Table of contents
Learning Objective
By the end of this lecture, you should be able to fully describe a Bacteria and all its characteristics. Remember, you are to go nowhere if you are not able to score upto 70% in the quiz.
Bacteria - The Bad and the Beautiful [Quick Facts about Bacteria]
- Bacteria are present almost everywhere in this world - From deep in the Earth's crust to the polar ice caps and oceans to inside the body of plants and animals.
- The number of Bacteria in your mouth is more than the entire world's population join together.
- Electronics, smartphones, Laptops hold a lot of bacteria. Single smartphone screens hold 18 times more Bacteria than a toilet handle.
- Smell of rain is caused by a Bacteria called Actinomycetes.
- Sweat itself is odourless. It's the Bacteria on the skin that mingles with it and produces body odour.
- 'Horseshoe Crab' blood is worth US $15,000 per litre due to its ability to detect Bacteria.
- Gonorrhea Bacteria are the strongest creatures on the earth as they can pull 100,000 times their own weight.
Introduction
Bacteria was discovered by Antonie Van Leeuwenhoek in 1676.
They were primitive life forms and the first living things to evolve.
Bacteria are unicellular and they belong to a group of organisms called Prokaryotes.
They are called prokaryotes because they have a prokaryotic cell—Cells with no well defined Nucleus.
Due to the presence of a rigid cell wall, bacteria maintain a definite shape, though they vary in shape, size, structure and arrangement.
Different shapes of Bacteria
When viewed with a Microscope, most Bacteria exist in three major shapes:
The Circular round shape called Coccus (Cocci for Plural).
The Rod shape or cylindrical shape called Bacillus (Bacilli for Plural).
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The curve or spiral shape called spirillum (Spirilla for Plural).
These three different shapes of Bacteria can be arranged in groups (because Bacteria don't always exist as a single unit).
Arrangement of the circular Bacteria (Cocci)
- When circular Bacteria or cocci exist in group of two, or in pair, they are called Diplococci.
- When circular Bacteria or cocci joins together to form chains (like several circles joined together forming a chain), they are called Streptococci.
- When circular Bacteria exist as group of four cells, or four cocci joined together, they form a Tetrad.
- When circular Bacteria or cocci are joined together forming an irregular ball or cluster, they are called Staphylococci.
- When cocci are arranged in a cuboidal manner they form a Sarcinae.
Arrangement of Bacilli
- When rod or cylindrical shaped Bacteria (Bacillus) exist in groups of two, they are called Diplobacilli.
- When rod or cylindrical shaped Bacteria (Bacilli) are joined together to form chains, they are referred to as Streptobacilli.
- When a Bacillus appears like a coccus, it is not a perfect rod shape and and it is not a perfect circular shape, this type of Bacteria is called Coccobacilli.
- When a Bacillus divides and its two new cells bend their shape like they are connected to each other at an angle, it is referred Palisade.
Arrangement of Spiralla
- Comma shaped spiral Bacteria are called Vibrio.
- Curve shaped Bacteria with not so many curves are referred to as Spirilla.
- Spiral shaped Bacteria with so many curves are referred to as Spirochetes.
Other shapes and Arrangement of Bacteria
Filamentous Bacteria: They are very long thin filament–shaped Bacteria. Some of them form branching filaments resulting in a network of filaments called ‘Mycelium’.
Star–shaped Bacteria: They look like stars.
Rectangular Bacteria: They are rectangular in shape.
Pleomorphic Bacteria: These ones can change their shapes so they do not have any exact shape.
Structure of a Bacterial Cell
Locomotion in Bacteria [How Bacteria Move]
The organ of the locomotion in Bacteria is small whips or hair like appendages called FLAGELLA.
Nutrition in Bacteria
Bacteria exist as both Autotrophic and Heterotrophic.
Autotrophic Bacteria
Most of these Bacteria do not contain chlorophyll, they either synthesise food through Chemosynthesis or Photosynthesis.
The photosynthetic Bacteria prepare their food by using sunlight energy in the presence of photosynthetic pigment called Bacteriochlorophyll or Chlorobium chlorophyll.
Photosynthesis in Bacteria is different from photosynthesis in green plants because Bacteria do not give out oxygen as a by-product. Such photosynthesis is called Anoxygenic photosynthesis. Example of Bacteria that carry out photosynthesis are:
Green sulphur Bacteria: The photosynthetic pigment is Chlorobium Chlorophyll and Sulphur is the by-product. E.g Chlorobium.
Purple Sulphur Bacteria: The photosynthetic pigment is Bacteriochlorophyll and Sulphur is a by-product. E.g Chromatium.
Non-sulphur Bacteria: The photosynthetic pigment is Bacteriochlorophyll and Sulphur is not a By-product. E.g Rhodopseudomonas.
On the other hand, the Chemosynthetic Bacteria prepare their food by using chemical energy in the absence of photosynthetic pigment. They get energy for food synthesis by the oxidation of certain inorganic substances such as ammonia, nitrites, nitrate, ferrous iron, hydrogen sulphides and a number of metalic or non matelic materials available in the environment. The bacteria absorb inorganic molecules of the substance into the body where the chemical reaction takes place . In this reaction the chemical bonds are broken and energy is released. This energy is used by the bacteria and this process is called chemosynthesis. It is divided into the following types:
Sulphur bacteria: They use chemical energy while there is oxidation of sulphur compound. E.g: Thiobacillus.
Hydrogen bacteria: They use chemical energy while there is oxidation of molecular hydrogen. E.g: Pseudomonas, Hydrogenomonas, Bacillus pectotrophus.
Iron bacteria: They use chemical energy while there is oxidation compound (Fe2+ to Fe3+). E.g:Leptothrix, Ferobacillus, Cladothrix.
Nitrifying bacteria: They use chemical energy while there is oxidation of nitrogen compound. E.g: Nitrosomonas, Nitrobacter.
Heterotrophic Bacteria
These are Bacteria that cannot synthesise their own food, instead they depend on other organisms.
They're divided into three:
Saprophytic Bacteria
They grow and feed on dead, decaying organic material and live by digesting and absorbing them.
Parasitic bacteria
Parasitic bacteria live on and within other organisms (host) and they obtain their nutrition from the host.
If the parasitic bacteria cause diseases and are harmful for their host they are called pathogenic. If the parasitic bacteria cannot cause diseases and are harmless for their host they are called non-pathogenic.
Symbiotic bacteria
Symbiotic bacteria live in close association with other living organisms so that they both are benefited to each other, neither of them is harmed. It is more like I gain, you gain [so we're gaining from each other].
Respiration in Bacteria
Some Bacteria exhibit Aerobic Respiration (involves Oxygen) while some others do not.
Bacteria that respire in the presence of Oxygen are called Obligate Aerobes – They require free oxygen to carry out cellular respiration.
Bacteria that respire in absence of Oxygen are called Anaerobes – They do not require free oxygen to carry out cellular respiration.
Anaerobes are split into two: We have Obligate Anaerobes: these ones do not like Oxygen at all and they cannot survive in the presence of Oxygen; And we have Facultative Anaerobes: these ones can live in an environment where there's oxygen or no oxygen.
Reproduction in Bacteria
Asexual reproduction is characteristic of all bacteria. Sexual reproduction was long through to be absent but investigation with the help of electron microscope have clearly demonstrated the exchange of genetic material in some species of bacteria.
Asexual reproduction
Asexual reproduction in Bacteria occur in two types:
- Binary Fission.
- Spore formation.
Binary Fission
In Binary Fission, Bacterial cell elongates and splits into two daughter cells, each with identical DNA to the parent cells.
Spore formation
At the beginning of spore formation, a septum forms separating the nascent spore from the rest of the cell and all of the genetic material of the cell is copied into the newly-forming cell.
The spore contents are dehydrated and the protective outer coatings are laid down. Once the spore is mature, it is released from the cell.
On germination, the spore contents rehydrate and a new Bacterium emerges and multiplies.
Parasexual mode of reproduction in Bacteria
This involves two parents who combine their DNA to produce a new organism.
The new organism is different from both of the parents.
There are Three parasexual mode of reproduction in bacteria:
- Conjugation
- Transformation
- Transduction
Conjugation
In conjugation, DNA is transferred between bacteria through a tube between cells. Conjugation produces an incompletely diploid “zygote” known as merozygote or partial zygote.
Transformation
In transformation, a bacterium takes up a piece of DNA floating in its environment and integrates its fragments into its own DNA. This DNA that is taken up from the environment is often DNA that's been shed by other bacteria. If the DNA is in the form of a circular DNA called a plasmid, it can be copied in the receiving cell and passed on to its descendants.
Transduction
In transduction, DNA is accidentally moved from one bacterium to another by a type of virus called Bacteriophage.
Summary
- Bacteria are prokaryotic, unicellular microorganisms, which lacking chlorophyll.
- The cell structure is simpler than that of other organisms as there is no nucleus or membrane bound organelles.
- Due to the presence of a rigid cell wall, bacteria maintain a definite shape, though they vary as shape, size and structure.
- Cocci, Bacilli and Spirilla are the major shapes of bacteria.
- So far as the arrangement is concerned, it may Paired (diplo), Grape-like clusters (staphylo) or Chains (strepto).
- Filamentous, star shaped, rectangular and pleomorphic are some other shapes and arrangement of bacteria.
- Mycoplasma gallicepticum are thought to be the world's smallest bacteria.
- Thiomargarita namibiensis is world’s largest bacteria.
- Bacterial cytoplasm is a complex mixture of carbohydrates, proteins, lipids, minerals, nucleic acids and water.
- The bacterial nucleus devoid of nuclear membrane, nucleolus, chromonemata and nuclear sap, such structure is called nucleoid or genophore.
- The organ of the locomotion is small whips or hair like appendages called flagella.
- Bacterial flagella may be polar or non polar.
- Nutrition in bacteria is both autotrophic and heterotrophic.
- The bacteria which synthesis their own food (organic compound) necessary for structure and metabolism from the simple inorganic compound is called autotrophic.
- Photosynthetic bacteria can prepare their food by using solar energy in the presence of photosynthetic pigment bacteriochlorophyll and chlorobium chlorophyll.
- Chemosynthetic bacteria prepare their food by using chemical energy in the absence of photosynthetic pigment.
- The heterotrophic bacteria which form the majority cannot synthesized organic compounds from the simple inorganic substances.
- Saprophytic bacteria grow in dead, decaying organic material and live by digesting and absorbing them.
- Parasitic bacteria live on and within other organisms (host) and they obtain their nutrition from the host.
- Parasitic bacteria may be pathogenic or non pathogenic to the host organism.
- Symbiotic bacteria live in close association with other living organisms so that they both are benefited to each other, neither of them is harmed.
- Asexual reproduction is characteristic of all bacteria.
- The most common way by which the bacteria reproduce itself is the Binary Process.
- Sporulation in bacteria is take place by the conidia, oidiospore, sporangiospore and endospore.
- Endospore production take place in unfavorable conditions.
- Sexual reproduction in bacteria is take place by the conjugation, transformation and transduction.
- In transformation, a bacterium takes up a piece of DNA floating in its environment.
- Transformation was discovered by Griffith in 1928.
- In transduction, DNA is accidentally moved from one bacterium to another by a virus.
- Transduction was first discovered by Zinder and Lederberg (1952) in Salmonella typhimurium.
- In conjugation, DNA is transferred between bacteria through a tube between cells. Conjugation was first discovered in Escherichia coli by Lederberg and Tatum (1946).
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Test Questions
Test: Bacteria
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Test: Bacteria
Total Questions: 30
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Quiz Answers
1. Binary Fission in Bacteria is similar to _
Mitosis
2. _ bacteria look like star
Star-shaped
3. Bacteria use _ for movement
Flagella
4. Photosynthesis that does not yield Oxygen as a by-product is what type of photosynthesis?
Anoxygenic photosynthesis
5. Oxidation of inorganic substances to release energy is termed as _
Chemosynthesis
6. In Binary Fission, daughter cells are not identical to the parent's cell
False
7. One of these is not a reproductive mechanism used by Bacteria
Disjunction
8. Nucleoid is found in a Bacterial cell
True
9. Small circular pieces of DNA found in a Bacterial cell is called?
Plasmid
10. Cylindrical shaped bacteria attach to one another to form a long chain is called?
Streptobacilli
11. Pleomorphic Bacteria have definite shape
False
12. _ differentiates an animal cell from a bacterial cell
Nucleus and Nuclear membrane
13. Bacteria are _
Prokaryotic
14. Members in a Bacterial colony are
Identical and Independent
15. A circular shaped Bacteria is called
Coccus
16. One of these is not found in a Bacterial cell
Endoplasmic reticulum
17. Saprophytic Bacteria grow and feed on...
Dead organic material
18. Diplobacilli are...
Rod shaped bacteria in pair
19. Disease causing parasitic bacteria are regarded to as _
Pathogen
20. Obligate Aerobes do not require oxygen before they can carry out cellular respiration.
False
21. A Bacterium takes a freely floating DNA and integrates it into its own, what is this phenomenon called?
Transformation
22. Which of these is known as the world's smallest Bacteria?
Mycoplasma gallicepticum
23. What method of reproduction is mostly used by all Bacteria
Binary Fission
24. Smell of rain is caused by a Bacteria called...
Actinomycetes
25. Facultative anaerobes cannot survive in an oxygen environment
False
26. A virus that transfers DNA from one Bacterium to another during transduction is called _
Bacteriophage
27. Bacteria is able to maintain a definite shape due to...
Cell wall
28. An organism gains and the other loses during symbiotic relationship
False
29. Endospore production does not take place in unfavorable conditions
False
30. What is transferred through a tube during Conjugation?
DNA
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