Bio-based lactate driven medium chain carboxylic acid production by Megasphaera hexanoica along with metabolomic analysis

Abstract

Waste-based biorefinery has advantages for waste management as well as renewable energy and chemical production. Several studies have been conducted to utilize various wastes through biorefinery, and medium chain carboxylic acids (MCCAs) production using chain elongation pathway in microorganisms is also one of the promising waste-based biorefinery. Not only MCCAs itself can be utilized as food additives, animal feeds, antimicrobial agents, it also can be used as biofuels and platform chemicals by conversion of its carboxyl group. MCCAs can be produced from short chain carboxylic acids (SCCAs) through a reverse β-oxidation (RBO) pathway which can be utilized in few bacteria. To elongate chain of SCCAs, electron donors (EDs) such as ethanol, lactate, sugars, and hydrogen are necessary. Among these EDs, lactate can be readily produced from carbohydrate-rich wastes such as food wastes, municipal wastes, and acid whey. Therefore, chain elongation using lactate as ED have economic and environmental benefits. Valorization of lactate and SCCAs through production of MCCAs, like caproate and caprylate, has been studied globally because of their decent value and applicability. In this study, using Megasphaera hexanoica, a MCCAs-producing bacterium, highest titer of 20.11 g/L of caproate production was achieved by balancing lactate and SCCAs as EDs and EAs respectively. In addition, caprylate production over 80% selectivity was also evaluated through regulating electron acceptors. Carbon flux from substrates to products was calculated and visualized based on 13C labeled lactate analysis. Furthermore, intracellular metabolites change according to supplemented electron donors was analyzed and interpreted. Through these investigations, it was possible to propose novel MCCAs production process from organic wastes using M. hexanoica as well as competitive differentiation of this strain was also presented.