Surface sensing for biofilm formation in Pseudomonas aeruginosa

YesAggregating and forming biofilms on biotic or abiotic surfaces are ubiquitous bacterial behaviors under various conditions. In clinical settings, persistent presence of biofilms increases the risks of healthcare-associated infections and imposes huge healthcare and economic burdens. Bacteria within biofilms are protected from external damage and attacks from the host immune system and can exchange genomic information including antibiotic-resistance genes. Dispersed bacterial cells from attached biofilms on medical devices or host tissues may also serve as the origin of further infections. Understanding how bacteria develop biofilms is pertinent to tackle biofilm-associated infections and transmission. Biofilms have been suggested as a continuum of growth modes for adapting to different environments, initiating from bacterial cells sensing their attachment to a surface and then switching cellular physiological status for mature biofilm development. It is crucial to understand bacterial gene regulatory networks and decision-making processes for biofilm formation upon initial surface attachment. Pseudomonas aeruginosa is one of the model microorganisms for studying bacterial population behaviors. Several hypotheses and studies have suggested that extracellular macromolecules and appendages play important roles in bacterial responses to the surface attachment. Here, I review recent studies on potential molecular mechanisms and signal transduction pathways for P. aeruginosa surface sensing.This work is supported by University of Bradfor

Molecular mechanism of alginate polymerisation and modifications in Pseudomonas aeruginosa : a thesis presented in partial fulfilment of the requirements for degree of Doctor of Philosophy in Microbiology at Massey University, New Zealand

Pseudomonas aeruginosa is an ubiquitous opportunistic human pathogen in immunocompromised patients. It is of particular relevance to cystic fibrosis (CF) patients where it frequently causes chronic bronchopulmonary infection and is the leading cause of morbidity and mortality. The decline in lung function is caused by the emergence of a mucoid variant showing excessive production of the exopolysaccharide, alginate. The alginate-containing biofilm matrix of this mucoid variant protects P. aeruginosa from the immune system and antibiotics. Here the alginate biosynthesis/modification/secretion multiprotein complex was investigated with regard to protein-protein interactions constituting the proposed multiprotein complex and the molecular mechanisms underlying alginate polymerisation and modifications. This study sheds light on the structure and function of various alginates from a material property and biological function perspectives. The binary interactions of AlgK-AlgE, AlgX-Alg44, AlgK-Alg44 and Alg8-Alg44 were identified proposing a new model for this multiprotein complex organisation. Proteinprotein interactions were found to be independent of c-di-GMP binding to PilZAlg44 domain. C-di-GMP-mediated activation of alginate polymerisation was found to be different from activation mechanism proposed for cellulose synthesis. This study showed that alginate polymerisation and modifications were linked. It was shown that the molecular mass of alginate was reduced by epimerisation, while it was increased by acetylation. It was determined that previously characterized proteins AlgG (epimerase) and AlgX (acetyltransferase) have mutual auxiliary and enhancing roles. Biofilm architecture analysis showed that acetyl groups lowered viscoelasticity of alginates and promoted cell aggregation, while nonacetylated polymannuronate alginate promoted stigmergy. Experimental evidence was provided that Alg44 boosted acetylation while the periplasmic domain of this protein was critical for protein stability and regulation of alginate modifications. Full-length Alg44 was purified and it was found to be a dimer in solution. Overall, this study sheds new light on the arrangement of the proposed alginate biosynthesis/modification/secretion multiprotein complex. Furthermore, the activation mechanism and the interplay between polymerisation and modification of alginate were elucidated and new functions and interactive role of alginate-polymerising and– modifying subunits were further understood