DNA is the genetic material for most living organisms on earth. The structure and chemical sequence of DNA determines how a cell functions. Small changes in DNA can lead to physiological changes within the cell. This is partly the reason why all humans have a distinct personality even though we have a 99.99% identical genetic makeup. All the differences can be attributed to the 0.01% variation in an individual’s DNA. Some of these variations are beneficial to the individual while others causes diseases or genetic disorders.
Just like humans, every other organism including the microscopic single-celled bacteria benefit from variations. However, in the case of bacteria, they have some extra-ordinary capabilities. They can uptake DNA from their environment. This allows bacteria to get the features of the DNA that they uptake. While some of the features could kill the bacterium, others could be helpful – perhaps to gain resistance against a certain antibiotic. Antibiotic resistant bacteria become very difficult to manage in the hospitals. Nearly a million people are affected by antibiotic-resistant bacteria each year, according to the World Health Organization. WHO has found evidence of these strains in nearly 490,000 people with tuberculous (1) and 500,000 people with other infectious diseases (2).
Although, it has been appreciated for a long time that bacteria are capable of uptaking external DNA, by a process known as natural transformation, how exactly they did it eluded scientists. In a new study published in Nature Microbiology, researchers headed by Assistant Professor Ankur Dalia made the first direct observation of natural transformation (DNA uptake) by a bacterium (3). They used a newly developed technique to stain (dye) the very thin hair-like appendages called pili on the bacteria (4). This technique allowed the researchers to directly observe pili of the bacterium that causes cholera, Vibrio cholerae, which are 10,000 times thinner than human hair. They simultaneously dyed the pili and DNA and observed that the bacteria actively sense the presence of DNA and uptake it using their pili.
As can be seen from the motion picture at the top of this page, the pilus (singular for pili) senses the DNA and attaches to it. Then, it retracts itself allowing the bacterium to take the DNA up (3).
Dalia says the pore is so small that the DNA would need to fold in half to fit through the opening in the cell.
“It’s like threading a needle,” said Ellison, who is first author on the study. “The size of the hole in the outer membrane is almost the exact width of a DNA helix bent in half, which is likely what is coming across. If there weren’t a pilus to guide it, the chance the DNA would hit the pore at just the right angle to pass into the cell is basically zero.”
After this exciting observation, Dalia and his group want to decipher the mechanism of how the pilus attaches to the DNA especially since the pilus protein involved in the process appears to interact with DNA in an entirely new way. They also want to study other tiny appendages on bacteria which have so far never been visualised.