Production of limonene from textile and cardboard wastes establishes a proof of concept for the sustainable production of terpenes.

Abstract

Cellulose containing textiles (cotton) and cardboard/carton-based wastes represent a large pool of untapped organic carbon. These wastes have enormous potential for utilization as carbon feedstocks in industrial biotechnology processes. Essentially, cotton/cardboard (CC) waste is pure cellulose (with some additives) in the form of polymerised glucose composed of β (1→4) linked D-glucose subunits. CC waste materials can be enzymatically hydrolysed to monomers of D-glucose in aqueous solution, to form ‘glucose juice’, which can then be fermented to bio-ethanol. In principle, value added chemicals could also be produced from glucose juice. Bioconversion of CC waste to other compounds of importance to industry could form the basis of environmentally attractive production routes. Terpenes are one of the largest and most diverse classes of natural compounds, and are of value to industry as they have a wide range of applications as flavourings, fragrances, pharmaceuticals, bio-pesticides and biofuels. Here, we investigated the bioconversion of CC waste to the exemplar terpene limonene as a proof-of-concept. Six different CC waste streams were enzymatically hydrolysed to glucose juice and used to produce limonene by fermentation of an engineered E. coli microbial cell factory. D-glucose content was determined in the glucose juice, and then metabolized by E. coli using an engineered heterogenic biolipid synthesis pathway (the mevalonate pathway) to produce limonene (300–700 mg L− 1), which was then partitioned into a nonane overlay. This study establishes an important proof-of-concept for terpene production from hydrolysed CC waste streams.