase, there is DNA topoisomerase-II for similar functions.

9. Ribosomes: The protein-making machinery has a 70S ribosome which is of two sub-units as 50S and 30S. 

While in other animals and plants, it is an 80S ribosome consisting of two sub-units 60S and 40S.

10. Absence of Cell organelles: Other cell organelles like mitochondria, Golgi bodies, endoplasmic reticulum are absent in a bacterial cell.

11. Flagella presence: Some of the bacteria are motile. They, especially the bacilli type have flagella. These are the organs of locomotion. They are long filamentous organs originating from the cell membranes. Flagella doesn't contain (9 + 2) arrangement.

12. Bacteria shape: The shape of bacteria is very characteristic to them. It is also easy to the identification of bacteria by recognition of shapes. These bacterial structures have specific shapes like a stick (bacilli), spherical (cocci), coma (cholera bacteria), spiral (spirochete), in a bunch of isolated, etc.

Fig: Different shapes of bacteria

13. Cosmopolitan distribution: Bacteria are the only organisms that show cosmopolitan distribution. They are present in the air, water, soil, snow, etc. They are present at very cold (minus degree) temperature regions and also very high-temperature regions. They can live in acidic environments (Helicobacter pyroli) and even basic environments (iron bacteria).

14. Resistance and tolerance: Some of the bacteria are highly resistant to adverse environments. Even they get tolerance to harsh chemicals and other stuff which destroy them. Hence irrational use of antibiotics. This has become so severe that World Health Organization warns of the rampant prevalence of resistant bacteria which can be incurable by currently available drugs.

Fig: Bactetial Cell structuture

Components of Bacterial Cell structure

1. Capsule:
· Capsule is the outermost layer of the bacterial cells and is also called a slime layer.
· When components are compactly arranged it is called a capsule
· and when loosely arranged it is called a slime layer.
· Presence or absence of capsule is genetically fixed.
· Presence of capsule is an indication of virulence (extremely harmful) of some bacteria. e.g.capsulated form of diplococcus causes pneumonia.
· Capsulated bacteria form the smooth colonies and are called S-type bacteria which are highly virulent.
· Capsule acts as an osmotic barrier and as a reserve food during food Scarcity.
Eg of capsulated bacteria: Clostridium, Klebsiella, Bacillus anthrasis, Neisseria meningitides. (CK-MB)

· Bacteria show plant, animal, and fungi like characters
(a) Animal-like:
· Reserved food is glycogen
· Heterotrophic mode of nutrition
· Absence of chlorophyll and motile in nature

(b) Plant-like:

· Presence of rigid cell wall
· Division by transverse binary fibrin

(c) Fungi like

· Heterotrophic mode of nutrition
· Presence of N-acetyl glucosa-amine (NAG) in the cell wall.

2. Cell wall:
· Helps in protection against mechanical and chemical injury and pathogens.
· On the basis of cell wall bacteria are divided into gram-positive and gram-negative.
· Bacterial cell wall is made up of murein or muramic acid peptidoglycan instead of cellulose.
(Except Azotobacter and Zymosarcina which have cellulosic)
· Bacterial cell wall is antigenic.

3. Plasma membrane:
· Inner to the cell wall.
· Typical tripartite structure.
· Sterols are completely absent in the cell membrane of bacteria.
· Plasma membrane modifies into mesosome and photosynthetic membrane in bacteria.
· Mesosome is equivalent to eukaryotic mitochondria that helps in respiration and distribution of nuclear materials during replication.
· Photosynthetic membrane is for photosynthesis.
· Genetic material – single circular double-stranded DNA without nuclear membrane and histone protein.
· Ribosome: 70 s (50 s + 30 s) type.

4. Flagella (4μ-5μ long)
· Surface appendage, helps bacteria to move and respond to certain stimuli
· Made up of protein flagellin and microtubules are absent.
· Prokaryotic flagella lack 9 + 2 arrangement.
· Arise from the basal granule called blepharoplast.
· Made up of one or three α-helical structures.
· Immunologically flagella provides H-antigen.

On the basis of Fagella, bacteria are of the following types:

Atrichous – Bacteria without flagella. e.g. Lactobacillus.
Monotrichous – only one flagella. e.g. Vibrio,
Lophotrichous – two or more flagella attached only at one end. e.g. Pseudomonas
Peritrichous – Flagella distributed all over the surface of the cell. e.g. E. Coli. Salmonella, clostridium
Amphitrichous – Flagella at both ends. eg. Nitrosomonas.

5. Pilli fimbriae:
· Hollow nonhelical appendages.
· Filamentous appendages projecting from the walls of some gram-negative bacteria.
· They are the extension of the plasma membrane.
· They are the extension of plasma membrane made up of basal body and a specific protein called pilin.
· Pili helps in reproduction and attachment with other bacteria. They form conjugation tubes during reproduction.

There are different types of pili as:
· Type I pili: play a major role in infection by facilitating the attachment of bacterial cell to host cell.
· Sex pili: Serves as portals of entry of genetic material from the donor to recipient cell during conjugation

6. Genetic materials:
(a) Nuclear genetic materials:
· Bacterial chromosome is also known as genome/genophore or bacteria prochromosome or incipient nucleus or nucleoid chromatin body or nuclear equivalent.
· DNA in bacteria are double helical and circular.
· Guanine and cytosine contents of the bacterial DNA are lesser than the adenine and thymine.
· DNA is surrounded by some typical protein, not by the histones.
· Histones are altogether absent in bacteria.
· DNA is freely scattered on the cytoplasm.
· Sometimes associated with the ribosome to form polyribosome.

(b) Plasmids and Episomes

· Plasmids are extrachromosomal additional rings of DNA that can replicate independently.
· Plasmids contains some important genes like nif genes (nitrogen-fixing genes), fertility factor, and resistance factor.
· There are 3-4 genes on plasmid except for 9 genes on E.coli.
· Plasmids are having independent existence and are often exploited as the genetic vehicles in genetic engineering.

Plasmids are of the following types:
R- develop resistant plasmid
Col- hemolytic effect (produces colicin which lyses other bacteria)
Nif- Nitrogen fixation
F- fertility
· Episomes are plasmids that can get temporarily associated with nucleoids.
· So, all plasmids are episomes but all the episomes are not plasmids.
· It consists of circular, supercoiled ds naked DNA and has no vital role in viability and growth of bacteria hence is called a dispensable autonomous element.
· Due to their independent existence plasmids are often used as a genetic vehicle in genetic engineering.
· Plasmids are capable of autonomous replication.

Gram staining Procedure:

Fig: Gram Staining procedure

Inference: from Gram staining
Staining Blue/purple: Gram-positive
Staining Red: Gram-Negative

A. Gram-positive Bacteria
· Has thick smooth homogenous single-layered cell wall.
· Made up of - peptidoglycan (80% mainly) and lipid (20%)
· Fimbriae/pili is absent, non-virulent, and non-pathogenic.
· Mostly produce exotoxin.
· On gram staining, they attain purple colour (p or positive)
· Mostly non-capsulated.
· Both horizontal and vertical linkage peptides are present.
· Periplasmic space or gel is present.
· Techoic acid is present.
· Mesosome is prominent.
· Sensitive to penicillin.
Eg: Streptococcus, Staphylococcus, Corynebacterium.

B. Gram-negative bacteria
· Cell wall is thin, wavy heterogeneous two-layered, more complex.
· Composed of lipoprotein (80% mainly) and peptidoglycan (20%)
· Pilli or fimbriae is present virulent and pathogenic and produces endotoxin.
· On gram staining, they appear RED colour.
· Mostly bacillus, capsulated, and flagellation common.
· Either horizontal or vertical peptide linkage is present.
· Periplasmic space or gel is present between two-layer.
· Techoic acid is present.
· Mesosome rare or absent. Eg: Escheria, salmonella etc.

· Gram-positive bacteria lack pili or fimbria, retain Gram's stain during the decolorizing process.

· Gram-negative bacteria generally bear pili or fimbriae, they do not retain gram staining during the decolorizing procedure.

Reproduction in bacteria

1. Vegetative reproduction
2. Asexual reproduction
3. Sexual reproduction

1. Vegetative reproduction:

A. Binary fission: Most common
· Takes 20-30 min to complete.
· Common in spherical bacteria
B. Budding: Rare method.
· Common in Bacillus
Note: Bacteria are also called fission fungi.

2. Asexual reproduction: 
Most common means of reproduction in bacteria.

(a) Endospore formation:
· Endospores are thick wall resting spores formed under unfavourable conditions. An endospore can remain inert for a long period. During favourable conditions, it may germinate and become a single active cell again.
· The process of endospore formation within the vegetative (parent) cell is known as sporulation or sporogenesis.
· Formation of bacteria from endospore is known as “reproduction without multiplication”
· Endospore means spore inside the bacterial cell.
· Endospore is more common in rod-shaped bacteria or bacillus form.
· Endospore is having a characteristic structure i.e having outer exosporium followed by spore coat, cortex, and spore wall.
· Enclospore is highly resistant to very high and low temperature, strong chemicals, acids, etc. due to calcium, dipiclonic acid, and peptidoglycan in the cortex.
(a) Dipicolinic acid(DPA): helps in stabilizing its protein.
(b) DPA and Ca provide resistance to heat.
· During the favourable condition outer layer of the endospore ruptures and active bacterial cells come out. This method of perennation is called reproduction without multiplication.
· Endospore after falling on a favourable medium germinates into the new bacterium. Only one endospore is formed per cell. [BPKIHS]
· The bacterial spore is the most resistant living structure known so far.

(b) Conidia formation: Rarely in some filamentous form of bacteria (Streptomyces).

(c) Zoospore formation: Motile spore formation occurs Rhizobium.

3. Sexual reproduction (Genetic Recombination)
Exchange of genetic materials is essential for sexual reproduction– 3 methods of genetic recombination.

(a) Transformation:
· Transfer of genetic materials from one bacteria to another without any body contact with unknown mechanism converting one form of bacteria into another(like capsulated form converting into non-capsulated).
· This was first of all discovered by Griffith(1928) on Diplococcus pneumonia. Hence it is also known as the Griffith effect (Transformation Griffith effect)
· During transformation, both donor and recipient must remain in a liquid medium having calcium chloride.
(Calcium chloride is needed to pick up the foreign DNA)Transformation

Fig: Showing Bacterial Transformation

b) Transduction:
· Process of transfer of genetic material from one to another with the help of virus or bacteriophage.
· Transduction was first of all reported on Salmonella typhimurium by Zinder and Lederberg.

(c) Conjugation:

· Discovered by Tatum and Lederberg
· Here Cell to cell union/direct contact occurs between two bacterial cells and the genetic material of one bacteria cell goes to another cell lengthwise through the conjugation tube formed by sex pili.
· First experiment was performed in E.Coli.

Fig: Showing Bacterial Conjugation

Difference Between Sexual and Asexual Reproduction

Asexual Reproduction Sexual Reproduction
Binary Fission Conjugation
Bacteria make exact copies of each other. Bacteria combine their genetic material.
This makes more of the same. This makes variety in bacteria

Nutrition in Bacteria

1. Autotrophic bacteria

A. Photoautotrophs

· Uses light for the chemical manufacture of food or for photosynthesis.
· In bacteria source of a hydrogen donor is H2S (Hydrogen sulfide). So sulphur is released during photosynthesis instead of oxygen.
· Source of carbon is atmospheric CO2.
H2S + CO2 -> Sulphur + Other sulphur compounds where H2S is oxidized to 'S'.
· Water is not used in bacterial photosynthesis.

· Bacteriochlorophyll as the photosynthetic pigment.
· Commonly found in sea oceans or bottom of the ponds where reduced sulphur and other compounds are freely available but the oxygen content is very low. E.g. green sulphur bacteria, purple sulphur bacteria.

B. Chemoautotroph
· Lack photosynthetic pigment and hence utilize the chemical energy to reduce CO2 to organic matter or food.
· Source of carbon: atmospheric CO2.
· Molecular oxygen (from the atmosphere) oxidizes the inorganic substance.

1. Nitrifying bacteria
· They oxidize ammonia to nitrite and then to nitrate.
(a) Nitrosomonas and Nitrosococcus.
Changes ammonia (NH3) to nitrite (NO2) during which energy is obtained.
NH4 + O2 -> NO2 + 2 H2O + energy

(b) Nitrocystis and Nitrobacter
Oxidizes nitrite (NO2) into nitrate (NO3)
i.e. NO2 + O2 -> NO3 + energy
Nitrate is a plant absorbable form of nitrogen.

2. Sulphur oxidizing bacteria – obtains energy by the oxidation of sulphur, H2S, or partially oxidized form of sulphur to sulphate.

3. Iron bacteria – obtain energy by the oxidation of ferrous ions to ferric ions.

2. Heterotrophic bacteria
· Require at least one organic compound as a source of carbon for growth and energy.
· They could be
(a) Saprophyte
· Depends on dead organic matter for food.
· Major decomposers in nature.
· Essential for the recycling of nutrients.

(b) Symbionts
· Rhizobium bacteria is found symbiotically in the root nodules of some leguminous plants which help in nitrogen fixation.
· Similarly E. coli lives symbiotically in the human intestine, which is responsible for the synthesis of vitamin B and vitamin K.
· Azobacter is a nitrogen-fixing bacteria like Rhizobium but is free-living in soil.

(c) Parasites – They obtain energy from the host body.
· Bacteria may not require atmospheric oxygen for respiration.

· Require oxygen for respiration
· Obligate Aerobes – oxygen is essential for respiration and survival. E.g. Diphtheria and T.B. causing bacteria.
Facultative Aerobes - Actually anaerobe but they can also live in presence of oxygen (aerobic condition).

Anaerobes - Do not need oxygen for respiration
· Obligate anaerobes. Truly anaerobic bacteria. E.g. Clostridium tetani
Facultative Anaerobes

· Actually aerobic but they can also live in anaerobic conditions.
· Alcohol is converted into acetic acid by bacteria like acetobacter.
· Bacteria are the source of antibiotics.
· Lactic acid bacteria (Lactobacilli) convert milk into yoghurt.

· Supposed to be oldest of the living fossils of ancient bacteria.
· Able to flourish in extreme environmental conditions. Such as lack, of oxygen, high salt concentration, high temp. and acidity.
· Posses a unique cell wall that consists of polysaccharides and proteins instead of murein.
They are:
(a) Methanogens
· Produce methane gas in biogas fermenters.
· They are obligate anaerobes (can survive under anaerobic conditions only) occurring in marshy areas.

(b) Halophiles (salt-loving)
· Obligate anaerobes, which can live in an extreme salt solution or salt-loving bacteria.

(c) Thermoacidophiles
· Obligate and facultative anaerobes.
· Temperature and salt-loving bacteria found in hot sulphur springs.

Importance of Bacteria

A. Importance of bacteria for the environment:
· Natural scavengers: Bacteria are the natural scavengers on the earth. They decay any dead and waste matter on the surface of the earth and in the soil. Hence there is no accumulation of dead corpses of animals over so long years of the emergence of life on earth. This degraded and decomposed substance ad to the fertility of plants or converts to biogas.
· Further they degrade any chemical or biochemical fallen on the soil and thereby detoxify the valuable soil. Thus they make it fit for the growth of plants & animal-safe survival on the earth. Even the vast amount of chemicals and other waste is degraded over a period of weeks in the water. Or else the soil and water would be toxic for further use.
· Nutrition: They are an important source of vegetative nutrition in the marine environment. They provide major & micro-nutrients required for the sustenance of marine animals. i.e. they form the starting point of the marine food chain.  

B. Importance of bacteria for plants:
As a source of manure (fertilizer enhancers).
· Bacteria are helpful for plants. They render the soil suitable for the growth of plants. They break down any dead and organic matter into humus so that the plants receive essential mineral elements for growth.
· Ammonifying bacteria which converts proteins, amino acids, and nucleic acids of dead bodies into ammonia. Ex: Bacillus.
· Nitrifying bacteria: Ammonia is also oxidized to nitrates by nitrifying bacteria. Ex: Nitrosomona, nitorbacter.

C. Importance of bacteria for animals:
· Bacteria like E. coli live in the gut intestines of animals in a symbiotic fashion. They are friendly bacteria helping in the degradation of unused food and helping in its expulsion from the body.
· Some bacteria like E.coli which are present in the body resist the growth of harmful bacteria like typhoid.

D. Medical Importance of bacteria
· There are many human-friendly bacteria in the body. Without them, the body would be susceptible to harmful infection.
· For antibiotic production: Antibiotics were found to be produced by bacteria and these antibiotics could rescue people from other harmful and pathogenic bacteria. Initially, most antibiotics were produced by fermenting large cultures of bacteria. Now synthetic ones are in large supply.

Common Bacterias and Antibiotics made from them:

Bacteria Antibiotics
Streptomyces venezuelae Chloramphenicol/chloromycetin
S. ramosus Terramycin
S. fradiae Neomycin
S. aureofaciens Chlortetracycline or Aureomycin
S. griseus Streptomycin
S. erythreus Erythromycin

· For the production of vaccines: Bacteria are used to produce vaccines by either separating their antigens or sometimes dead form or else even live one with lack of pathogenic character.
Ex: TB-vaccine is one where dead bacteria of TB are administered to build up resistance to tuberculosis in humans. Once administered, these bacteria cannot cause disease. But the body will be able to produce antibodies to kill any infection of mycobacterium.
· Probiotics: Bacteria are also part of probiotics. These are friendly bacteria that can be used to fight infections. They are specially used to treat diarrhoea in children.

Source of Protein: Methylophhilus methylotrophs (used methane)

Human Disease:
Syphilis: Treponema pallidum
Meningitis: Neisseria meningitides
Food poisoning: Also c/a botulism caused by clostridium botulinum.
Tetanus: Clostridium tetani
Plague:Yeserenia pestis

Plant Disease:
Brown rot potato = Pseudomonas solanacearum
Citrus canker = Xanthomonas citri
Black rot of cabbage = Xanthomonas campestris
Leaf spot of cucumber = Xanthomonas cucurbitae
Leaf blight of rice = Xanthomonas oryzae

· For genetic engineering: Bacteria have short reproduction cycles. Some of them can divide in minutest o produce new daughter cells. This factor of bacteria is used in biotechnology to produce biological compounds. Products like insulin, vitamin- B12, etc. are supplied on large scale on a continuous basis due to their manufacture using genetically modified bacterial cells.

For an idea check → rDNA technology applications.

Importance of bacteria in agriculture

Bacteria play a vital role in agriculture for disease prevention and enhancing fertility.

1. Bio-pesticides: They act as bio-pesticides to kill disease-causing diseases to crops and aid in higher yield.
Ex: Bacillus thuringiensis is one example of a pesticide to kill pests. Some species of bacillus, pseudomonas act as antifungals.
These bacteria are such that when applied they kill only the disease-causing pests and insects. But they do not harm the plant or farmer. Because they are specifically harmful to pests.
Further, they are not harmful to the soil, unlike chemical fertilizers. Chemical fertilizers pollute the soil, air, and water around. But the use of bio-pesticides avoids this problem. Further, they are less expensive.

2. Organic manure: Composting is a way to make natural manure. This manure imparts fertility to the soil.
Some farmers even make their own organic compost by use of kitchen and other vegetable waste. This waste is allowed to decompose in presence of moisture, air, carbon, and nitrogen ingredients. Check out organic composting.

3. Biofertilizers: When bacteria like blue-green algae are left into agricultural soil, they fix natural manure in the form of nitrogen from the air for better growth and yield of crops.
Also when a crop is harvested, the plant remains are allowed to degrade in the soil. Under rainfall, this waste material is acted on by bacteria to decompose it. This organic material acts to increase the water retention capacity of the soil. Further, the organic waste acts as natural manure and gives essential nutrients to the next crop.
Further, these bacteria play role in nitrogen fixation.

Importance of Bacteria in the Nitrogen Cycle

1. Fix nitrogen in soil: Bacteria like chlorella are used as green manures to increase soil fertility. There absorb nitrogen from the air and fix it in the soil. Thus the nitrogen content of the soil increase and provides fertility to crops. Ex: cyanobacteria.

2. Crop rotation: Farmers cannot grow the same crop year after year. If they do so, the yield of crop drops, and also the subsequent crops are affected by pests and diseases. To avoid this, the farmers opt for crop rotation. This crop rotation is done by alternating crops with a leguminous crop. For example a farmer growing cotton this year will opt for a leguminous crop like groundnut or peanut next year. This not only destroys the pests of the previous crops but also builds fertility. The rise in fertility due to leguminous crop is due to the presence of symbiotic bacteria in the roots.
The rhizobium is an example of such bacteria. These bacteria reside in the nodes of the roots of leguminous plants and help absorb nitrogen from the air and fix it in the roots. In turn, these bacteria extract nutrition from the plant (symbiosis). Thus bacteria help the plant and also build fertility in the soil.

Importance of Bacteria for Industry

Bacteria are also useful for industrial & commercial purposes
· Fiber industry: Bacteria like Clostridium butyrcum are used in retting of flax, sun hemp to extract the clear fibre.

· Tea and tobacco: Micrococcus and Bacillus megatherium are used in curing tea and tobacco.

· For beverage industry: For this industry, bacteria contribute to the fermentation of wine used as beverages to form alcohol.

· Dairy industry: In the dairy industry and homes ferments milk to produce curd.

· Sterilization: This is a process to eradicate microbial contamination from finished products. Few bacteria are used as biological indicators for sterilization validation. These bacteria are available commercially as strips containing spores.

Economic Importance of Bacteria

Bacteria are sold in different forms as seen before like
a. Medicine (probiotics), antibiotics, insulin, and other medicines are obtained from them.
b. Agriculture as bio-pesticides and fertilizers. In fact, this is a big industry and makes a lot of money.
c. In making beverages and fibres.

Thus bacteria are of great economic importance to humans, animals, and the environment around them.


· E.Nocard and E.R Raux (1898) discovered a new type of organism called mycoplasma or PPLO.
· They are often called PPLO (Pleuro Pneumonia like organisms) or jokers of the plant kingdom.

Main characteristics of Mycoplasma
· Smallest, simplest, unicellular, nonmotile, a highly pleomorphic organism without a cell wall.
· Mycoplasma is filterable through the bacterial filter.
· Mycoplasma is resistant to penicillin because of lack of cell wall.
· They multiply by binary fission and elementary bodies.
· DNA is linear, never circular.
· They need sterol from outside for their growth.
· Causes various plant diseases like the little leaf of brinjal, Bunchy top of papaya.
· Alcohol is converted into acetic acid by Acetobacter
· Chloramphenicol is obtained from Streptomyces venequelae.
· Lactic acid bacteria convert milk protein to the cord.


· It is intermediate between bacteria and viruses.
· These are obligate intracellular parasites of the Gut of arthropods.
· Compared to bacteria Rickettsiae have a smaller size, smaller genome, and long generation time.
· Weil Felix test is performed to diagnose the rickettsial disease.
· Rocky mountain spotted fever, Typhus fever is caused by rickettsiae.

High Yielding Points for Entrance Exams.

1. In Gram-positive bacteria PTM is present:
P = plasmid, retain purple colour, large peptide glycan (80%)
T = Techoic acid
M = mesosomeso @ fimbrae absent

2. Gram-positive bacteria secrets Exotoxin (a toxin produced by living)
Eg: streptococcus, Streptomyces, listeria, corynebacterium, clostridium @ 2SLC

3. Gram-negative secrets endotoxin (n = n)
Eg: E. coli, Salmonella, Klebsiela, Pseudomonas, Proteus @ KEEPS

4. All the plasmids are episomes but all the episomes are not plasmids.

5. Nitrate bacteria: N2 →  NO-3
Eg: Nitrobacter

6. Nitrite bacteria: NO-3 
Eg: Nitrosomonas

7. Denitrifying bacteria:
Eg: Pseudomonas

8. Rikettesia is intermediate between bacteria and virus, obligate intracellular parasite of arthropods gut, Weil flex test -> Diagnostic test of rickettsia diseases

9. Mycoplasma is non-motile, considered to be bacteria but has linear DNA (bacteria has circular one) 1st discovered by E.Nocard and E.R RAUX @ NMR

10. Bacteria capsule is the outermost covering of the bacterial cell which acts as the osmotic barrier and reserves food during starvation.

11. Bacteria cell wall is antigenic.

12. Bacterial cell wall is devoid of cellulose (except AZOTOBACTER and ZYMOSARCINA.

13. Minamata disease is caused by E. coli by converting mercury compounds in water into methyl mercury.

14. Plant takes nitrogen in the form of nitrate NO-3

15. Bacterial plasma membrane is devoid of sterol.

16. Pilli is mainly present in the case of the gram-ve bacteria (which is the extension of plasma membrane)

17. Bacterial cell wall is made up of lipids and peptidoglycan or muramic acid or mucopeptide while Cell membrane is made up of phospholipid + protein + polysaccharides.

18. Endospore is the most resistant living structure due to calcium dipiclonic acid + peptidoglycan.

19. Conjugation was discovered in E.coli by Tatum and Lederberg (@ TALEju)

20. Transduction was discovered in salmonella by Zinder and Lederberg (@ sale lezi dog)

21. Transformation was discovered in diplococcus by Griffith.

22. Endospore formation occurs during unfavourable conditions and under favourable conditions, the outer layer of endospore rupture, and bacterial cell comes out called reproduction without multiplication.

Also, Read Notes of Other Lessons of Botany:

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