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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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THANK YOU