Although we tend to use the two terms interchangeably, microbes and bacteria are not exactly the same thing. Let’s see why.
All these terms are formed through the taxonomic study of living beings, that is, through the branch of systematic biology that explores the kinship relationships between the current organisms on the planet and their ancestors. Even so, not all classificatory terms are based on evolutionary history, since the word that concerns us today, “microbe”, is an operative concept devoid of any taxonomic or phylogenetic relationship .
Thus, it is usual for problems to arise in the general population when it comes to differentiating commonly used terms of unknown origin. For this reason, in this article we show you the differences between microbes and bacteria , two widely related words, but with different implications and characteristics on some specific fronts.
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What are the differences between a microbe and a bacterium?
First of all, and before listing differences, it is necessary to understand what makes both terms similar. According to the Dictionary of the Royal Spanish Academy (RAE), a microbe or microorganism is defined as a “unicellular organism only visible under a microscope” . From a more biological and less linguistic point of view, these beings are unicellular individual entities that present an elementary biological structure (in contrast to the multicellularity and tissue formation that characterizes animals and plants).
Therefore, we will all agree with the statement that all bacteria are microbes. But beware, things get interesting when you take into account that, indeed, not all microbes fall within the bacterial domain. So, let’s start with the differences between microbe and bacteria.
1. All bacteria are microbes, but not all microbes are bacteria
The world of microbes is clearly compartmentalized, because as we have said, it is a heterogeneous group of living beings (or non-living, as we will see below) that have little to do with each other beyond a basic organization system and a microscopic structure.
In this “mixed bag”, that is, within the microbes, we find viruses, bacteria and archaea, protozoa, microscopic algae and microscopic fungi . As we can see, both prokaryotic organisms (their cell has free DNA in the cytoplasm, that is, there is no nuclear envelope) and eukaryotes (which have their hereditary material wrapped in a cell nucleus) are included in this term. Of course, we are dealing with a group with great physiological diversity.
When we immerse ourselves in the world of bacteria (remember that they are included in microbes) things get considerably complicated, because here we are dealing with a taxonomic group that has to classify these microscopic living beings through an evolutionary history. For this reason, in the first place, the “bacteria” and “archaea” domains are clearly differentiated, since despite being both microorganisms that share certain characteristics, they present enough differences at the biochemical and genetic level to consider their excision.
Thus, within bacteria we can find as many classification criteria as the variety of microorganisms in the environment . These divisions can be according to their shape (cocci, bacilli and spirilla), metabolism (autotrophic, heterotrophic, phototrophic, chemotrophic and organotrophic), nutritional types, cell wall and staining capacity (GRAM positive and GRAM negative) or their possible potential for generate damage to the host they inhabit (pathogenic or non-pathogenic), among many other divisions.
Of course, all this terminological conglomerate makes one concept clear: no matter how much microbes encompass more types of organisms, it is clear that the terminological division of bacteria must be more exact, since there is indeed a taxonomic and phylogenetic interest in classifying them. this level.
2. Bacteria have a very marked morphology
No matter how simple they are considered in terms of structure, if we begin to explain the morphology of all microorganisms, we may never finish. Therefore, to exemplify the differences between microbes and bacteria, it is better that we describe the general features of the latter grouping and compare it with the rest. Thus, some typical morphological characteristics of bacteria are the following :
- They are unicellular organisms without a properly delimited nucleus.
- They have a single circular chromosome located in a region of the cytoplasm called the nucleoid.
- They reproduce asexually by binary fission.
- They have a protective cell wall above the plasma membrane (with exceptions).
Only with these four points do we get an idea of the clear differentiation between bacteria and other microbes, since, for example, viruses lack the machinery to self-replicate themselves (they cannot carry out asexual reproduction), and therefore require a host that allows them to spread. On the other hand, protozoa are unicellular Protists, that is, eukaryotic microorganisms with a delimited nuclear membrane that differentiates the nucleus from the rest of the cell, unlike bacteria and archaea.
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We only need a couple of examples to realize that bacteria are completely different from other microbes . Whether presenting an advanced biological organization (compared to viruses) or an ancestral structure (compared to fungi and protozoa), it can be seen that these groups have little in common beyond their small size.
One last remark of great interest is to remind all readers that not all microbes are considered living beings by many scientific communities, as shocking as that may sound. This is the exceptional case of viruses, since they lack a cellular structure, that is, the most basic level of organization that gives life to the different beings on the planet. These small molecules made up of a protein capsid and genetic information roam the environment in search of cells to kidnap in order to replicate themselves, since they lack the functionality and autonomy of other living beings. Although there is still controversy, viruses are not living beings in the eyes of biology.
When talking about different groups, it is normal that the diversity of species and biomass accumulated on earth is different depending on the order or taxon in which we are looking. Let’s give some examples:
- Recent studies estimate that there are about a trillion species of prokaryotes (bacteria and archaea) on planet Earth.
- This translates into an amount of 70 million tons of biomass, that is, 15% of the terrestrial biomass.
- On the other hand, calculating the number of existing virus species is impossible, since they are the most widespread biological entity on the entire planet.
- Despite this, viruses only account for 0.2 million tons of planetary biomass.
- When we increase in morphological complexity, the numbers go down, since 30,000 species of protozoa have been found.
This does not imply that some microorganisms are more important than others from an ethical and moral point of view, but of course, without bacteria, life as we know it would not be possible. Despite this appreciation, microscopic viruses, protozoa and fungi also play an essential role in the evolutionary mechanisms of living beings, because by infecting other animals, they promote an evolutionary arms race and the survival of the strongest in the world. natural environment, leading to long-term genetic selection .
Therefore, we can ensure that all microbes, however tiny they may be, play an essential role in life as we know it today. If we take a practical example, a virus would be the size of a tennis ball, a bacterium the size of half a court, and a eukaryotic cell the size of an entire stadium. Despite these differences in morphology and biomass, all beings that we cannot see are vital pieces for the functioning of ecosystems and of ourselves, both as individual entities and as a species.
- We recommend you read: “The 3 functions of the microbiome in our body”
Conclusions
As we have seen, the differences between microbes and bacteria are not only reduced to a scale of size. As much as bacteria are included within microorganisms or microbes, they present many differences with the rest of the former of this heterogeneous group, among which are their groups, morphology, diversity of species and contribution of biomass, among many other issues. .
For all these reasons, one idea should be clear at the end of this reading: all bacteria are microbes, but not all microbes are in the group of bacteria . Despite this, the importance of each microorganism or higher entity in the ecosystems and in the functioning of the Earth is more than documented.
Bibliographic references
- What are microbes? AMC.edu.mx, science magazine. Collected on September 15 at https://www.amc.edu.mx/revistaciencia/images/revista/68_2/PDF/QueSonMicrobios.pdf
- Atlas, R.M., & Bartha, R. (2002). Microbial ecology and environmental microbiology. Pearson-Addison Wesley.
- Bacteria, National Human Genome Research Institute. Collected on September 15 at https://www.genome.gov/es/genetics-glossary/Bacteria
- Iglesias, M.T. (2008). Study of the carbon of the microbial biomass in disturbed soils. Lazaroa, 29, 117.
- Perez, M., & Mota, M. (2008). Bacterial morphology and structure. Topics in Medical Bacteriology and Virology, 2, 23-42.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.