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PhD thesis defense of Manar HARB

PhD thesis defense

Manar HARB, PhD student at MAPIEM lab, under the supervision of:

will defend her PhD thesis in Microbiology on the topic:

Study of biofilm formation in Shewanella oneidensis and the role of transcriptional regulators from the FleQ family

on January 22th, 2020 at 02:00PM, at the Amphi X300, Building X, University of Toulon

before a jury composed of :


Microorganisms attach to surfaces and form a community called biofilms. Within a biofilm, bacteria are encapsulated in a matrix made of exopolysaccharides, nucleic acids and proteins. Biofilm formation is a problem because bacteria are notoriously recalcitrant to biocidal treatment when growing as a biofilm. Understanding how bacteria adhere and form biofilm is crucial to develop new coatings or treatments with antibiofilm properties. Our study focused on biofilm formation in the aquatic bacterium Shewanella oneidensis. We studied in particular the mode of regulation of biofilm formation involving the intracellular messenger c-di-GMP and one of its effectors belonging to the FleQ transcriptional regulator family.

We showed that S. oneidensis was able to form biofilm of different aspects depending on growth conditions. Among the extracellular matrix compounds tested, most of the compounds secreted by these bacteria were eDNA, proteins and sialic acid. A flrA mutant (homologous to fleQ in S. oneidensis) is affected in its ability to swim or form biofilm and c-di-GMP also has an impact on these two mechanisms. From chromatin immunoprecipitation sequencing (ChIP-seq) and transcriptomic (RNA-seq) studies, we showed that FleQ from Pseudomonas aeruginosa and FlrA from S. oneidensis regulate expression of genes involved in flagellum biosynthesis, exopolysaccharides production, anaerobic or microaerobic respiration and modulate expression of prophage genes. We proposed that FlrA/FleQ is a major regulator of biofilm formation controlling different facets of biofilms: from bacteria attachment mediated by the flagellum, to exopolysaccharide production, through diverse mechanisms involved in cells aggregation or dispersion or DNA release and including adaptation to environmental conditions of biofilm formation such as microaerobic growth.


c-di-GMP, S. oneidensis, P. aeruginosa, FlrA, FleQ, biofilm, Tn-seq, RNA-seq, ChIP-seq

Laboratoire MAPIEM (EA 4323) - http://mapiem.univ-tln.fr/PhD-thesis-defense-of-Manar-HARB.html - mapiem@univ-tln.fr