title: A staphylococcal GGDEF domain protein regulates biofilm formation independently of cyclic dimeric GMP.
abstract: Cyclic dimeric GMP (c-di-GMP) is an important biofilm regulator that allosterically activates enzymes of exopolysaccharide biosynthesis. Proteobacterial genomes usually encode multiple GGDEF domain-containing diguanylate cyclases responsible for c-di-GMP synthesis. In contrast, only one conserved GGDEF domain protein, GdpS (for GGDEF domain protein from Staphylococcus), and a second protein with a highly modified GGDEF domain, GdpP, are present in the sequenced staphylococcal genomes. Here, we investigated the role of GdpS in biofilm formation in Staphylococcus epidermidis. Inactivation of gdpS impaired biofilm formation in medium supplemented with NaCl under static and flow-cell conditions, whereas gdpS overexpression complemented the mutation and enhanced wild-type biofilm development. GdpS increased production of the icaADBC-encoded exopolysaccharide, poly-N-acetyl-glucosamine, by elevating icaADBC mRNA levels. Unexpectedly, c-di-GMP synthesis was found to be irrelevant for the ability of GdpS to elevate icaADBC expression. Mutagenesis of the GGEEF motif essential for diguanylate cyclase activity did not impair GdpS, and the N-terminal fragment of GdpS lacking the GGDEF domain partially complemented the gdpS mutation. Furthermore, heterologous diguanylate cyclases expressed in trans failed to complement the gdpS mutation, and the purified GGDEF domain from GdpS possessed no diguanylate cyclase activity in vitro. The gdpS gene from Staphylococcus aureus exhibited similar characteristics to its S. epidermidis ortholog, suggesting that the GdpS-mediated signal transduction is conserved in staphylococci. Therefore, GdpS affects biofilm formation through a novel c-di-GMP-independent mechanism involving increased icaADBC mRNA levels and exopolysaccharide biosynthesis. Our data raise the possibility that staphylococci cannot synthesize c-di-GMP and have only remnants of a c-di-GMP signaling pathway.
authors.affiliation: School of Biomolecular and Biomedical Science, Ardmore House, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Linda M
authors.initials: LM
authors.lastname: Holland
authors.forename: Sinéad T
authors.initials: ST
authors.lastname: O'Donnell
authors.forename: Dmitri A
authors.initials: DA
authors.lastname: Ryjenkov
authors.forename: Larissa
authors.initials: L
authors.lastname: Gomelsky
authors.forename: Shawn R
authors.initials: SR
authors.lastname: Slater
authors.forename: Paul D
authors.initials: PD
authors.lastname: Fey
authors.forename: Mark
authors.initials: M
authors.lastname: Gomelsky
authors.forename: James P
authors.initials: JP
authors.lastname: O'Gara
mesh_terms: D000595:Amino Acid Sequence; D018441:Biofilms / Q000254:growth & development*; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000378:metabolism; D029968:Escherichia coli Proteins; D017353:Gene Deletion; D018628:Gene Dosage; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D019761:Phosphorus-Oxygen Lyases / Q000235:genetics / Q000378:metabolism*; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis; D016415:Sequence Alignment; D017384:Sequence Deletion; D013211:Staphylococcus aureus / Q000201:enzymology / Q000235:genetics; D013212:Staphylococcus epidermidis / Q000201:enzymology / Q000235:genetics / Q000502:physiology*
chemical_list: D029968:Escherichia coli Proteins; D011135:Polysaccharides, Bacterial; C062025:bis(3',5')-cyclic diguanylic acid; D019761:Phosphorus-Oxygen Lyases; C060720:diguanylate cyclase; D006152:Cyclic GMP