8 Living with microorganisms
- Henrique Lins de Barros is a physicist and researcher at the Brazilian Center for Research in Physics (CBPF), as well as an affiliated professor with the Carlos Chagas Institute and Center for the History of Sciences, Technology and Epistemology (HCTE), both of which are part of the Federal University of Rio de Janeiro (UFRJ). He has an undergraduate degree and MA in atomic physics from the Catholic University of Rio de Janeiro (PUC-Rio) and a PhD from CBPF. He is a former director of the Museum of Astronomy and Related Sciences (MAST) in Rio de Janeiro, and he has authored papers and books published in various countries in the areas of biophysics and the history of technology. He has received the National Order of Scientific Merit (2001) and Order of Aeronautical Merit (2004), among other awards.
There are more than 7 billion of us human beings, living on Earth’s surface, our only habitat. Despite our different genders, beliefs, cultures and habits, we are all equal, while each of us is also unique. We are capable of adapting to changes and feeling the stimulations of the environment in which we live, and although we say we have just five senses (seeing, hearing, smelling, touching and tasting), in fact we have many more. We may not perceive this consciously, but in some way we feel nuances. It is said that our eyes are sensitive to a range of colors going from deep red to violet, the “seven colors” of the rainbow, but our body feels infrared and ultraviolet radiation. Our auditory system, like our sense of smell, touch or taste, is extremely sensitive and gives us information about the environment around us. We are in constant interaction with the world, exchanging matter, energy and information.
Every living being that inhabits Earth is connected to the world around it. There is no life without a relationship with everything else. The human body is not isolated from the environment in which it lives, and it needs it to maintain its individuality. Like all beings, humans are altering the world, and to remain alive they need to adapt their body and maintain their integrity in a constantly transforming environment. Thus, the human body also lives in a state of permanent internal imbalance, or rather dynamic equilibrium.
We have trillions of cells, which developed from a single initial cell, fertilized when a sperm found an egg, transforming it into a zygote. All the cells in our body, which are constantly being renewed, come from this zygote, this primordial cell.
Each of us is the habitat for a large number of microscopic organisms (microorganisms or microbes), which inhabit our body and are vital to us. Without them we would not live, as they regulate many of our physiological processes. Each of these microorganisms measures around one thousandth of a millimeter in diameter – roughly 1,000 times smaller than one of our cells – but they are so numerous that in total they weigh around 2 kilograms within each human being.
Tiny organisms produce proteins that are indispensable for our survival. […] Every day we eliminate billions of these microorganisms and replace them with others, given that their growth rate is astonishingly high. This enormous population of bacteria, archaea and so on constitutes our “microbiome”, our internal ecosystem.
These tiny organisms produce proteins that are indispensable for our survival, participating in the digestion of various substances and aiding our immune system. They produce B12 complex vitamins and soluble fibers, clean our skin and eyes, and are present in many other vital processes. Every day we eliminate billions of these microorganisms and replace them with others, given that their growth rate is astonishingly high. This enormous population of bacteria, archaea and so on constitutes our “microbiome”, our internal ecosystem. There are thousands of different species that live with us, distributed in different parts of our body, such as our mouth, nose, ears and throat.
These microorganisms have played an important role in the history of evolution. Life on Earth arose millions of years after the planet cooled down, 3.4 billion years ago, based on a combination of existing chemical elements. There is not one specific element for life, but rather the organization, in a favorable environment, of complex molecular structures. The first organisms were microscopic and unicellular: the precursors of bacteria, they were capable of metabolizing inorganic elements, transforming them into complex molecules. Around 1.5 billion years ago there arose the first multicellular organisms. Thus, the evolution of life occurred through many leaps of growing complexity.
This history is punctuated by various periods of mass extinctions, which threatened life on our planet. [1]. The best known, although not the biggest, occurred around 65 million years ago, putting an end to the reign of the dinosaurs, possibly due to the impact of a meteorite in the Yucatan Peninsula, in Mexico. Other extinctions took place on many occasions, but their causes are not fully known. It is estimated that changes to the environment have been due to volcanic activities, earthquakes, temperature rises or falls, reductions in the amount of oxygen in the oceans, and continental drift, which has radically altered the planet’s surface, resulting in new environments unsuited to some species, which have been unable to adapt. Many hypotheses have been proposed, including one that concerns changes in Earth’s magnetic field.
Earth has a magnetic field that protects it from electrically charged particles from the Sun, which hit the planet (solar wind). This field serves as a shield; without it, Earth would suffer the effects of this radiation in an intense manner, and life on its surface would not be possible.
The discovery of bacteria that produce tiny magnetic crystals and orientate themselves in the direction of Earth’s magnetic field provides an example of interaction between living beings and environmental conditions. Work in this area has shown that multicellular bacteria exist, which supports the idea that evolution has taken place in leaps and bounds toward increased complexity of biological organization, essential to the maintenance of adaptive conditions.
We are immersed in a world of varied stimuli, and our biome adapts to its environment to maintain our health. Accordingly, we feel the variations of different factors that interact with us, and Earth’s magnetic field may be giving us important information for our dynamic equilibrium.
Research carried out using large telescopes, space probes and other sophisticated instruments has shown the existence of a hundred planets that orbit stars far from the Sun, many with characteristics similar to those of Earth. These observations lead to the hypothesis of finding life in other worlds. Organized structures, capable of duplicating themselves, metabolizing and maintaining their form, despite environmental uncertainties, may look very different from the ones we know, and they may be considered alive – but in another life.
Every time we delve into an area of knowledge, a new field of greater complexity opens up, in a sequence that seems endless. The very origin of life on Earth is an open question. According to some researchers, given favorable conditions, life emerges in a short time. According to others, life is extremely complex and does not arise at random from a combination and organization of available elements, and so it is not easily produced.2 [2]
One of the fundamental issues is that we do not know how to characterize a living organism. It is immersed in its surroundings and fights to maintain its individuality.
After a long history, many species have disappeared, giving way to others, as the environment was no longer suitable for their existence. Life goes on, however. It is the great diversity of life forms that guarantees their continuity.
We therefore do not know how to define what life is. In the view of some researchers, it is a system capable of renewing itself, regulating its own composition and conserving its limits.[3]. In other words, a living being is a system that maintains its individuality during its existence, despite changes in the environment. Thus, after a long history, many species have disappeared, giving way to others, as the environment was no longer suitable for their existence. Life goes on, however. It is the great diversity of life forms that guarantees their continuity.
We, who call ourselves Homo sapiens sapiens, appeared on Earth less than 100,000 years ago, which is very recent if compared with many other animal species that have inhabited the planet for tens of millions of years. In recent centuries, since the second Industrial Revolution, changes in the environment caused by the indiscriminate use of technologies have caused alterations in the composition of air and waters, the temperature regime, and the incidence of solar radiation that reaches the planet’s surface, and which could lead to an environment that is unsuited to us, jeopardizing our survival. Perhaps we are condemned to be one of the species with a short time of existence.
Although we may state that we are individuals, endowed with a single body, we also need to remember that we are a combination of many organisms that are invisible to our eyes, which sustain us. The microbiome that each of us is also adapts to external conditions and is constantly changing, in a dynamic, mutable and elastic process, but one that has its limits. If the world that surrounds us undergoes larger alterations, we may stop being viable. That is what life on Earth is like: it tells us a story, but we do not know what its end will be.
[1] Henrique Lins de Barros, "Biodiversidade em questão", Rio de Janeiro: Claro Enigma/Fiocruz, 2011.[2] Cf. Charbel Niño El-Hani e António Augusto Passos Videira (orgs.), "O que é vida?"" Rio de Janeiro, Relume Dumará, 2000. [3] Cf. Lynn Margulis e Dorion Sagan, "O que é vida?", Rio de Janeiro: Jorge Zahar, 2002.