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Difference between Archaebacteria and Eubacteria, Practice Problems and FAQs

Microorganisms are those living organisms which are not visible to our naked eyes. Which is the organism that comes to your mind, when you think about microorganisms? Yes, bacteria and viruses are two important microbes that will come into our mind immediately. But viruses are considered non living outside a host cell, as they are obligate intracellular parasites. So the next one is bacteria. We know bacteria as a villain which affects our health by causing many diseases like cholera (Vibrio cholerae), tetanus (Clostridium tetani) etc. But they were there on the Earth millions of years before us.

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Fig: Bacteria and virus

According to R. H. Whittaker’s five kingdom classification bacteria is included under the Kingdom Monera. It includes unicellular prokaryotes. Monerans are present everywhere, from ocean bottoms, dry deserts to hot springs. Bacteria can be classified into two groups under the Kingdom Monera. They are the archaebacteria and eubacteria.

Fig: Classification of Kingdom Monera

The primitive bacteria is called the archaea and true bacteria is called eubacteria. What do you think? Do these two groups have the same ancestors or not? These two bacteria evolved separately from a common ancestry and they share a common ancestry with eukaryotes. Both archaea and eubacteria have almost the same structure, but they differ in many characters. Let’s discuss more about their differences in this article.

Table of contents

Archaebacteria

The group of primitive prokaryotes that appeared earliest on the Earth are called archaebacteria. They are called the primitive bacteria and considered as living fossils.

Fig: Archaebacteria

Habitats of archaebacteria

They usually live in extreme climatic conditions like hydrothermal vents, salt pans, salt marshes, hot sulphur springs etc. Most of the archaebacteria are obligate anaerobes but they can also be facultative anaerobic.

Fig: Habitats of archaea

Cell wall of archaebacteria

The cell structure of archaebacteria and eubacteria are similar. But the cell walls of archaea lack a peptidoglycan layer. Instead of this, their cell walls contain complex polysaccharides (non-cellulosic) and complex polypeptides. It is mainly made of pseudomurein. The cell membrane is highly complex and composed of branched chain lipids. This helps them to survive in the extreme heat and pH. The 16s ribosomal ribonucleic acid or 16s rRNA of archaebacteria are different from that of the eubacterial 16s rRNA.

Classification of archaebacteria

Archaebacteria are classified into three different groups on the basis of their habitat. They are as follows:

  • Methanogens
  • Halophiles
  • Thermoacidophiles

Methanogens

The methane producing bacteria are called methanogens. They can produce methane from the sewage. They are obligate anaerobes.

Fig: Methanogens

Habitats of methanogens

Methane and biogas are produced by methanogens through the fermentation of cellulose in cow dung. They are present in the rumen of cattle, in marshes, swamps and bogs. Examples are Methanobacterium and Methanococcus in the marshes and Methanosarcina in the rumen of cattles.

Fig: Habitat of methanogens

Halophiles

The archaebacteria that are found in extremely salty conditions (salt lakes, tidal pools, salt brines, salted fishes etc.) are called halophiles. They are rod shaped and found frequently associated with coccus bacteria. They are obligate anaerobes. They possess a pigment called bacteriorhodopsin in their membranes, which gives them a purple colour. The pigment captures energy. Examples include Halobacterium and Halococcus.

Fig: Salty marshes - Habitat of halophiles

Thermoacidophiles

The archaebacteria present in the places where temperature is approximately 80℃ and medium is acidic (pH = 2) are called thermoacidophiles. They are usually found in hydrothermal vents and hot sulphur springs. They can also survive at 100℃ temperature. They are facultative anaerobes and chemoautotrophs. An example is the Thermus aquaticus.

Fig: Habitat of thermoacidophiles

Eubacteria

The prokaryotic and basically unicellular organisms that lack a true nucleus are called eubacteria. They are the simplest, smallest and the most successful prokaryotic microorganisms. Bacteria was first discovered by Leuwenhoek in 1676.

GIF: Eubacteria

Habitat of eubacteria

All the bacteria except archaebacteria are called eubacteria or true bacteria. Aerobic and anaerobic respiration is present in eubacteria. But it varies from one form to another. Eubacteria can be found everywhere such as the oceans, hot springs, dry deserts, soils etc.

Fig: Habitat of eubacteria

Nutrition in eubacteria

Extremely high degree of metabolic diversity is shown by eubacteria. Most of the eubacteria in the kingdom Monera are heterotrophic (Salmonella typhi) but some are autotrophic (green sulphur bacteria).

Cell wall of eubacteria

Eubacteria can be either Gram positive or Gram negative. Bacterial cell wall is made up of peptidoglycans (N-acetyl muramic acid and N-acetyl glucosamine). A single DNA, plasmids and episomes are present in the bacterial cell.

Structure of bacteria

The major parts of a bacterial cell are as follows:

  • Cell wall
  • Plasma membrane
  • Surface appendages
  • Cytoplasm
  • Nucleoid
  • Cell organelles

Fig: Bacterial cell structure

Morphological types of bacteria

Bacteria fall under two major groups and they are unicellular and mycelial. Unicellular bacteria occur in four common forms and they are as follows:

  • Cocci
  • Bacilli
  • Vibrios
  • Spirilla

Cocci

Spherical or ovoid forms are called cocci. Examples include Diplococcus (in pairs), Streptococcus (arranged in a chain), and Staphylococcus (arranged in clusters).

Fig. Cocci

Bacilli

Rod shaped or cylindrical celled bacteria are called bacilli. Examples include Escherichia coli and Bacillus anthracis.

Fig: Bacilli

Vibrios

Curved or comma shaped bacteria are called vibrios. An example is Vibrio cholerae.

Fig: Vibrio

Spirilla

Rigid, wavy and spiral forms of bacteria are called spirilla. Examples include Spirillum voluntas.

Fig: Spirillum

Gram positive and Gram negative bacteria

Composition of bacterial cell walls differ in various bacteria. Gram Staining is a differential staining method which differentiates bacteria as per the cell wall composition. Hence the bacteria takes up different stains in Gram’s staining. According to the result of the Gram staining process there are two types of bacteria and are as follows:

  • Gram positive bacteria
  • Gram negative bacteria

Gram positive bacteria

Those bacteria which show purple colour in the Gram staining are called Gram positive bacteria. The cell wall of this bacteria contains more peptidoglycan and less quantity of lipids.

Fig: Cell wall structure of Gram positive bacteria

Gram negative bacteria

Those bacteria which appear in pink colour in the Gram staining are called Gram negative bacteria. It possesses less peptidoglycan and more lipids.

Fig: Cell wall structure of Gram negative bacteria

Difference between archaebacteria and bacteria

The major differences between archaebacteria and bacteria are as follows:

Archaebacteria

Eubacteria

They are called primitive bacteria

They are called true bacteria

Seen in extreme conditions

Most of them cannot survive in extreme conditions

Habitats include hot springs, ocean depths, salty marshes, etc.

They are seen everywhere in the environment like soil, water, inside living organisms, etc.

Cell wall is made up of pseudopeptidoglycan or pseudomurein

Cell wall is made up of peptidoglycan or murein

Ether bonds are present in the lipid membrane (Isoprenoid moieties are ether linked to the glycerol-1-phosphate (G1P))

Ester bonds are present in the lipid membrane

Metabolic activities include methanogenesis

Metabolic activities include aerobic and anaerobic respiration, fermentation, chemosynthesis and photosynthesis

Most are anaerobic

Both aerobic and anaerobic forms present

Kreb’s cycle is absent

Kreb’s cycle is present in aerobic bacteria

Use a related pathway to breakdown the glucose

Glycolysis is the pathway to breakdown the glucose

Major three types are methanogens, halophiles and thermoacidophiles

Major two types are Gram positive and Gram negative bacteria

Endospores are not formed

Endospore formation is seen in Gram positive bacteria

Fig: Endospore

Non pathogenic bacteria

Most are pathogenic bacteria

Examples include Pyrococcus furiosus, and Sulfolobus acidocaldarius

Examples include Streptococcus pneumoniae and Yersinia pestis

Fig: Archaebacteria

GIF: Bacteria

Practice Problems

Q1. Find out the wrong statement regarding the archaebacteria from the following.

A. The primitive prokaryotes that appeared earliest on the Earth
B. They usually live in extreme climatic conditions like hydrothermal vents, salt pans, salt marshes, hot sulphur springs etc.
C. Most of the archaebacteria are obligate aerobes
D. The cell walls of archaea bacteria lack a peptidoglycan layer

Solution: The group of primitive prokaryotes that appeared earliest on the Earth are called archaebacteria. They are called the ancient bacteria and considered as living fossils. They usually live in extreme climatic conditions like hydrothermal vents, salt pans, salt marshes, hot sulphur springs etc. Most of the archaebacteria are obligate anaerobes but they can also be facultative anaerobic. The cell structure of archaebacteria and eubacteria are similar. But the cell walls of archaea bacteria lack a peptidoglycan layer. Hence the correct option is c.

Fig: Archaebacteria

Q2. Match the following.

Column A (Archaebacteria)

Column B (Examples)

I) Methanogens

i) Halobacterium

II) Halophiles

ii) Methanococcus

III) Thermoacidophiles

iii) Thermus aquaticus

A. I - ii, II - i, III - iii
B. I - ii, II - iii, III - i
C. I - ii, II - iii, III - i
D. I - i, II - ii, III - iii

Solution: Archaebacteria are classified into three different groups on the basis of their habitat. They are methanogens, halophiles and thermoacidophiles. The methane producing bacteria are called methanogens. Examples are Methanobacterium and Methanococcus in the marshes and Methanosarcina in the rumen of cattles. The archaebacteria that are found in extremely salty conditions (salt lakes, tidal pools, salt brines, salted fishes etc.) are called halophiles. Examples are Halobacterium and Halococcus. The archaebacteria present in the places where temperature is approximately 80℃ and medium is acidic (pH = 2) are called thermoacidophiles. An example is the Thermus aquaticus. Hence the correct option is a.

Q3. Given below are some of the major differences between the archaea and bacteria. Find out the correct differences.

I) Habitat : Archaea - Hot springs, ocean depths, salty marshes; Bacteria - Everywhere in the environment.
II) Cell wall : Archaea - Pseudopeptidoglycan, Bacteria - Peptidoglycan
III) Bonds in the lipid membrane : Archaea - Ether bonds, Bacteria - Ester bonds
IV) Pathogenicity - Archaea - Non pathogenic, Bacteria - Pathogenic

a. I, II and III
b. I, III and V
c. I, II, III and V
d. All the above

Solution: Archaebacteria is seen in extreme conditions like hot springs, ocean depths, salty marshes, etc. Eubacteria is seen everywhere in the environment like soil, water, inside living organisms, etc. Cell wall of archaea is made up of pseudopeptidoglycan. Cell wall of eubacteria is made up of peptidoglycan. Ether bonds are present in the lipid membrane of archaea and it is ester bonds in eubacteria. Archaea is nonpathogenic, but eubacteria is pathogenic. Hence the correct option is d.

Fig: Bacteria

Q4. Staphylococcus is included under which of the following groups of bacteria?

A. Cocci
B. Bacilli
C. Vibrio
D. Spirilla

Solution: Bacteria fall under two major groups and they are unicellular and mycelial. Unicellular bacteria occur in four common forms and they are cocci, bacilli, vibrio and spirilla. Spherical forms are called cocci. Examples include Diplococcus (in pairs), Streptococcus (arranged in a chain), and Staphylococcus (arranged in clusters). Hence the correct option is a.

Fig. Cocci

FAQs

Q1. Which is the site of glycolysis and the Krebs cycle in bacteria?
Answer:
The site of glycolysis and Krebs cycle in the bacteria is the cytoplasm. Pyruvate is the product of glycolysis and it can be further broken down to generate more energy. Krebs cycle or fermentation are the two possible outcomes for the breakdown of pyruvate.

Q2. What is the reason for archaea to become non pathogenic?
Answer:
Archaea use different co-factors in the biochemical reactions when compared to the eubacteria. Hence the nutrients provided by the eukaryotes can not be used by the archaebacteria. This is one reason for the archaea to become non pathogenic. They share some characteristics with the known pathogens, which describes their potential to become pathogenic, but have not discovered any pathogenic archaea yet.

Q3. What is Lokiarchaeota?
Answer:
A proposed phylum of the archaea is called Lokiarchaeota. There was a previous group called Deep Sea Archaeal Group or DSAG and the phylum Lokiarchaeota includes all the members of DSAG. It is also known as Marine Benthic Group B (MBG-B). Asgard is a superphylum and Lokiarchaeota is a part of this. Other phylum included in the superphylum Asgard are Thorarchaeota, Odinarchaeota, Heimadallaarchaeota and Helarcheaota.

Q4. How did archaea help in the evolution of life on Earth?
Answer:
Archaebacteria are considered to have played a significant role in the evolution of life on Earth. These are the representatives of primitive groups of organisms that transformed the initial environment by accumulating organic substances before the evolution of photosynthesis.

 

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