The 3 differences between viruses and bacteria

Viruses and bacteria often generate similar clinical pictures in affected patients.

Various 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 an infection of viral or bacterial origin are very different, so knowing the differences between viruses and bacteria is essential.

Despite both being considered potentially pathogenic microscopic organisms for humans, other animals and plants, there are many more factors that differentiate them than qualities that unify. Here we show you some of the most important differential characteristics between viruses and bacteria.

Related article: "The 5 types of viruses, and how they work"

Main differences between viruses and bacteria: a matter of microscopy

Before addressing the many differences between these microorganisms, it is always good to remember 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.

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They move on microscopic scales (micrometers to nanometers in length), even though 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 superficial, since as we will see below, the differential elements are much more numerous. We explore them below.

1. morphological differences

The differences between viruses and bacteria are so abysmal that there is a burning debate in the scientific community, since there is no doubt that bacteria are living beings, but this cannot be said if we talk about viruses.

In general, various investigations conclude that viruses are structures of organic matter that interact with living beings, but that they are not biological forms by themselves. Because?

1.1 Acellularity

According to the definition of official organisms, a cell is a "fundamental anatomical unit of all living organisms, usually microscopic, made up of cytoplasm, one or more nuclei, and a membrane that covers it surrounds".

This requirement is fulfilled by bacteria, because although they only have one cell that makes up their entire body, it has all the requirements to be considered a living form. The bacterial cell is composed of the following elements:

Pili: external hair 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: below the capsule. Supports osmotic pressures and cell growth.
Cytoplasmic membrane: under the cell wall. Phospholipid bilayer that defines the shape of the cell.
Cytoplasm: internal part of the bacterial cell, which contains the cytosol and organelles.
Ribosomes: organelles responsible for protein synthesis.
Vacuoles: storage structures for substances and waste products.

All of these features are common to the complex cells that make up eukaryotic organisms, but for example, bacteria lack mitochondria, chloroplasts, and a delimited nucleus. Speaking of nuclei and genes, These microorganisms have their genetic information in a structure called a nucleoid., which consists of a circular free DNA double strand closed by a covalent bond.

As we have been able to see, bacteria have a unicellular structure that is not as complex as that of the cells that make up us, but that does not fall short biologically speaking either. In the case of viruses, we have much less to tell:

They present one or more segments of RNA or DNA, either single or double stranded.
Capsid: cover formed by the repetition of a protein (capsomere) that protects genetic information.
Envelope: only present in some types of viruses. Envelope of lipoprotein nature that surrounds the capsid.

So that, the structure of the virus does not meet the requirements to be considered a cell. If this is the minimum basis of any living being, are viruses biological organisms? Due to its acellularity, in a strict sense we can say no.

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1.2 Morphological diversity

Due to its greater biological complexity, Bacteria have a wide variety of forms.. Some of them are the following:

Cocci, spherical in shape. Diplococci, tetracocci, stretococci and staphylococci.
Rod-shaped bacilli.
spiral bacteria. Spirochetes, spirilla and vibrios.

In addition, many bacteria have flagellar structures that allow them to move through the environment. If they have a single flagellum they are called monotric, if they have two (one at each end) lophotric, if they present a group at one amphitric end, and if they are distributed throughout the body, peritric All this information highlights the bacterial morphological diversity.

When referring to viruses, we find ourselves, once again, with a much more bleak structural landscape.. There are helical, icosahedral, enveloped, and some with slightly more complex shapes that do not fall into any of the previously named groups. As we can see, its morphology is very limited.

You may be interested in: "The 3 types of bacteria (characteristics and morphology)"

2. A differential reproductive mechanism

Perhaps the biggest difference between viruses and bacteria is their way of infecting the host and multiplying within it. Next, we do not plunge into the world of the reproduction of these microorganisms.

2.1 Bipartition

Bacteria, both free-living and pathogenic, reproduce asexually in the usual way by bipartition.. The complete genome of the cell replicates itself exactly before each reproductive episode, since unlike Unlike eukaryotic cells, bacteria are capable of replicating all of their DNA throughout the cell cycle autonomously. This happens thanks to the replicons, units with all the information necessary for the process.

To keep things simple, we will limit ourselves to saying that the cytoplasm of the bacterium also grows, and eventually At this point, a division occurs in which the parent bacterium splits in two, each with a genetically engineered nucleoid. equal.

2.2 Replication

For viruses to multiply, the presence of a eukaryotic cell that they can hijack is essential.. Viral replication is summarized in the following steps:

Adhesion of the virus to the cell that it is going to infect.
Penetration, entry of the pathogen into the host cell by a process of endocytosis (viroplexy, typical penetration or fusion).
Denudation, where the virus capsid degrades, 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 within the cell.
Release of new viruses through cell lysis, breaking its wall and killing it.

The replication of the genetic information of the virus is very varied, since It depends a lot on whether it is made of DNA or RNA.. The essential idea of this whole process is that these pathogens hijack the mechanisms of the cell. infected from the host, 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 alien mechanism to multiply. In the case of pathogens, they require the environmental conditions or the nutrients of the organism they invade to grow and survive.

Even so, intrinsically and theoretically, if a non-living organic environment existed with all the qualities of the body of the infected, they would not have to invade it. This is why many pathogenic bacteria can be isolated from culture media under laboratory conditions.

The case of viruses is completely different, since their existence cannot be conceived without a cell to parasitize. Some viruses are not harmful in themselves because they do not harm the host, but they all have in common the requirement of the cellular mechanism for its 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 roles essential in the biogeochemical cycles of the earth (such as nitrogen fixation atmospheric).

Viruses are, on the other hand, infectious agents that in many cases are not even considered living beings. This is not to say that they do not perform important functions, as they are an essential means of horizontal gene transmission and great drivers of biological diversity. The relationship between the virus and the host is a constant biological race, since both evolve together, one to infect and the other to avoid infection or fight it.

Bibliographic 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). Topics of Bacteriology and Medical Virology. 3rd Ed. Montevideo: FEFMUR Book Office, 65-90.
Brock, T. D., Madigan, M. T., & Abbot, V. T. (1993). Microbiology (No. 579.2 BRO). Mexico: Prentice Hall Hispanoamericana.
R. Arbiza, J. Viral biology. Collected on July 11 in http://www.higiene.edu.uy/cefa/2008/BiologiaViral.pdf.
Ruchanksy, D. Introduction to virology. Collected on July 11 in http://www.higiene.edu.uy/cefa/bacto/introvir2011.pdf.