Biobased PET from lignin using an engineered cis, cis-muconate-producing Pseudomonas putida strain with superior robustness, energy and redox properties

Abstract

Polyethylene terephthalate (PET), the most common synthetic polyester today, is largely produced from fossil resources, contributing to global warming. Consequently, sustainable sources must be developed to meet the increasing demand for this useful polymer. Here, we demonstrate a cascaded value chain that provides green PET from lignin, the world's most underutilized renewable, via fermentative production of cis, cis-muconate (MA) from lignin-based aromatics as a central step. Catechol, industrially the most relevant but apparently also a highly toxic lignin-related aromatic, strongly inhibited MA-producing Pseudomonas putida MA-1. Assessed by 13C metabolic flux analysis, the microbe substantially redirected its carbon core fluxes, resulting in enhanced NADPH supply for stress defense but causing additional ATP costs. The reconstruction of MA production in a genome-reduced P. putida chassis yielded novel producers with superior pathway fluxes and enhanced robustness to catechol and a wide range of other aromatics. Using the advanced producer P. putida MA-10 catechol, MA could be produced in a fed-batch process from catechol (plus glucose as additional growth substrate) up to an attractive titer of 74 g L-1 and a space-time-yield of 1.4 g L-1 h-1. In terms of co-consumed sugar, the further streamlined strain MA-11 achieved the highest yield of 1.4 mol MA (mol glucose)-1, providing a striking economic advantage. Following fermentative production, bio-based MA was purified and used to chemically synthetize the PET monomer terephthalic acid and the comonomer diethylene glycol terephthalic acid through five steps, which finally enabled the first green PET from lignin.