Why do amoeba move away from light

In , Liang Li and Edward Cox at Princeton University reported that the amoeba Dictyostelium is twice as likely to turn left if its last turn was to the right and vice versa, pointing to the existence of a rudimentary memory. The following, Toshiyuki Nakagaki at Hokkaido University in Sapporo, Japan, found further evidence of that amoeboid memory. They exposed Physarum amoeba to temperatures fluctuating regularly between cold and warm. It was already known that the cells become sluggish during cold snaps, but Nakagaki's team found that the amoeba slowed down in anticipation of cold conditions, even when the temperature changes had stopped.

Some specialized species of amoebae live as parasites inside the bodies of other animals. The disease amoebic dysentery amoebiasis is caused by one such type of amoeba, Entamoeba histolytica , which invades and destroys the tissues of the intestinal wall. Members of another genus, Acanthamoeba , are commonly found in soil and contaminated water and cause painful corneal ulcers, usually from improper sterilization of contact lenses in contact lens solutions.

The term "amoeboid" means having no definite shape to the cell and able to alter shape. Amoeboid movement is a type of motility of a cell in which cytoplasmic streaming directional flow of cytoplasm extrudes outward from the cell to form pseudopodia so that the cell can change its location. It is exhibited not only by amoebae themselves but also by some types of cells in multicellular animals including leukocytes white blood cells. Locomotion An amoeba moves by first advancing a pseudopodium from a point on its surface; the living matter then flows forward into the projection Fig 2.

Digestion The formation of pseudopodia also enables amoeba to feed. Respiration For respiration — the taking in of oxygen and removal of carbon dioxide — the gases simply diffuse through the whole of amoeba's permeable surface. Water removal Under a microscope, a bubble of liquid can be seen to form periodically inside an amoeba's body.

Sensitivity Amoeba has no special sense organs. The nucleus The nucleus can be clearly seen with a microscope as a darkish spot inside the body. Reproduction and the spore state Reproduction is almost always asexual , generally by by binary fission , though sometimes by multiple fission of the nucleus. Primitive intelligence? Amoebae and disease Some specialized species of amoebae live as parasites inside the bodies of other animals. Light micrograph of Entamoeba histolytica , which causes the infection amoebiasis, showing amoebae blue invading the lining of the colon.

Amoeboid The term "amoeboid" means having no definite shape to the cell and able to alter shape. Related categories. Others may use bits of material from their environment, such as minerals and plants.

To learn more about the newfound amoeba, Lahr would need more specimens. Two years later, another Brazilian scientist sent him pictures of the same species from a river. But the bonanza came in It was enough for her and Lahr to begin a detailed study of the species.

They examined the microbes under a microscope. The amoeba, they found, built its hat-shaped shell from proteins and sugars that it made. The big question is why the microbe needs that shell. Lahr suspects many more amoeba species await discovery. Scientists still know little about amoebas. Most biologists study organisms that are either simpler or more complex.

Microbiologists, for instance, often focus on bacteria and viruses. Those microbes have simpler structures and can cause disease. Zoologists prefer to study larger, more familiar animals, such as mammals and reptiles. He is an environmental scientist at the University of York in England. But when scientists do peer at these odd little organisms, they find big surprises.

Some amoebas carry bacteria that protect them from harm. They live in soil, ponds, lakes, forests and rivers. If you scoop up a handful of dirt in the woods, it will probably contain hundreds of thousands of amoebas. But those amoebas may not all be closely related to one another. Some organisms are amoebas for only part of their lives. They can switch back and forth between an amoeba form and some other form.

Like bacteria, amoebas have just one cell. But there the similarity ends. For one thing, amoebas are eukaryotic Yoo-kair-ee-AH-tik. Bacteria have no nucleus. In some ways, amoebas are more similar to human cells than to bacteria. Also unlike bacteria, which hold their shape, shell-free amoebas look like blobs. Their structure changes a lot, Lahr says.

Their blobbiness can come in handy. Amoebas move by using bulging parts called pseudopodia Soo-doh-POH-dee-uh. An amoeba can reach out and grab some surface with a pseudopod, using it to crawl forward. Pseudopodia also help amoebas eat. That allows this microbe to swallow bacteria, fungal cells, algae — even small worms. Some amoebas eat human cells, causing sickness. Still, some species can be lethal. The disease they cause kills tens of thousands of people each year, mostly in areas that lack clean water or sewer systems.

But if it gets inside the nose, it can travel to the brain where it feasts on brain cells. This infection is usually deadly. The good news: Scientists know of only 34 U.

A scientist named Sebastian Hess recently discovered the tricks some amoebas use to eat. He studies eukaryotic microbes in Canada at Dalhousie University. Hess has loved watching tiny critters through a microscope since he was a kid. Ten years ago, Hess punched through the ice of a frozen pond in Germany. He collected a sample of water and took it back to his lab.

Through the microscope, he saw something odd. Green spheres were wiggling like tiny bubbles inside strands of green algae. So Hess mixed algae containing the green balls with other algae. The wiggling spheres popped out of the algae and started swimming. Shortly afterward, they invaded other algal strands.

That means they can switch between two forms. In one form, they swim or glide using tail-like structures called flagella Fluh-JEH-luh. When the swimmers find food, they transform into amoebas. Their shape becomes less rigid. In the center of the second electrophoresis block we placed the experimental chamber that allowed us to obtain a laminar flux when it was closed and the addition and extraction of cells when it was open. These three glasses were for only one use.

This glass structure Fig. It was reusable after cleaning. The modified slide was placed in the central platform of the second electrophoresis block. To avoid medium going across the modified slide from below, we placed an oil drop in the central platform of the block of electrophoresis, on which the modified slide was placed.

It is very important that the oil drop expands to cover the entire width of the experimental chamber. In the center of the modified slide, without any glue, we placed the central piece and the two sliding lateral pieces leaving short distance between all of them.

To note, it is crucial that the amoebae do not remain for more than a few seconds in the micropipette tip to avoid the adhesion of the amoeba to the inner surface of the tip. Once the amoebae were placed under the central piece of the chamber, we waited for two minutes to allow the cells to stick to the surface of the modified slide.

Then, we filled the wells of the electrophoresis blocks with simplified Chalkley medium up to the level necessary to contact with the base of the modified slide, but not the two sliding lateral pieces. Later, the two sliding lateral pieces were pushed with two micropipette tips until they contact with the liquid in the wells. Next, the two sliding lateral pieces are pushed to contact the central piece in the chamber.

This way, a laminar flux can be established throughout the inner space of the experimental chamber. Considering that the amoebae that had shown a specific behavior were needed to perform further experiments, the cells were collected opening the sliding lateral pieces with the tip of a micropipette. Set of videos intended only for didactical purposes. They are merely descriptive, to make easier the understanding of our experimental procedure and the reproducibility of our studies.

Note that steps 5 to 8 are performed directly under the microscope, and we have not filmed them under the microscope for better visualization. In summary, the experimental chamber consisted in a sliding glass structure. The sliding lateral pieces could be displaced in the longitudinal direction. This way, when the sliding pieces were closed an inner laminar flux was available in the chamber and, when they were open, the placement and collecting of the cells were possible easily.

Once starved, only the cells that were strongly attached to the substrate, actively moving through it and showing a little amount of thin pseudopodia were used in the experiments. The experiments were always made with small groups of cells. For instance, in Amoeba proteus along the induction process, we analyzed a total of cells that were studied in 32 different times experimental replicates analyzing them in groups of 4—10 cells each number of cells per replicate.

Scenario 1 was repeated 32 times. Scenarios 2 and 3 were performed 27 and 9 times, respectively. The induction process was usually performed using around 7 cells per experiment, sometimes as few as 4 or 5 and other times as many as 9 or 10, the average being 6—8 cells. The number of cells analyzed in the scenarios depended on how many cells appeared to be conditioned in the first step, so that the number of cells per experiment is lower each time, for instance, in scenario 1, the number of cells was usually between 2 and 4.

Finally, in scenarios 2 and 3 the experiments were performed using fewer amounts of cells per experiment, usually 1—3 which were the cells that migrated towards the cathode during the conditioning process. Compared to Amoeba proteus , the Metamoeba leningradensis showed a more varied array of behaviors and shapes. These cells were also more difficult to handle, as they were more prone to strongly stick to the micropipette tips, while usually showing a weaker attachment to the glass chambers.

An electric field was applied to the first electrophoresis block, which was then conducted to the second by the two agar bridges. Direct measurements taken with a multimeter in the second block where the cells were placed showed that the strength of the electric current oscillated between All the experiments where the only stimulus was an electric field were performed in an electrophoresis block that had never been in contact with any chemotactic substance.

Groups of 4 to 10 amoeba were placed in the experimental chamber. Once all the cells were attached to the glass surface, the laminar flux was stablished by gently closing the structure using the sliding cover glasses. Next, the peptide, nFMLP was introduced in the left well of the electrophoresis block. When the cells were subjected to both stimuli at the same time induction process , a new population response arose.

This population behavior, in Amoeba proteus , showed that about half the amoebae cells migrated towards the anode where the nFMLP peptide was placed , and approximately the other half of the cellular population migrated to the cathode Fig. Accordingly, the cellular migration response under two simultaneous stimuli is notoriously different from that observed when the stimuli were separated Figs. In all our experiments, we used the same concentration of nFMLP. In order to homogenize the solution and accelerate the creation of a chemotactic gradient in the experimental chamber we carefully mixed the content of the left well until the amoebae appeared to start moving towards it.

The generation of an nFMLP peptide gradient was evaluated by the measurement of its concentration in the middle of the experimental chamber. Peptide concentration was calculated extrapolating the values from a standard curve with known concentration of the fluorescein-tagged peptide Fig. All measurements were duplicated and the experiment was repeated three times.

Fluorescence was measured in 96 well glass bottom black plates P The motility of the cells was recorded using a digital camera attached to a SM-2T stereomicroscope. In order to quantify and compare the directionality of cell migration towards the anode or the cathode, we computed the cosines of the angles of displacement of each amoeba More precisely, we calculated the cosine of the angle formed between the start and final positions of each cell.

Consequently, we were able to analyze quantitatively if an amoeba moved towards the cathode positive values of the cosine , or towards the anode negative values. Next, to estimate the significance of our results, we studied first if the distribution of cosines of angles came from a normal distribution, by applying the Kolmogorov-Smirnov test for single samples. Besides the p-value, we have reported the Z-statistic of the Wilcoxon rank-sum test Note that the signs of the cosines from the second and third scenarios were changed to perform the respective tests with the galvanotaxis without previous induction Fig.

Researchers involved in the quantitative analysis of the cellular trajectories were never aware of what scenario each trajectory belonged to. Further information on research design is available in the Nature Research Reporting Summary linked to this article.

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