In the Caribbean mangrove forest, scientists have discovered a species of bacteria that grows into the size and shape of human eyelashes.

These cells are the largest bacteria ever observed and are thousands of times larger than more familiar bacteria such as E. coli. Jean-Marie Volland, a microbiologist at the Joint Genome Institute in Berkeley, California, said:

Dr. Voland and his colleagues presented a study of a bacterium called Thiomargarita Magnifica at Journal Science on Thursday.

Scientists once thought that bacteria were too simple to make large cells. However, Thiomargarita Magnifica turned out to be very complex. Most of the bacterial world has not yet been investigated, so it is quite possible that we are waiting for the discovery of larger and more complex bacteria.

It’s been about 350 years since Dutch lens grinder Antonie van Leeuwenhoek sharpened his teeth and discovered the bacteria. When he placed the plaque under a primitive microscope, he was surprised to see unicellular organisms swimming. During the next three centuries, scientists discovered many more types of bacteria, all of which were invisible to the naked eye. For example, E. coli cells are about 2 microns, or less than 1 / 10,000 inch.

Each bacterial cell is an organism of its own, which means it can grow and divide into new bacterial pairs. However, bacterial cells often live together. Van Leeuwenhoek’s teeth were covered with a jelly-like film containing billions of bacteria. In lakes and rivers, several bacterial cells stick together to form small filaments.

We humans are multicellular organisms, and our body is composed of about 30 trillion cells. Our cells are also invisible to the naked eye, but are usually much larger than bacterial cells. Human egg cells can reach about 120 microns in diameter, or 5/1000 inches.

Cells of other species can grow even larger. The green alga Caulerpataxifolia produces blade-shaped cells that can grow to a length of one foot.

When a gap emerged between small and large cells, scientists turned to evolution to understand it. Animals, plants and fungi all belong to the same evolutionary lineage called eukaryotes. Eukaryotes share many adaptations that help build large cells. Scientists have inferred that without these adaptations, bacterial cells would have to remain small.

First, large cells need physical support to prevent them from collapsing or falling apart. Eukaryotic cells contain hard molecular wires that act like poles in a tent. However, bacteria do not have this cytoskeleton.

Large cells also face chemical challenges. As its volume increases, it takes time for the molecule to drift, meet the right partner, and carry out the correct chemical reaction.

Eukaryotes have evolved solutions to this problem by filling cells with small compartments. There, different forms of biochemistry occur. They leave the DNA wrapped around a sac called the nucleus, along with molecules that can read genes and make proteins. Alternatively, when the cell regenerates, the protein produces a new copy of the DNA. Each cell produces fuel in a pouch called mitochondria.

Bacteria do not have the compartments found in eukaryotic cells. In the absence of a nucleus, each bacterium usually carries a loop of DNA that floats freely within it. They also do not have mitochondria. Instead, they usually produce fuel with molecules embedded in the membrane. This arrangement is suitable for small cells. However, as the volume of the cell increases, there is not enough space on the surface of the cell for enough fuel-producing molecules.

The simplicity of the bacteria seemed to explain why they were so small. They just didn’t have the complexity essential to grow.

However, according to Shailesh Date, founder and co-author of the Complex Systems Institute in Menlo Park, California, this conclusion was made too quickly. Scientists made a thorough generalization of bacteria after studying only a small part of the world of bacteria.

“We just scratched the surface, but we were very dogmatic,” he said.

That doctrine began to break in the 1990s. Microbiologists have discovered that some bacteria have their own independently evolved compartments. They also discovered a species that is visible to the naked eye. For example, Epulopiscium fishelsoni came to light in 1993. Bacteria that inhabit the surgeon’s fish grow to a length of 600 microns, which is larger than a grain of salt.

Olivier Gros, a biologist at the University of Antilles, discovered Thiomargarita magnifica in 2009 while exploring the mangrove forests of Guadeloupe, a collection of Caribbean islands that are part of France. The microbes looked like miniature pieces of white spaghetti, forming a coat on the leaves of dead trees floating in the water.

Initially, Dr. Gross didn’t know what he found. He thought that spaghetti could be a fungus, a small sponge, or another eukaryote. But when he and his colleagues extracted DNA from laboratory samples, it revealed that they were bacteria.

Dr. Gross worked with Dr. Voland and other scientists to investigate strange creatures in more detail. They suspected that the bacteria might have tiny cells attached to the chains.

It turned out that was not the case. When researchers looked inside the bacterial noodles with an electron microscope, they noticed that each was a giant cell of its own. The average cell length was about 9,000 microns, with the largest being 20,000 microns, long enough to span the diameter of the penny.

Research on Thiomargarita Magnifica is slowly progressing, as Dr. Valant and his colleagues do not yet understand how to grow bacteria in their laboratory. For now, Dr. Gross needs to collect a fresh supply of bacteria every time the team performs a new experiment. He can find them not only leaves, but also oyster shells and plastic bottles sitting on the sulfur-rich deposits of mangrove forests. However, bacteria seem to have an unpredictable life cycle.

“For the past two months, I haven’t been able to find them,” said Dr. Gross. “I don’t know where they are.”

Within the cells of Thiomargarita magnifica, researchers have discovered a strange and complex structure. Various types of compartments are embedded in these membranes. These compartments are different from those of our own cells, but they have the potential to grow Thiomargarita Magnifica to a huge size.

Some plots are like fuel production plants, where microorganisms can harness the energy of nitrates and other chemicals consumed by mangroves.

Thiomargarita magnifica also has other compartments that closely resemble the human nucleus. Each compartment, which scientists call pepin after a small seed of fruit like kiwi, contains a loop of DNA. Thiomargarita magnifica has hundreds of thousands of loops, each hidden in its own pepin, whereas a typical bacterial cell has only one loop of DNA.

Even more surprising, each pepin contains a factory for building proteins from its DNA. Petra Levin, a microbiologist at Washington University in St. Louis who was not involved in the study, said:

The vast supply of Thiomargarita magnifica DNA can increase the amount of extra protein needed. Each pepin may create a special set of proteins needed in a unique area of ​​the bacterium.

Dr. Voland and his colleagues hope to be able to confirm these hypotheses after the bacteria have begun to grow. They also tackle other mysteries, such as how tough bacteria are without a molecular skeleton.

“You can use tweezers to remove one filament from the water and put it in another container,” said Dr. Volland. “How it combines and how it gets its shape — these are the questions we haven’t answered.”

Dr. Date said he may be waiting to find more giant bacteria, perhaps even larger than Thiomargarita Magnifica.

“We really don’t know how big they can be,” he said. “But now this bacterium has shown us the way.”

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