# Mixed Waste Streams for Bioproduction: Exploring Bacterial Wax Ester Production in Nitrogen‐Rich Acidogenic Fermentate

## TL;DR

Researchers used waste-derived fatty acids to produce bacterial wax esters, achieving high yields and demonstrating the potential of mixed waste streams for bioproduction.

## Contribution

First reported production of bacterial wax esters from a raw, mixed waste stream using acidogenic fermentate as the sole carbon source.

## Key findings

- WE accumulation reached 37% of cell dry weight, the highest in ADP1 to date.
- WE titres of over 160 mg/L were achieved from volatile fatty acids in mixed waste streams.
- Synthetic media achieved up to 190 mg/L of WE, but translating this to fermentate was challenging.

## Abstract

Microbial lipids offer a promising alternative to petrochemicals, but high associated costs and low conversion efficiencies pose barriers to their commercialisation. In particular, sugar‐based feedstocks are too expensive for the production of commodity chemicals, and recently attention has turned to volatile fatty acids (VFAs) as a cheaper, more widely available carbon source. Acidogenic fermentation can be used to produce high concentrations of VFAs from municipal and agricultural waste. By harnessing metabolically engineered
Acinetobacter baylyi
ADP1, the suitability of VFAs as sole carbon sources for wax ester (WE) production was investigated. These studies resulted in the highest WE accumulation in ADP1 achieved to date, at 37% of cell dry weight, and the first reported production of bacterial WEs from a raw, mixed waste stream, utilising fermentate as the sole carbon source. WE titres of over 160 mg/L from VFAs were achieved, highlighting the unique benefits of mixed feedstocks typically considered problematic for bioproduction. Finally, the potential advantages of employing fermentates rich in longer chain VFAs are explored. In synthetic media, WE titres up to 190 mg/L were achieved, but translation to fermentate was challenging, emphasising the need for continued research in this area.

The bacterium
Acinetobacter baylyi
ADP1, a known source of biogenic wax esters, and its glyoxylate shunt knockout mutant, were demonstrated to grow on short‐chain fatty acids and directly on acidogenic fermentate from arrested anaerobic digestion of biomass. Compositional control of the fermentate results in different growth and wax accumulation behaviour.