# Mutations Affecting Cellular Levels of Cobalamin (Vitamin B12) Confer Tolerance to Bactericidal Antibiotics in Burkholderia cenocepacia

## TL;DR

This paper shows that mutations affecting vitamin B12 levels in a lung pathogen help it survive antibiotic treatment by reducing harmful oxygen molecules.

## Contribution

The study reveals a novel link between vitamin B12 metabolism and antibiotic tolerance in Burkholderia cenocepacia.

## Key findings

- Mutations in cobalamin biosynthesis genes confer tolerance to tobramycin and other bactericidal antibiotics.
- Reduced reactive oxygen species production in mutants is linked to TCA cycle overload due to succinyl-CoA depletion.
- Microaerobic conditions enhance antibiotic tolerance in both wild-type and mutant strains.

## Abstract

The Burkholderia cepacia complex (Bcc) consists of opportunistic pathogens known to cause pneumonia in immunocompromised individuals, especially those with cystic fibrosis. Treating Bcc pneumonia is challenging due to the pathogens' high multidrug resistance. Therefore, inhalation therapy with tobramycin powder, which can achieve high antibiotic concentrations in the lungs, is a promising treatment option. In this study, we investigated potential mechanisms that could compromise the effectiveness of tobramycin therapy. By selecting for B. cenocepacia survivors against tobramycin, we identified three spontaneous mutations that disrupt a gene encoding a key enzyme in the biosynthesis of cobalamin (Vitamin B12). This disruption may affect the production of succinyl-CoA by methylmalonyl-CoA mutase, which requires adenosylcobalamin as a cofactor. The depletion of cellular succinyl-CoA may impact the tricarboxylic acid (TCA) cycle, which becomes metabolically overloaded upon exposure to tobramycin. Consequently, the mutants exhibited significantly reduced reactive oxygen species (ROS) production. Both the wild-type and mutants showed tolerance to tobramycin and various other bactericidal antibiotics under microaerobic conditions. This suggests that compromised ROS-mediated killing, due to the impacted TCA cycle, underlies the mutants’ tolerance to bactericidal antibiotics. The importance of ROS-mediated killing and the potential emergence of mutants that evade it through the depletion of cobalamin (Vitamin B12) provide valuable insights for developing strategies to enhance antibiotic treatments of Bcc pneumonia.