Sexual Reproduction in Bacteria

Sexual reproduction in bacteria is different from Eukaryotic organism. In Eukaryotic organisms ,the male and female gamete cells are produced whose fusion takes place to form zygote but sexual reproduction in bacteria is different because no gamete cells are produced and thus no fusion of cells to form zygote takes place .In bacteria genetic recombination takes place between two bacterial cells.The bacteria which transfer a part of genetic material is called donor and which receive the genetic material is called receipient. Thus the bacterial cell become diploid cell from haploid cell and since a part of genetic material are only exchanged .So it is called merozygote or partial zygote. The merozygote contain all DNA of its past cell and exogenote or a part of DNA from others. This genetic recombination between two bacteria takes place in three methods namely transformation, conjugation and transduction.

Reproduction in bacteria

Bacteria can reproduce both by asexual and sexual method. So it is said reproduction in bacteria as

1)     Asexual reproduction

2)     Sexual reproduction

1)     Asexual reproduction

          Bacteria can reproduce asexually by simple fission and binary fission method. Both fissions takes place during favourable climate.

The whole process can be grouped into three steps. The whole process can be grouped into three steps. They are

a)     Depletion of genetic material (DNA)

b)    Separation of DNA into newly formed two independent cells.

c)     Cytokinesis .

Since bacteria donot have spindle fibre so the two daughter cells formed may or may not contain equall loofs of DNA. So some time vinary fission result in the formation of cell with out nucleoid. And another cell containing two nucleoid. The genetically identical population of bacteria produced from asexual reproduction from a single parent is called clone.

 

Introduction of photo-hetrotrophs and chemo-hetrotrophs

 3) Photo-heterotrophs:

           This bacteria uses organic compound as the source of carbon. They oxidizes  the organic compound to get energy for growing. This bacteria is also known as Photo-organotrophs. Example Non –sulphur bacteria.

 4)  Chemo-hetrotrophs:

                     This bacteria is also called  chemo-organotrophs. This also             use organic compoundas the source of carbon . They produce energy from oxidation –reduction of organic compound which is used for growth of bacteria. Example E. coli

detail of types of chemo-autotrophs

Nitrifying bacteria

                      These bacteria makes nitrogen available to plants. They are present in soil. The Nitrosomonas and Nitrosococcus oxidizes ammonia to nitrate. The Nitrobactera and Bactoderma converts nitrite to nitrate.

Reaction      nitrosomonas

 2NH₃ +3O₂    →    2HNO₂ + 2H₂O +  158 Kcalorie

                                    nitrobacter

  HNO₂ + O₂ →    HNO₃ + 43kcalorie

Hydrogen bacteria

                 These bacteria oxidizes hydrogen to water in presence of oxygen .Example Hydrogenomonas

Reaction

 2H₂ +O₂ →  2H₂O + 56 kcalorie

Sulphur bacteria

             This bacteria is found in hot spring  containing hydrogen sulphide .They first oxidizes hydrogen to sulphur. This sulphur is conerted to sulphuric acid. The acid undergo reaction with soil to form sulphate. Example Beggiatoa and Thiobacillus thioxidans.

  Reaction

2H₂S +O₂  → 2S + H₂O +energy

2S +  2 H₂   → 2H₂SO₄  + energy

Iron bacteria

      This bacteria changes ferrous compound into ferric compound. The energy evolved from the oxidation is used for converting carbondioxide to food. Example or iron bacteria are Leptothrix, Cladothrix, Spiruphyllum and Ferrobacillus.

Reaction

 2FeHCO₃ + H2O +O  →  2Fe(OH)₃ + CO₂ +29 K calorie

 2FeCO₃ + 6H₂O   →  Fe(OH)₃ + 4CO₂ + 81 k calorie

Methane bacteria

    This bacteria oxidizes methane to CO2 . Thus methane provide both cargon and energy.

 CH₄ +O₂  →  CO₂ + H₂O + energy

Example : Methanosomonas

Introduction of Chemoautotrophs with its type

    Chemoautotrophs are the bacteria which uses energy evolved from chemical reaction as source of energy . It also uses atmospheric CO2 to prepare food. Chemoautotrophs are of following types

                  I.      Nitrifying bacteria

               II.      Hydrogen bacteria

            III.      Sulphur bacteria

           IV.      Iron bacteria

              V.      Methane bacteria

Detail of types of Photoautotrophs

1)     Purple sulphur bacteria:-

         These bacteria contain purplish pigment called bacteriochlorophyll. It uses water and hydrogen donor to convert CO₂ as food in presence of sunlight. The function of bacteriochlorophyll is similar to chlorophyll of green plants.

  Reaction

 2CO₂ +35H₂O→2(CH₂O)+2NaHSO₄+Energy

Example: Chromatium okeni

2)     Purple non sulphur bacteria

               In this bacteria food is prepared in presence of light with CO₂ and organic substance.Here CO₂ is reduced to food by the hydrogen donor organic substance.

Reaction

  6CO₂+12CH₃CHOHCH₃→C6H₁₂O₆+12CH₃COCH₃+6H₂O

Example:- Rhodospirillum rubrum

3)     Green sulphur bacteria:-

          These bacteria converts CO₂ into organic compounds by reducing with H2S. Example Chlorobium limicola

Reaction    light

  2H₂S+CO₂→CH₂O+2S+H₂O+Energy

Introduction of Photoautotrophs with its types

Phptoautotrophs are such types of bacteria which synthesize their own food in presence of sunlight . They use CO₂ of nature to prepare their food . They use hydrogen from water,H₂S and hydrogen toreduce carbondioxide . These bacteria have the pigment bacterioviridin, bacteriochlorophyll or chlorobium chlorophyllthat trap the light for synthesize. Photoautotrophs are of following types.

1) Purple sulphur bacteria

2) Purple non sulphur bacteria

  3) Green sulphur bacteria

Formation of endospore

 

Endospores are formed from well nourished bacteria when the vegetative growth is unsuitable for it . The cell of bacteria elongate, along with elongation of DNA towards the two ends of cell .When the strands of DNA coil at two ends it breaks to form two parts . One of the DNA coil to form helical structure . The cytoplasm around it also become dense and the cell membrane grows inwardly to form septum. The septum divide the cytoplasm and surround the DNA forming two unequal parts. Soon the wall is developed around it. This structure undergoes dehydration, contraction and soon many layer of cortex, spore coat and exosporium  are developed when it becomes mature endospore is liberated from bacteria.

introduction of endospore and its physiological properties

Endospores:

              Endospore is the highly resistant body produced in the cytoplasm of bacteria. It is mostly produced in rod shaped bacteria of genus bacillus Spirilla. Endospore help to protect the bacteria during

      Unfavourable condition.

Physiological property of Endospore:

1)     Endospore can withstand to high temperature and dessication.

2)      It can remain alive for many years under adverse environmental condition.

3)     Endospores are more resistant to toxic chemicals than the vegetative cells of bacteria.

4)     They may remain for many years.

5)     They are not killed in long time boiling.

introduction of plasmids and its function

Plasmids:

Plasmids are numerous structure similar to nucleoid . It also contain many pieces of DNA and is also without cell membrane. It is 1/100 of nucleoid DNA and is circular innature . Generally they replicate autonomously but sometime some of them also integrate to form nucleoid DNA in presence of or help of nucleoid.

               Plasmid during conjugation are also called episomes .This episome help in transfer of genetic material between different bacteria.

Bacteria cell also posses some gene which are resposnsible for the resistance to variety of antibiotic and production of certain protein antibiotic called Colicins or Bacteriocins.

Nuclear material of bacteria

  Bacteria do not have well developed nucleus as Eukaryotic cells.

  It has thin, circular coiled structure of  a DNA molecule called 

  nucleotide or bacterial chromosome. The nucleoid do not have 

  nuclear membrane. The bacteria DNA is 2 to 3% of cell weight

  but covers 10 or more % of volume of cell.

                           In some bacteria the DNA is attach to the 

  mesosome where as in   some it is also attached to the cell 

  membrane. Bacterial DNA do not have histone protein and 

  does not coil to form well defined chromosome during 

  multiplication.The bacteria DNA form chromosome because

  it lacks RNA

Bacterial Ribosomes and its type

             Ribosomes are minute cell organelles found scattered in cytoplasm. It is about 100 A in diameter . It is maded up of RNA and protein . In Eukaryotic cells, ribosomes are attached to Endoplasmic reticulum but since the bacteria lacks Endoplasmic reticulum, the ribosomes are found scattered in cytoplasm. Ribosomes are of two types called 70S and 80 S ribosome. These ribosome themselves consist of two units. The bacteria ribosome are 70S type. When the concentration of Mg++ decreases, the70S dissociate into 50S and 30S units. The 50S unit or larger unit consist of two RNA and 34 proteins and 30S unit consist of one RNA and 21 different protein. The molecular weight of bacterial ribosome is 2.5×10⁶ dalton. The bacteria RNA occur in three forms .They are 1) messanger RNA(m-RNA)  2) ribosomal RNA(r-RNA) and 3) transfer RNA(t-RNA). The function of ribosome is to synthesize protein.

Chromatophore and cytoplasm of bacteria

Chromatophore:-

    Chromatophore are the photosynthetic cell organelles in bacteria which contain photosunthetic pigment( chlorophyll) along with enzymes and electron carrier for photosynthetic phosphorylation.These are single membranous vesicular structure.

Cytoplasm:-

           The cytoplasm is granular, viscous liquid which is present in cell of bacteria between cell membrane and nuclear material. It is compound of carbohydrate, protein ,fat ,lipid ,inorganic ions ,vitamins coenzyme and varities of compounds of low molecular weight. It also contain RNA and ribosomes.

Nutrition in bacteria

Bacteria are generally divided into two types on the basis of types of nutrition. They are autotrophic and hetrotrophic. Beside these two bacteria has also been grouped into Photosynthetic and chemosynthetic on the basis of energy source they use for making food. Photosynthetic bacteria are those bacteria which utilize light as source of energy to manufacture food.

         Chemsynthetic bacteria are those bacteria which uses energy evolved from oxidation of chemicals that are either or organic or inorganic chemicals as source of energy to manufacture food.

Bacteria can be divided into following four types on the basis of source of carbon and energy they use. They are

    1) Photo autotrophs

    2) Chemo autotrophs

    3) Photo hetrotrophs

    4) Chemohetrotrophs

Mesosomes and its functions

Mesosomes:-

        Mesosomes are complex , intracellular, membranous structure formed by the infolding of cytoplasmic membrane .It is simple tubular or vesicular invagination in the cytoplasm. It is present in both the gram negative and gram positive except few gram negative bacteria. The chemical composition is similar to cell membrane.

Function of mesosomes:-

1)     It increase the surface area for enzymes action of respiration.

2)     It helps in DNA replication during the cell division in daughter cell by being attached with bacterial chromosome.

3)     It helps in cross wall formation before the cell division and on endospore formation.

Functions of cytoplasmic membrane

                   The function of cytoplasmic membrane are as follow.

1)     It is semipermeable membrane ,so it controls the entrance of nutrients and exit of waste from cell. It is permeable to molecule of low molecular weight.

2)     It helps to take certain extracellular enzyme and other chemicals by active transport system called permeases.

3)     It contains some of the enzymes which are necessary for synthesis and transport of peptidoglycan, teichoic acid and other membrane components.

4)     It contain large number of respiratory enzyme but help in production of chemical energy that are used by cells.

5)     During replication it produces nuclear material DNA.

 

Cytoplasmic membrane of bacteria

                     It lies beneath the cell wall. It is also called plasmamembrane. It is about 70 nm in thickness. It is composed of phospholipid and protein . It consist of 60% of protein ,30%of lipid and 10% of carbohydrates. It is differentiated into three layers out of which the two outer layer is 2.5 nm and the middle one is 5 nm .All the combination of cytoplasm of bacteria is similar to Eukaryotic cell, except it lacks  sterols. Due to the lack of sterol it has high resistance to antibiotic.

Introduction of Spheroplasts and L-form bacteria

Spheroplasts:-

           Spheroplasts is the bacteria without peptidoglycan layer in cellwall. This is done by treating gram negative bacteria with lysozyme in a hypertonic medium in the presence of penicillin.

L-Form:-

        L-form bacteria was first of all discovered by Dr Kleinberger in laboratory of Lister Institute in London while studying Streptobacillus moniliformes .The bacteria donot have cell wall. It can be formed from both Gram positive and Gram negative bacteria. This bacteria is formed when the bacteria losses the ability to manufacture peptidoglycan .while studying Streptobacillus it was formed and again reverted to  original bacteria.

Introduction of Protoplasts

         The bacteria without cell wall but having cell membrane ,capsule and protoplasm is called protoplast.

                             Some bacteria when treated with enzyme lysosome, their cellwall dissolve without destroying any internal structure . This is because the enzyme lysozyme hydrolyses the bond between N-acetyl muramic acid and N-acetyl glucosamine. These bacteria without cell wall is called Protoplast. Protoplast posses many of the physiological characteristics except they are non-motile ,unable to divide.

Composition of cell wall of Gram Positive bacteria

The cell wall of gram positive bacteria is thick about 25-30 nm.  It contain 20-80% of peptidoglycan. The cell wall is rigid and strong structure because the peptidoglycan are repeatedly cross linked .The cell wall of gram negative contain peptidoglycan ,protein  and polysaccharides. Beside these three ,the gram positive bacteria has fourth layer of carbohydrate molecules called Teichoic acid that are linked with muramic acid of peptidoglycan and bind the cell wall with plasmamembrane or cell membrane.The teichoic acid plays important role.It regulate the action of enzyme autolysin which lossen the bonds of peptidoglycan, It also regulate the normal cell division of gram positive bacteria.

Cell wall of bacteria

                         Cell wall is present under the capsule and above the cell membrane. It is multilayered and 10 to 100nm in thickness. The composition of cell wall of bacteria is different from that of plants and fungi. The cell wall of plants is composed of cellulose and the cell wall of fungi is composed of chitin but the cell wall of bacteria is composed of complex polymeric compound called peptidoglycan or mucopeptide or mucocomplex.

Peptidoglycan has two main groups called carbohydrate ( amino sugar) and aminoacid .The carbohydrate is peptidoglycans are N-avcetylglucosamine. The amino acids are L-alanine, D-alanine D-glutamic acid and either diaminopimelic acid (DAP) or the structurally related lysine.

                                           The function of cell wall is to provide rigidity and shape to the bacterial cell. Any way the composition of the  cell wall of Gram negative and Gram Positive bacteria are different

Capsule and its function in bacteria

              Capsule is the slime, gelatinous layer outside of cellwall of bacteria cell. Capsule are generally made of polymers of polysachhrides. In some , it is also made up of one polypeptide containing only one or two amino acids . Capsule is the protective layer that protect the cell wall from dryness and harmful agents. Capsule help to determine the degree of harmful on host. Those bacteria which have capsule,they are more harmful than other without capsule. The capsule can be present on both gram positive and gram negative.

Pellicle and its function in bacteria

        Bacteria on cell membrane posses numerous fine hair like structures which are 3 to 25 nm in diameter and 0.5to 20 um in length . It is also made up of protein called pillin. There are different types of pilli on the basis of their function. One type of pilli is called ‘f’ or sex-pilli which help in sexual reproduction by forming conjugation tube to transfer DNA from donor to receipient. There are also another type of pilli which help the bacteria to come near the surface of liquid where it can get oxygen. There are also third type of pilli which help to attach the bacteria to tissue and suck nutrients from tissue of plants and animals.

Motile form of bacteria

                Almost all spiral bacteria and half of the bacilli are motile form and the cocci  are non motile type.

 Electron microscope study shows that flagella has three parts namely filament ,hook and basal body . The filament consist of three or more longitudinal fibril of fibrous protein called flagellin which are twisted to form  a core . The basal end of filament is attached to hook which in turn attached tobasal body also called kinetoplast. The  basal body is made up of a rod and two or more rings which are for attaching with cellwall  and cellmembrane.

Types of bacteria on the basis of flagella

Flagella:-

       Flagella are fine hair like structure present on motile form of bacteria . They are 12 to 30 nm in diameter and 3 to 12 um long. The flagella is composed of protein. There are also bacteria with out flagella called atrichous. On the basis of flagellation ,the rod shaped bacteria are classified into four groups by Leifson as

1)     Monotrichous bacteria having flagella at one end .   

2)     Diplotrichous bacteria having flagella at two ends of cell.

3)     Lophotrichous bacteria having many flagella at one end of bacteria.

4)     Peritrichous bacteria having flagella distributed allover the body.

Composition of wall of bacteria

                                 Gram negative bacteria wall are thin and contain higher percentage of lipid. Gram positive bacteria wall are also thin but do not contain lipid.

         Cellular structure of bacteria consist of cell envelop made up of cell wall and cell membrane . some bacteria has also third layer called capsule . The motile form of bacteria contain flagella. Gram negative bacteria also contain hair like called pilli.

                       The cell envelop encloses protoplasm which is differentiated

into central coiling of chromosome called nucleoid and outer called cytoplasm containing mesosome , fat granules and ribosomes.

Types of bacteri on basis of bacterial staining

Bacterial staining       

                       Bacteria can be differentiated into two as gram positive and gram negative .This was first done by Danish Physician named Christian Gram in 1884.

                In this process a smear of bacteria is heated and then violet dye is added to stain it for thirty seconds. Then it is rinsed and iodine solution is added. When iodine is added it is turned to deep blue. The iodised smear is treated with 95% alcohol. This decolourises some of the bacteria and then saffrin is added. When saffrin is added the decolourised bacteria change to red. These red bacteria are called  Gram negative bacteria and the non decolourised bacteria change to purple and are called Gram positive.

  Smear of bacteria---heated—violet dye added—rinsed—added iodine solution—turn smear to red – treated with 95% alcohol – decolourises some of bacteria – added sffrin – change decolourised bacteria to red and non decolourised  remain purple—red called Gram negative – purple called Gram positive.

Introduction of Bacteria

                               

Bacteria

             The bacteria are microscopic organism which are plants of microscopic nature . They are found everywhere in air ,water and soil. They are unicellular plants . They are in different shapes. Some are spherical, round, spiral and rod in shape.

                                    Bacteria are useful as well as harmful. Some  importances of bacteria are as listed below .

1)     The bacteria present in the digestive system help to digest food.

2)     The bacteria help in converting milk to curd .

3)     The bacteria present in soil help in decomposition of the dead body of plants and animals.

Introduction of thallophyta

These are the simplest non flowering plants.They may be microscopic or visible to our eyes.

Their bodies are not well differentiated into root, stem and leaves.The body of these plants are  called Thallus as they are formed by an undifferentiated mass of cells.Their bodies are unicellualar or multicellular.These plants are found mostly in damp and moist places.