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Kingdom Monera: Eubacteria - Nutrition, Respiration, Reproduction, Practice Problems, FAQs

You all know that eubacteria are able to reproduce, respire, and obtain nutrition. Using a single cell, they perform all these activities.

How do they do that? 

Is it different from plants and animals? 

Well, yes! 

Different bacteria show different modes of nutrition. 

Eubacteria reproduce asexually only? 

Yes, but they also show genetic recombination. 

They can respire aerobically as well as anaerobically, which varies from bacteria to bacteria. Let’s try to understand these characteristics of eubacteria in depth.

Table of contents:

Nutrition in bacteria

Bacteria show an extremely high degree of metabolic diversity. Most of the bacteria in the kingdom Monera are heterotrophic but some are autotrophic. 

Classification of bacteria 

On the basis of nutrition, bacteria are classified into two major categories as follows:

  • Autotrophs
  • Heterotrophs

Autotrophs

These bacteria synthesise their own food. They can be of two types as follows: 

Photosynthetic autotrophs

Chemosynthetic autotrophs

  • These bacteria use light energy for food synthesis.
  • Photosynthetic pigment is bacteriochlorophyll and is contained in spherical bodies called chromatophores.
  • Photosynthesis in these bacteria is non-oxygenic.
  • They use chemical energy for synthesising food instead of light energy. 
  • They perform oxidation of chemical compounds to obtain chemical energy.

Examples include the following:

  • Purple sulphur bacteria like Chromatium.
  • Green sulphur bacteria - Chlorobium.
  • Purple non-sulphur bacteria - Rhodospirillum.

 

Examples include the following:

  • Nitrifying bacteria - They oxidise nitrogenous compounds and obtain energy 
  • Nitrosomonas, Nitrococcus, etc.



Fig: Photoautotrophic - Chlorobium



Fig: Chemoautotrophic - Thiobacillus

Heterotrophs

These bacteria cannot manufacture their own food. They receive their food from dead organic matter or living organisms. They are of different types as follows:

Saprophytic bacteria

Parasitic bacteria

Symbiotic bacteria

These bacteria obtain their food from dead and decaying matter.

They live on or within the body of living hosts and obtain nutrition from them. 

Some nitrogen fixing bacteria live in symbiotic association with the roots of some plants and derive nutrition from the plant.

Example: Escherichia coli

Example: Clostridium tetani

Example: Rhizobium


Fig: Saprotrophic -  Escherichia coli


Fig: Parasitic -  Clostridium tetani


Fig: Symbiotic -  Rhizobium

Respiration

On the basis of the mode of respiration, bacteria are of two types:

  • Aerobic 
  • Anaerobic 

Aerobic bacteria 

They will live and grow normally in the presence of oxygen. They are of the following types: 

Obligate aerobic

Facultative anaerobic

These are completely aerobic, that means they can live only in the presence of oxygen and die in the absence of oxygen.

These are normal aerobic bacteria and can survive in the absence of oxygen also.

Example: Bacillus subtilis

Example: Clostridium tetani

Anaerobic bacteria 

These bacteria cannot grow or live normally in the presence of oxygen. They are of two types as follows:

Obligate anaerobic bacteria 

Facultative aerobic 

These are completely anaerobic bacteria and die in the presence of oxygen. 

These are normal anaerobic bacteria but can live in the presence of oxygen.

Example: Clostridium botulinum

Example: Most photosynthetic bacteria

Reproduction

Bacteria reproduce by two methods as follows:

  • Asexual reproduction
  • Parasexual reproduction

Asexual reproduction

It involves only one parent and there is no recombination of genetic materials. It is of two types as follows:

Binary fission

This is considered the most common reproductive method in bacteria. It occurs under favourable conditions. Cell division is called amitosis due to the absence of spindle formation. In this method, the DNA replicates first and then the bacterial cell divides into two daughter cells due to formation of transverse septum in the centre of each cell. 

Process of binary fission

Chromosomes attached to the mesosome replicate first. A new mesosome is created and is attached to the daughter chromosome. A membrane started forming between the daughter nucleoids and pushed them to the opposite sides. The cytoplasm forms two daughter protoplasts with the genetic materials. A transverse septum is formed in the centre of the cell and two daughter cells are formed. 


Fig: Binary fission

Spore formation

Spores are highly resistant structures which can withstand high temperatures, radiation, antibiotics and chemicals. These are formed to evade unfavourable conditions. Spores may be formed within the cell (endospore) or outside the cell (exospore). Under favourable conditions, spores germinate into bacterial cells.


Fig: Types of spores

Process of endospore formation

A part of the protoplast containing the nuclear body first stores food during endospore formation. It then undergoes dehydration to form a condensed mass called endospore primordium. This primordium then secretes a wall around it. Later more wall materials are deposited by the cytoplasm surrounding the primordium and form an endospore. Endospores once liberated are dispersed by the air currents and germinated on falling on a suitable medium. 

Parasexual reproduction

The sexual reproduction is absent in bacteria because it does not involve the fusion of male and female gametes to produce a diploid zygote. Parasexual reproduction involves transfer of some genes from a bacterium to another bacterium. 

Types of parasexual reproduction

There are three methods of parasexual reproduction in bacteria as follows:

Transformation

It is the process in which bacteria takes up the foreign DNA from its surroundings and gets transformed into another kind. It was first discovered in Streptococcus pneumoniae by Griffith in 1928.


Fig: Transformation

Conjugation

It is the process in which F plasmid with fertility factor is transferred from one bacterium (the donor) to another with the help of sex pilus. It was discovered for the first time in Escherichia coli by Lederberg and Tatum.

During this process the donor cell first gets attached to the recipient cell. At the region of contact the sex pilus grows to form a conjugation tube. The plasmid of the donor cell replicates and the copy is shared with the recipient through the conjugation tube. 


image

Fig: Conjugation

Transduction 

In this method the transfer of genetic materials from one bacteria to another takes place through the agency of bacteriophages. It was first discovered by Zinder and Lederberg in Salmonella typhimurium

In this process the bacteriophage attacks the bacteria and integrates its genome within the host cell DNA. The viral genome either remains dormant and enteris into lysogenic cycle or enters into lytic cycle. Once a lysogenic cell is exposed to some external stimulus it will enter into the lytic cycle.

The virus genome is integrated with the host genome in both cases. The phage genome carries some of the bacterial genome with it due to this and integrates it into the genome of the new recipient cell. Here, only a few genes have the possibility of entering into the recipient cells.


Fig: Transduction 

Practice Problems

Q1. Find the incorrect match.

Column I

Column II

Obligate aerobic

Completely aerobic and dies in the absence of oxygen

Facultative aerobic

Normally aerobic bacteria but can survive in the absence of oxygen

Obligate anaerobic

Completely anaerobic bacteria and die in the presence of oxygen

Solution: Facultative aerobic bacteria are normally anaerobic but can survive in the presence of oxygen. Hence option 2 is correct. 

Q2. Name the bacteria which synthesise ATP by the oxidation of inorganic compounds such as nitrates and ammonia.

A. Archaebacteria
B. Photosynthetic autotrophs
C. Chemosynthetic autotrophs
D. Heterotrophs

Solution: Chemosynthetic bacteria oxidise inorganic compounds such as ammonia, nitrates, and nitrites to synthesise ATP using the released energy. Thus, option c is correct.

FAQs

Question 1. Mention the types of parasexual methods used by eubacteria?
Solution: The three types of parasexual methods in eubacteria are transformation, transduction and conjugation.

  • Transformation - It is the process in which bacteria takes up the foreign DNA from its surroundings and gets transformed into another kind. 
  • Conjugation - It is the process in which F plasmid with fertility factor is transferred from one bacterium (the donor) to another with the help of sex pilus.
  • Transduction - It is the process of transfer of genetic materials from one bacteria to another through the agency of bacteriophages.

Question 2. What is the difference between photosynthetic and chemosynthetic bacteria?
Solution: The major difference between photosynthetic and chemosynthetic autotrophs is the source to obtain energy. Photosynthetic bacteria use sunlight energy to synthesise food while chemosynthetic bacteria oxidise inorganic chemicals such as nitrates, ammonia etc., to synthesise ATP.

Question 3. Name the method of reproduction in bacteria in which a transverse septum is created in 
the centre of the bacteria cell and it divides into two daughter cells?
Solution: Binary fission is the aseuxal mode of reproduction in bacteria in which a bacteria divides into two through transverse septum in the centre of the cell.

Question 4. Name a bacteria that survives in the absence of oxygen but dies in the presence of oxygen? 
Solution: Clostridium botulinum is an obligate anaerobic bacteria which survives in the absence of oxygen and dies in the presence of oxygen.

Question 5. Suppose you found a bacterium in garbage then what would be the mode of nutrition of this bacterium?
Solution: The bacterium growing in garbage feeds on dead and decaying matter. Thus, its mode of nutrition is saprophytic.

Question 6. Bacteria have the ability to survive in high temperatures, dry conditions, and the presence of antibiotics by forming a special structure. Name the mode of reproduction used by bacteria during unfavourable conditions?
Solution: Bacteria reproduce by spore formation during unfavourable conditions either by forming an exospore, that is, spore formed outside the cell or endospore, that is, spore formed inside the cell.

Related Topics

Eubacteria: Habitat, Shape, structure, motility, pili 

Kingdom Monera: Archaebacteria, Cyanobacteria, Mycoplasma, Rickettsia, Actinomycetes, Practice Problems and FAQs 

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