# A Novel Link Between Electron Transport Chain Modulation and mcl‐PHA Production in Pseudomonas aeruginosa 5300 Using Azide as a Modulator

## TL;DR

This study shows how using azide can boost mcl-PHA production in Pseudomonas aeruginosa by altering the electron transport chain.

## Contribution

A novel link between electron transport chain modulation and mcl-PHA production using azide is established.

## Key findings

- Azide increased mcl-PHA content from 39.4% to 66.4% cell dry weight in Pseudomonas aeruginosa.
- Oleic acid and azide shifted electron transport chain activity, increasing NADH consumption and mcl-PHA accumulation.
- mcl-PHA production was achieved rapidly in nutrient-enriched conditions, which was previously unreported.

## Abstract

Medium chain length polyhydroxyalkanoates (mcl‐PHA) are elastomeric biodegradable bioplastics produced by a few bacteria. The large‐scale mcl‐PHA production remains limited by the low yield of bacterial strains and biomass reduction due to prolonged nutrient limitation in the media. In the present study,
Pseudomonas aeruginosa
MCC 5300 produced mcl‐PHA copolymer of about 39.4% cell dry weight (CDW) at a short duration of 24 h of growth in tryptic soy broth media containing oleic acid and the PHA content was enhanced up to 66.4% CDW in the presence of azide. The production of mcl‐PHA at such a short duration was not reported previously in nutrient‐enriched conditions. The application of azide enhanced mcl‐PHA production in the bacteria. Oleic acid shifted the electron transport chain (ETC) from the cytochrome c pool to the ubiquinol pool. The inhibition of bo3‐oxidase by azide increased electron flux towards bd‐oxidase to maintain proton gradient for oxidative phosphorylation, causing depletion of cellular reduced‐redox cofactor levels. The increased mcl‐PHA accumulation in bacteria compensated for the loss of reduced‐redox cofactors, thus maintaining cellular redox homeostasis. Hence, the study invokes a novel link between the ETC and mcl‐PHA production.

The oleic acid and azide inhibited the cytochrome c oxidase activity in
Pseudomonas aeruginosa
MCC 5300, shifting the electron flux towards bd‐oxidase. This resulted in more NADH consumption to maintain the proton gradient for energy generation. The rapid depletion of NADH triggered high mcl‐PHA accumulation.