Grapevine

Research discovers protein that determines spiral shape of bacteria

Bacteria come in a surprising variety of shapes. In addition to rod-shaped representatives such as the widely known model bacterium E. coli, there are numerous curved and even spiral-shaped bacteria. Curvature is crucial to the ability of bacteria to colonize surfaces and move in viscous environments—and thus also to cause disease, as is the case for Vibrio cholerae or Helicobacter pylori. Researchers worldwide are working to understand the molecular details of bacterial cell curvature, with the hope of someday being able to influence it and thus potentially combat pathogens.

Now an international research team led by Max Planck Fellow Martin Thanbichler, Professor at the University of Marburg, Germany, has provided new insights into the shape of the photosynthetic bacterium Rhodospirillum rubrum. This species is widespread in the environment and has biotechnological potential because it can utilize carbon monoxide, fix nitrogen and produce both hydrogen and building blocks for bioplastics.

The study is published in the journal Nature Communications.

The researchers were surprised to find that in Rhodospirillum two so-called porins—channel-like proteins that so-far were only known to be only responsible for the exchange of nutrients across the outer membrane of bacteria—are arranged helically in the outer curvature of the cell. These structures are closely connected to the cell wall by another protein, the lipoprotein PapS. Surprisingly, when PapS was missing or when the researchers prevented it from binding to the porins, the cells became completely straight.

The cells of R. rubrum (wild type) are naturally spirally curved. Without the gene that codes for the lipoprotein PapS, they take on a straight shape. The curvature of the cells is achieved by a helically coiled structure of porins in the outer cell membrane, which form a stable interaction with the lipoprotein PapS. These proteins accumulations enclose the biosynthetic machinery that is responsible for the formation of the cell wall and thus lead to locally increased cell elongation, causing the cell body to distort into a spiral shape. Credit: Sebastian Pöhl (University of Marburg)