# Pseudovibriamide B from marine sponge-associated bacteria acts as a selective antibiotic antidote

## TL;DR

A compound from marine bacteria can selectively protect certain microbes from a broad-spectrum antibiotic, offering a potential strategy for microbiota protection.

## Contribution

Pseudovibriamide B is shown to act as a selective antibiotic antidote with narrow-spectrum activity.

## Key findings

- PB selectively protects Bacillus cereus and a marine sponge-associated Bacillus sp. from blasticidin S.
- An overexpression strategy increased PB production three-fold, enabling detailed testing.
- The MAC assay was developed to quantify antidote activity and minimum effective concentrations.

## Abstract

Broad-spectrum antibiotics, while effective against pathogens, can disrupt microbiota leading to dysbiosis. In natural systems, where most antibiotic classes were first identified, some collateral damage control may have evolved as a microbiota protection strategy to the production of broad-spectrum antibiotics. In this work, we investigated whether pseudovibriamide B (PB), a depsipeptide produced by the marine sponge isolated bacterium Pseudovibrio brasiliensis Ab134, can function as a selective antidote to the commercial broad-spectrum antibiotic blasticidin S. An analogue of blasticidin S, named P10, was previously isolated from marine sponges. To improve access to PB and enable testing of the hypothesis, we developed an overexpression strategy targeting core biosynthetic genes, resulting in a more than three-fold increase in PB production. Additionally, we established an assay for antidote testing, the Minimum Antidote Concentration (MAC) assay, which enabled robust identification of antidote activity and quantification of the minimum concentration required to rescue a strain at a given antibiotic dose. The MAC assay revealed that PB selectively protects Bacillus cereus and a marine sponge-associated Bacillus sp., but not pathogens or other sponge-associated isolates, indicating narrow-spectrum antidote activity. These findings support a role of pseudovibriamides as selective antibiotic antagonists and provide a framework for future work of natural antidotes for targeted microbiota protection both in ecological and clinical settings.