Bacteria harbour secret weapons against antibiotics

In the paper, researchers from Princeton University in New Jersey describe how they observed two similar strains of E. coli bacteria quickly developing similar levels of antibiotic resistance using surprisingly different genetic mutations. Developing different solutions to the same problem shows the bacteria have a diverse arsenal of genetic "weapons" they can develop to fight antibiotics, potentially making them more versatile and difficult to defeat.

The research team used a custom-made microfluidic device that contains approximately 1,000 connected microhabitats in which populations of bacteria grow. The device generates complex gradients of food and antibiotic drugs similar to what might be found in natural bacterial habitats like the gut or other compartments inside a human body.

By sequencing the genomes of wild type and GASP bacterial colonies that has been exposed to the antibiotic ciprofloxacin (Cipro), the researchers found different genetic mutations could lead to similar levels of antibiotic resistance. For example, two different mutant strains emerged: one of the antibiotic-resistant GASP strains evolved in such a way that it no longer needed to make biofilms in order to survive stress. It did so by "borrowing" a piece of leftover DNA from a virus that infects bacteria. The other strain did not do this excision, indicating that in evolution the strains can hedge their bets.

Viruses routinely inject their own DNA into bacteria and sometimes DNA sequences remain that no longer seem to have any function in terms of viral replication. Under normal circumstances the leftover DNA may neither help nor hinder the bacteria, but in times of stress the bacteria can use the new DNA to rapidly evolve antibiotic resistant mutations.

The results demonstrate the diversity of the tools that bacteria have to fight stress.

For further details see:

Qiucen Zhang, Julia Bos, Grigory Tarnopolskiy, James C. Sturm, Hyunsung Kim, Nader Pourmand, and Robert H. Austin. You cannot tell a book by looking at the cover: cryptic complexity in bacterial evolution. Biomicrofluidics, 2014 DOI: 10.1063/1.4894410

Posted by Tim Sandle