Newly-Discovered Soil Bacterium May Fight Dangerous Microbes

Antibiotic resistance in bacteria is a serious problem at the moment. As microbes become resistant to the effects of the antibiotics that once killed them, some dangerous organisms are becoming much more difficult to destroy. If this process continues, there could be major and even tragic consequences for our health. Researchers have discovered a few new species or strains of bacteria in soil that offer some hope in the form of the chemicals that they produce. A multinational team at Swansea University in Wales has found a new species of bacterium in Irish soil that destroys some potentially very harmful bacteria in lab equipment.

Streptomyces sp.

Photo credit: CDC Public Health Image Library, public domain license

Special Soil

The Irish soil sample was obtained from an area known as the Boho Highlands, which is located in Fermanagh in Northern Ireland. The region contains alkaline soil. It's interesting that the soil has a reputation for healing abilities. In the past, people used to wrap some of the earth in cloth and apply the bundle to injured areas. The area was once inhabited by druids. It's important to note that harmful as well as helpful organisms live in soil, so applying soil to injuries could be dangerous. Certain components of the soil might be helpful, however.

In general, scientists have paid little attention to folk medicine, relying on experimental discoveries in the lab instead. Some scientists are now exploring materials and substances  traditionally believed to have medicinal benefits by different cultures, a subject known as ethnopharmacology. One of the scientists involved in the Boho Highlands research once lived in the area and was aware of the soil's reputation. Exploring unusual sources of help (according to current medical beliefs) seems like a good idea in our fight against harmful bacteria.

A New Version of Streptomyces

The Streptomyces genus of bacteria contains many species, some of which have proved to be very valuable for us. A large number of antibiotics have come from various members of the genus. One of the earliest was streptomycin. The bacteria exist as filaments and produce chains of spores, as shown in the photo above. Though their morphology may remind people of fungi, they are true bacteria. They are chiefly found in the soil and amongst decaying plants. They are known for the "earthy" odour that they produce. The smell is caused by a chemical called geosmin that is released when the bacteria die. 

The researchers who examined the Irish soil were looking for a new species or strain of Streptomyces, and they found one. The researchers have named the organism Streptomyces sp. myrophorea. They say that its closest known relative has “57% of genome relatedness.” The species name is not written in italics because at the moment it hasn’t been officially recognized as a new species. The bacterium releases a pleasant scent resembling that of oil of wintergreen. Its species name comes from the Greek myro, which means fragrance, and phorea, which means carrier.

The new bacterium inhibited the growth of four out of six major multi-drug resistant pathogens (microbes that cause disease), including:

·        vancomycin-resistant Enterococcus faecium

·        methicillin-resistant Staphylococcus aureus, or MRSA

·        Klebsiella pneumoniae

·        carbapenum-resistant Acinetobacter baumannii

The major drug-resistant pathogens are so important that a special collective name is used to refer to them. The ESKAPE pathogens are Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and species of Enterobacter.

Gram Positive and Negative Bacteria

The researchers found that the newly-discovered soil bacterium inhibited both gram-positive and gram-negative bacteria. This is important because gram-negative bacteria are usually harder to kill. The scientists don’t know the identity of the bacterial chemical that is harming the pathogens. They are investigating this question, however.

Gram-positive bacteria (such as Streptomyces) are covered by a cell membrane, which is in turn covered by a cell wall. Gram-negative ones have a inner cell membrane and a cell wall, but they also have another membrane outside of the wall. Unfortunately, the structure of their cell covering protects them from many antibiotics.

Gram negative and positive bacteria were given their designation due to their different behaviours during a staining process known as the Gram stain test. Gram-positive bacteria appear pink after the process and gram-negative bacteria look violet. The different colours are due to the different nature of the layers around the cell. The staining process is named after Hans Christian Gram, who created it in 1884.

Hopeful Research

The research is interesting and hopeful. It was carried out in lab equipment, however, not in a living organism. Results inside the body are sometimes different from those in laboratory containers. Nevertheless, investigators are finding some interesting soil bacteria that are potentially useful in the fight against antibiotics. The new species of Streptomyces may be one of them.

The researchers involved in the Boho highlands research say that they have found other bacteria in the soil that make antibiotics. They hope that these may fight additional species of pathogens.

References

Bacteria in Irish soil halts growth of superbugs from the Eurekalert news service

Gram staining information from Carleton College

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).