Title: Microbial synthesis of a branched-chain ester platform from organic waste carboxylates

Abstract

Processing of lignocellulosic biomass or organic wastes produces a plethora of chemicals such as short, linear carboxylic acids, known as carboxylates, derived from anaerobic digestion. While these carboxylates have low values and are inhibitory to microbes during fermentation, they can be biologically upgraded to high-value products. In this study, we expanded our general framework for biological upgrading of carboxylates to branched-chain esters by using three highly active alcohol acyltransferases (AATs) for alcohol and acyl CoA condensation and modulating the alcohol moiety from ethanol to isobutanol in the modular chassis cell. With this framework, we demonstrated the production of an ester library comprised of 16 out of all 18 potential esters, including acetate, propionate, butanoate, pentanoate, and hexanoate esters, from the 5 linear, saturated C2-C6 carboxylic acids. Among these esters, 5 new branched-chain esters, including isobutyl acetate, isobutyl propionate, isobutyl butyrate, isobutyl pentanoate, and isobutyl hexanoate were synthesized in vivo. During 24 h in situ fermentation and extraction, one of the engineered strains, EcDL208 harnessing the SAAT of Fragaria ananassa produced 63 mg/L of a mixture of butyl and isobutyl butyrates from glucose and butyrate co-fermentation and 127 mg/L of a mixture of isobutyl and pentyl pentanoates from glucose and pentanoatemore » co-fermentation, with high specificity. These butyrate and pentanoate esters are potential drop-in liquid fuels. This study provides better understanding of functional roles of AATs for microbial biosynthesis of branchedchain esters and expands the potential use of these esters as drop-in biofuels beyond their conventional flavor, fragrance, and solvent applications.« less

Authors:

Layton, Donovan S.; Trinh, Cong T.

Publication Date:

Thu Dec 01 00:00:00 EST 2016

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER). Biological Systems Science Division

OSTI Identifier:

1286298

Alternate Identifier(s):

OSTI ID: 1629031

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Published Article

Journal Name:

Metabolic Engineering Communications

Additional Journal Information:

Journal Name: Metabolic Engineering Communications Journal Volume: 3 Journal Issue: C; Journal ID: ISSN 2214-0301

Publisher:

Elsevier

Country of Publication:

Netherlands

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES; Carboxylate platform; Ester platform; Branched-chain ester; Modular cell; Biological upgrading; Organic waste; Lignocellulosic biomass; Isobutyl esters