We're better off if chemicals we use in everyday life are created from renewable resources using biotechnology - currently many of those chemicals are instead derived from fossil resources.

Phenol, a starting material for the production of numerous industrial chemicals and polymers, including bisphenol A and phenolic resins, is an important commodity chemical, and its production depends entirely on the chemical synthesis from benzene, and its annual production exceeds 8 million tons worldwide.

Microbial production of phenol would seem to be a non-viable process considering the high toxicity of phenol to the cell. but a new paper has reported the successful development of an engineered Escherichia coli (E. coli) strain which can produce phenol from glucose.

E. coli has been a workhorse for biological production of various value-added compounds such as succinic acid and 1,4-butanediol in industrial scale. However, due to its low tolerance to phenol, E. coli was not considered a viable host strain for the biological production of phenol.

The research team noted the genetic and physiological differences of various E. coli strains and investigated 18 different E. coli strains with respect to phenol tolerance and engineered all of the 18 strains simultaneously. If traditional genetic engineering methods were used, this would have taken years to do but they used synthetic small RNA (sRNA) technology they recently developed (Nature Biotechnology, vol 31, pp 170-174, 2013). 

The sRNA technology allowed the team to screen 18 E. coli strains with respect to the phenol tolerance, and the activities of the metabolic pathway and enzyme involved in the production of phenol. The research team also metabolically engineered the E. coli strains to increase carbon flux toward phenol and finally generated an engineered E. coli strain which can produce phenol from glucose.

The team also developed a biphasic extractive fermentation process to minimize the toxicity of phenol to E. coli cells. Glycerol tributyrate was found to have low toxicity to E. coli and allowed efficient extraction of phenol from the culture broth. Through the biphasic fed-batch fermentation using glycerol tributyrate as an in situ extractant, the final engineered E. coli strain produced phenol to the highest titer and productivity reported (3.8 g/L and 0.18 g/L/h, respectively).

The strategy used for the strain development and the fermentation process will serve as a framework for metabolic engineering of microorganisms for the production of toxic chemicals from renewable resources.