COMPOSITION OF THE MICROBIAL WORLDTURNING POINTS IN MICROBIAL RESEARCH

MICROORGANISMS AND THE EVOLUTION OF THE EARTHMODERN AGE OF MICROBIOLOGY

MICROBIOLOGY

Microbiology is a branch of biology dealing with study of microorganisms

DISCOVERY OF MICROBIAL LIFE

The exact beginning of the knowledge about the existence of microorganisms can be traced back only to the latter part of the seventeenth century

Antony van Leeuwenhoek first recorded observations of microorganisms ( bacteria,yeasts and protozoa) seen in water,faeces,teeth scrappings etc ….

Antony van Leeuwenhoek

* began making and using simple microscopes

* often made a new microscope for each specimen

* examined water and visualized fungi,algae and

protozoa : ‘animalcules’

COMPOSITION OF THE MICROBIAL WORLD

Viruses

Bacteria

Archaea

Protozoans

Fungi

Algae

BACTERIA

Single celled Lacks well organized nucleus The nuclear material is not surrounded by nuclear

membrane (nucleoid) Some bacteria are autotrophic;they possess

bacteriochlorophyll May be saprophytic,mutualistic or parasitic

Bacterial cell wall is a dense layer, surrounding the plasma membrane

The main constituent of the cell wall is peptidoglycan It gives shape & rigidity to the cell The organelles like mitochondria,endoplasmic

reticulum,golgi apparatus are absent

Bacteria reproduce asexually Multiply most commonly by binary fission The motile bacteria possess one or more flagella

ARCHAEA

They often occur in extreme aquatic & terrestrial habitats, which may be anaerobic,hypersaline or hyperthermophilic

They also seen in very low temperature environments Rod - shaped,spherical,spiral,lobed,

plate shaped,irregularly shaped or pleomorphic

Some are unicellular,others are filamentous or aggregates

Diameter – 0.1 to 15 micrometer Both gram positive & gram negative are present Reproduction - binary fission,fragmentation,budding

ALGAE

They are mostly photoautotrophs Primarily they inhabit aquatic habitatsThe vegetative body does not show any differentiation

into various tissue systems

They possess mostly unicellular sex organs without a jacket of sterile cells around them

They show progressive complexity in reproductionThey do not develop embryo after fusion of gametes

during sexual reproductionThey show distinct alternation of generations

PROTOZOANS

o Protozoa are mostly free livingo They are mostly aquatic,inhabiting fresh and marine

waters and damp placeso Parasitic and commensal protozoa live over or inside

the bodies of animals and plants

o Protozoa are unicellular o They contain one or more nuclei and organelles,with

little or no histological differentiation into tissues and organs

o They occur singly or form loose colonies in which individuals remain alike and independent

o Vegetative body of protozoa is naked or bounded by a pellicle

o The shape of the cell usually constant but changes with changing environment

o The single cell performs all the essential vital activities hence there is little or no physiological division of labour

o Locomotary organs are pseudopodia or flagella or cilia;they may be absent

o Nutrition – may be holozoic (animal like), halophytic (plant like),saprophytic or parasitic

o Reproduction – asexually by binary or multiple fission & budding

o Sexually by conjugation of the adults or by the fusion of gametes

FUNGI

Vegetative body is usually represented by a filament called hyphae

Hyphae together are referred to as myceliumHyphae are septate or non-septateCell wall is mainly made up of chitin often called

‘fungus cellulose’

Vegetative body is not divided into root,stem and leaves Has no specialized tissues for the internal transport of

water & nutrientsThey are heterotrophs;may be parasites or saprophytesThey lack chlorophyll

Food is stored in the form of glycogenBoth, sexual & asexual reproduction are presentAsexual reproduction – Sporangiospores & ConidiaSexual reproduction – Antheridia & Oogonia

VIRUSES

All viruses are obligate parasitesThey multiply only within their living host cellsMetabolically inert outside the host cellThey are ultramicroscopic; can only be viewed with

electron microscope

Viruses are actually nucleoproteinsThe proteinaceous coat surrounds the nucleic

acid,which forms the central core of the virus particlesThe viral genetic material ,may be either DNA or RNAThey are easily transmitted from infected host to the

healthy ones through various agencies

Viruses are host specific They have no metabolic activities of their own They utilize the metabolism of host cells

MICROBES AND ORIGIN OF LIFE

Abiogenesis• Men of ancient times believed that all living organisms

could spring forth spontaneously from non – living matter

• This belief has been referred to as Doctrine of Spontaneous Generation or Abiogenesis

• They believed that frogs,snakes and mice could be born of moist soil

• Flies could emerge from the manure,and that maggots could arise from the decaying corpses

• This idea continued until the mid 19 th century with great oppositions against it

Redi’s Experiment (1626-1679)• Francesco Redi,an italian physician, demonstrated that

abiogenesis does not exist

• He took rotting meat pieces and placed them in jars

• He sealed some of these jars tightly and left others open

• In a few days, maggots appeared in open jars only

• Redi concluded that the maggots arise from the eggs laid down by the parent flies

• That the maggots can not appear spontaneously

John Needham’s Experiment (1745)• Needham heated chicken broth and nutrient fluids

before pouring them into covered flasks

• The cooled solutions showed existence of tiny organisms in them

• He claimed that the organisms are originated spontaneously from the nutrient fluids

Pasteur’s Experiment (1861) In his swan-necked flask experiment he took various

type of broths (yeast water,sugared yeast water,urine etc)

Then,softened the neck of the flasks under a flame & drew it out in the shape of ‘S’ looking like the neck of swan

• The broths of these flasks were boiled until they steamed through the necks,and then cooled

• The broths so treated in the flasks did not decay

• There were no signs of microbes in them after days,weeks and even months though they were open to free air

• Pasteur’s unique swan-necks of the flasks trapped air – borne microorganisms before they could reach the broth and flourish in it

• Definitely discredited the doctrine of spontaneous generation

LANDMARK EVENTS IN MICROBIAL RESEARCH

contributor year contributionJansen & Jansen 1590 microscopeLeeuwenhoek 1677 animalculesEdward Jenner 1798 Smallpox vaccinationPasteur 1860 fermentationRobert Koch 1876-77 Causation of anthraxRobert Koch 1882 Causation of TBMetchnikoff 1882 phagocytosisChristian Gram 1884 Gram staining Pasteur 1885 Rabies vaccineRichard petri 1887 Petri dishLandsteiner 1902 Blood group

Svedberg 1923 ultracentrifugeFleming 1929 penicilinKnoll & Ruska 1932 Electron microscopeAvery,Macleod & Mc Carty

1944 DNA hereditary material

Watson & Crick 1953 Double helix modelSalk & sabin 1957 Polio vaccineJacob & monod 1961 Operon conceptT.O.Diener 1971 Discovery of viroidsBoyer et al 1972-73 DNA cloning

techniqueLue Montagnier 1983 Discovery of HIVMullis 1983 - 84 PCR

MODERN AGE OF MICROBIOLOGY

• Biochemistry

• Microbial genetics

• Molecular biology

• Recombinant DNA technology

• Gene therapy

• Serology

• Immunology

• Chemotherapy

Biochemistry

Microbes used as model systems for biochemical reactions Practical applications: Design of herbicides & pesticides diagnosis of illness and monitoring responses to treatment Treatment of metabolic diseases Drug design

Microbial genetics Avery,MacLeod and McCarty : genes are contained in molecules of DNA

Beadle and Tatum : • a gene’s activity is related to protein function

• Translation of genetic information into protein explained

• Rates and mechanisms of genetic mutation investigated

• Control of genetic expression by cells described

Molecular biology• Explanation of cell function at the molecular level

• Pauling proposed that gene sequences could provide understanding of evolutionary relationships

Serology The study of blood serum

ImmunologyThe study of the body’s defence against specific pathogens

ChemotherapyTreatment of a disease with chemicals

Chemotherapeutic agents are obtained from the microbes,plants & animals

Recombinant DNA technologyIt is a technology which allows DNA to be produced via artificial means

Gene therapyInserting a missing gene or repairing a defective one in humans by inserting desired gene into host cells

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