Bacteria have variations in their shape. On the basis of their shape bacteria are of different types.
1. Coccus/Cocci -
# These bacteria are spherica.l
# These are smallest bacteria.
# Maximum resistant bacteria.
Eg. Diplococcus pneumoniae

2. Bacillus/Bacilli -
#This group includes most of the bacteria.
# These are rod shaped.
eg. E.coli, Bacillus anthracis

3. Spirillum/Spirilla -
These are spiral shaped bacteria.
e.g. Spirillum volutans, Treponema

4. Comma/Vibrio -
# These are comma shaped bacteria.
e.g. Vibrio cholarae.

Bacteria are motile as well as non motile. Movement in bacteria takes place by means of flagella.
On the basis of flagella bacteria are of following types:-
1. Atrichous -When flagella are absent, it is called atrichous form. e.g. Micrococcus, Pasteurella
2. Monotrichous- When only one flagellum on one end of the bacterium. e.g. Vibrio, Thiobacillus, Psuedomonas.
3. Amphitrichous- When single flagellum is present on both the ends of bacterium. e.g. Nitrosomonas
4. Lophotrichous- Wh.en a bunch of flagellum is present on both end of bacterium. e.g. Salmonella
5. Cephalotrichous- When a bunch of flagella is present on one end of bacteria. e.g. Corynebacterium
6. Peritrichous- when flagella are found on the whole body of bacterium. e.g. E.coli, Salmonella typhi

STRUCTURE OF FLAGELLA
A flagellum of bacteria is made up of three parts.
(1) Basal body (2) Hook (3) Filament

1. Basal body -
A. It is the basal part of flagellum and rod shaped in structure.
B. It lies with in the cell wall and cell membrane.
C. This proteinaceous rod shaped structure is surrounded by two pairs of rings.
(i) Outer pair (ii) Inner pair
D. Outer pair of ring lies within the cell wall. One ring of this pair L and the another called P.
E. Inner pair of ring lies with in the cell membrane. One ring of this pair is called S and the another is M.
F. In Gram (+) bacteria only one pair of rings (inner pair) is found.

2. Hook-
A. It connects the basal body to filament.
B. It is the middle part of flagellum.
C. It is some part lies with in the cell wall.

3. Filament -
A. It is cylindrical hollow structure made up of protein monomers.
B. Each monomers is minade up of flagellin protein. Fllagellin is a contraclilc protein.
C. These monomers are arranged spirally in 4+4 manner.

1. Bacterial cell wall is covered by numerous hair like structures called pili. Pili are smaller than the flagella. (Pl.- Pili - Sing. Pillus).
2. They are of two types- (A) Longer pili, (B) Shorter pili
3. Longer pili is also known as "F" pili or "sex" pili. Longer pili occurs in only donar (F+ or male) bacteria and help in conjugation. These are absent in recipient bacteria or female.
4. The shorter pili take part in attachment.These are also known as "infective" pili or fimbriae". These are found only in pathogenic bacteria.
Structure-
1. Every pilus is cylindrical hollow structure and composed of protein monomers.
2. Each monomer is made up of "pilin" protein. Pilin is non-contractile protein.
3. Pili do not play role in motility.

Though the baclerial structure is very simple, they are very complex in behaviour.
Bacterial cell has a chemically complex cell envelope.The cell envelope consists of a tightly bound three layered structure.
(1) Outermost glycocalyx (may be capsule thick and tough or slime layer- loose sheath).
(2) Cell wall
(3) Cell membrane
Although each layer of the envelope performs distinct function they act together as a single protective unit.
1. Glycocalyx (Capsule or slime layer)-
Loose and thin layer is called slime layer and thick and tough layer is called capsule.
A. When bacteria are surrounded by capsule, called as capsulated bacteria. Formation of capsule is done by cell membrane. Capsulated
bacteria are mostly pathogenic.
B. Capsule is made up of polysaccharides and polypeptides while layer is made up of only polysaccharides.
C. Glycocalyx protects the bacteria from W.B.C and also helps in colony formation.

2. Cell Wall -
Bacterial cell wall is made up of mainly peptidoglycan or murein which is a type of muco-peptide.
In Gram(+) bacteria cell wall is single layered and thick. It is made up of peptidoglycan. Lipids are also present but in less quantity.
While in Gram(-) bacteria cell wall is double layered. Inner layer is thin and compared of peptidoglycan while outer layer is thick and made up of lipo-polysaccharide.
L- form- Bacterial cell wall can be distorted by lysozyme enzyme. When bacterial cell wall is removed artificially by Lysozyme thin, bacteria are called L- form (Lister form).

3. Cell membrane -
Bacterial cell membrane is made up of lipoprotein ( unit membrane) like the eukaryotic membrane.

4. Cytoplasm -
A. In bacterial cytoplasm membrane bound cell organelles viz. Mitochondria, Chloroplast, E.R, Lysosome, Golgibody, Microbodies etc. are absent.
B. Bacterial cytoplasm shows no streaming or cyclosis.

Cytoplasmic organelles -

1. Mesosomes-A Mesosome was discovered by F.James. The cell membrane of bacleria invaginates (extensions) in cytoplasm
at different places and form mesosomes or chondrioid. These extensions are in the form of vesicles, tubules and lamellae.
B. These are functionally mitochondria like structures. Oxidative enzymes are found in mesosome. On the basis of position and function mesosomes are of two types
(a) Peripheral mesosome - They are situated near the cell mem. in peripheral part and their main function is cell respiration and cell wall secretion.
(b)Central mesosome- They are situated deep in cytoplasm and their main function is providing help in DNA replication and cell division. These are connected with nucleoid.

2. Storage granules -
Reserve material in prokaryotic cells are stored in the cytoplasm in the form of inclusion bodies. These are not bounded by any membrane system and lie free in the cytoplasm.
A.Glycogen granules- They store carbohydrate.
B. Volutin granules- These are also konwn as metachrornatic granules. The volutin granules are phosphate polymers and function as storage reservoir for phosphate.

3. Photosynthetic structure-
Some eubacteria have the capacity of photosynthesis.
In photosynthesis eubacteria many photosynthetic pigments are present.

4. Chromatin material (Nucleoid) -
A. Nucleus of bacterial cell is called nucleoid or genophore or incipient nucleus or fibrillar nucleus. Nuclear membrane and nucleolus are absent.
B. True chromosomes are also absent in bacterial cells. Instead they contain a single chromosome. It consists of a ds circular naked DNA (without histone) and non-histone proteins. Non histone proteins are polyamines. Nucleoid is connected to mesosome.
C. Beside the main DNA another small and ds-circular DNA is also present in bacterial cell which is called Plasmid. It is also known as extra chromosomal or extranuclear genetic material. (The term 'Plasmid' was given by Lederberg).
D. Plasmids have the ability to replicate independently.
(1) For fertility factor (F- plasmid): On the basis of presence or absence of F- factor, there are two mating types of bacteria.
(a) F+ - Cells, carrying 'F' factor acts as donor and are called F+ or male.
(b) F- - Cells, lacking 'F' factor acts as recipient and are called F- or female.
When 'F' plasmid is attached with main DNA, it is designated as episome and this type of cell is known as Hfr cell ( the word episome was given by Jacob & Wollman).
(2) R-factor - Resistance to antibiotics.

Gram Staining technique :
1. First of all H.C. Gram differentiated bacteria on the basis of staining.
2. In the first step of this method bacteria are stained with Crystal Violet or gentian violet and then KI solution.
3. After staining, bacteria are washed with Acetone or Ethyl alcohol. After washing some bacteria retain the stain
and some bacteria are decolourised.
4. Bacteria which retain stain (violet or purple) are called. Gram(+) and bacteria which decolourise are known as Gram(-). Gram(-) bacteria are counter stained by saffranine.

Compared to many other organisms, bacteria as a group show the most extensive metabolic diversity. Most of the bacteria are heterotrophic but some are autotrophic. On the basis of nutrition bacteria are classified into following three categories.

1. Autotrophs :
These bacteria use light or chemical energy for their own food synthesis.
On the basis of source of energy autotrophs are of following two types.

(i) Photosynthetic autotrophs -
#These bacteria use light energy for food synthesis.
#In these bacteria photosynthesis is non oxygenic.
#They need hydrogen ion for photosynthesis, so hydrogen ion is received from sources like inorganic sulphur compound (Thiosulphate) or organic compound (Amino acids, Isopropyl alcohol, Fatty acid).
Some photosynthetic bacteria are :-
- Purple sulphur bacteria - e.g. Chromatium
- Green sulphur bacteria- e.g. Chlorobium, Thiolhrix
- Purple non sulphur bacteria- e.g. Rhodospirillum, Rhodopseudomonas.

(ii) Chemosynthetic autotrophs -
# These are nonphotosynthetic autotrophs i.e., photosynthetic pigments are absent.
# They use chemical energy instead of light energy for food synthesis.
# Chemical energy is obtained from oxidation of chemical compounds.
# These bacteria oxidise chemical compounds and release energy which is used for food synthesis.
e.g. Nitrifying bacteria- They oxidise nitrogenous compounds and obtain energy.
Nitrite bacteria - Converts ammonia into Nitrite. e.g., Nitrosomonas or Nitrococcus
Nitrate bacteria - Convert nitrite into nitrates. e.g. Nitrobacter
2. Heterotrophs :
� Most of the bacteria are heterotrophic i.e. they can not manufacture their own food.
� They receive their own food from dead organic matter or living organism.
These are of following types- (a) Saprophytic (b) Parasitic

Saprotrophic bacteria- These bacteria obtain food from dead and decaying organic matter.
These are also of two types-

(a) Obligate saprotrophic - These bacteria obtain food only from dead organic matter.
These are completely saprotrophs.
e.g. Bacillus vulgaris, Clostridium botulinum

(b) Facultative parasite- These are normally saprophytic in nature, but in the absence of dead organic matter they can become parasitic.
e�g� Psuedomonas, Staphylococcus

Parasitic bacteria- They obtain their food from living organism.
These are also of two types-

(a) Obligate parasite- They always remain parasitic.
e �g. Mycobacterium leprae

(b) Facultative Saprotrophic- They are normally parasitic in nature but in the absence of living host.
may become saprotrophs
e.g. Mycobacterium tuberculosis

3. Symbiotic bacteria
These bacteria conwrt atmospheric nitrogen into nitrogenous compounds like Amino acid. Or Salts of ammonia.
e.g. Rhizobium

On the basis of respiration bacteria are of two types
1. Aerobic bacteria
These are of two types
(A) Obligate aerobic- These are completely aerobic and die in the absence of Oxygen. eg. Azotobacter
(B) Facultative anaerobic -These are normally aerobic bacteria but can survive in the absence of Oxygen
eg. Acetobacter aceti, Clostridium letani

2. Anaerobic bacteria
These are of two types.
(A) Obligate anaerobic - These are completely anaerobic bacteria and do not have capacity of aerobic respiration. e.g. ''Clostridium -botulinum
(B) Facultative aerobic- These are normally anaerobic but also have capacity of aerobic respiration. e.g. Fermentation bacteria except Acetobacter aceti.

Bacteria reproduce by two methods
(1) Asexual reproduction (2) Genetic recombination

Asexual reproduction -
(i) Binary fission -
(a) This is the most common method of bacterial reproduction.
(b) Under favourable conditions first of all DNA replication takes place in bacterial cell, bacterial cell divides into two dauqbter cells due to formation of transverse septum in the centre of the cell. Each daughter cell grows into a new bacterium.
Under favourable conditions, the cells of bacteria divides after every 20 minutes.,
(ii) By Endospore - Endospore formation occurs under unfavourable conditions .
(a) It is a highly resistant structure. It is resistant to high temp., radiations antibiotics and chemicals.
(b) It is also known as "reproduction without multiplication".
(c) Endospore is highly resistant structure due to presence of Ca-dipicolitmate in cortex.
(d) Endospore is stained by Nigrosin reagent.
(e) Endospore formation is seen in mostly bacillus type of bacteria.

1. Ammonification - Ammonifying bacteria -
Some bacteria convert Protein (present in decaying plants & animals) into Ammonia.
e.g., Bacillus vulgaris, Bacillus mycoides, Bacillus ramosus

2. Nitrification- Nitrifying bacteria-
These bacteria convert Ammonia in to Nitrite and later into Nitrate.
{Nitrosomonas > NO2 (Nitrite) Nitrobacter > NO3 (Nitrate)
These bacteria convert the atmospheric nitrogen into nitrogenous compounds like amino acids, nitrate or ammonium
salts.
Nitrogen fix at ion is done by two methods -
(A) Symbiotically- Some bacteria live symbiotically and do nitrogen fixation.
e.g. Rhizobium -In the root nodules of legurnes such as alfalfa, sweet clover. sweet pee, lentils, garden pea, broad bean, clover beans.
Aerorhizobium -In the stern nodules of Sesbania
Azospirillum- Found on root surface of cereals i.e., superficial symbiosis (eq. Wheat, Hice, Maize).

Frankie (Filamentous bacteria)- In root nodules of non leguminous plant Casurina and Alnus plants.
(B) Asymbiotically- Some bacteria occur free in soil and do nitrogen fixation.
e.g. Clostridium, Chromatium, Azotobacter, Azospirillum, Beijernickia Rhodomicrobium, Rhodospirillum, Rhodopseudomonas
Note : Azotobacter and Beijemickia are aerobic. Rhodospirillumis anaerobic bacteria. Both Rhizobium and Frankia are living in soil, but as symbionts can fix atmospheric nitrogen.
4. Dairy products -
Dairy products are formed with the help of bacterial fermentation.
Curd - It is made by milk.
Milk
Streptococcus lactis or-> Curd
Lactobacillus lactis
Note: Lactobacillus lactis (LAB/Lactic acid bacteria) increas vitamin B 1 2 in curd LAB also help in checking the disease causing microbes in stomach.

(1) Mycolic acid - Long chain of fatty acid present in all filamentous bacteria. eg- Noccardia, Mycobacterium.
(2) Bacteriods - symbio bacteria which are present in root nodules of plants are known as bacteriods. eg- Rhizobium.
(3) Pus Bacteria :
� Staphylococcus ( produces yellow pus )
� Pseudomonas ( produces blue pus )
(4) Nif-gene - "Nitrogenase Inducing factor"
� nif gene is present in all nitrogen fixing bacteria.
(5) Bacillus thuringiensis- this bacterium is related with "Bt toxin"
(6) Teichoid acid is found in Gram(+) bacteria.