Bacteria and Virus: Types, Characteristics, Reproduction and Differences

July 22, 2022 Kusum Wagle Global Health, Uncategorized 0

What is Bacteria?

  • Bacteria is a single-cell microscopic organism present in every environment inside or outside the organism
  • Bacteria was first discovered by Antony Van Leeun Hook in 1676
  • The word ‘Bacteria’ is derived from Greek word Bakteria meaning cane (rod)
  • Bacteria are usually few meters in length but have wide range of shapes and exist in millions of communities together
  • Bacteria are the earlier form of life and their fossils can be found from 2.5 billion years ago

Types/forms of Bacteria

There are various types/forms of bacteria on the basis of following:

1. On the basis of morphology

2. On the basis of need for oxygen

  • Aerobic: Those required oxygen to live
  • Anaerobic: Those who don’t require oxygen to live
  • Facultative aerobic: Those which can adjust in presence or absence of oxygen

3. On the basis of staining

  • Gram positive: Those which turn purple, violent or blue while staining
  • Gram negative: Those which turn pink or red while staining

4. On the basis of pathogenicity

  • Pathogenic: Those which cause disease in human
  • Non-pathogenic: Those which doesn’t cause disease in human

Characteristics of Bacteria

  • Bacteria are single cell organism which lacks cell organelles such as chloroplast, mitochondria and true nucleus
  • A double stand DNA which is continuous and circular is present in the nucleoid
  • Cell membrane and cell wall is made up of peptidoglycan and together they are often referred as cell envelop
  • Some bacteria, along with plasma membrane contain an additional membrane called as capsule
  • They have single chromosome as a genetic material
  • They can act as decomposer for recycling nutrients

Bacteria Reproduction

  • Under an optimum condition bacteria can reproduce in every 20 minutes
  • Various factors such as temperature, food availability influence the reproduction of bacteria
  • They mainly reproduce through two methods:
    • Asexual: Binary fission
    • Sexual: Conjugation

What is Virus ?

  • Virus are the microscopic organism which are much smaller than bacteria
  • They are non-cellular particles made up of genetic materials and protein that can invade living cells
  • They are infectious agents that can show both characteristics of living and non- living
  • Martinus Willian Beijerinck in 1897 first coined the name ‘virus’ meaning poison

Classification of Virus

Viruses can be classified under the morphology and replication:

a) On the basis of morphology

1. Helical symmetry

  • It consist of nucleic acid enveloped by a hollow protein cylinder or capsid which is in helical shape
  • Example: Tobacco mosaic virus

2. Icosahedral symmetry

  • It is nearly like a spherical shape and has a rigid shape giving protection to genome
  • Example: Most animal virus like adenovirus, toga virus

3. Complex symmetry

  • It has complex structural component making it differ from above two
  • Example: Pox virus

b) On the basis of replication

1. RNA virus genome

  • Around 70% of the virus are RNA virus
  • Inside the capsid it can have either single strand or double strand RNA virus
  • Example: Corona virus, Toga virus

2. DNA virus genome

  • Linear double strand DNA is found as genome
  • However some exceptional case such as papova virus contain circular DNA genome and single strand found in parvovirus family
  • Example: Herpes virus, adenovirus etc.

Characteristics of Virus

  • Virus are smaller than bacteria and their size ranges between 20-300 nanometer
  • They are non-living and non-cellular in structure
  • They contain either one type of nucleic acid; DNA or RNA but never both
  • They consist of nucleic acid surrounded by a protein coat capsid and sometimes they can have an additional lipoprotein layer as envelope
  • They lack cellular organelles such as ribosomes and mitochondria
  • They are obligate cellular parasite and reproduce only inside a host body. Outside the host cell, they are inactive
  • Some viruses can also have spikes to attach themselves to host cell
  • Virus affect only the specific host cells

Reproduction of Virus

  • Viral reproduction takes place by lytic infection or through lysogenic infection

1. Lytic infection

  • During lytic infection, a virus enters the host cell, makes a copy of itself, and causes the cell to burst, orlyse
  • Bacteriophage, which is a virus that infects and replicates within a bacterium, attaches itself and infects the host cell

2. Lysogenic infection

  • Lysogenic virus doesn’t let the host cell to lyse away
  • It can remain dormant for a period of time
  • Here the viral DNA gets integrated with the host cell DNA where it gets copies with the host cell DNA
  • Viral DNA gets multiplied with the host cell DNA and each daughter cell created is the infected DNA

Difference between Bacteria and Virus

Basis of difference                      Bacteria                              Virus
What are they Bacteria are the living organisms Virus are considered as non- living organism and are living organism only inside a host body
Living or non-living Bacteria are free-living cells that can live inside or outside a body Viruses are a non-living collection of molecules that need a host to survive.
Size They are larger and visible under a light microscope and measures about 2 to 8 micrometers. They are submicroscopic and visible under electron microscope with size ranging from 20 to 300 nanometers
Structure They are unicellular and has single circular chromosome with peptidoglycan cell wall They lack cells and has DNA/RNA strands with a protein coat instead of a cell wall
Reproduction Bacteria consist of single cell that can generate energy, make its own food, move and reproduce, mainly through binary fission. Virus only grow and reproduce inside of the host cells they infect
Way of living They are self-sufficient and have their own metabolism and multiply by themselves They need a host and can multiply with external help only
Type of infection caused They cause localized infection They cause systemic infection
Diseases Bacterial diseases include pneumonia, tuberculosis, tetanus and food poisoning. Diseases caused by viral infection include polio, measles, influenza, AIDS and COVID-19.
Benefits Some of the bacteria are also beneficial for the human body in many cases Viruses are usually harmful and can be beneficial in genetic engineering
Prevention Infection can be prevented through antibiotics Vaccine can prevent the viral infection

References and For More Information

https://biologydictionary.net/bacteria/

https://www.medicalnewstoday.com/articles/157973

https://www.livescience.com/51641-bacteria.html

https://www.sciencedirect.com/topics/medicine-and-dentistry/virus-type

https://www.healthline.com/health/viral-diseases#gastrointestinal

https://onlinedegrees.und.edu/blog/types-of-viruses/

https://microbenotes.com/differences-between-bacteria-and-virus/

About Kusum Wagle 214 Articles
Hello and greetings everyone! I am Kusum Wagle, MPH, WHO-TDR Scholar, BRAC James P. Grant School of Public Health, Bangladesh. I have gained profound experiences in public health sector under different thematic areas of health, nutrition, sexual and reproductive health, maternal and newborn health, research etc., targeting diverse audience of different age groups. I have performed diverse roles ranging from lecturer in the public health department of colleges, nutrition coordinator, research coordinator and consultant, in different programs, projects and academic institutions of Nepal. I also hold immense experience in working closely and persistently with government organizations, non-government organizations, UN agencies, CSOs and other stakeholders at the national and sub-national level. I have successfully led and coordinated different projects involving multi-sector participation and engagement. Moreover, I am also regularly involved in the development of different national health related programs and its guidelines.