The Gram-Negative-Eating-Gram-Negative Bacteria: A Necessary Inhabitant for Your Gut Microbiome!

It can be surprising exactly how much of you isn’t really made up of “you.” For example, your gut is the home of trillions of bacteria, some of which benefit you, others that are just there to exist [1]. These bacteria are kept in relatively constant numbers, so when the inhabitants of the gut are changed, it can lead to the development of diseases. Therefore, it is important to understand how exactly bacteria in our body interact with the microbiota.

Arrow points to the gram-negative bacteria Bdellovibrio bacteriovorus, a bacteria that preys on other gram-negative bacteria, and it is a possible inhabitant of the human gut [2].

Recently the gram-negative bacteria Bdellovibrio bacteriovorus, which acts as a predator in microbiomes by eating other gram-negative bacteria, has been found in terrestrial and aquatic ecosystems as well as animal intestines. It is hypothesized by Valerio Iebba (et al. 2013) that it is also present in the human gut. To find out, a PCR test, which is the amplification of a single part of the DNA strand, was carried out on intestinal and faecal biopsies in order to see if there was any B. Bacteriovorus in the gut. Patients ranged from healthy to suffering from Inflammatory Bowell Diseases, Celiac disease, and Cystic Fibrosis. Results show that DNA was only present and abundant in the healthy individuals. Furthermore, it reveals that populations exist in higher concentrations in the duodenum, or the section of the intestines closest to the stomach, and that concentrations gradually went down closer to the rectum. As a result, Iebba (et al. 2013) believe that B. bacteriovorus plays a big role in controlling the gut microbiome, and prevents other bacteria from running rampant. Further studies wish to test B. bacteriovorus as a possible candidate for a therapeutic strategy to restore balance to the intestinal ecosystem

Work Cited
1. Iebba V, Santangelo F, Totino V, Nicoletti M, Gagliardi A, De Biase RV, Cucchiara S, Nencioni L, Conte MP, Schippa S, 2013, Higher Prevalence and Abundance of Bdellovibrio bacteriovorus in the Human Gut of Healthy Subjects, PLoS One 8(4):e61608.

2. http://farm3.staticflickr.com/2717/4187842186_721dcd0d36_o.jpg

Feast Your Eyes on This: Loa Loa, the African Eye Worm

This week, we are going to deviate from the usual format. Instead of taking a quick look at a specific article, we will be looking at the life cycle and taxonomy of a particular organism. Without further ado, here he is:

The arrow points to Loa Loa, the organism we will be looking at today [1].

Meet the parasitic nematode Loa Loa, otherwise known as the “African Eye Worm.” Loa Loa is found in 11 countries West Africa, and infects 12 million people as of today [2]. While it generally wanders around underneath the skin of humans, it is most easily seen when crossing the eyelid, hence the name. It is also one of three worms that cause the condition filariasis, or swelling of the skin caused by the movement of Loa Loa [2]. 

Loa Loa belongs to the phylum Nematoda, or roundworms as they are commonly called. About 28,000 species have been identified, and over half of them are parasitic. This means that it lives inside another organism at the expense of the host’s comfort and health. Loa loa actually has multiple hosts, depending on what part of its life cycle it is in. Its definitive host, or the host in which it reproduces, is the human, while its reservoir host, or the host in which it develops and grows, is the deer fly [2].

The life cycle of the Loa Loa [2]

When an infected deer fly bites a human, it transfers Loa Loa larvae into the person. It then takes up residence in the subcutaneous tissue, or the tissue of fat cells directly underneath the skin until it is sexually mature in one year. Adults measure anywhere between 30-34 mm long and 0.35-0.42 mm thick, and they can live for 17 years [2]. Once they sexually reproduce, the females release microfilaria, which are very early stages of the Loa Loa. These microfilaria are taken up by a biting, uninfected deer fly, where the microfilaria travel to the gut, and eventually the thoracic muscles of the fly [2]. After two weeks, the microfilaria develop into larvae, and move to the proboscis of the fly, ready to be transferred to a human upon a bite.

The Deer Fly, the reservoir host of the Loa Loa [3]

The most common treatment to remove this parasite is DEC, which is a drug that kills the microfilaria [2]. Alternatively, Ivermectin can be used to target the adults in the body. However, both treatments can have some extreme side effects, including death. If a person has high quantities of microfilaria, treatment with DEC is usually not advised because it can cause brain diseases such as encephalopathy [2]. 

So next time you travel to West Africa, be wary of deer flies, for if an infected one bites you, you could be the home of this eye-popping parasite!

Works Cited

1. http://www.stanford.edu/class/humbio103/
ParaSites2006/Loiasis/Index.html

2. http://www.parasitesinhumans.org/
loa-loa-eye-worm.html

3. http://www.stanford.edu/class/humbio103/
ParaSites2004/Loiasis/adult%20deer%20fly.jpg

 

The origins of Mixed Chimerism: Closer than you might think!

Hematopoietic stem cell transplantation (HSCT) is a dangerous procedure reserved for patients with life-threatening cancer such as leukemia or multiple myeloma [1]. It is the process of adding stem cells which give rise to blood cells to the blood after damaging the immune system using chemotherapy or radiation. When this treatment is successful, it results in a phenomenon called Donor Chimerism, or a state in which the body accepts and incorporates the stem cell from the donor into the body [2]. However, some patients have developed an intermediate stage where some original stem cells from the patient remain in the body, yet the donor stem cells are also incorporated. This state is called Mixed Chimerism, and it results when 5-95% of the original stem cells remain [3].

A table of what these Hematopoietic stem cells can become. Since there is such a wide variety of blood cells that it can form, it is important to have a healthy supply of them [4].

In this week’s article, Arwen Stikvoot’s team compared patients with full Donor Chimerism with those that showed mixed chimerism over a period of 9.5 years in order to determine what caused mixed chimerism. They compared a number of factors including age, genders of donors and recipients, fraction of body irradiated, and relation of donor and recipient. While their sample size was rather small, they concluded that the most significant factor of mixed chimerism is if the donor and recipient were siblings. This would make sense since sibling cells would share the most similarities between any two organismal cells. As such, the immune system is not as likely to attack and kill those cells being donated to the recipient. This also implies that mixed chimerism is not necessarily correlated with a worse prediction of outcome than donor chimerism if it is true that it is simply a side effect of a sibling donor. While this sounds like good news, it’s important to keep in mind that this study had a low sample size, and to confirm that these findings are correct would require more patients to study.

Works Cited

1. Ringden, O., Remberger, M., Svahn B.M., Barkholt, L., Mattsson, J., Aschan, J., Le Blanc, K., Gustafsson, B., Hassan, Z., Omazic, B., Svenberg, P., Solders, G., Von Dobeln, U., Winiarski, J., Ljungman, P., Malm, G., (2006), “Allogeneic hematopoietic stem cell transplantation for inherited disorders: experience in a single center” Transplantation 8: pp. 718–725

2. Stikvoort, A., Gertow, J., Sundin, M., Remberger, M., Mattsson, J., Uhlin, M., 2013, “Chimerism Patterns of Long-Term Stable Mixed Chimeras Post hematopoietic Stem Cell Transplantation in Patients with Nonmalignant Diseases: Follow-up of Long-term Stable Mixed Chimerism Patients.” Biol. Blood Marrow Transplant, Available online 24 February 2013, ISSN 1083-8791, 10.1016/j.bbmt.2013.02.015.

3. Baron, F., Sandmaier, B.M., 2006, “Chimerism and outcomes after allogeneic hematopoietic cell transplantation following nonmyeloablative conditioning”, Leukemia, 20: pp. 1690–1700.

4. http://en.wikipedia.org/wiki/File:Blood_cells_differentiation_chart.jpg

Arbusucular Mycorrhiza: Protecting Your Soil Carbon as Temperatures Rise!

Last week, we went to China in order to take a look at the diversity of the lichen Usnea longissima, and how it can have multiple photosynthetic partners. This week, we return to China in order to look at another fungus. Arbuscular mycorrhiza (AM) is a type of fungus that grows inside the roots of plants. It’s function is to help the plant absorb nutrients that the plant needs such as water and phosphorous, and in exchange the plant provides the fungus with 4-20% of the sugars it makes through photosynthesis (Hu, et al. 2013).

 

A microscope image of arbuscular mycorrhizae in flax root cells. The black dots indicate where the fungus in imbedded into the root cells. Original Source.

It was previously thought that higher temperatures and warmer environments would increase the amount of fungus present outside of the root system, which would increase the amount of organic matter in the soil compared to colder environments. However, studies done by Rillig (et al. 2002) suggest that this is not the case, and that increased temperatures, despite increasing the growth of fungus, actually resulted in lower levels of organic matter in the soil. This suggests that there are other environmental factors at work here. To find out, Rillig joins forces with Yajun Hu, who worked on the diversity of lichens in the last article, in order to determine what exactly these environmental factors are. To do this, they went to the arid grasslands of northern China and compared the abundance of AN to various soil and climate conditions.

 

The sites in China where samples of environmental conditions and growth of AM were measured. Original Source

What they discovered in this article was that AM growth and density was correlated with increased temperatures, soil clay content, and pH. At the same time, this growth was negatively correlated with nitrogen and carbon availability in the soil. These findings suggest that AM could play a key role in reducing the losses of soil carbon in infertile soil under high temperature.

 

Works Cited

Hu, Y., Rillig, C.R., Xiang, D., Hao, Z., Chen, B., (2013) Changes of AM Fungal Abundance along Environmental Gradients in the Arid and Semi-Arid Grasslands of Northern China. PLoS One 8(2).

Rillig MC, Wright SF, Shaw MR, Field CB (2002) Artificial climate warming positively affects arbuscular mycorrhizae but decreases soil aggregate water stability in an annual grassland. Oikos 97: 52–58.

Insights on the Diversity of the Chinese Lichen Usnea longissima.

If you ever find yourself lost in the woods one day, and you need to find some easily accessible food, you may want to consider trying the strange green flakes that grow on the sides of trees and rocks. These structures may not look appetizing, but they have been important food sources in northern Europe, America, and China.  These are lichens, and they are made up of a fungus called an Ascomycete, and a photosynthesizing bacteria or algae working together in a symbiotic relationship. The fungus surrounds its photosynthetic partner and provides it with minerals and water in exchange for nutrients which its partner produces.

(A species of the lichen Usnea longissima, courtesy of http://2.bp.blogspot.com/_Ie_lbIIVz7o/TFmFTVGpcoI/AAAAAAAAEyY
/x4Zkqx2WDHY/s1600/Usnea+subfloridana.jpg)

The above lichen, Usnea longissima, is particularly popular in China since it is used in the preparation of traditional foods and medicine. While there have been many studies in terms of its morphological characteristics, pharmaceutical use, and distribution, very little has been done in the study of the actual symbionts. This week, we take a quick look at an article by Yuzhe He and Zhiguo Zhang (2012), which analyzes the genetics of the organisms involved in this particular type of lichen. After breaking open the lichen and separating the symbionts, He and Zhang extracted the DNA of each symbiont and amplified it using a technique called Polymerase Chain Reaction (PCR). The amplified DNA was then analyzed and compared to other species of fungus and bacteria. 

He and Zhang found out that there are many different types of fungi including Usnea, Alectoria, and Punctellia. However, the interesting thing was that these fungi formed a symbiosis with two different algae, Poteriochromanas and Trebouxia. This is rather strange since lichens usually only have algal symbiont per species, and those that have multiple algal symbionts do not have cross-phyla symbionts. This is the first occurrence of a lichen being formed from two different phyla, and it is a rather exciting new insight in the diversity of the microbial inhabitants of this lichen.

He, Y., Zhang, Z., 2012, Diversity of Organism in Usnea longissima lichen, African Journal of Microbilogy, 6(22): 4797-4804