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Wall teichoic acids are dispensable for anchoring the PNAG exopolysaccharide to the Staphylococcus aureus cell surface

¹ Laboratory of Microbial Biofilms, Instituto de Agrobiotecnología, Universidad Pública de Navarra-CSIC-Gobierno de Navarra, 31006 Pamplona, Spain
² Channing Laboratory, Department of Medicine, Brigham Women's Hospital, Harvard Medical School, Boston, MA 02115, USA
³ Centro de Investigación y Tecnología Animal, Instituto Valenciano de Investigaciones Agrarias (CITA-IVIA), Apdo 187, 12400 Segorbe, Castellón, Spain

Correspondence
Iñigo Lasa
ilasa{at}unavarra.es

Biofilm formation in Staphylococcus aureus is usually associated with the production of the poly-N-acetylglucosamine (PNAG) exopolysaccharide, synthesized by proteins encoded by the icaADBC operon. PNAG is a linear β-(1-6)-linked N-acetylglucosaminoglycan that has to be partially deacetylated and consequently positively charged in order to be associated with bacterial cell surfaces. Here, we investigated whether attachment of PNAG to bacterial surfaces is mediated by ionic interactions with the negative charge of wall teichoic acids (WTAs), which represent the most abundant polyanions of the Gram-positive bacterial envelope. We generated WTA-deficient mutants by in-frame deletion of the tagO gene in two genetically unrelated S. aureus strains. The tagO mutants were more sensitive to high temperatures, showed a higher degree of cell aggregation, had reduced initial adherence to abiotic surfaces and had a reduced capacity to form biofilms under both steady-state and flow conditions. However, the levels as well as the strength of the PNAG interaction with the bacterial cell surface were similar between tagO mutants and their corresponding wild-type strains. Furthermore, double tagO icaADBC mutants displayed a similar aggregative phenotype to that of single tagO mutants, indicating that PNAG is not responsible for the aggregative behaviour observed in tagO mutants. Overall, the absence of WTAs in S. aureus had little effect on PNAG production or anchoring to the cell surface, but did affect the biofilm-forming capacity, cell aggregative behaviour and the temperature sensitivity/stability of S. aureus.