{"id":134500,"date":"2023-11-15T07:10:00","date_gmt":"2023-11-15T06:10:00","guid":{"rendered":"https:\/\/renewable-carbon.eu\/news\/?p=134500"},"modified":"2023-11-09T11:06:53","modified_gmt":"2023-11-09T10:06:53","slug":"microbial-upcycling-of-waste-pet-to-adipic-acid","status":"publish","type":"post","link":"https:\/\/renewable-carbon.eu\/news\/microbial-upcycling-of-waste-pet-to-adipic-acid\/","title":{"rendered":"Microbial Upcycling of Waste PET to Adipic Acid"},"content":{"rendered":"\n\n\n

Microorganisms can be genetically engineered to transform abundant waste feedstocks into value-added small molecules that would otherwise be manufactured from diminishing fossil resources. Herein, we report the first one-pot bio-upcycling of PET plastic waste into the prolific platform petrochemical and nylon precursor adipic acid in the bacterium\u00a0Escherichia coli<\/em>. Optimizing heterologous gene expression and enzyme activity enabled increased flux through the\u00a0de novo<\/em>\u00a0pathway, and immobilization of whole cells in alginate hydrogels increased the stability of the rate-limiting enoate reductase BcER. The pathway enzymes were also interfaced with hydrogen gas generated by engineered\u00a0E. coli<\/em>DD-2 in combination with a biocompatible Pd catalyst to enable adipic acid synthesis from metabolic\u00a0cis<\/em>,cis<\/em>-muconic acid. Together, these optimizations resulted in a one-pot conversion to adipic acid from terephthalic acid, including terephthalate samples isolated from industrial PET waste and a post-consumer plastic bottle.<\/p>\n\n\n\n

Introduction<\/h3>\n\n\n\n

Synthetic pathways to industrial chemicals can be designed and assembled in living cells using modern synthetic biology. This enables the bioproduction of target compounds from renewable resources via fermentation and is emerging as an elegant and viable alternative to multistep synthesis from diminishing fossil fuels. (1,2)<\/a> Many of these pathways proceed via the fermentation of carbohydrate feedstocks via primary metabolic reactions in vivo<\/em>. However, this approach also enables the upcycling of waste carbon from existing industrial processes to create circular economies, avoiding the environmental consequences of landfill and\/or incineration processes. This includes the upcycling of plastic-waste-derived small molecules from post-consumer polyethylene terephthalate (PET)\u2500a thermoplastic material used throughout the modern chemical industry to create a wealth of everyday products. The global demand for this material exceeds 30 M ton\/year, of which >80% is designed to be single use, leading to ca. 25 M ton\/year of post-consumer PET waste and contributing to the global plastic waste crisis. (3,4)<\/a><\/p>\n\n\n\n

Although chemical and biological approaches to the depolymerization and recycling of PET waste are being investigated, bio-upcycling technologies to convert plastic waste into higher value small molecules are less established. (5\u221212)<\/a> This approach is attractive as the PET depolymerization products ethylene glycol and terephthalic acid (TA) are microbial metabolites and therefore viable substrates for de novo<\/em> metabolic pathway design. To this end, Kim et al. previously reported the bioconversion of PET-derived ethylene glycol into glycolic acid in Gluconobacter oxydans<\/em>and TA into vanillic acid, muconic acid, gallic acid, and pyrogallol in engineered E. coli<\/em>MG1655 in 33\u201393% yield. (13)<\/a> More recently, Werner et al. reported the high-level bioproduction of \u03b2-ketoadipate from bis<\/em>(2-hydroxyethyl)terephthalate (BHET) in 76% yield in engineered Pseudomonas putida<\/em>KT2440. (14)<\/a> This was also achieved by Sullivan et al. in 73% yield using P. putida<\/em>AW307 and benzoate isolated from chemically modified mixed plastic waste. (15)<\/a> In 2021, our lab reported the conversion of post-consumer PET from a waste plastic bottle into the vanilla flavor compound vanillin in 79% yield in engineered E. coli<\/em>MG1655 RARE. (16)<\/a><\/p>\n\n\n\n

Following on from this work, we sought to expand the range of small molecules that can be accessed via microbial synthesis from terephthalic acid. Adipic acid (AA) is an aliphatic 1,6-dicarboxylic acid and prolific platform chemical that is used throughout the materials, pharmaceuticals, fragrances, and cosmetics industries. It is currently manufactured on a 2.6 M ton\/year scale from petrochemically derived benzene via the nitric acid-catalyzed oxidation of cyclohexanol and cyclohexanone. The process is highly energy intensive and releases a mol\/mol equivalent of nitrous oxide into the atmosphere. These emissions have been shown to significantly contribute to global greenhouse gas levels; (17)<\/a> 1 kg of N2<\/sub>O equates to 298 kg CO2<\/sub> equivalents. As a result, the bioproduction of adipic acid from renewable feedstocks has been an active area of research.<\/p>\n\n\n\n

Recent work has included the high-level production of the adipate analogue \u03b2-ketoadipate from\u00a0d-glucose by Rorrer et al. in engineered\u00a0P. putida<\/em>\u00a0KT2440 and the one-pot bioconversion of lignin-derived guaiacol to adipic acid by our laboratory in engineered\u00a0Escherichia coli<\/em>\u00a0(Figure 1<\/a>A).\u00a0(18,19)<\/a>\u00a0However, the microbial synthesis of adipic acid directly from waste PET remains an outstanding challenge in the field of chemical biotechnology. Herein we report the first one-pot bioproduction of adipic acid from terephthalic acid and terephthalate waste in engineered\u00a0Escherichia coli<\/em>. The reaction proceeds in aqueous media at room temperature and produces adipic acid in 79% conversion (115 mg\/L) in 24 h when cells are immobilized in alginate hydrogels (Figure 1<\/a>B). Together, this study validates the use of microbial cells as a viable biotechnology for the upcycling of plastic-derived small molecules and PET plastic waste.<\/p>\n\n\n

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Figure 1. Microbial biotransformation and fermentation approaches to adipic acid and adipate analogues. (A) Carbohydrate fermentation in\u00a0P. putida<\/em>\u00a0and valorization of lignin aromatics in\u00a0E. coli<\/em>. (B) Proposed bio-upcycling of terephthalic acid to adipic acid. \u00a9<\/strong> ACS Publications<\/figcaption><\/figure><\/div>\n\n\n

For full report, results and discussion please click here<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

Microorganisms can be genetically engineered to transform abundant waste feedstocks into value-added small molecules that would otherwise be manufactured from diminishing fossil resources. Herein, we report the first one-pot bio-upcycling of PET plastic waste into the prolific platform petrochemical and nylon precursor adipic acid in the bacterium\u00a0Escherichia coli. Optimizing heterologous gene expression and enzyme activity […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_robots_primary_cat":"none","nova_meta_subtitle":"A de novo biosynthesis pathway is reported in the bacterium Escherichia coli to convert terephthalate waste from post-consumer and industrial PET samples into the industrial chemical and nylon precursor adipic acid","footnotes":""},"categories":[5572,17143],"tags":[10416,12518,14460,14007,14462,20700,15515],"supplier":[20035,11602],"class_list":["post-134500","post","type-post","status-publish","format-standard","hentry","category-bio-based","category-recycling","tag-circulareconomy","tag-feedstocks","tag-microbial","tag-pet","tag-plasticwaste","tag-thermoplastic","tag-upcycling","supplier-acs-central-science","supplier-university-of-edinburgh"],"_links":{"self":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts\/134500","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/comments?post=134500"}],"version-history":[{"count":0,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts\/134500\/revisions"}],"wp:attachment":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/media?parent=134500"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/categories?post=134500"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/tags?post=134500"},{"taxonomy":"supplier","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/supplier?post=134500"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}