Hidden structures in bacterial DNA revealed

Researchers have described the 3D structure of the genome in the extremely small bacteria Mycoplasma pneumoniae. They discovered previously unknown arrangements of DNA within this tiny bacteria, which are also found in larger cells. Their findings suggest that this type of organization is a universal feature of living cells.

Using a technique called Hi-C, which reveals the interactions between different pieces of DNA, the researchers created a three-dimensional 'map' of the Mycoplasma chromosome. They then used super-resolution microscopy to prove that this computer-generated map matched up with the real-life chromosome organisation inside bacterial cells.

The researchers discovered that Mycoplasma's circular chromosome is consistently organised the same way in all the cells, with a region called the Origin (where DNA copying begins) at one end of the structure and the midpoint of the chromosome located at the opposite end. This is a similar arrangement to that seen in some other larger bacterial species.

The scientists also used the Hi-C technique to study more detailed patterns of organisation within the Mycoplasma genome. In recent years, scientists all over the world have investigated the organisation of chromosomes inside cells from species ranging from larger bacteria to human. Next Generation Sequencing has allowed scientists to 'read' the DNA sequence of any genome, but this doesn't reveal how genetic information is managed and organised in the crowded and bustling biological environment inside a cell. Now, new tools have revealed complex organisational structures within the genomes of larger organisms, with certain regions of chromosomes clustered together to form domains containing genes that are switched on or off together.

However, it was thought that these domains would not be found in Mycoplasma, because its genome is so small and it only makes around 20 different DNA binding proteins responsible for organising the chromosome, compared to the hundreds made by other bacterial species.

Intriguingly, the researchers found that even the tiny Mycoplasma chromosome is organised into distinct structural domains, each containing genes that are also turned on or off in a co-ordinated way.

For further details see:

Marie Trussart, Eva Yus, Sira Martinez, Davide Baù, Yuhei O. Tahara, Thomas Pengo, Michael Widjaja, Simon Kretschmer, Jim Swoger, Steven Djordjevic, Lynne Turnbull, Cynthia Whitchurch, Makoto Miyata, Marc A. Marti-Renom, Maria Lluch-Senar, Luís Serrano. Defined chromosome structure in the genome-reduced bacterium Mycoplasma pneumoniae. Nature Communications, 2017; 8: 14665 DOI: 10.1038/ncomms14665

Posted by Dr. Tim Sandle