# Lactobacillus rhamnosus YQ001 binds with GII.4 human noroviruses and inhibits viral replication in zebrafish larvae

## TL;DR

A Lactobacillus rhamnosus strain inhibits norovirus replication in zebrafish larvae by binding to the virus and reducing immune responses.

## Contribution

The study identifies a probiotic strain that synergistically inhibits norovirus through cell-free supernatant and membrane proteins.

## Key findings

- L. rhamnosus YQ001's fermentation broth reduced viral RNA titers by 2.18 log10 copies in zebrafish larvae.
- Membrane proteins from L. rhamnosus YQ001 bind to GII.4 noroviruses, inhibiting replication.
- The probiotic's cell-free supernatant reduced immune gene upregulation in infected zebrafish.

## Abstract

Human noroviruses (HuNoVs) are the primary cause of viral gastroenteritis globally. Nevertheless, available anti-HuNoV approaches remain limited. The current study revealed that a Lactobacillus rhamnosus strain, that is, L. rhamnosus YQ001, originated de Man, Rogosa and Sharpe (MRS)-based fermentation broth (FB) and cell-free supernatant (CFS) could significantly inhibit the replication of GII.4 HuNoVs in zebrafish larvae (Danio rerio), reducing viral RNA titers by approximately 2.18 log10 and 1.12 log10 copies, respectively. In addition, the inhibitory effect of FB was significantly stronger than that of CFS (P < 0.05), while L. rhamnosus YQ001 alone demonstrated no inhibitory effect. Zebrafish larvae injected with FB-treated GII.4 HuNoVs demonstrated reduced immune responses (i.e., significantly decreased upregulation of innate immune genes, ifn and mx, P < 0.05), compared to those of larvae injected with untreated GII.4 HuNoVs. Additionally, in situ capture RT-qPCR and enzyme-linked immunosorbent assay suggested that membrane proteins, especially C2JVE6, C2JX39 and C2K0J4, in L. rhamnosus YQ001, could bind to GII.4 HuNoVs. Altogether, the current study demonstrated the inhibitory effect of L. rhamnosus YQ001 originated FB and CFS on GII.4 HuNoVs in zebrafish larvae and identified the binding capacity of membrane proteins from L. rhamnosus YQ001. Collectively, these results highlight the synergistic effect of CFS and cell membrane proteins in GII.4 HuNoV control.

Human noroviruses (HuNoVs) are the leading cause of viral gastroenteritis globally, yet effective antiviral treatments remain limited. The current study demonstrated that Lactobacillus rhamnosus YQ001 could inhibit GII.4 HuNoV replication in zebrafish larvae. The cell-free supernatant and membrane proteins originated from L. rhamnosus YQ001 did work synergistically in GII.4 HuNoVs control. The membrane proteins could bind to the viral capsid. These findings offer a unique insight into the antiviral mechanisms of L. rhamnosus YQ001, laying the groundwork for developing probiotic-based foods to anti-HuNoVs.