How do small things make a big difference? June 2014Lesson 5: How do microbes interact with humans?

Group 2: Our Skin Microbiome

Our skin is home to a wide variety of microbes including bacteria, archaea, fungi, viruses and mites. Before advanced genome sequencing technology, scientists took samples of different areas of the skin and cultured these in the laboratory. However, certain bacteria, such as staphylococci, will outgrow other types of microbes in laboratory settings (Figure 1). Scientists could not observe the other types of microbes living on the skin because staphylococci grew exceedingly better than the other microbes on the culture plates.

Thanks to advances in genome sequencing, scientists have discovered the specific species of microbes that inhabit the skin. Scientists can now take a sample of microbes from the skin, isolate the ribosomal RNA, amplify it to make millions of copies, and then use computer aided technology to sequence the different types of ribosomal RNA present. This information helps scientists identify the wide variety of specific microbes present on the skin.

Scientists still have many questions about the beneficial roles of microbes that live on the skin. Currently, skin microbes are referred to as commensals, with the microbes benefiting from living on the skin and the human host not receiving beneficial nor harmful effects. Research has shown that Staphylococcus epidermidis is present in overwhelmingly great quantities on the skin of healthy people. S. epidermidis, then, must somehow out-compete other bacteria for space and resources, providing a protective “shield” from potentially harmful microbes. The question then becomes, are skin microbes true commensals or do they offer some beneficial effect for the human host?

Scientists are also currently researching how the different types of microbes fill their niches in the various ecological communities present on the skin (Grice et al., 2009). Perhaps these large communities provide resources for each other, much like M. smithii uses Bacteroides’ hydrogen products in its metabolism of food. As Figure 2 shows, each area of the skin has a different environment (i.e. oily, moist, dry, or other), which promotes the growth of certain types of microbes over others. While this figure shows major advancements in the characterization of the different skin microbes, scientists want to know how this information can help to develop new treatments and therapies for skin infections. By understanding which types of microbes a healthy human’s skin should have, scientists can determine how to protect the skin microbiome while combating the invading microbes.

Figure 1: Genome sequencing of the microbes present on the skinImage taken from: Kong, 2011

Figure 1: Genome sequencing of the microbes present on the skinImage taken from: Kong, 2011

Figure 1: Genome sequencing of the microbes present on the skinImage taken from: Kong, 2011

How do small things make a big difference? June 2014Lesson 5: How do microbes interact with humans?

References:

Grice, E.A., Kong, H.H., Conlan, S., Deming, C.B., Davis, J., Young, A.C.,…Segre, J.A. (2009). Topographical and temporal diversity of the human skin microbiome. Science, 324(5931), 1190-1192.

Grice, E.A. & Segre, J.A. (2011). The skin microbiome. Nature Reviews Microbiology, 9, 244-253.

Kong, H.H. (2011). Skin microbiome: Genomics-based insights into the diversity and role of skinmicrobes. Trends in Molecular Medicine. 17(6), 320-328.

Leja, D. (N/A). Skin microbiome [Graphic]. Bethesda, MD; National Human Genome Research Institute. Retrieved January 31, 2014, from http://www.genome.gov/dmd/img.cfm?node=Photos/Graphics&id=85320

Figure 2: Our skin is covered in microbes but not all areas have the same types or distribution of microbes. This figure shows what scientists found when they sampled 20 different skin sites. Each skin site is written in a different color to indicate the type of environment: oily (blue), moist (green), and dry (red). Each pie chart shows the relative abundance of different bacterial types found at that skin site. The distributions of microbes depend a great deal on the different microenvironments of the skin sites. (Grice & Segre, 2011; Kong, 2011)Image from: Darryl Leja, NHGRI

How do small things make a big difference? June 2014Lesson 5: How do microbes interact with humans?

Expert Group Student Sheet

Group 2: Our skin microbiome

1. According to the reading, how have genome sequencing technologies helped researchers identify the different types of microbes on the skin?

1b. Can you think of any problems that might have been associated with the use of the old methods?

2. How do the different environments of the skin contribute to the types of microbes found in these specific areas?

How do small things make a big difference? June 2014Lesson 5: How do microbes interact with humans?

3. Why are skin microbes considered commensal organisms?

3b. Is it possible that skin microbes are mutualistic organisms, meaning they provide benefits to another organism as well as themselves, and not commensal? How do you know this?

4. Currently, what do scientists know about the niches, or specific ecological roles, that the skin microbes fill in the skin ecosystem?

4b. How do they hope more research in this area will be beneficial to human health?