Bacteria That Attack and Live Inside Amoebas

The more I learn about bacteria, the more they fascinate me. They may be small, but they aren't simple. They communicate with one another, mount attacks together or on their own, produce an array of interesting chemicals, and live in an amazing variety of habitats. New research from ETH Zurich has shown that at least one kind of bacterium contains dagger-like structures that attack but don't destroy amoebas. After the attack has finished, the bacterium lives inside the amoeba.

Amoeba proteus by Cymothoa exigua, CC BY-SA 3.0 

Amoebas

Like bacteria, amoebas (or amoebae) are single celled organisms, but their internal structure is more complex. Scientists are discovering that this doesn't necessarily mean that their behaviour is also more complex, however. An amoeba is a predator. It produces extensions from its body called pseudopods ("false feet") which enable it to move and catch prey. The amoeba moves by flowing into the pseudopods. It feeds by surrounding smaller creatures with the pseudopods, engulfing the organisms, and then digesting them with chemicals inside a food vacuole. The feeding process is known as phagocytosis. Bacteria are a major food source for amoebas.

Phagocytosis in an amoeba by Kate Taylor, CC0 public domain license

Attack of Amoebophilus Bacteria

A bacterium called Amoebophilus has developed a way to protect itself from an amoeba attack. It destroys the food vacuole that traps it. After this destruction, the bacterium stays in the amoeba and even reproduces inside it, becoming a symbiont living inside a host.

The "micro-dagger" of the bacterium is located within a sheath attached to the inner membrane of its cell. Although the researchers refer to the dagger in the singular, the structure actually contains multiple piercing devices. The sheath attaching the structure to the membrane is spring-loaded. When the sheath contracts, it sends the dagger through the membrane and into the target. In the case of an Amoebophilus inside an amoeba, the target is the food vacuole. It's vital that the bacterium gets out of the vacuole before the digestive enzymes destroy it.

The mechanism by which the dagger destroys the membrane of the food vacuole is not yet known. The destruction may be simply due to mechanical disruption. There may be another factor at work, however. The dagger may contains enzymes that digest the membrane of the vacuole. Researchers have found that the genome of the bacterium contains instructions for making these enzymes.

It might be expected that once the bacterium is out of the food vacuole it would then break through the membrane of the amoeba and escape into the outside world. This isn't what happens, however. The bacterium stays inside the amoeba and lives there. Further research needs to be done to discover the details of its life inside the amoeba.

Multiple bacteriophages attack a bacterium by Dr. Graham Beards, CC BY 3.0 

A Possible Link to Bacteriophages

The researchers say that the bacterial genes involved in the dagger production are very similar to certain genes found inside bacteriophages, or phages. Phages are viruses that attack bacteria. The bacteriophage genes are needed in order for the virus to pierce the bacterial membrane. Phages pierce the membrane in a similar way to Amoebophilus, except only one spike or piercing device is present. The researchers think that at some time in the past the phage genes were inserted into the bacterial genome.

The ETH Zurich research is exciting because the scientists used a new imaging technique to see the entire dagger structure of the bacterium. Previously only components of the system had been seen. The knowledge that has been gained adds to the growing evidence that despite their microscopic size bacteria are far more complex than we thought.

Reference: The News Release

ETH Zurich. "Bacteria stab amoebae with micro-daggers." ScienceDaily. www.sciencedaily.com/releases/2017/08/170817141531.htm. (accessed August 18, 2017).

California Sheephead: Beautiful, Impressive, and Vulnerable Fish

                                      A male California sheephead
                                    Ed Bierman, CC BY 2.0 License

I think that California sheephead are beautiful and impressive fish. They have some unusual characteristics. They are colourful animals—especially the males—that can grow up to three feet long and weigh up to thirty-six pounds. They have white chins and large, protruding canines. The fish above also has red eyes, a fleshy bump on its forehead, a black head and tail, and red on its middle section. This indicates that it's a male. Females are light pink in colour. All California sheephead start their life as females. Many change to males years later and are therefore said to be protogynous (capable of changing from female to male). 

The scientific name of the California sheephead is Semicossyphus pulcher. Pulcher is the Latin word for beautiful, so it seems that the namer of the fish agrees with my opinion about its appearance. The fish can be found from Monterey Bay in California to the Gulf of California in Mexico. It usually lives around reefs and in kelp beds. It's carnivorous and prefers to eat animals with hard shells, including crabs, lobsters, mussels, and sea urchins. Its large and sharp teeth and its powerful jaws are useful for crushing its prey. A bony plate in its throat is used to grind shells.

                                           

                    This male has paler colouration than the one above.
                                   Its canine teeth can be seen.
                               Kristin Riser, public domain license

The fish are diurnal, which means that they hunt during the day and sleep at night. They enter a cave or a crevice to sleep and secrete a protective mucus cocoon around their body. Potential predators are unable to smell the fish through the mucus.

The fish live in a harem-like structure during the breeding season, which lasts from July to September. A dominant male travels with a group of females and fertilizes their eggs. He drives away any other other males that approach. The age at which a female changes to a male varies considerably. It seems to depend on both environmental and social cues. Some fish change genders as early as five years of age while others don't change until they are thirteen. The fish have been known to live for as long as fifty years, but most are thought to live around twenty years.

Unfortunately, the California sheephead is classified in the Vulnerable category of the Red List established by the IUCN, or International Union for Conservation of Nature. The animal is vulnerable due to its popularity as a food fish. The larger fish are often considered to be the prime catch, but these are generally males. This means that the ratio of males to females is altered, which can have a negative effect on the population. Regulations have been put into effect to improve the situation. Hopefully they are successful.

References

California sheephead information from the Monterey Bay Aquarium
Sheephead facts from fishbase (an online fish database)
Information about the sheephead fish from the IUCN

Mary Anning's Fossils and the Cliffs at Lyme Regis

Mary Anning was a nineteenth century fossil collector and paleontologist who made important contributions to science. The fossils came from the Jurassic period and were obtained from the cliffs and beaches of Lyme Regis in England. The cliffs were once part of the seabed. Even today they contain a rich source of fossils.

Mary developed an impressive knowledge of local life in the Jurassic. Though she eventually became respected by geologists, she didn't receive as much attention as she deserved. She lived at a time when science was predominantly the domain of males. She also came from a poor family and had little social standing, which further hindered the attention that she received from the scientific community.

Mary Anning
 Unknown artist (created before 1842)
Public domain license

Mary Anning's Life

Mary was born in 1799. Her father died when she was only eleven, leaving his family in debt. Fortunately, he was a keen fossil hunter and had passed on his skills to his family. The family was short of money but were able to survive by collecting and selling fossils. The fossils became more than just a means of survival for Mary. She studied, analyzed, and documented her discoveries, moving out of the realm of being only a collector and into the realm of paleontology.

Mary's fossils were sent to scientists, museums, and private collections, but often the fact that she had discovered a particular fossil was omitted or forgotten. In addition, scientists sometimes presented her discoveries to an audience without acknowledging that Mary had found and prepared the fossil.

Life was often financially difficult for Mary, but there were times when she was better off than others. In 1817 a wealthy fossil collector became a supporter of the Anning family. He sold his own fossil collection and gave the proceeds to the family. He was also careful to attribute their discoveries to them. This helped to publicize the family's activities as well as to aid them financially, at least for a while. As her life progressed, Mary's fortunes rose when a commercially desirable fossil had recently been found and fell when there was a prolonged gap between significant discoveries.

An ichthyosaur skeleton

Photo by Adam Dingley

CC BY-SA 3.0 License

Later Life

Mary eventually become recognized as a dedicated and careful fossil collector by scientists. In 1838 she received an annuity from the British Association for the Advancement of Science. In addition, she received a stipend from the Geological Society of London. These regular sums of money were probably very helpful for her. Unfortunately, Mary died from breast cancer in 1847 while she was still relatively young. The Quarterly Journal of the Geological Society published her obituary. The society didn't admit women until 1904.

Lyme Regis

Lyme Regis is a town on the southern coast of England. Its coastline forms part of a World Heritage Site. The cliffs and the beach beside them are a rich source of fossils. Even 170 years after Mary's death, people successfully hunt for fossils in the area. The cliffs are eroding rapidly, a process that continually adds new fossils to the beach. It also means that visitors need to be careful that they don't get hit by falling pieces of rock.

There are two versions of the painting of Mary Anning shown above. The one that I've included is reportedly the earlier one. The second version is similar but not identical and is said to be a copy of the first one. It's important to note that using a pick to hammer the unstable cliffs as Mary apparently did at Lyme Regis is dangerous. She nearly died in a landslide that killed her dog, though I don't know the immediate cause of this event.

A cast of a plesiosaur

Photo by Adrian Pingstone

Public domain license

Mary's Discoveries

The Jurassic period lasted from approximately 199.6 million years ago (mya) to 145.6 mya. Mary found many fossils from this time period. The first major discovery happened when she was only a child. When she was twelve, her brother Joseph found the skull of an ichthyosaur. A few months later Mary found the rest of the animal. This was the first complete ichthyosaur skeleton to be discovered. Ichthyosaurs were marine reptiles that had a fish-shaped body.

Mary was also the first person to discover a complete (or almost complete) plesiosaur skeleton. Plesiosaurs were marine reptiles with a long neck, a small head, and flippers. Another important discovery was a skeleton of Pterodactylus macronyx, which is now known as Dimorphodon. The animal was a type of pterosaur. Pterosaurs were flying reptiles with wings. Mary also found other interesting and often significant items, including fossilized ink sacs that resembled those of today's octopuses and squid.

The discovery of coprolites demonstrates how Mary's work helped scientists. She noticed that coprolites—or bezoar stones as they were known then—were often found in the abdominal region of ichthyosaur specimens. She also noticed that the stones contained fossilized bones of fish and other creatures. Based on these facts, a geologist named William Buckland proposed (correctly) that the stones were fossilized feces.

The interest in Mary Anning's work has been revived in recent times, and rightly so, I think. Her discoveries were important in their own right and also enabled scientists to discover more about life in the Jurassic period.

References 

Mary Anning biography from the San Diego Supercomputer Center website (which includes biographies of female scientists)

The Three Mary Annings from the University of Waterloo

Information from UCMP (University of California Museum of Paleontology)

A Biodegradable Sanitary Pad Based on a Seaweed Ingredient

The disposal of sanitary pads (or napkins) and related products creates a big environmental problem that needs to be solved. Women need some kind of protection during menstruation. A sanitary pad is a popular choice, but unfortunately most brands are not biodegradable and collect in the environment as waste after use. Researchers at the University of Utah have created a new pad which they say is effective, comfortable, and safe for the environment. It relies on a substance from brown algae or brown seaweed for its ability to absorb liquids.

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Brown Algae in Norway
Photo by Ximonic, CC BY-SA 4.0

Each year, nearly 20 billion sanitary pads, tampons and applicators are dumped into North American landfills. (Quotation Source: University of Utah News Release)

Biodegradable Products

Biodegradable products would seem to be a solution for the environmental problems cause by discarded sanitary pads. There are problems with at least some of these products, however. Complaints include the fact that they don't absorb enough fluid, don't fit properly, or are uncomfortable. The researchers at the University of Utah have created what they believe is a "better sustainable sanitary pad".

                            Candida albicans growing on agar in a yeast form
                                            and in a filamentous form.
                                       Photo by Garnhami, CC BY-SA 4.0

The SHERO Pad 

The University of Utah researchers say that their product is thinner than other biodegradable pads. It's known as a SHERO pad and is composed of four layers. The outer layer is made of the same material as tea bags. Below this is a cotton layer that helps to absorb liquid. Next is a highly absorbent substance called agarose, which is obtained from brown algae. The last layer of the pad is made from corn and serves as a moisture barrier.

Agarose is a polymer and a polysaccharide that is obtained from the agar in seaweed. Polymers are long molecules made of repeating subunits. In a polysaccharide, the subunits are sugar molecules. In biology, the word "sugar" refers to a family of chemicals instead of just sucrose, or table sugar. 

Agar (sometimes known as agar-agar) is a substance obtained from certain algae that forms a gel when added to water. It's often supplied to the public in a dried form as a powder or flakes. When water is added to the dried agar, the gel is produced. Agar is used as a vegetarian substitute for gelatin. It's also a common substrate for bacteria in the petri dishes used in biology and medical labs. Agarose is one of the chemicals in agar that is responsible for its ability to form gels.

The inventors of the new pad say that once discarded it will break down within forty-five days to six months. The difference in time presumably depends on the environmental conditions. The pads are said to be completely degradable, unlike some pads that claim to be so. 

The average woman will menstruate for about four decades and use an estimated 16,800 sanitary pads or tampons in the process — that’s 250 to 300 pounds of waste. In the U.S. alone, some 12 billion pads and 7 billion tampons are disposed of annually. (Quotation Source: grist.org)

Creating and Selling the Pad

The SHERO pad was created for women in developing countries, especially those in Guatemala. In fact, its creation was stimulated by a request from a Guatemalan advocacy group for women and children. Safe drinking water and public sanitation are sometimes unavailable in the country, especially in rural areas. Discarded sanitary napkins add to the pollution burden.

The researchers have launched a startup company and hope to have the product available in Guatemala and for sale in the United States within a year. They also say that it may be possible for communities in some parts of Guatemala to produce the pads themselves from local materials, as long as they have a grinding stone and a press. It will be interesting to see how practical this process is. It will also be interesting to see if the pads are as effective and as biodegradable as the researchers believe.

Reference

University of Utah News Report 

Maintaining and Controlling the Blood-Brain Barrier

The blood-brain barrier, or BBB, is a layer of cells that stops specific substances in the blood from entering brain tissue. This is an essential job, since the brain controls our body and keeps us alive. It must be protected from harmful materials. Sometimes, though, researchers are frustrated when a medication that could help a neurological problem is unable to enter the brain due to the presence of the BBB. Understanding how the barrier works and learning how to safely modify its actions are important endeavours.

Salmon contains DHA, which helps to keep the
blood-brain barrier strong. (Public domain photo)

The Blood-Brain Barrier

The blood-brain barrier consists of tightly packed endothelial cells that line the capillaries around and inside the brain. The membranes of adjacent cells in the barrier are joined by so-called "tight junctions", which block the passage of virtually all materials. Materials are forced to travel through the cells in the barrier in order to enter the brain tissue. This enables the cells to have some control over the passage of the materials.

The blood-brain barrier does allow some substances to enter the brain, including nutrients such as oxygen, glucose, amino acids, and water. Brain cells need these chemicals in order to survive. Lipid-soluble substances can also pass through the barrier. Bacteria, other pathogens, and substances that could act as neurotoxins are blocked, however.

Role of an Omega-3 Fatty Acid

Researchers at the Harvard Medical School have recently explored the role of a specific type of omega-3 fatty acid in the blood-brain barrier. Their research has shown that the chemical is important for maintaining the integrity of the BBB and enabling it to block the movement of substances. The fatty acid in question is docosahexaenoic acid, or DHA. It's found in oily fish and certain algae. The researchers have found that the endothelial cells in brain capillaries have two to five times more DHA than the ones in lung capillaries.

The blood-brain barrier protects the brain. 

(Public domain photo)

A Transporter Protein

The endothelial cells lining blood vessels around and in the brain contain a protein known as Mfsd2a. This protein transports lipids, or fatty materials, including ones containing DHA. It moves the lipids with DHA into the membrane of the endothelial cells, which keeps the BBB strong. 

The protein also inhibits transcytosis in the cells. This is a process in which a substance enters a cell via vesicle formation (endocytosis), moves to the opposite membrane of the cell, and then leaves the cell in another vesicle (exocytosis). A vesicle is a small, membranous sac. The cell has other ways to transport materials, but some substances must move through the cell by transcytosis.

The Harvard researchers have bred mice with a mutated form of the gene that codes for the Mfsd2a protein. The mutation in the gene causes an altered protein to be produced. The altered protein can no longer transport lipids containing DHA. As a result, the mice develop "leaky" blood-brain barriers which allow the passage of materials that are normally blocked. In addition, the formation of the vesicles needed in transcytosis is no longer inhibited, which also increases the passage of materials. The same results occur when mice lack the Mfsd2a protein entirely.

Human Applications

Assuming that the process discovered in mice works the same way in humans, it might be useful to us. If we could temporarily block the activity of the Mfsd2a protein, we might be able to send medications for treating Alzheimer's disease, brain cancer, strokes, and other conditions into the brain. The problem is that we need to do this without allowing harmful substances into the brain, or at least while limiting their entry. Hopefully we will discover how to do this as we learn more about how the blood-brain barrier works.

Research Reference

Role of omega-3 fatty acids in keeping the blood-brain barrier closed

Wax Worms and Moths: Caterpillars That Digest Plastic Bags

A preserved greater wax moth
Photo by Sarefo, CC BY 3.0 License

A Caterpillar That Eats Plastic

The wax worm (or waxworm) is a caterpillar that feeds on the wax in beehives, among other things. Scientists in Spain have just made what could be a very useful discovery about the caterpillar's abilities. It can eat and digest the polyethylene that is used to make plastic bags. This means that it might be useful in reducing plastic pollution. Plastic waste normally breaks down very slowly and is harmful to many organisms, especially in the ocean where much of the waste collects.

The wax worm that's being investigated by the researchers is the larval form of an insect known as the greater wax moth, or Galleria mellonella. The discovery that the caterpillars can digest polyethylene was made by accident. The insects were being stored in plastic bags. The researchers noticed that multiple holes were appearing in the bags and realized that the caterpillars were actually eating the plastic. They later discovered that the insects change the polyethylene into ethylene glycol.

The Greater Wax Moth

The greater wax moth is native to Europe and Asia but has been introduced to other areas. It invades beehives as well as stored honeycombs from the hives. A honeycomb is made of wax produced by the bees' wax glands and contains hexagonal chambers that are used to store honey and pollen. The female wax moth lays several hundred eggs inside a chamber or in cracks in a hive. 

According to agricultural experts, wax moths are rarely successful in healthy beehives. They can be a big problem in unhealthy hives where they are able to reach the honeycomb without resistance from bees, however. They can also be a problem for honeycombs taken out of a hive.

The wax moth's eggs hatch into larvae, or caterpillars. The larvae are white, brown, or grey in colour. They form tunnels in the honeycomb by chewing through the wax. They line these tunnels with a web of silk.

Eventually a larva surrounds itself by a silken cocoon and becomes a pupa. Inside the pupa, the larva undergoes metamorphosis and becomes an adult. The moth leaves the hive and breeds, enabling the life cycle to begin again. 

Digesting and Recycling Plastic 

The plastic bags used to package store goods for consumers are usually made of polyethylene. The ability of wax worms to digest the polyethylene could be very helpful. Researchers don't yet know whether the caterpillar is digesting the plastic with enzymes that it produces or whether bacteria in its gut are doing the digesting, as happens in Plodia interpunctella. This is another moth whose larvae eat wax from honeycomb. It's classified in the same family as the greater wax worm and is commonly known as the Indian mealmoth. Other researchers have discovered that the larva of a particular beetle can digest plastic. The lesser wax worm eats beeswax, but as far as I know researchers haven't explored whether it can digest polyethylene.

Reducing the use of plastic bags or at least recycling them is an important process right now. Some stores are charging for plastic bags to reduce their use. Although curbside recycling programs generally don't accept the bags, some places do. A supermarket near my home has a collection bin for recycling plastic bags, for example.

In the near future, we might be recruiting specific insects and bacteria to break up our plastic. This almost certainly won't reduce the need to reduce the creation of plastic pollution, but it could be a great aid in removing the waste that has been or is created.

References

A new solution for plastic waste?
The greater wax moth