Formation of biofilms

Scientists at The Scripps Research Institute have unravelled a complex chemical pathway that enables bacteria to form clusters called biofilms. Such improved understanding might eventually aid the development of new treatments targeting biofilms.

Biofilm formation is a an important phenomenon that occurs when bacterial cells adhere to each other and to surfaces, at times as part of their growth stage and at other times to gird against attack. In such aggregations, cells on the outside of a biofilm might still be susceptible to natural or pharmaceutical antibiotics, but the interior cells are relatively protected. This can make them difficult to kill using conventional treatments.

Past research had also revealed that nitric oxide is involved in influencing bacterial biofilm formation. Nitric oxide in sufficient quantity is toxic to bacteria, so it's logical that nitric oxide would trigger bacteria to enter the safety huddle of a biofilm.

Many bacteria also have H-NOX domains, including key pathogens, so this seemed the best starting point for the investigation. From there, the team turned to genomic data. Genes for proteins that interact are often found adjacent to one another.

Based on this fact, the researchers were able to infer a connection between the bacterial H-NOX domain and an enzyme called histidine kinase, which transfers phosphate chemical groups to other molecules in signaling pathways. The question was where the phosphates were going.

To learn more, the researchers used a technique called phosphotransfer profiling. This involved activating the histidine kinase and then allowing them to react separately with about 20 potential targets. Those targets that the histidine kinase rapidly transferred phosphates to had to be part of the signaling pathway.

The experiments revealed that the histidine kinase phosphorylated three proteins called response regulators that work together to control biofilm formation for the project's primary study species, the bacterium Shewanella oneidensis, which is found in lake sediments.

Further work showed that each regulator plays a complementary role, making for an unusually complex system. One regulator activates gene expression, another controls the activity of an enzyme producing cyclic diguanosine monophosphate, an important bacterial messenger molecule that is critical in biofilm formation, and the third tunes the degree of activity of the second.

The research paper is:

Lars Plate, Michael A. Marletta. Nitric Oxide Modulates Bacterial Biofilm Formation through a Multicomponent Cyclic-di-GMP Signaling Network. Molecular Cell, 2012

Posted by Tim Sandle