# Discovery of a Marine Beauveria bassiana Polysaccharide with Antiviral Activity Against Tobacco Mosaic Virus

## TL;DR

A marine fungus produces a polysaccharide that shows antiviral effects against tobacco mosaic virus in plants.

## Contribution

A marine-derived fungal polysaccharide is shown to activate multiple antiviral pathways in plants.

## Key findings

- EPSs reduced TMV symptoms and maintained chlorophyll levels in Nicotiana benthamiana.
- EPSs enhanced antioxidant enzymes and upregulated defense-related genes.
- EPSs combined with Ribavirin activated multi-pathway antiviral immunity.

## Abstract

Tobacco mosaic virus (TMV) threatens crop yield and quality, while chemical antivirals offer limited efficacy and potential environmental hazards. Marine fungal polysaccharides are promising eco-friendly alternatives due to their biocompatibility and biodegradability. Here, extracellular polysaccharides (EPSs) from the deep-sea fungus Beauveria bassiana T2-2 was isolated, characterized, and produced under optimized conditions (28 °C, 200 rpm, 9 days, pH 8, inoculum 4%) using an L9 (34) orthogonal medium, yielding 3.42 g/L, which is a 48% increase over unoptimized culture. EPSs were glucose-rich, with a molecular weight of 3.56 × 104 Da, containing 90.05% total sugar, 0.28% protein, 1.15% uronic acid, and 1.18% sulfate. In a Nicotiana benthamiana–TMV model, EPSs alleviated viral symptoms, maintained chlorophyll content, enhanced antioxidant enzymes (SOD, POD, CAT), reduced malondialdehyde, and upregulated defense genes in SA, ET, ROS, and phenylpropanoid pathways. EPSs, alone or combined with Ribavirin, activated multi-pathway antiviral immunity, highlighting its potential as a sustainable plant-protective agent.