`color{Brown} ✓✓ color{Brown} mathbf("GENERAL HABITAT")`

● They are the `color{Violet}"most abundant"` micro-organisms.

● Bacteria occur almost everywhere.

● Hundreds of bacteria are present in a handful of soil
.
● They also live in `color{Violet}"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 `color{Violet}"parasites"`.


`color{Green}♣ color{Green} "Just for Curiousity"`

A handful of soil has more bacteria than there are people on planet Earth.

`color{blue} ul(mathtt ("Prokaryotes))` : A prokaryote is a unicellular organism that lacks a `color{Violet}"membrane-bound"` nucleus (karyon), mitochondria, or any other membrane-bound organelle. The word prokaryote comes from the Greek (pro) "before" and (`color{Violet}"karyon"`) "nut or kernel".

`color{blue} ul(mathtt ("Eukaryotes))` : A eukaryote is any organism whose cells have a nucleus and other organelles enclosed within membranes.

`color{green} ✍️ color{green} mathbf("KEY CONCEPT")`

● All the monerans are `color{Violet}"prokaryotic"` (primitive nucleus) and microscopic.

Bacteria has a chemically complex cell envelope consist of a tightly bound 3 layered structure:

(1) Outermost `color{Violet}"glycocalyx"` (may be capsule thick and tough or slime layer- loose sheath)
(2) Cell wall- non cellulosic and rigid made up of mainly `color{Violet}"peptidoglycan or murein"` which is a type of mucopeptide .
(3) Cell membrane- Made up of `color{Violet}"lipoprotein"`

Based on the structure of cell wall, bacteria are either `color{Violet}"gram positive or gram negative"`. The differences are given below:



● They are either single celled or form colonies

● Bacteria are grouped under four categories based on their shape.

● They are as follows:

`star` `mathtt "Spherical Coccus"` (pl.: cocci) : 𝘚𝘵𝘳𝘦𝘱𝘵𝘰𝘤𝘰𝘤𝘤𝘶𝘴
`star` `mathtt "Rod-shaped Bacillus"` (pl.: bacilli) : 𝘌.𝘤𝘰𝘭𝘪
`star` `mathtt "Comma-shaped Vibrium"` (pl.: vibrio): 𝘝𝘪𝘣𝘳𝘪𝘰 𝘤𝘩𝘰𝘭𝘦𝘳𝘢
`star` `mathtt "Spiral Spirillum"` (pl.: spirilla) : 𝘚𝘱𝘪𝘳𝘪𝘭𝘭𝘶𝘮 𝘷𝘰𝘭𝘶𝘵𝘢𝘯𝘴

● Compared to many other organisms, bacteria as a group show the most extensive metabolic diversity.

● Some of the bacteria are
`star` `color{blue}"Autotrophs"` : meaning auto (self)- troph (nutrition) i.e., they synthesise their own food (complex organic substrates) from inorganic substrates, using either light or chemical energy.

● Among autotrophs, they could be
`star` `color{blue}"Photosynthetic Autotrophs"` : Prepare their own organic substrates using light energy.
`star` `color{blue}"Chemosynthetic Autotrophs"` : Prepare their own organic substrates using energy from the oxidation of chemical compounds

● The vast majority of bacteria are
`star` `color{blue}"Heterotrophic"` : meaning hetero (others) - troph ( nutrition) i.e., they do not synthesise their own food but depend on other organisms or on dead organic matter for food. They are mostly chemosynthetic.

● Some are also `color{blue}"saprotrophytic"` (Feeding, absorbing or growing upon decaying organic matter ), others are `color{blue}"parasitic"` or some are even `color{blue}"symbionts"` (organism that is very closely associated with another, usually larger, organism) .

`color{Green}♣ color{Green} "Just for Fun"`

The term `color{Violet}"Parasitic"` comes from the Greek word `color{Violet}"parasitos"` meaning "eating at another's table." The adjective parasitic is used in a scientific context for describing an organism that lives in or on another animal or plant (a host), taking what it needs to stay alive (food or protection) while often injuring the host.

`color{blue}"Binary fission"` : Binary fission ("division in half") is a kind of asexual reproduction in bacteria and other prokaryotes that involves the splitting of a parent cell into two equal halves, producing two new independent cells. The genetic material is replicated during this process and also split equally between the two daughter cells.

`color{blue}"Bacterial Spore"` : A bacterial spore is a structure produced by bacteria that is resistant to many environmental or induced factors (extreme temperatures, lack of moisture/drought, exposure to chemicals and radiation, low nutrient levels, antibiotics and disinfectants) that the bacteria may be subjected to and helps the bacteria to survive in the extreme condtions.

`color{blue}"Bacterial conjugation"` : Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells.

`color{green} ✍️ color{green} mathbf("KEY CONCEPT")`

● Bacteria reproduce mainly by `color{Violet}"binary fission"` .

● Sometimes, under unfavourable conditions, they get encysted an produce `color{Violet}"spores"` .

● They also reproduce by a sort of sexual reproduction by adopting a primitive type of DNA transfer from one bacterium to the other called `color{Violet}"Conjugation"` .

They were the first to be formed on our planet and they are present now with their primitive characters. Thus, they are called the `color{Violet}"Oldest living fossils"`.

● These bacteria are special since they live in some of the most harsh habitats such as

`star` extreme salty areas `color{Violet}"halophiles"`

`star` hot springs `color{Violet}"thermoacidophiles"`

`star` marshy areas `color{Violet}"methanogens"`

● Archaebacteria (ancient bacteria) differ from other bacteria in having a different `color{Violet}"cell wall structure"` (made up of complex polysaccharides and complex polypeptides) .This feature is responsible for their survival in extreme conditions.

● Cell membrane of archaebacteria is highly complex because of `color{Violet}"branched lipid chain"`.

● In archaebacteria sequence of nucleotide in `color{Violet}"16s rRNA"` is different from other prokaryotes.

● Methanogens are present in the guts 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, .

`color{Green}♣ color{Green} "Just for Curiousity"`

Archaebacteria, because of the extreme environments they thrive in are sometimes called `color{Violet}"extremophiles"`. They are the ideal candidates for studying the field of the origin of life on earth (astrobiology) and the life on other planets (exobiology).

`color{blue}"Peptidoglycan"` : A mesh likepolymer that is composed of polysaccharide and peptide chains and is found especially in bacterial cell walls — also called mucopeptide, murein.

`color{green} ✍️ color{green} mathbf("KEY CONCEPT")`

● There are thousands of different eubacteria or `color{Violet}"true bacteria"` .

`color{green} ✓✓ color{brown} mathbf("STRUCTURE")`


● They are characterised by the presence of a rigid cell wall ( made up of `color{Violet}"Peptidoglycan"`), and if motile, a flagellum.

● The cyanobacteria are unicellular, colonial or filamentous. The colonies are generally surrounded by gelatinous sheath.


`color{green} ✓✓ color{brown} mathbf("MODE OF NUTRITION")`

`color{blue} ul(mathtt ("Photosynthetic autotrophs"))`

● The cyanobacteria (also referred to as `color{Violet}"blue-green algae"`) have chlorophyll a similar to green plants and are photosynthetic autotrophs. They are the marine or terrestrial algae. They often form blooms in polluted water bodies.

● Some of these organisms can fix atmospheric nitrogen in specialised cells called `color{Violet}"heterocysts"` , e.g., Nostoc and Anabaena.
These are also used as `color{Violet}"bio fertilizers"` for their nitrogen fixing ability.


`color{blue} ul(mathtt ("Chemosynthetic autotrophs"))`

● 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.

`color{blue} ul(mathtt ("Heterotrophs"))`

● Heterotrophic bacteria are the 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.

● The Mycoplasmas are organisms that completely `color{Violet}"lack a cell wall"`.

● They are the `color{Violet}"smallest"` living cells known and can survive without oxygen.

● Many mycoplasma are pathogenic in animals and plants

Bacteria have a major economic importance in the human society. They have a positive impact through their use in industrial and agricultural processes. They negatively impact other organisms including humans by causing diseases.

Their Benefecial impacts are:






Their Negative effects are: