Ethylene glycol and glycolic acid production from xylonic acid by Enterobacter cloacae

Abstract

Background: Biological routes for ethylene glycol production have been developed in recent years by constructing the synthesis pathways in different microorganisms. However, no microorganisms have been reported yet to produce ethylene glycol naturally. Results: Xylonic acid utilizing microorganisms were screened from natural environments, and an Enterobacter cloacae strain was isolated. The major metabolites of this strain were ethylene glycol and glycolic acid. However, the metabolites were switched to 2,3-butanediol, acetoin or acetic acid when this strain was cultured with other carbon sources. The metabolic pathway of ethylene glycol and glycolic acid synthesis from xylonic acid in this bacterium was identified. Xylonic acid was converted to 2-dehydro-3-deoxy-D-pentonate catalyzed by D-xylonic acid dehydratase. 2-Dehydro-3-deoxy-D-pentonate was converted to form pyruvate and glycolaldehyde, and this reaction was catalyzed by an aldolase. D-xylonic acid dehydratase and 2-dehydro-3-deoxy-D-pentonate aldolase were encoded by yjhG and yjhH, respectively. The two genes are part of the same operon and are located adjacent on the chromosome. Besides yjhG and yjhH, this operon contains four other genes. However, individually inactivation of these four genes had no effect on either ethylene glycol or glycolic acid production; both formed from glycolaldehyde. YqhD exhibits ethylene glycol dehydrogenase activity in vitro. However, a low level of ethylene glycol was still synthesized by E. cloacae ΔyqhD. Fermentation parameters for ethylene glycol and glycolic acid production by the E. cloacae strain were optimized, and aerobic cultivation at neutral pH were found to be optimal. In fed batch culture, 34 g/L of ethylene glycol and 13 g/L of glycolic acid were produced in 46 hours, with a total conversion ratio of 0.99 mol/mol xylonic acid.Conclusions: A novel route of xylose biorefinery via xylonic acid as an intermediate has been established.

Production of 2,3-dihydroxyisovalerate by Enterobacter cloacae

“…E. cloacae S1 is a strain used for ethylene glycol and glycolic acid production [12]. Here the 2,3butanediol production ability of this strain was tested.…”

“…E. cloacae S1 is a strain that was isolated from the soil, and this strain produces high levels of ethylene glycol and glycolic acid when cultured with xylonic acid as a carbon source. This strain is a high natural 2,3-butanediol producer and the gene replacement method suitable for this bacterium has been established [12]. The genome of E. cloacae S1 has been sent to GenBank with the accession number of VSZU00000000.…”

Ethylene glycol and glycolic acid production by wild‐type Escherichia coli

“…All conversion ratios were less than 1, suggesting that a fraction of intermediates of the ethylene glycol and glycolic acid synthesis from xylonic acid might be converted to other products. This is different from ethylene glycol and glycolic acid production by wild-type Enterobacter cloacae, which has a total conversion ratio of nearly 1 mol/mol [17]. It has been mentioned that glycolic acid can be converted to glyoxylate into the glyoxylate cycle [20].…”

“…However, E. coli might not be the best workhorse for ethylene glycol and glycolic acid production. In our recent research, Enterobacter cloacae has shown higher efficiency in ethylene glycol and glycolic acid production on xylonic acid than the E. coli here [17]. The traditional way of biological utilization of biomass includes the hydrolysis of biomass to monosaccharides, which are further used as a carbon source by microorganisms for their growth and production of various products.…”