Characterization of the outer membrane proteome of Francisella noatunensis subsp. orientalis

Abstract

Aims The aims of the current study were to characterise the outer membrane proteins (OMPs) of Francisella noatunensis subsp. orientalis (Fno) STIR‐GUS‐F2f7, and identify proteins recognised by sera from tilapia, Oreochromis niloticus, (L) that survived experimental challenge with Fno. Methods and Results The composition of the OMPs of a virulent strain of Fno (STIR‐GUS‐ F2f7), isolated from diseased red Nile tilapia in UK, was examined. The sarcosine‐insoluble OMP fraction was screened with tilapia hyper‐immune sera by western blot analysis following separation of the proteins by 1D SDS‐PAGE. Liquid chromatography‐electrospray ionisation‐tandem mass spectrometry (LC‐ESI‐MS/MS) was used to identify the various proteins present in the OMP profile. Two hundred and thirty‐nine proteins were identified, of which 44 were found in the immunogenic band recognised by the tilapia hyperimmune serum. In silico analysis was performed to predict the function and location of the OMPs identified by MS. Conclusions Using a powerful proteomic‐based approach in conjugation with western immunoblotting, proteins comprising the outer membrane fraction of Fno STIR‐GUS‐F2f7 were identified, catalogued and screened for immune recognition by tilapia sera. Significance and Impact of the study The current study is the first report on the characterisation of Fno OMPs. The findings here provide preliminary data on bacterial surface proteins that exist in direct contact with the host's immune defences during infection and offer an insight into the pathogenesis of Fno.