The first time Frances Westall came across the bacteria was on a voyage with the American oceanographic vessel Joides Resolution. It was 1987 and the ship was crossing the South Atlantic with a number of scientists on board, including this red-haired South African geologist, who had studied her career at the British University of Edinburgh.
He already had experience in oceanographic vessels, since for his doctoral thesis, carried out at the University of Cape Town (South Africa), he had traveled the Indian Ocean. Another new mission with the German ship Polarstern took him through Antarctic waters. The glistening rock sediments collected from the ice featured traces of organisms well known to her and others she was unaware of but deeply intrigued her. “I discovered my first bacteria by chance,” she says proudly.
The electron microscope and collaboration with other scientists facilitated the official encounter with bacteria and opened the doors to a complex world that, from then on, would take him to visit laboratories in Germany (the Alfred Institute for Polar and Marine Research). Wegener, from Bremerhaven) and France (the Biogeology Laboratory of the University of Nantes) in search of scientific thrills. “Looking at these tiny fragments of gold-coated rocks,” he says passionately, “is like searching for hidden treasures.”
Later, as he confesses, it was love that led him to Bologna, although the sentimental episode ended with what he describes as “a disastrous experience.” However, at the oldest university in Europe, he decided to stay to develop his safest passion, and currently works in the Microbiology laboratory of the Department of Food Protection and Valorisation of this center.
In this kingdom he painstakingly registers hundreds of photographs, fragile testimonies of traces of life left behind by very simple organisms. “Now I am concerned with fossil bacteria in the oldest rocks on Earth, within general research on the origin of life and as a model for searching for extraterrestrial life.”
Although most of her roommates are dedicated to living bacteria, the ones that populate our food dishes, and she also uses them for her research, she prefers to observe the ancient ones of the species. His specialty is called paleobiology and it has gained special relevance as a result of the discovery of signs of life in a Martian rock found in Antarctica and some marks that could make one think that it is the fossil of a bacterium. But to Frances Westall the finding of traces of life in the rock ALH 84001 leaves her cold: “I have not been able to study the rock of Mars. I would have liked, and I requested a sample from NASA, but they did not give it to me. I do not see traces life, the evidence in the Mars meteorite is equivocal. The structures seen in the electron microscope are too small to be bacteria, and most of them look like crystalline structures to me. But I would need to study the material myself before secure it, “says Westall.
NASA refused their request for collaboration, on the pretext that their findings did not correspond to ongoing research programs. “But when I presented the project, my interlocutor was very interested in learning about my fossilization methods. And then I received a letter from Carl Sagan asking for my publications.”
How can you hold your opinion of the Martian rock against that of other scientists? Precisely, his works, presented at a congress in Capri (Italy) and at the International Conference on the Origin of Life, held in Orleans (France), and published in scientific journals such as Palaeontology and Sedimentology, are aimed at establishing what Traces of fossils were bacteria and which were not, and how different types of these organisms are fossilized, some of which are extraordinarily resistant to fossilization.
He is not the only person who disputes the biological origin of the Martian fossil. Some believe that they are capricious formations, and the American paleobiologist William Schopf has also drawn attention to the size of these traces, smaller than any known bacteria.
“The oldest cellular structures on Earth,” says Westall, “are preserved in shallow marine waters, hydrothermal sediments or lakes converted to silica, such as archaea formations discovered in Australia and South Africa.” It should be clarified that archaea or archaebacteria are a somewhat different way of life from what was known until recently. Biologists previously thought that there were only two forms of life: prokaryotes, which are cells without a nucleus, like bacteria, and eukaryotes, which are cells with a nucleus, like those of unicellular algae, protozoa, and multicellular animals and plants. But, in 1977, the scientists Woese and Fox found a third type of organism that differed from the others in its RNA sequences, and they called it archaebacteria or archaea. Since then, three different forms of life have been known: true bacteria, eukaryotes, and archaea.
The fossils of the oldest traces of life found on Earth were presented by William Schopf and were 3.46 billion years old, although other scientists from the Gustaf Arrhenius laboratory, from La Jolla (United States), showed evidence of life, still much disputed, that they could be 3,870 million years old.
But what Westall is studying are specifically traces of microorganisms that are one micron (millionth of a meter) long or even less, filamentous, round or ovoidal forms, and that come from microorganisms that lived at various times, the oldest of 3,500 millions of years.
“Bacteria play a major role in the formation of sedimentary rocks. Understanding this phenomenon, as well as the process of its fossilization in these same rocks, is for me the fundamental step before issuing hypotheses about what they were before they were rocks. Because some fossils do not correspond to bacteria; perhaps they are crystalline structures, other types of cells or spherical or ovoidal structures the size of these microorganisms. “
To solve the enigma, this South African researcher subjects living microbes to processes similar to those that occur in nature and observes their reactions with the help of a scanning electron microscope. Let us remember that the fossilization process is nothing other than the substitution of inorganic organic matter; in this case, silica. Thus he has discovered that Gram negative bacteria do not fossilize the same as Gram positive ones. These two types are distinguished from each other by the composition of their cell walls.
Westall has found that Gram-positive ones, such as Bacillus laterosporous, take less than a week to silicify. In a colony of these bacteria, which has the same shape as a honeycomb, it is appreciated that the cell walls have been replaced by a robust 0.6-micron-thick silica crust, and the protoplasm – the content of the bacteria -, by siliceous granules. Bacillus spores also fossilize dramatically.
The same is not the case with Gram negative bacteria. Although their silicification occurs quickly – in seven days, more or less – and their envelopes are thicker than the others, they are preserved in the form of very thin crystals, rather than in the form of a crust. Despite this, the special arrangement of these crystals makes it possible to distinguish the double cell wall structure that characterizes these bacteria.
“In view of these results -concludes Westall-, we can deduce that the bacteria that fossilize forming more robust crusts are easier to be preserved in the rocks. The amount of mineral that is in the medium and the time it takes in petrify.”
It is not difficult to understand why Frances Westall has been immersed in this issue for years. Faced with her Anglo-Saxon rigor, her enthusiasm is Latin, as she is truly fascinated by the inhabitants of her microworld:? Bacteria are exciting; for example, they have a surprising way of communicating, especially for such primitive beings. It is a direct interaction between the external environment and the DNA modules, in such a way that pieces of DNA are transformed in response to environmental changes. This DNA adapted to a certain environment is transmitted to the? Children? bacteria and the cycle continues. This is the same trick they use to adapt to antibiotics and other bactericides?
These microorganisms are also characterized by their bulimia: “As soon as there is something to eat, there is a bacterium – says the scientist -. They are in the first step of the diet and, as soon as there is something organic biodegradable, they arrive first, they metabolize the material and turn it into a form that can be assimilated by another more complex organism, such as mold. Others come to eat the mold, and so on. “
Their voracity and their ability to survive are two reasons why some think that bacteria, and not man, are the living beings that have had the greatest fortune in the evolution of species. “This is a difficult question, and I do not know if it is fair to say it. Surely, they were the first existent beings at the beginning of the history of the Earth – in fact, there is even talk of protobacteria, antecedents of bacteria, but it is not yet known. he has found none – and they will be when life on Earth is extinct. As they are very simple organisms, they are more adaptable to changes in ecological conditions. I do not think that one can speak of fortune. “
And she jokingly adds: “Surely the bacteria are going to survive me, but I feel happy to be on Earth and to have an interesting life, perhaps much more complicated than yours. The truth is that I would rather be me than a bacterium.”
Philippe Plailly / Amelia Die
This interview was published in March 1997, in number 190 of VERY Interesting
