Bacteria and the body

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Welcome to the Bacteria-on-your-skin learning project.

This article over at noted that there are many more bacteria growing on the skin of healthy individuals than we previously knew. Included in the article are distributions of different bacteria on people's skin.

Estimating values from the article, it appears, on average: 50% of bacteria are "actinobacteria" then with a wide varibability between subjects: 25% of bacteria are Firmicutes and another 25% are proteobacteria. On one subject, 24% of his or her bacteria was "other".

What are these different types of bacteria that probably grow on skin then?


According to Wikipedia:Firmicutes:

The Firmicutes are a division of bacteria, most of which have Gram-positive cell wall structure. A few, the Mollicutes or mycoplasmas, lack cell walls altogether and so do not respond to Gram staining, but still lack the second membrane found in other Gram-negative forms. Others, such as Megasphaera, Pectinatus, Selenomonas, and Zymophilus have a porous pseudo-outer-membrane that causes them to stain Gram-negative. Originally the Firmicutes were taken to include all Gram-positive bacteria, but more recently they tend to be restricted to a core group of related forms, called the low G+C group in contrast to the Actinobacteria. They have round cells, called cocci (singular coccus), or rod-shaped forms.

Many Firmicutes produce endospores, which are resistant to desiccation and can survive extreme conditions. They are found in various environments, and some notable pathogens. Those in one family, the heliobacteria, produce energy through photosynthesis.

The group is typically divided into the Clostridia, which are anaerobic, the Bacilli, which are obligate or facultative aerobes, and the Mollicutes. On molecular trees the first two groups show up as paraphyletic or polyphyletic, as do their main genera, Clostridium and Bacillus. It is likely these groups will undergo revision.

Firmicutes play an important role in beer, wine, and cider spoilage.

Researcher Jeffrey Gordon and his colleagues found that obese humans and mice had a lower percentage of a family of bacteria called Bacteroidetes and more Firmicutes. But they are not sure if Firmicutes cause obesity or if people who are obese grow more of that type of bacteria.

While there are currently more than 274 genera within the Firmicutes phylum, Notable genera of Firmicutes include... Wow. Not having advanced training in biology, that is way over my head. Let's break it down...

Gram-positive bacteria[edit]

Gram-positive bacteria are classified as bacteria that retain a crystal violet dye during the Gram stain process. Gram-positive bacteria will appear blue or violet under a microscope, whereas Gram-negative bacteria will appear red or pink. The difference in classification is largely based on a difference in the bacteria's cell wall structure. Okay, so what?

In the original bacterial phyla, the Gram-positive forms made up the phylum Firmicutes, the name now used for the largest group. It includes many well-known genera such as Bacillus, Listeria, Staphylococcus, Streptococcus, Enterococcus, and Clostridium. It has also been expanded to include the Mollicutes, bacteria like Mycoplasma that lack cell walls and so cannot be stained by Gram, but are derived from such forms.

The actinobacteria are another major group of Gram-positive bacteria; they and the Firmicutes are referred to as the high and low G+C groups based on the guanine and cytosine content of their DNA. If the second membrane is a derived condition, the two may have been basal among the bacteria; otherwise they are probably a relatively recent monophyletic group. They have been considered as possible ancestors for the archaeans and eukaryotes, both because they are unusual in lacking the second membrane and because of various biochemical similarities such as the presence of sterols.

The Deinococcus-Thermus bacteria also have Gram-positive stains, although they are structurally similar to Gram-negative bacteria.

Both Gram-positive and Gram-negative bacteria may have a membrane called an S-layer. In Gram-negative bacteria, the S-layer is directly attached to the outer membrane. In Gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Unique to Gram-positive bacteria is the presence of teichoic acids in the cell wall. Some particular teichoic acids, lipoteichoic acids, have a lipid component and can assist in anchoring peptidoglycan, as the lipid component is embedded in the membrane.

That still doesn't tell me a whole lot of useful information. That makes me wonder if learning about Firmicutes could give me any knowledge that can enhance my health, happiness or wellbeing.


An endospore is a dormant, tough, non-reproductive structure produced by a small number of bacteria from the Firmicute family. The primary function of most endospores is to ensure the survival of a bacterium through periods of environmental stress. They are therefore resistant to ultraviolet and gamma radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants. Endospores are commonly found in soil and water, where they may survive for long periods of time. Some bacteria produce exospores or cysts instead.

So this is what about 25% of the bacteria on my skin produce. I am morbidly fascinated.


50% of the bacteria on my skin might be actinobacteria... From wikipedia:Actinobacteria

The Actinobacteria or Actinomycetes are a group of Gram-positive bacteria. Most are found in the soil, and they include some of the most common soil life, playing an important role in decomposition of organic materials, such as cellulose and chitin. This replenishes the supply of nutrients in the soil and is an important part of humus formation. Other Actinobacteria inhabit plants and animals, including a few pathogens, such as Mycobacterium.

Some Actinobacteria form branching filaments, which somewhat resemble the mycelia of the unrelated fungi, among which they were originally classified under the older name Actinomycetes. Most members are aerobic, but a few, such as Actinomyces israelii, can grow under anaerobic conditions. Unlike the Firmicutes, the other main group of Gram-positive bacteria, they have DNA with a high guanine and cytosine concentration.

Interesting things to note: some produce spores, and some decompose organic material.


Perhaps 25% of the bacteria on our skin may be proteobacteria.

Wikipedia:Proteobacteria says: The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera. Others are free-living, and include many of the bacteria responsible for nitrogen fixation. The group is defined primarily in terms of ribosomal RNA (rRNA) sequences, and is named for the Greek god Proteus (also the name of a bacterial genus within the Proteobacteria), who could change his shape, because of the great diversity of forms found in it.

All Proteobacteria are Gram-negative, with an outer membrane mainly composed of lipopolysaccharides. Many move about using flagella, but some are non-motile or rely on bacterial gliding. The last include the myxobacteria, a unique group of bacteria that can aggregate to form multicellular fruiting bodies. There is also a wide variety in the types of metabolism. Most members are facultatively or obligately anaerobic and heterotrophic, but there are numerous exceptions. A variety of genera, which are not closely related, convert energy from light through photosynthesis. These are called purple bacteria, referring to their mostly reddish pigmentation.


From Wikipedia:Gram-negative

Gram-negative bacteria are those that do not retain crystal violet dye in the Gram staining protocol. Gram-positive bacteria will retain the dark blue dye after an alcohol wash, whereas Gram-negative bacteria do not. In a Gram stain test, a counterstain is added after the crystal violet, which colors all Gram-negative bacteria a red or pink color. The test itself is useful in classifying two distinctly different types of bacteria based on structural differences in their cell walls.

Many species of Gram-negative bacteria are pathogenic, meaning they can cause disease in a host organism. This pathogenic capability is usually associated with certain components of Gram-negative cell walls, in particular the lipopolysaccharide (also known as LPS or endotoxin) layer.

Interesting things to note[edit]

Many proteobacteria are pathogenic, gram negative, and RNA.

Conclusions and what I have learned[edit]

It is interesting to know that the various bacteria on my body have different classifications. I assumed this was the case considering my previous schooling but had no idea what they were or the different characteristics of each.

It would be interesting to know what the hygenic habits are of the participants of this study. When was their last shower? How clean do they keep their rooms. What sort of environments do they frequent. It seems using an ecological systems approach more data/insights could be gleamed about the methods of creating the most healthy environments. While all these individuals are "healthy" perhaps some of them have a sore throat more often than others or perhaps some have colds more often than the others.

This learning project is an experiment in Wikiversity for my own satisfaction and learning. Please, if you are interested, add to it, edit it, improve it etc.

External links[edit]