Bacteria-norovirus capsid P protein complex binding to and removal from Romaine lettuce

Abstract

Norovirus is a very contagious virus that causes acute gastroenteritis. Contaminated produce is a main vehicle for dissemination of human noroviruses (HuNoVs). As HuNoVs could bind to bacteria effectively, it is highly possible that produce could be contaminated by bacteria-HuNoVs complex. In this study, we used a bacterial-surface-display system to express genogroup I (GI) or genogroup II (GII) HuNoV capsid protein (P protein) on the surface of bacteria. The bacteria-P protein complex (BPC) was used to characterize the conditions for binding to Romaine lettuce extract and removal of the bound BPCs. We demonstrated both GI and GII BPCs could bind to extract from leaf (LE) and vein (VE) effectively. Carbohydrates in LE and VE were involved in GI BPCs binding, and both carbohydrates and proteins were involved in GII BPCs binding. Saliva from both type A and O secretors could completely block binding of both BPCs to LE and VE. Saliva from type B secretors only partially blocked binding of GII but not GI BPCs to LE and VE. However, LE- and VE-bound BPCs could not be reversely removed by washing solution containing free HBGAs from saliva. The binding of GI BPCs to LE and VE was enhanced when pH was below pI (6.1) of GI and reduced when pH was above pI of GI ( p  < 0.05). The optimal binding for GII BPCs to LE and VE occurred at pI (6.4) of GII. All LE- or VE-bound BPCs could be reversely removed by washing with low (3.0–5.0) or high (9.0–10.0) pH buffer. The effect of ionic strength (NaCl and MgCl 2 , from zero to 100 g/L) on binding of BPCs to LE and VE was tested. The optimal ionic strength for binding of BPCs to LE and VE was 10.0 g/L (GI) and 5.0 g/L (GII) for NaCl, and 5.0 g/L for MgCl 2 . LE- and VE-bound BPCs could be reversely removed by washing with high ionic solutions. All LE- or VE- bound BPCs could be released when washed with NaCl concentrations of above 75.0 g/L (GI) and 25.0 g/L (GII), or with MgCl 2 concentrations of above 75.0 g/L (GI) and 50.0 g/L (G