Influence of microorganisms

Structure of Bacteria and Viruses

Bacteria versus Virus comparison chart

Present Absent Peptidoglycan / Lipopolysaccharide No cell wall. Protein coat present instead. Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. A virus is a small infectious agent that replicates only inside the living cells of other organisms. Living organism Opinions differ on whether viruses are a form of life or organic structures that interact with living organisms. No No Unicellular; one cell No cells; not living DNA or RNA enclosed inside a coat of protein. Fission- a form of asexual reproduction Vaccines prevent the spread and antiviral medications help to slow reproduction but can not stop it completely. Yes Yes, in some Yes Yes Localized Systemic Some bacteria are beneficial (e.g. certain bacteria are required in the gut) Viruses are not beneficial. However, a particular virus may be able to destroy brain tumors (see references). Viruses can be useful in genetic engineering. Larger (1000nm) Smaller (20 - 400nm)

Bacteria	Virus
Ribosomes
Cell wall
Introduction (from Wikipedia)
Living attributes
Nucleus
Number of cells
Structures
Reproduction
Treatment
Enzymes
Virulence
Infection
Benefits
Size

Virus - Bacteria Differences

Scanning electron micrograph of Escherichia coli bacilli

• The biggest difference between viruses and bacteria is that viruses must have a living host - like a plant or animal - to multiply, while most bacteria can grow on non-living surfaces.
• Bacteria are intercellular organisms (i.e. they live in-between cells); whereas viruses are intracellular organisms (they infiltrate the host cell and live inside the cell). They change the host cell's genetic material from its normal function to producing the virus itself.
• There are some useful bacteria but all viruses are harmful.
• Antibiotics cannot kill viruses, but can kill most bacteria, with the exception of most Gram-negative bacteria.
• An example of a disease caused by bacteria is strep throat and an example of an affliction caused by a virus is the flu.

Video Explaining the Differences

This video explains the overall differences between bacteria and viruses.

Structure and contents of a typical Gram positive bacterial cell

Differences in Reproduction

Bacteria carry all the "machinery" (cell organelles) needed for their growth and multiplication. Bacteria usually reproduce asexually. In case of sexual reproduction, certain plasmids genetic material can be passed between bacteria. On the other hand, viruses mainly carry information - for example, DNA or RNA, packaged in a protein and/or membranous coat. Viruses harness the host cell's machinery to reproduce. Their legs attach onto the surface of the cell, then the genetic material contained inside the head of the virus is injected into the cell. This genetic material can either use the cell's machinery to produce its own proteins and/or virus bits, or it can be integrated into the cell's DNA/RNA and then translated later. When enough "baby" viruses are produced the cell bursts, releasing the new viral particles. In a sense, viruses are not truly "living", but are essentially information (DNA or RNA) that float around until they encounter a suitable living host.

Transmission electron microscope (TEM) image of a recreated 1918 influenza virus

Living vs. Nonliving

Bacteria are living organisms but opinions vary on whether viruses are. A virus is an organic structures that interacts with living organisms. It does show characteristics of life such as having genes, evolving by natural selection and reproducing by creating multiple copies of themselves through self-assembly. But viruses don't have a cellular structure or their own metabolism; they need a host cell to reproduce. It should be noted that bacterial species such as rickettsia and chlamydia are considered living organisms despite the same limitation of not being able to reproduce without a host cell.

References