Unusual Bacteria: Strange Facts About Fascinating Microbes
Interesting and Diverse Organisms
Bacteria are fascinating microbes. Many people think of them as simply causers of disease. While it's true that some of them can make us sick, many are harmless or even beneficial. Researchers are discovering that some bacteria have amazing abilities that are interesting in their own right and may also be helpful to humans in the future.
Although most bacteria are made of a single microscopic cell, they are not as simple as was previously believed. Bacteria can communicate with each other and coordinate their actions. Some can survive in extreme environmental conditions which would kill humans; some can produce light; and some can detect and respond to magnetic fields. Several kinds are predators that attack other bacteria.
This article describes unusual features of some of the known bacteria. As scientists explore nature, they're finding new bacteria and learning more about the previously identified ones. They may soon discover many more surprising facts about the microbes in our world.
Studies have shown that bacteria fall into two distinct groups, based on their different characteristics. These groups are known as the kingdoms Eubacteria and Archaebacteria or as the domains Bacteria and Archaea. In the latter classification scheme, archaeons (members of the Archaea domain) aren't considered to be bacteria.
Extremophiles: Living in Extreme Environmental Conditions
Some bacteria live in extreme environments and are known as extremophiles. "Extreme" environments (by human standards) include those with a very high or very low temperature, those with a high pressure, salinity, acidity, alkalinity, or radiation level, or those with no oxygen.
Microbes known as archaeons frequently live in extreme conditions. Archaeons look similar to bacteria under a microscope, but they are very different genetically and biochemically. They are often referred to as bacteria, but most microbiologists feel that this term is inaccurate.
Examples of Extremophiles
- Halophilic bacteria live in salty environments.
- Salinibacter ruber is a rod-shaped, orange-red bacterium that grows best when it's living in ponds that contain 20% to 30% salt. (Seawater contains about 3.5% salt by weight.)
- Some halophilic archaeons survive very well in water that is almost saturated with salt, such as the Dead Sea, salt lakes, natural brines, and pools of evaporating sea water. Dense populations of archaeons may develop in these habitats.
- Halophilic archaeons often contain pigments called carotenoids. These pigments give the cells an orange or red color.
- Thermophilic bacteria live in hot environments
- Hyperthermophilic bacteria live in extremely hot environments which have a temperature of at least 60°C (140°F). The optimal temperature for these bacteria is greater than 80°C (176°F).
- Bacteria living around hydrothermal vents in the ocean require a temperature of at least 90°C (194°F) in order to survive. A hydrothermal vent is a crack in the Earth's surface from which geothermally heated water emerges.
- Some archaeons survive around deep-water vents at a temperature of greater than 100°C (212°F). The high pressure prevents the water from boiling.
- In 2013, scientists discovered a bacterium called Planococcus halocryophilus (OR1 strain) living in permafrost in the High Arctic. The bacterium was reproducing at -15°C —a low-temperature record so far—and was able to survive at -25°C.
- Deinococcus radiodurans, sometimes called "the world's toughest bacterium", can survive cold, acid, dehydration, a vacuum, and radiation a thousand times stronger than a human can withstand.
Bioluminescence: Producing Light
Bioluminescent bacteria are found in sea water, in sediments on the ocean bottom, on the bodies of dead and decaying marine animals, and inside ocean creatures. Some marine animals have specialized light organs which contain bioluminescent bacteria.
A flashlight fish is an interesting example of an animal containing luminescent bacteria. There are a number of different kinds of flashlight fish, all belonging to the same family (the Anomalopidae). The fish have a bean-shaped light organ, or photophore, below each eye. The light from the organ turns on and off like a flashlight. In some fish the light is "turned off" by a dark membrane that covers the photophore and is turned on again when the membrane is removed. The action of the membrane resembles that of an eyelid. In other fish the photophore is moved into a pocket in the eye socket to hide the light.
The flashlight fish is nocturnal. It uses its light to communicate with other fish and to attract prey. The light also helps the fish to avoid predators. The predators are often confused by the light turning on and off and find it difficult to locate the fish as it changes direction in the water.
The light of the flashlight fish is made by bacteria living in the light organ. The bacteria contain a molecule called luciferin, which releases light when it reacts with oxygen. An enzyme called luciferase is necessary for the reaction to happen. The bacteria benefit from living in the light organ of the flashlight fish by receiving nutrients and oxygen from the fish's blood.
Flashlight Fish With Bioluminescent Bacteria
The flashlight fish in the video above is Photoblepharon palpebratus. It's often known as the eyelight fish.
Bacterial Communication and Quorum Sensing
Bacteria communicate with each other via the transmission of signalling molecules between different cells. Signaling molecules are chemicals that are produced by bacteria and bind to receptors on the surface of other bacteria, triggering a response in the ones that receive the chemicals.
Researchers are discovering that many bacterial species are able to detect the amount of signalling molecule that is present in their environment in a process called quorum sensing. These species respond to a chemical signal only when the concentration of the molecule reaches a specific level.
If only a few bacteria are present in an area, the level of signalling molecule is too low and the bacteria don't respond to its presence. If a sufficient number of bacteria are present, however, they produce enough signalling molecule to trigger a specific response. All the bacteria then respond in the same way at the same time. The bacteria indirectly detect their population density and change their behaviour when a "quorum" is present.
Quorum sensing allows bacteria to coordinate their actions and produce a stronger effect on their environment. For example, pathogenic bacteria (ones that cause disease) often have an improved ability to attack the body when they coordinate their behaviour.
The Hawaiian Bobtail Squid (Euprymna scolopes)
Quorum Sensing in a Luminescent Bacterium
The Hawaiian bobtail squid has an interesting use for luminescent bacteria. The tiny squid is only about an inch long. It's nocturnal and spends the night buried in sand or mud. At night it becomes active and feeds mainly on crustaceans, such as shrimp and prawns. The squid has a light organ in the lower part of its body that contains a bioluminescent bacterium called Vibrio fischeri. Interestingly, this is the only species of bacteria that has been found in the organ.
The bacterial cells produce a signalling molecule known as an autoinducer. As the autoinducer accumulates inside the light organ, it eventually reaches a critical level that activates the luminescence genes of the bacteria. The process is an example of quorum sensing.
The light emitted by the bacteria helps to prevent the squid's silhouette from being seen by predators swimming below the squid. The light from the photophore matches the light reaching the ocean from the moon, camouflaging the squid and preventing it from casting a shadow. This phenomenon is known as counter-illumination.
In the morning the squid carries out a process called venting. Most of the bacteria in the photophore are released into the ocean. Those that are left reproduce. When night arrives, the bacterial population is once again sufficiently concentrated to produce light. The daily venting means that the bacteria never become so numerous that they can't obtain enough food and energy for light production.
Bacteria in the Hawaiian Bobtail Squid Light Organ
Both the bacteria and the squid benefit from their relationship. The squid is camouflaged when it's active. The bacteria use amino acids and sugars in the light organ as food. They are also protected while they are inside the squid.
Predatory bacteria attack and kill other bacteria. Researchers are discovering that they are widespread in aquatic habitats and in soil. Two examples of these bacteria are described below.
- Vampirococcus lives in freshwater lakes with a high sulphur content. It attaches to a much larger, purple bacterium called Chromatium and absorbs the liquid from its prey, killing it. This process reminded early researchers of a vampire sucking blood and gave them the idea for the bacterium's name.
- Unlike Vampirococcus, Bdellovibrio bacteriovorus attaches to another bacterium and then enters it instead of staying on the outside. It produces enzymes to digest the outer covering of its prey and also rotates, allowing it to drill its way into the prey.
- Bdellovibrio reproduces inside its prey.and then destroys it.
- The predator can swim at the amazing rate of 100 cell lengths a second, making it one of the fastest-moving of all known bacteria.
Some researchers are investigating the possibility that predatory bacteria could be used to attack bacteria that are harmful to humans.
Bdellovibrio Attacks E. coli
Detecting and Responding to Magnetic Fields
Scientists didn't realize that certain bacteria could detect magnetic fields until a 1975 discovery by Richard P. Blakemore, a scientist at Woods Hole Oceanographic Institution. Magnetic bacteria, also called magnetotactic bacteria, detect and respond to the Earth's magnetic field (or to the field created by a magnet placed near them).
- Blakemore noticed that some bacteria always moved to the same side of the slide when he was observing them under a microscope.
- He also observed that if he placed a magnet next to a slide, certain bacteria always moved towards the north end of the magnet.
- Magnetic bacteria contain special organelles called magnetosomes.
- Magnetosomes contain either magnetite or greigite, which are magnetic crystals.
- Each magnetic crystal is a tiny magnet, which has a north pole and a south pole, just like other magnets.
- Since magnets are attracted to each other via their opposite poles, the magnetic crystals in the bacteria are attracted to the Earth's magnetic field.
Scientists are investigating ways in which the magnetic properties of bacteria might help humans.
Bacteria Moving in Response to a Magnet
Bacteria are tiny organisms and live in many different habitats. Some of these habitats are inhospitable to humans or difficult for us to explore. It's very possible that there are amazing abilities of bacteria still to be discovered and that some of these abilities may improve our lives. The results of future research should be interesting.
Questions & Answers
© 2013 Linda Crampton