Bacteria and fungi produce biofilms whenever they adhere to a surface to protect themselves from environmental stressors, including antibiotics. Biofilm-related infections are therefore often hard to treat and do not respond well to antibiotic treatment. As an opportunistic pathogen of the respiratory tract Burkholderia cenocepacia is often responsible for hospital-acquired infections. While Burkholderia has an innate resistance to antibiotics, it also forms biofilms, rendering the treatment of these infections especially cumbersome. Burkholderia shares several similarities with Pseudomonas aeruginosa, both in the type of infections it causes, and the difficulty of treatment. In Pseudomonas, the wsp (wrinkly spreader phenotype) system is a chemosensory signal transduction system that triggers biofilm formation. The system is also present in Burkholderia. So, Dr. Andrea Sass and their colleagues at Ghent University wondered if the wsp cluster of genes serves a similar purpose in both species.
In Burkholderia, the wsp cluster is regulated by methylation in the promoter of an upstream gene called wspH. Deletion of the enzyme that methylates the promoter increases expression of both wspH and the wsp cluster downstream of it, suggesting that these genes are part of the same operon. However, wspH is fairly far from the rest of the cluster, and thus its role in the regulation of the wsp cluster has not been investigated before. With a clever genetic approach, the researchers could indeed determine that wspH is expressed together with the other wsp genes in Burkholderia.
After figuring out the components of the wsp cluster, the researchers wanted to determine the effects of the expression of this operon in the formation of biofilms. They used EbbaBiolight 680 to track the formation of a pellicle biofilm at the air-liquid interface in static cultures of Burkholderia, and found that mutants overexpressing wspH; were much faster in forming a biofilm than others. This was accompanied by an increase of c-GMP within the bacterial cells, which is a common regulator of cell motility and biofilm formation. The c-GMP signal resulted in the expression of the wsp cluster, which produces exopolysaccharides that increase the hydrophobic properties of the cell surface.
Overexpressing only the other wsp genes - and not wspH - had, instead, only mild effects on the formation of biofilms, indicating a central role of wspH in the initiation of biofilm formation.
Being able to observe the temporal dynamics of biofilm formation and the effects of putative regulatory factors in live cultures is key to the development of new treatments. These treatments may combat the microbe-protective biofilms and prevent re-infections, and non-toxic trackers like EbbaBiolight are an invaluable tool to achieve this.