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Classification of Microorganisms
CHAPTER 2
Classification:
• All living organisms are classified into groups based on very basic,
shared characteristics.
OR
• Arrangement of organisms into groups based on their mutual similarities
or evolutionary relatedness.
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Taxonomy :
•The field of biology dealing with identifying, naming,
and classifying species. Every species has a unique two-part name situating it within a genus, and is further assigned to a series of higher-order taxonomic rankings.
Taxonomic hierarchy
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Prokaryotes
• Prokaryotes are the single-celled organisms
• The size of most prokaryotes is between 1 µm and 10 µm, but can vary in size from 0.2 µm to 750 µm.
• The prokaryotes are divided into two domains: ▫ the bacteria: unicellular microorganisms that have wide range of shapes and
diverse in habitat.
▫ the archaea: single-celled prokaryotic microorganisms similar to bacteria but possess some genes and several metabolic pathways that are closely related to those of eukaryotes.
• Exists in different shapes like, coccus, bacillus, spirillum.
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General characteristics of Bacteria
• Bacteria are prokaryotic organisms without cell defined organelles
like mitochondria, Golgi bodies, Endoplasmic reticulum, etc.
• Microscopic, unicellular, they may occur singly or aggregations to
form colonies.
• They posses rigid cell wall. Cell wall is made up of peptidoglycan
and Lipo polysaccharides.
• Absence of well defined nucleus. i.e., DNA is not enclosed in a
nuclear membrane.
• Most of the bacteria are heterotrophic. Some bacteria are autotrophic,
posses chlorophyll, which is not in plastids. Instead it is found
scattered.
• Motile bacteria posses one or more flagella.
• The common method of multiplication is binary fission.
• True sexual reproduction is lacking, but genetic recombination occurs
by conjugation ,transformation and transduction.
• Endospore formation
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Groups of bacteria:
• Gram positive bacteria: Those bacteria when they are stained in gram
stain results in purple color.
• Gram negative bacteria: Those bacteria when they are stained in gram
stain results in pink color.
• The mycoplasma- lack a cell wall around their cell membrane
• The Archaea- Cell wall lacking peptidoglycan outside the plasma
membrane-
Nutrition of bacteria:
They exhibits different modes of nutrition level such as-
• Autotrophic bacteria: These bacteria are able to synthesize their own food. For e.g.: Phototropic bacteria and chemosynthetic bacteria
• Heterotrophic bacteria: These bacteria are unable to synthesize their own food, hence they depends on other organic materials. For e.g.: saprophytic bacteria-these bacteria feeds on dead and decaying matter.
• Symbiotic bacteria: These bacteria have a mutual benefit from other organisms. For e.g.: nitrogen fixing bacteria (or) rhizobium.
• Parasitic bacteria: These bacteria are present in plants, animals and human beings. These bacteria feeds on host cells and causes harm to the host.
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Respiration in bacteria:
• Anaerobic bacteria: does not require oxygen for respiration.
• Aerobic bacteria: require oxygen for respiration.
Bacterial Cell structure
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Beneficial effects of Bacteria
• Decay and decomposition
• Enhancing Soil Fertility
• Bacteria in industry
• Bacteria in medicine
• Bacteria in genetic engineering and
biotechnology
Harmful effects of Bacteria
• pathogenic bacteria
• Agents of disease
• Food spoilage
• Loss of fertility
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FUNGI
General characteristics of Fungi
• Fungi are eukaryotic (multicellular or unicellular)
• Fungi are a very diverse group and grow in wide range of habitats
• Some live in salt or fresh water, most are terrestrial
• Have a cell wall composed of carbohydrate chitin
• Fungi are achlorophyllous-lack the chlorophyll pigments
• They are incapable of photosynthesis and so are heterotrophic (mode of
nutrition is by absorption)
• Fungi can reproduce both sexually and asexually
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Classification based on Nutrition
• Saprophytes – absorb nutrients from dead matter, usually made efficient
by presence of hyphae
• Parasitic – obtain nutrients directly from other living things
• Mutualistic/Symbiotic – absorb nutrients by having a mutualistically
beneficial relationship with other living organism
Environmental Impact
• Decomposition helps in nutrient and
carbon recycling
• Symbiosis with plants, animals algae
and cyanobacteria cause beneficial
impact on the environment as a whole
• Used as biosynthetic factories to
produce drugs, antibiotics, alcohols etc
• Cause animal, human and plant
diseases and allergies
• Produce toxins (mycotoxins) which
cause food spoilage
•
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Importance of Fungi
• Recycling – fungi along with bacteria help in recycling of dead material
by decomposition and conversion to a usable form again
• Mycorrhizae and plant growth – cause beneficial plant growth and
development by mycorrhizal associations
• Food – some mushrooms are consumed as food source. Fungi is also
used in the production of cheeses, beer and wine, bread, some cakes, and
some soya bean products.
• Medicines – used to make antibiotics (most common is penicillin
derived from Penicillium). Many species make metabolites that act as
pharmacologically active drugs
• Biocontrol – some species of fungi can be extremely useful for
controlling insect pests of crops. The spores of the fungi are sprayed on
the crop pests.
• Bioremediation - Certain fungi can degrade insecticides, herbicides, and
heavy fuels and turn them into carbon dioxide, water, and basic elements
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• Crop diseases – some species are useful in biocontrol while some are
parasites of plants. Spore dispersal is very efficient and can cause
destruction of entire crop
• Animal diseases – parasitic fungi can cause diseases and allergies in
humans and animals
• Food spoilage – molds cause food spoilage by recycling of organic
matter
Algae
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General characteristics of Algae
• Eukaryotic organisms (unicellular or multicellular)
• Have chlorophyll and can carry out photosynthesis
• Lack many distinct cell and tissue types found in land plants
• Have variety of shapes and forms
• Phytoplankton is a population of free floating microorganisms, mainly
composed of unicellular algae
• Most algae are photoautotrophic, some are chemoheterotrophic
• Reproduction occurs in sexual and asexual (fragmentation or spore
formation) form
Symbiotic Algae
• Some species form symbiotic relationships in which algae supply
photosynthates to host organism providing protection to algae
• Lichens – an association of fungus and photosynthetic symbiont
• Coral reefs – they require endosymbiotic algae to stay in a healthy state.
In its absence coral bleaching occurs (deterioration of reef)
• Sea sponges – green algae are found in associations with surface
sponges. Algae provides oxygen and sugars in return for protection
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Types of Algae
• Green Algae – named so because of presence of green chloroplasts,
most are symbiotic
• Red Algae – named so because of a red pigment phycoerythrin, almost
all are marine species, formation of coral reefs
• Brown Algae– carotenoid pigment fucoxanthin mask green chlorophyll,
found in aquatic environments
Types of Algae
• Diatoms – silica cell wall (unique), found in ocean and river beds, silica
shells give rise to diatomaceous earth
• Dinoflaggelates – unicellular algae with stiff cellulose plates, lack
chloroplast and are dependent on other species for food, carnivores
mostly, blooms can cause oxygen depletion
• Cyanobacteria – single celled prokaryotes, both beneficial (natural
fertilizers) and harmful (blooms and toxins)
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Importance of Algae
• Provide food for people and livestock- nutritious because of their high
protein content and high concentrations of minerals and vitamins
• Brown algae yield alginic acid, which is used to stabilize emulsions and
suspensions (syrup, ice-cream, paint)
• Have medicinal properties- used to cure diarrhea, cough and
hypertension
• Algae can also serve as indicators of environmental problems in aquatic
ecosystems
Importance of Algae
• Used in forensic medicine (diatoms in lungs indicate death due to
drowning)
• Seaweeds are a critical source of three chemical extracts used
extensively in the food, pharmaceutical, textile, and cosmetic industries
(e.g. Agar)
• Seaweeds also are applied to soils as a fertilizer and soil conditioner -
their high concentrations of potassium and trace elements improve crop
production
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Importance of Algae
• Nitrogen fixation by some species in soil
• Provide oxygen by photosynthesis in aquatic environments
• Important source of food for other organisms
The world of parasites
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What are Protozoa
•A diverse group of mostly motile unicellular
eukaryotic organisms
•Defined as unicellular protists with animal-like
behaviour, such as movement
• Protists with plant-like behaviour e.g. photosynthesis
•Heterotrophic eukaryotes
•Obligate aquatic organisms
Characteristics of Protozoa
• Length from 10 to 52
micrometers, but can grow as
large as 1 mm.
• Easily seen with a microscope.
• Largest protozoa known as
deep-sea dwelling
xenophyophores, which can
grow up to 20 cm in diameter.
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Characteristics of Protozoa
•Formerly considered to be part of the
protista family.
•Can be flagellates (motile with flagella),
ciliates (motile with cilia), and amoebas
(motile by means of pseudopodia).
Positive aspects
•Play important roles in the fertility of soils
•Grazing on soil bacteria, regulate and maintain
bacterial populations— in the active growing
phase
•Enhances the rates at which bacteria decompose
dead organic matter
•Studies have shown that the presence of
protozoans in soils enhances plant growth.
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Positive aspects
•Biological processing of human and domestic animal
sewage; activity of the protozoa; extraction and
digestion of bacteria and other suspended particles;
water supply rendered fit for consumption by humans
and other creatures.
• Any change in our environment which threatens the life
of a balanced community of protozoans threatens also
the continuity of a clean water supply for humans.
Negative aspects
•Malaria – Plasmodium falciparum – Anopheles mosquito
• Sleeping sickness – Trypanosoma brucei – Tsetse fly
•Amoebic dysentery – Entamoeba histolytica
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Living or non-living?
What are Viruses • Infective agent
•A nucleic acid molecule
•A protein coat
•Too small to be seen by light
microscopy
•Able to multiply only within the
living cells of a host
•Direct the synthesis of structures
to transfer viral nucleic acid to
other cells.
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Positive aspects
•Viruses are often considered to be agents of small
scale evolutionary change:
little packets of genes that can be packaged
moved from organism to organism or from phylum to
phylum
provide a continuous supply of fresh genetic
information to organisms.
Negative aspects •There are numerous diseases related to viruses:
Plant diseases: Tobacco mosaic, Banana bunchy top
Animal diseases: bird flu, swine flu
Human diseases: Hep C, AIDS, Ebola,
Bacteriophagy
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