Engineered magnetosomes fused to functional molecule (protein A) provide a highly effective alternative to commercial immunomagnetic beads

BackgroundMagnetosomes (also called bacterial magnetic nanoparticles; BMPs) are biomembrane-coated nanoparticles synthesized by magnetotactic bacteria (MTB). Engineered BMPs fused to protein A (termed F-BMP-FA) bind antibodies (Abs) automatically, and thus provide a series of potential advantages. However, no report so far has systematically evaluated functional applicability of genetically engineered BMPs.ResultsWe evaluated properties of F-BMP-FA, and developed/optimized culture methods for host strain Magnetospirillum gryphiswaldense F-FA, F-BMP-FA extraction conditions, conditions for Ab conjugation to F-BMP-FA surface, and procedures for antigen detection using F-BMP-FA/Ab complexes (termed BMP-A-Ab). Fed-batch culture for 36h in a 42-L fermentor resulted in yields (dry weight) of 2.26g/L for strain F-FA and 62mg/L for F-BMP-FA. Optimal wash cycle number for F-BMP-FA purification was seven, with magnetic separation following each ultrasonication step. Fusion of protein A to BMPs resulted in ordered arrangement of Abs on BMP surface. Linkage rate 962g Ab per mg F-BMP-FA was achieved. BMP-A-Ab were tested for detection of pathogen (Vibrio parahaemolyticus; Vp) surface antigen and hapten (gentamicin sulfate). Maximal Vp capture rate for BMP-A-Ab was 90% (higher than rate for commercial immunomagnetic beads), and detection sensitivity was 5CFU/mL. F-BMP-FA also bound Abs from crude mouse ascites to form complex. Lowest gentamicin sulfate detection line for BMP-A-Ab was 0.01ng/mL, 400-fold lower than that for double Ab sandwich ELISA, and gentamicin sulfate recovery rate for BMP-A-Ab was 93.2%.ConclusionOur findings indicate that engineered BMPs such as F-BMP-FA are inexpensive, eco-friendly alternatives to commercial immunomagnetic beads for detection or diagnostic immunoassays, and have high Ab-conjugation and antigen-adsorption capacity.