Candida Infection Biology – fungal armoury, battlefields ... - FINSysB

Identification of Candida albicans genes involved in biofilm
formation by an over-expression approach
Vitor Cabral 1,2 , Sadri Znaidi 1,2 , Mélanie Legrand 1,2 , Keunsook Lee 3 , Sophie
Bachelier-Bassi 1,2 , Murielle Chauvel 1,2 , Tristan Rossignol 1,2 , Carol Munro 3 ,
Christophe d’Enfert 1,2
1 Institut Pasteur, Unité Biologie et Pathogénicité Fongiques, Département Génomes et
Génétique, F-75015 Paris, France; 2 INRA, USC2019, F-75015 Paris, France; 3 Aberdeen
Fungal Group, University of Aberdeen, School of Medical Sciences, Institute of Medical
Sciences, Aberdeen, AB25 2ZD, United Kingdom
Candida albicans is the major fungal pathogen of humans, being responsible for
benign superficial infections and devastating systemic infections. These latter
infections are often associated with the formation of biofilms on medical devices.
Biofilms are polymicrobial communities adherent to biotic or abiotic surfaces and
are especially resistant to antifungal agents making them difficult to treat. Despite
recent progress, the molecular mechanisms that underlie the formation of biofilms
and the basis for their tolerance to antifungals remain to be fully understood.
Here, we have undertaken to identify and characterize C. albicans genes whose
over-expression alters biofilm formation. To this aim we have developed through
the Gateway cloning methodology a partial C. albicans ORFeome that includes
531 ORFs and a corresponding collection of C. albicans over-expression strains,
each having a unique C. albicans gene controlled by a doxycycline-inducible
promotor and a unique molecular barcode. This collection has been used to
evaluate the fitness of each strain in competition experiments, taking advantage of
their molecular barcoding for individual microarray-based quantification. First, the
fitness of the strains in planktonic cultures with or without over-expression of the
genes has been studied, revealing 8 genes whose over-expression reduces fitness
(6 related to cell cycle, DNA damage and check-point; 2 involved in filamentation).
Second, the fitness of the strains in biofilms with or without over-expression of the
genes has been investigated. None of the genes whose over-expression altered
fitness in planktonic cultures were identified in this analysis. Strikingly, we observed
a strong enrichment for genes encoding cell wall proteins and genes involved in
budding regulation among those genes whose over-expression altered fitness in
biofilms. Current experiments are aimed at confirming the results of these pool
experiments through analysis of individual over-expression mutants and further
understanding the role of the identified genes in biofilm formation.
We are grateful to the European Commission for funding the FINSysB Marie Curie Initial Training Network
(PITN-GA-2008-214004).
56