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Classification of Microorganisms

Before the existence of microbes was known, all organisms

were grouped into either the animal kingdom or the plant

kingdom.

When microscopic organisms with characteristics of animals

and plants were discovered late in the seventeenth century,

a new system of classification was needed. Still, biologists

could not agree on the criteria for classifying these new

organisms until the late 1970s.

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At the beginning :there are two kingdoms- Monera- Protista

Earlier classification :

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Monerais oldest (earliest cell), prokaryotic

& structurally simple cell

Protistais youngest (latest cell), eukaryotic

& more structurally complex cell

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The Protista developed to fourkingdom : Protista, Fungi, plantae

and animalia

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In 1978, Carl Woese devised a system of classification based

on the cellular organization of organisms. It groups all

organisms in three domains as follows:

1. Bacteria (cell walls contain a proteincarbohydrate

complex called peptidoglycan)

2. Archaea (cell walls, if present, lack peptidoglycan)

3. Eukarya, which includes the following:Protists (slime molds, protozoa, and algae)

Fungi (unicellular yeasts, multicellular molds, and

mushrooms)

Plants (mosses, ferns, conifers, and flowering plants)Animals (sponges, worms, insects, and vertebrates

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The Three-Domain System

Figure 10.1

Euryarchaeota

Crenarchaeo

ta

Korarchaeota

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Domains Archaea

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In the late 1970s, a distinctive type of prokaryotic cell was

discovered. Most strikingly, the cell walls of these

prokaryotes lacked the peptidoglycan common to most

bacteria. It soon became clear that they also shared many

rRNA sequences, and the sequences were different fromeither those of the Domain Bacteria or the eukaryotic

organisms. These differences were so significant that these

organisms now constitute a new taxonomic grouping, theDomain Archaea.

B t i d A h

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Bacteria and Archaea

Bacteria and Archaea are both prokaryotes and

their DNA is arranged in circular structures calledplasmids (they have no nucleus and the DNA is not

arranged in chromosomes). Prokaryote derived

from the Greek Promeaning before and karyon

meaning a kernel [i.e. a nucleus].

However, they have substantial differences in their

biochemistry, cell wall structure and othermolecular details.

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Bacteria vs. Archaea

Bacteria are inhibited by antibiotics Streptomycin

and Chloramphenicol but Archaea are not.

Archaea in common with Eukarya have histoneproteins associated with their DNA, have introns

in their DNA, and have several kinds of RNA

polymerase. Bacteria lack these features.

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Domain Bacteria Includes most of the bacteria people are familiar

with including disease-causing species(Salmonella; Vibriocholerae which causes

cholera), nitrogen-fixing (Nitrosomonas) and

parasites (Borreliaburgdorferiwhich causes Lyme

disease).

Bacteria play a major role in decomposition and

many live symbiotically with other organisms

including humans helping to break down orsynthesize foods needed by the host.

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contain unique genetic sequences in their rRNA seem more closely related to Domain Eukarya than to

bacteria

have unique membrane lipids & cell wall construction live in the most extreme habitats in nature,

extremophiles

adapted to heat salt acid pH, pressure & atmosphere

includes: methane producers, hyperthermophiles,

extreme halophiles, and sulfur reducers

Domain Archaea

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Figure 11.27 Archaea. Pyrodict ium abyssi , an unus ual member of

the archaea found growing in deep-ocean sediment at a

temperature of 110C. The cells are disk-shaped with anetwork of tubules (cannulae). Most archaea are more

conventional in their morphology.

S

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The Three-Domain System

Table 10.1

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Ph ll ti t f h

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Phyllogenetic tree of archaea

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Phylum/Class Order Important Genera Special

Features

DOMAIN ARCHAEA

Crenarchaeota (Gram-Negative)

Desulfurococcales Pryidictium Hyperthermophiles

Sulfolobales Sulfolobus Hyperthermophiles

Euryarchaeota (Gram-Positive to Variable)

Methanobacteriales Methanobacterium Methanogens

Halobacteriales Halobacterium Require high salt

concentration

Halococcus Require high saltconcentration

Ph ll ti d M t b li di it f h

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Phyllogenetic and Metabolic diversity of archaea

A.

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B.

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hanks

for your kind attention

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Sahara desert

Life in the extremes

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Lake Magadi, Tansania


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Yellowstone National Park


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Mars

Climate and Life

Postulated Mars-Biosphere

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ANTARCTICA, 1984

Documents

12. Archaea