Disturbance of the bacterial cell wall specifically interferes with biofilm formation

Abstract

In nature, bacteria communicate via chemical cues and establish complex communities referred to as biofilms, wherein cells are held together by an extracellular matrix. Much research is focusing on small molecules that manipulate and prevent biofilm assembly by modifying cellular signalling pathways. However, the bacterial cell envelope, presenting the interface between bacterial cells and their surroundings, is largely overlooked. In our study, we identified specific targets within the biosynthesis pathways of the different cell wall components (peptidoglycan, wall teichoic acids and teichuronic acids) hampering biofilm formation and the anchoring of the extracellular matrix with a minimal effect on planktonic growth. In addition, we provide convincing evidence that biofilm hampering by transglycosylation inhibitors and D-Leucine triggers a highly specific response without changing the overall protein levels within the biofilm cells or the overall levels of the extracellular matrix components. The presented results emphasize the central role of the Gram-positive cell wall in biofilm development, resistance and sustainment.

Beyond the Wall: can D-Amino Acids and Small Molecule Inhibitors Eliminate Infections?

“…It was observed that biofilm interference by DAAs is partially or fully rescued by addition of d -Alanine [9,10]. In agreement with the hypothesis that d -Alanine blocks the incorporation of DAAs into the bacterial envelope, incorporation of 14 C-d -Leucine into the cell wall is largely inhibited by applying access to d -Alanine [10].…”

“…It cleaves the bond formed between DAA and tRNA, freeing the tRNA to reconnect to the correct l -amino acid. In B. subtilis, the presence of a defective dtd allele sensitized the cells to the application of DAAs [10,13], which would be consistent with a general toxic effect of tRNA-DAA on translation. However, the biofilm inhibition clearly occurred at sub-toxic concentrations even in the presence of a defective dtd allele [10].…”

“…In B. subtilis, the presence of a defective dtd allele sensitized the cells to the application of DAAs [10,13], which would be consistent with a general toxic effect of tRNA-DAA on translation. However, the biofilm inhibition clearly occurred at sub-toxic concentrations even in the presence of a defective dtd allele [10]. In addition, and in contrast to the expectations that the addition of d -Alanine will further impair translation and thus biofilm growth, its application actually rescued biofilm formation [9,10].…”

“…The specific mechanisms that link cell-wall interference and biofilm formation remain to be determined. Intriguingly, macro-analysis of B. subtilis biofilms indicated that DAAs induced a malfunction of the anchoring of the extracellular matrix to the cell wall [10,11]. DAAs can also directly interfere with protein translation, leading to production of defective proteins.…”

“…It was first reported in Escherichia coli and B. subtilis that tRNA molecules are charged with d -tyrosine in the presence of tyrosyl tRNA synthetase [12], followed by similar reports on d -Valine, d -Aspartate and d -Tryptophan. Noncanonical DAAs were suggested to have a global role in inhibition of protein translation [13], although, this hypothesis was never tested directly, and a later study found no change in the overall protein levels in treated biofilm cells [10].…”