How do scientists read a whole microbial community from one gene?
Many microbes cannot be grown in a dish, so scientists read one gene they all share: a barcode that is part constant, part different in every species.
▶ Start the storyScientists read a whole microbial community by sequencing one gene that every bacterium shares, the 16S rRNA gene, and using it as a barcode. This matters because many microbes cannot be grown in a dish. Identifying skin bacteria used to depend on culture, and many varieties did not grow and so were hidden from science. Reading DNA directly removes that bottleneck, and the 16S gene has even been used to describe new species that have never been cultured.
The gene is a good barcode because it is part constant and part variable. It is highly between different species of bacteria and archaea, as it evolves slowly. It also contains that give species-specific signature sequences. The conserved stretches around them let scientists design universal , short pieces of DNA that can copy the same part of the gene in all sorts of bacteria. The copied pieces are then sequenced and compared. Carl Woese and George Fox pioneered the use of 16S rRNA in 1977 to sort out the family tree of microbes.
Step 1: Take a sample
Stool, skin swab or saliva; no culture dish needed.
Step 2: Copy the 16S gene
Universal latch onto stretches.
Step 3: Sequence the copies
Machines read the variable regions in each copy.
Step 4: Cluster and count
Similar sequences are grouped, often at 97% similarity, and counted.
Step 5: Names, not jobs
Low-resolution: tells who is there, not what they do.
At scale this became a census. The Human Microbiome Project, launched in 2007 with $170 million from the NIH Common Fund, analysed more than 5,000 samples from 242 healthy volunteers, from sites including mouth, nose, skin, stool and vagina. It extracted the data by identifying 16S rRNA, and calculated that more than 10,000 microbial species occupy the human ecosystem.
The barcode has limits. It is fast and relatively inexpensive, but only a low-resolution classification: closely related species can share up to 99 percent of their 16S sequence. So 16S tells you roughly who is there, not what they are doing.
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Recap
16S sequencing reads a barcode gene to say who is in a microbial community, but not what they are doing or whether they cause anything.
💡 A trick to remember it · A name tag on every microbe: the constant part lets us grab it, the variable part says who it is, and the tag never says what the wearer does.
Surprising fact · Closely related species can share up to 99% of their 16S sequence, so the barcode cannot always tell them apart.
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No source, no claim. Every fact in this lesson (16 claims) cites at least one of these.