A novel sialic acid utilization and uptake system in the periodontal pathogen Tannerella forsythia

Tannerella forsythia is a key contributor to periodontitis, but little is known of its virulence mechanisms. In this study we have investigated the role of sialic acid in biofilm growth of this periodontal pathogen. Our data show that biofilm growth of T. forsythia is stimulated by sialic acid, glycolyl sialic acid, and sialyllactose, all three of which are common sugar moieties on a range of important host glycoproteins. We have also established that growth on sialyllactose is dependent on the sialidase of T. forsythia since the sialidase inhibitor oseltamivir suppresses growth on sialyllactose. The genome of T. forsythia contains a sialic acid utilization locus, which also encodes a putative inner membrane sialic acid permease (NanT), and we have shown this is functional when it is expressed in Escherichia coli. This genomic locus also contains a putatively novel TonB-dependent outer membrane sialic acid transport system (TF0033-TF0034). In complementation studies using an Escherichia coli strain devoid of its outer membrane sialic acid transporters, the cloning and expression of the TF0033-TF0034 genes enabled an E. coli nanR nanC ompR strain to utilize sialic acid as the sole carbon and energy source. We have thus identified a novel sialic acid uptake system that couples an inner membrane permease with a TonB-dependent outer membrane transporter, and we propose to rename these novel sialic acid uptake genes nanO and nanU, respectively. Taken together, these data indicate that sialic acid is a key growth factor for this little-characterized oral pathogen and may be key to its physiology in vivo.