# Organic acid toxicity, tolerance, and production in Escherichia coli biorefining applications

## TL;DR

This paper reviews how E. coli is affected by organic acids and how it can tolerate them, with examples of successful production processes.

## Contribution

The paper provides a comprehensive overview of organic acid toxicity and tolerance mechanisms in E. coli for biorefining.

## Key findings

- Organic acids are toxic to E. coli at concentrations below those needed for economical production.
- E. coli uses multiple tolerance mechanisms like decarboxylation and ion transporters to survive low pH.
- Examples of successful organic acid production processes in E. coli are discussed.

## Abstract

Organic acids are valuable platform chemicals for future biorefining applications. Such applications involve the conversion of low-cost renewable resources to platform sugars, which are then converted to platform chemicals by fermentation and further derivatized to large-volume chemicals through conventional catalytic routes. Organic acids are toxic to many of the microorganisms, such as Escherichia coli, proposed to serve as biorefining platform hosts at concentrations well below what is required for economical production. The toxicity is two-fold including not only pH based growth inhibition but also anion-specific effects on metabolism that also affect growth. E. coli maintain viability at very low pH through several different tolerance mechanisms including but not limited to the use of decarboxylation reactions that consume protons, ion transporters that remove protons, increased expression of known stress genes, and changing membrane composition. The focus of this mini-review is on organic acid toxicity and associated tolerance mechanisms as well as several examples of successful organic acid production processes for E. coli.