The 3 differences between viruses and bacteria
What are the characteristics that make it possible to distinguish between bacteria and viruses?
Viruses and bacteria often generate similar clinical pictures in affected patients.
Several studies indicate that this may be due, in part, to the fact that the cellular immune responses to both pathogens share several similarities. Even so, the treatments for viral and bacterial infections are very different, so it is important to know the differences between viruses and bacteria. the differences between viruses and bacteria is essential..
Although both are considered microscopic organisms potentially pathogenic for humans, other animals and plants, there are many more factors that differentiate them than qualities that unify them. Here we show you some of the most important differential characteristics between viruses and bacteria.
Main differences between viruses and bacteria: a question of microscopy
Before addressing the many differences between these microorganisms, it is always useful to recall the attributes that unify them, it is always useful to recall the attributes that unify them.. Some of them are the following:
- Both viruses and bacteria can be considered germs, since they are microorganisms with pathogenic potential.
- They move on microscopic scales (from micrometers to nanometers in length), although viruses are much smaller.
- Unlike the cells of eukaryotic living beings, the genetic information of both is not compartmentalized in a nucleus.
- Infections caused by both activate the immune system, generating general inflammatory responses and episodes such as fevers.
All these similarities are very superficialAs we will see below, the differential elements are much more numerous. They are explored below.
1. Morphological differences
The differences between viruses and bacteria are so abysmal that there is a heated debate in the scientific community, since there is no doubt that bacteria are living beings, but this cannot be affirmed if we talk about viruses. There is no doubt that bacteria are living beings, but this cannot be affirmed if we talk about viruses..
In general, several investigations conclude that viruses are structures of organic matter that interact with living beings, but that they are not Biological forms in themselves. Why is this so?
1.1 Acellularity
According to the official definition of organisms, a cell is a "fundamental anatomical unit of all living organisms, usually microscopic, consisting of cytoplasm, one or more nuclei, and a surrounding membrane."
This requirement is fulfilled by bacteriaAlthough they have only one cell that makes up the totality of their body, it has all the requirements to be considered a living form. The bacterial cell is composed of the following elements:
- Pili: external hair-like agents with a function of adhesion to surfaces or gene transfer between bacteria.
- Capsule: outermost layer of the bacterium, formed by a series of organic polymers. It protects it from adverse environmental conditions, among others.
- Cell wall: underneath the capsule. Supports osmotic pressures and cell growth.
- Cytoplasmic membrane: under the cell wall. Phospholipid bilayer that delimits the shape of the cell.
- Cytoplasm: inner part of the bacterial cell, containing the cytosol and organelles.
- Ribosomes: organelles responsible for protein synthesis.
- Vacuoles: storage structures for substances and waste products.
All these features are common to the complex cells that make up eukaryotic organisms, but for example, bacteria lack mitochondria, chloroplasts and a bounded nucleus. Speaking of nuclei and genes, these microorganisms have their genetic information in a structure called nucleoidwhich consists of a free circular double-stranded DNA closed by a covalent bond.
As we have seen, bacteria have a unicellular structure that is not as complex as that of the cells that compose us, but which is not biologically speaking, either. In the case of viruses, we have much less to count:
- They present one or more RNA or DNA segments, either double or single stranded.
- Capsid: a shell formed by the repetition of a protein (capsomer) that protects the genetic information.
- Envelope: only present in some types of viruses. A lipoprotein envelope surrounding the capsid.
Thus, the structure of viruses does not qualify as a cell, the structure of viruses does not qualify as a cell.. If this is the minimum basis of any living being, are viruses biological organisms? Due to their acellularity, in a strict sense we can say that they are not.
1.2 Morphological diversity
Due to their greater biological complexity bacteria present a wide variety of forms. Some of them are the following:
- Cocci, spherical in shape. Diplococci, tetracocci, streptococci and staphylococci.
- Bacilli, rod-shaped.
- Spiralized bacteria. Spirochaetes, spirillae and virrios.
In addition, many bacteria have flagellar structures that allow them to move through the medium. If they have a single flagellum they are called monotrophic, if they have two (one at each end) lophotrophic, if they have a group at one end amphitrichic, and if they are distributed throughout the body, peritrichic. All this information highlights the bacterial morphological diversity.
When we refer to viruses, we find, once again, a much more desolate structural landscape.. There are helical, icosahedral, enveloped, and some with slightly more complex shapes that do not fall into any of the previously mentioned groups. As we can see, their morphology is very limited.
2. A differential reproductive mechanism
Perhaps the biggest difference between viruses and bacteria is their way of infecting the host and multiplying within it. We will now dive into the world of reproduction of these microorganisms.
2.1 Bipartition
Bacteria, both free-living and pathogenic, usually reproduce asexually by bipartition.. The entire genome of the cell replicates itself exactly before each reproductive episode, because unlike eukaryotic cells, bacteria are able to replicate their entire DNA autonomously throughout the cell cycle. This happens thanks to replicons, units with all the information necessary for the process.
To keep things simple, we will limit ourselves to say that the cytoplasm of the bacterium also grows, and when the time comes, a division takes place in which the mother bacterium splits in two, each with a genetically identical nucleoid.
2.2 Replication
For viruses to multiply, the presence of a eukaryotic cell that they can hijack is essential.. Virus replication is summarized in the following steps:
- Attachment of the virus to the cell to be infected.
- Penetration, entry of the pathogen into the host cell by a process of endocytosis (viroplexia, typical penetration or fusion).
- Denudation, where the virus capsid is degraded, leaving the genetic information free.
- Replication of the genetic information of the virus and synthesis of its proteins, hijacking the biological mechanisms of the infected cell.
- Assembly of the viral structure inside the cell.
- Release of the new virus by cell lysis, breaking its wall and killing it.
The replication of the genetic information of the virus is very varied, as it depends on whether the virus is composed of depends very much on whether it is composed of DNA or RNA.. The essential idea of this whole process is that these pathogens hijack the mechanisms of the infected host cell, forcing it to synthesize the nucleic acids and proteins necessary for its assembly. This reproductive difference is essential to understanding viral biology.
3. A diverse biological activity
These differences between viruses and bacteria in terms of reproduction, condition the biological niches in which both microorganisms develop..
Bacteria are prokaryotic organisms that can be parasites or free-living, since they do not require an external mechanism to multiply. In the case of pathogens, they require the environmental conditions or nutrients of the organism they invade in order to grow and survive.
Even so, intrinsically and theoretically, if there were a non-living organic medium with all the qualities of the infected body, they would have no reason to invade it. This is why many pathogenic bacteria can be isolated in culture media under laboratory conditions.
The case of viruses is completely different, since their existence is inconceivable without a cell to parasitize. Some viruses are not harmful in themselves as they do not harm the host, but all of them have in common the requirement of a cellular mechanism for their multiplication.. That is why all viruses are considered obligate infectious agents.
Conclusions
Both viruses and pathogenic bacteria are microscopic agents that can be considered germs in the strict sense of the word, since they parasitize a living being and benefit from it. Even so, in the case of bacteria there are thousands of free-living species, which also play essential roles in the biogeochemical cycles of the earth (such as, for example, the fixation of atmospheric nitrogen).
Viruses, on the other hand, are infectious agents that in many cases are not even considered living beings. This does not mean that they do not perform important functions, as they are an essential means of horizontal gene transmission and major drivers of biological diversity. The relationship between virus and host is a constant biological race, as both evolve in tandem, one to infect and the other to avoid infection or fight it.
Bibliographical references:
- Pitha, P. M. (2004). Unexpected similarities in cellular responses to bacterial and viral invasion. Proceedings of the National Academy of Sciences, 101(3), 695-696.
- Betancor, L., Gadea, M., & Flores, K. (2008). Bacterial genetics. Institute of Hygiene, Faculty of Medicine (UDELAR). Temas de Bacteriología y Virología Médica. 3rd Ed. Montevideo: Oficina del Libro FEFMUR, 65-90.
- Brock, T. D., Madigan, M. T., & Abad, V. T. (1993). Microbiology (No. 579.2 BRO). Mexico: Prentice Hall Hispanoamericana.
- R. Arbiza, J. Biologia viral. Retrieved July 11 from http://www.higiene.edu.uy/cefa/2008/BiologiaViral.pdf.
- Ruchanksy, D. Introduction to virology. Retrieved July 11 from http://www.higiene.edu.uy/cefa/bacto/introvir2011.pdf.
(Updated at Apr 12 / 2024)