• Youngest biological sciences
  • Started in middle of nineteenth century- Mendelian genetic & natural selection
  • Microbiology now stands with older biological science that is zoology and botany
  • Microbiology is the study of microscopic forms of life concerned with microorganism structure, function, nutrition, reproduction, heredity, chemical activities, classification, identification.


  • Not readily visible with naked eyes
  • Every living organism are dependent on microorganism directly or indirectly
  • Microorganism are single and multicellular  organisms that donot include tissue specialization
  • Groups of microorganism includes- bacteria, cyanobacteria, algae, fungi(mould & yeast), protozoa, nematodes, viruses and some viroids and prions.
  • Microorganism are present in all environment
  • From human beings they are parts of our world.
  • Have beneficial influence in our daily life.
  • Breads-made of yeast- that ferment sugar and carbonate the dough before baked.
  • Cheese,yogurt,sour cream require microorganism.
  • As a fertilizer in plants or microorganism reduced nitrogen for plant growth
  • Antibiotics for bacteria disease(Strep throat,pneumonias,gonorrhea,syphilis)
  • Used as vaccinetetanus,diphtheria,whooping cough,measles & mumps
  • Microbes plays important part in waste disposal.
  • Recycling essential nutrient •Microbes produces- organic acid,solvent and enzyme

Produces amino acid, vitamins, growth factors, therapeutic enzymes for curing malnutrition and health problem of human being.

  • Roles of extraction of metals from ores
  • As a fuel(by using agriculture waste and extreta)- biogas,gasohol
  • Genetic engineering technology- produce new form organisms by inserting specific pieces of foreign materials(genes)
  • Microorganism is directed to produce protein such as
  • Hormones- insulin(treatment of diabetes),tissue plasminogen activator(TPA- treatment of heart attack victim),
  • Antiviral agent-inteferons(treatment of cancers and disease caused by virus),
  • Human growth factors(increase bone growth),
  • Amino acids
  • As a food spoilage agent
  • Human disease — Acquired Immune Deficiency Syndrome(AIDS),herpes,legionnaires disease,influenza,Tuberculosis,typhoid,dermatomycoses,dysentery,malaria.
  • Animal disease – Burucellosis,tularemia
  • Plant disease – Mildews,rusts,smuts,cankers,leaf spoils etc

French scientist Louis Pasteur expressed- The role of infinitely small is infinitely large.He was first scientist to recognize biological function of microbes.

Microbiology: A multifaceted Science

  • It is more than just a taxonomic study of microorganism.
  • It is also concerned with role of organism in causing disease
  • Microbiologist study wide range of microscopic form of life and their activity in natural and artificial environment.
  • Field of microbiology includes the study of bacteria, algae, fungi(mould & yeast), protozoa, virus and subviral agents of disease.
  • Bacteriology- study of unicellular procaryotic organism known as bacteria.
  • It deals with the uses of bacteria in industry
  • Role of bacteria in ecology of world
  • Bacterial genetics,structure and multiplication
  • Mechanism by which bacteria cause disease
  • Bacteriologist is a person who studies bacteriology
  • Mycology– is a study of fungi,including moulds,mushroom and yeast.
  • Fungi have a wide variety of sizes,colours,shapes.
  • Non photosynthetic.
  • Many live in soil & play important part in decomposition of organic matter.
  • Produces several kind of food & antibiotics
  • Causes disease in humans,animals & plants.
  • Mycologist study about fungi.
  • Phycology(Algology)- It can be unicellular & multicellular giant kelp(50m or more)
  • Beautiful colours – brown,green,red and yellow
  • Photosynthetic.
  • It increases level of dissolved oxygen in their immediate environment and serve as food sources for humans & livestock.
  • Phycologist study algae
  • Protozoology – larger than most other organism
  • Complex- structure & activities
  • Found –sewage,water,intestinal tract of insects and damp soil.
  • Feed on other microorganism and dead organic matter.
  • Harmless
  • But few causes disease such as malaria, amoebiasis, sleeping sickness, leishmaniasis etc.
  • Parasitic animals.
  • Arthropods of medical importance are subject matter of parasitology.
  • Protozoologist study protozoa.
  • Virology – study of noncellular(acellular) organism called viruses.
  • Structure & reproduction of viruses for studing disease and how to control.
  • Different multiplication than other organism.
  • Virus depend on host cell for growth & reproduction.
  • Obligate intracellular parasites •Microorganism can be infected by cells.
  • Virologist study virus


  • MICROBIAL ECOLOGY – Study the relation between microorganism & environment
  • MICROBIAL MORPHOLOGY & CYTOLOGY – Study of shapes and the microscopic & submicroscopic details of microbial cells(ultrastructure).It involve the technique of electron microscopy.
  • MICROBIAL PHYSIOLOGY – Study of microorganism function. Metabolic activities, effect of environment on microbial synthetic pathways and nutritional requirement of different groups are studied.
  • MICROBIAL GENETICS – Study of genes, inheritance pattern, genetic exchange between microbes, how genes is expressed within organism, control of cellular activities,effect of mutation(genetic change)
  • MICROBIAL TAXONOMY – Naming & classification of microorganism on basis of similarities & differences.
  • MOLECULAR BIOLOGY – Programming genetic system and creation of macromolecules & important biological chemicals in organism. It deals with DNA and protein synthesis in organism
  • BIOCHEMISTRY – Concerned with chemical basis of living matter and varies metabolites reaction associated with them.
  • BIOPHYSICS- Principles of physics apply to living organism.



  • Animals differ from plants as they lack typical structure of plants, such as leaves, stems & roots.
  • They are active motile, non-photosynthetic and quite complex
  • Plants are opposite of animals in all these respects.
  • Until 1830,taxonomic status of most life forms remained fairly constant.
  • Discovery of wide variety of microorganism presented biologist with several problems.
  • Some microorganisms presented as either plant or animals, many could not.
  • Presence of outer structure called cell wall which could define microbial cell as plants.
  • Animal like cell such as protozoa did not have this structure.
  • Such cell ingest and capture solid foods but plants cannot.
  • Thus algae, bacteria, fungi(moulds and yeast) were grouped into plantae and protozoa as animalia.
  • Some microorganism got the properties of both plant & animals.


  • Difficulties were there in applying 2kingdom classification on microorganism.
  • Microorganism differ widely in metabolic and structural properties.
  • Some are plant like ,some are animal like & some totally different.
  • In 1866 Ernst Haekel proposed 3 kingdom to eliminate confusion.
  • Kingdom was names Protista (Derived from Greek word-primitive or first)
  • The new kingdom consists single celled microbes such as algae,bacteria,fungi and protozoa and multicellular which was not differentiated or organized into tissue or organ such as higher plant or animals.
  • It was never universally accepted.

1957- Roger Stanier

  • They distinguished two subgroups based on cellular characteristics
  • Lower protist – procaryotes – primitive nucleus- All bacteria eubacteria, cyanobacteria, archaeobacteria, rickettsia, chlamydia, mycoplasma )
  • Higher protist – Eucaryotes- well defined nucleus- algae, fungi, protozoa
  • Virus are left out of this scheme.


characteristics of eukrayotic cells and prokaryotic cells


  • 2 Kingdom & 3 kingdom is over simplified and many biologist favours dividing organisms among 5 kingdom as first suggested by R.H Whittaker 1969
  • Organisms are place in 5 kingdoms on basis of atleast 3 major criteria.
  • Cell type- procaryotes or eucaryotes
  • Level of organization- solitary and colonial unicellular organization or multicellular
  • Mode of nutrition
  • In Whittaker’s system,
  • Animalia contains- multicellular organism with wall less eucaryotic cell and primarily ingestive nutrition.
  • Plantae contain- multicellular plants with called eucaryotes and primariliy photoautotrophic nutrition and pinocytosis.

Other 3 kingdom

  • Monera – procaryotes in Bergey’s manual
  • Fungi– eucaryotes, multinucleated organism, with nuclei dispersed in a walled and often septate mycelium, nutrition is absorptive
  • Protista– least homogeneous and difficult to define – eucaryotic with unicellular organization, either in a form of solitary cell or colonies of cell lacking true tissue.
  • They may have ingestive, absorptive or photoautotrophic nutrition
  • Includes algae, protozoa and simple fungi
Penicillium labeled cropped

An environmental isolate of Penicillium

  1. hypha
  2. conidiophore
  3. phialide
  4. conidia
  5. septa


  • IN 1977 Carl R. Woese proposed a three kingdom of classification.
  • Grouping of all bacteria into procaryotes in 5 kingdom system is based on microscopic observation
  • Woese proposal was based on Modern techniques in molecular biology and biochemistry that reveal two types of procaryotics cells
  • Ribosomes are not same in all procaryotic cell
  • Comparing sequence of nucleotides in ribosomal RNA(rRNA) from different kind of cells there are 3 distinctly different cell groups,the eucaryotic and 2 different procaryotes – Eubacteria (true bacteria) and Archaeobacteria (ancient)
  • Woese believed that Archaeobacteria and Eubacteria(Procaryotes in 5 kingdom) having similar appearance should form their own separate branches Evolutionary tree.
  • All Eucaryotes- protista, Fungi, plant and Animal in Whittaker’s system)should be grouped into third kingdom.
  • Difference in membrane lipid structure,transfer RNA molecules and sensitivity to antibiotics also support classification of 3 kingdom.
PhylogeneticTree Woese 1990

Difference between Archeobacteria and Eubacteria

  • Archeobacteria- never contain peptidoglycan
  • Lives in extreme environment
  • Do all unusual metabolic processes

Archeobacteria includes 3 groups

  • Methanogens– strict anaerobes- produce methane from carbondioxide
  • Extreme Halophiles- require high concentration of salt for survival
  • Thermoacidophiles– grow in hot acidic environment


  • Mitochondria and chloroplast,two eucaryotic structure are descended from procaryotes.
  • It become trapped in large cell and established endosymbiosis relation with it.
  • Mitochondria is though to be actively metabolizing bacteria an Chloroplast as photosynthesizing descent occurred in Eucaryotic cells.
  • Many portion remain unclear, biochemical and metabolic differences donot support the idea.
  • With the discovery of archeobacteria, common ancestor of all form of life & evolution of eucaryotic cell become approachable.


  • Virus have definite property that set them apart from all other life form
  • Neither procaryotes nor eucaryotes
  • Virus are not cell
  • Virus consists of DNA or RNA surrounded by protein coat
  • After invading living cells,virus use metabolic and genetic machinery of host cell to reproduce.
  • Virus infect bacteria,algae,protozoa,fungi .
  • Boundry between living and non living.
  • They undergo mutation(genetic change)
  • Have mean of replicating and increase in number
  • Obligatory intracellular parasites
  • Virus get incorporated in host cell and resemble host cell.
  • Origin of Virus hypothesis
  • Arose from independently replicating strands of nucleic acids(Plasmid)
  • Developed from degenerative cells through many generation-lost its ability to grow but can grow when associated with living cell

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