Structure characteristics and function of a novel extracellular polysaccharide from Bacillus thuringiensis strain 4D19

Bacillus thuringiensis (Bt) are entomopathogenic bacteria that produce different kinds of insecticidal proteins. However, studies on Bt exopolysaccharides are lacking. Here, we aimed to explore the characteristics and insecticidal synergism of EPS, an exopolysaccharide from Bt strain 4D19. The molecular weight of EPS-2 was 58.0 kDa, which consisted of mannose (44.2%), GlcN (35.5%), D-GalN (8.0%), glucose (5.5%), arabinose (5.1%), galactose (0.9%), Man-UA (0.3%) and Glc-UA (0.2%). The toxicity of insecticidal proteins against Plutella xylostella was increased by adding EPS. EPS-2 bound to Cry1Ac protoxin and promoted the binding of Cry1Ac protoxin to the gut membrane of P. xylostella, but did not bind to activated toxins. These results suggested that EPS-2 may bind to the protoxin C-terminal region to enhance insecticidal activity. Our findings indicated that Bt strains produce exopolysaccharide to enhance the toxicity of insecticidal crystal proteins, which could be applied in biopesticide research and product development.