Recent progress in microbial cell surface display systems and their application on biosensors

Microbial cell surface display technology is a recombinant technology to express target proteins on the cell membrane,which can be used to redesign the cell surface with functional proteins and peptides.Bacterial and yeast surface display systems are the most common cell surface display systems of prokaryotic and eukaryotic proteins,that are widely applied as the core elements in the field of biosensors due to their advantages,including enhanced stability,high yield,good safety,expression of larger and more complex proteins.To further promote the performance of biosensors,the biomineralized microbial surface display technology was proposed.This review summarized the different microbial surface display systems and the biomineralized surface display systems,where the mechanisms of surface display and biomineralization were introduced.Then we described the recent progress of their applications on biosensors for different types of detection targets.Finally,the outlooks and tendencies were discussed and forecasted with the expectation to provide some general functions and enlightenments to this aspect of research.

Cell Surface Display of Red-Grouper Nervous Necrosis Virus Capsid Protein on <i>Pichia pastoris</i>

Nervous necrosis virus (NNV), the etiological agent of viral nervous necrosis, has a high mortality rate of 100% in hatchery-reared larvae and juveniles. At present, there are still no effective vaccines available for NNV. Pichia pastoris surface display of viral capsid proteins was generated in hopes of developing an oral vaccine against red-grouper-nervous-necrosis virus (RGNNV) in fish. Fingerlings or juveniles that showed clinical signs of NNV infection were proved by RT-PCR for the appearance of expected length of 198 bpcDNA and further analysis by DNA sequencing. The DNA fragment containing AGα1 linked to RG-NNVRNA2, 2100 bp in length, was inserted into pPIC9K vector. Linearlized plasmids were electroporated into P. pastoris GS115 (mut+His?) and yeast isolates that had Muts?His+ and resistance phenotype at 4 mg/mL geniticin were selected to determine the integration of the target gene by PCR reaction. The extracted cell walls from the yeasts cultured in buffered-methanol-complex medium (BMMY) through an induction of 0.5% methanol for 6 days, were investigated for the fusion proteins by western blot. A protein band of 73 kDa predicted to be the fusion protein and a non-specific one of 56 kDa were detected. Staining of the fusion proteins expressing cells with corresponding antibodies revealed their presence of NNVRNA2, but varied the intensity of detected signals from cell to cell by confocal laser scanning fluorescence microscopy. The predicted fusion proteins tertiary structure also confirmed exposed conformation of the fusion protein on the cell wall. In this study, the capsid proteins from the red-spotted grouper nervous necrosis virus were successfully expressed on the cell surface of P. pastoris but still low levels of fusion protein expression. Further studies are required to optimize fully surface protein expression prior to evaluate the possible use of the constructed recombinant yeast as an oral vaccine against RG-NNV infection.