methodologies-for-studying-b-subtilis-biofilms-as-model-for

Methodologies for Studying <em>B. subtilis</em> Biofilms as a Model for Characterizing Small Molecule Biofilm Inhibitors

This work assesses different methodologies to study the impact of small molecule biofilm inhibitors, such as D-amino acids, on the development and ...

Weizmann Institute of Science

Many bacteria mediate important life-style decisions by varying levels of the second messenger c-di-GMP. Behavioral transitions result from the coordination of complex cellular processes such as motility, surface adherence or the production of virulence factors and toxins. While the regulatory mechanisms responsible for these processes have been elucidated in some cases, the global pleiotropic effects of c-di-GMP are poorly understood, primarily because c-di-GMP networks are inherently complex in most bacteria. Moreover, the quantitative relationships between cellular c-di-GMP levels and c-di-GMP dependent phenotypes are largely unknown. Here, we dissect the c-di-GMP network of Caulobacter crescentus to establish a global and quantitative view of c-di-GMP dependent processes in this organism. A genetic approach that gradually reduced the number of diguanylate cyclases identified novel c-di-GMP dependent cellular processes and unraveled c-di-GMP as an essential component of C. crescentus cell polarity and its bimodal life cycle. By varying cellular c-di-GMP concentrations, we determined dose response curves for individual c-di-GMP-dependent processes. Relating these values to c-di-GMP levels modeled for single cells progressing through the cell cycle sets a quantitative frame for the successive activation of c-di-GMP dependent processes during the C. crescentus life cycle. By reconstructing a simplified c-di-GMP network in a strain devoid of c-di-GMP we defined the minimal requirements for the oscillation of c-di-GMP levels during the C. crescentus cell cycle. Finally, we show that although all c-di-GMP dependent cellular processes were qualitatively restored by artificially adjusting c-di-GMP levels with a heterologous diguanylate cyclase, much higher levels of the second messenger are required under these conditions as compared to the contribution of homologous c-di-GMP metabolizing enzymes. These experiments suggest that a common c-di-GMP pool cannot fully explain spatiotemporal regulation by c-di-GMP in C. crescentus and that individual enzymes preferentially regulate specific phenotypes during the cell cycle.

Bi-modal distribution of the second messenger c-di-GMP controls cell fate and asymmetry during the caulobacter cell cycle.

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.

Article	Year
Bi-modal distribution of the second messenger c-di-GMP controls cell fate and asymmetry during the caulobacter cell cycle. PLoS genetics\| PubMed ID: 24039597	2013
Disturbance of the bacterial cell wall specifically interferes with biofilm formation. Environmental microbiology reports\| PubMed ID: 26472159	2015

Tabitha Bucher

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