A new ether bond-splitting enzyme found in Gram-positive polyethylene glycol 6000-utilizing bacterium, Pseudonocardia sp. strain K1

Abstract

Pseudonocardia sp. strain K1 is the only Gram-positive bacterium among the bacteria aerobically metabolizing polyethylene glycol (PEG). Generally, PEG is metabolized by an oxidative pathway in which a terminal alcohol group of PEG is oxidized to aldehyde and to carboxylic acid and then an ether bond is oxidatively cleaved. As the cell-free extract of Pseudonocardia sp. strain K1 has PEG dehydrogenase, PEG aldehyde dehydrogenase and diglycolic acid (DGA) dehydrogenase (DGADH) activities, all of which are constitutively formed, the strain has a metabolic pathway similar to that so far known. We purified an ether bond-splitting enzyme as DGADH. The molecular mass of the enzyme was estimated to be 55 kDa; and it consisted of two identical subunits. The enzyme oxidatively cleaved both an ether bond of PEG 3000 dicarboxylic acid and DGA. The N-terminal amino acid sequence of the purified enzyme had high homology with various superoxide dismutases and the enzyme had also superoxide dismutase activity. The atomic absorption spectrum showed that approximately one atom of Fe was included in each subunit of the enzyme. DGADH activity increased in the cells grown in a PEG medium supplemented with FeCl(3). Thus, we concluded that the enzyme purified from Pseudonocardia sp. strain K1 is a new ether bond-splitting enzyme.

Dual regulation of a polyethylene glycol degradative operon by AraC-type and GalR-type regulators in Sphingopyxis macrogoltabida strain 103

“…Research to date on PEG degradation in micro-organisms has mainly concentrated on characterization of the relevant enzymes (Yamanaka & Kawai, 1989;Schramn & Schink, 1991;Frings et al, 1992;Sugimoto et al, 2001;Yamashita et al, 2004;Ohta et al, 2005). The structural and regulatory features of the degradative genes have not been reported yet.…”

“…An ether-bond splitting enzyme was suggested to be hydroxyacid dehydrogenase in S. terrae (Enokibara & Kawai, 1997) or superoxide dismutase in the Gram-positive PEG degrader Pseudonocardia sp. strain K-1 (Yamashita et al, 2004). The gene encoding the PEG-DH, pegA, was cloned from S. terrae (Sugimoto et al, 2001).…”

Biodegradation of Ether Pollutants by Pseudonocardia sp. Strain ENV478

“…Although no genes that are obviously involved in 2HEAA metabolism are apparent in the cloned THF operon of strain K1, this strain does produce a diglycolic acid dehydrogenase that cleaves ether bonds adjacent to terminal carboxyl groups in short-chain ethers (41). The lack of such activity or the inability of 1,4-dioxane or its metabolites to induce this or similar activity in strain ENV478 also could limit 2HEAA metabolism.…”

“…This suggests either that an alternative degradation pathway was present in fungi, that 2HEAA was rapidly degraded to these products by the fungi and was not detected in the analyses performed in the study, or that the derivatization method used in the study did not allow detection of 2HEAA. Degradation of 2HEAA to these products could be facilitated by a dehydrogenase related to the diglycolic acid dehydrogenase of strain K1, which cleaves ether bonds adjacent to terminal carboxyl groups in both short-chain ethers (diglycolic acid) and long-chain polymers (polyethylene glycol) (41). A lack of a similar enzyme activity in ENV478 or a stringent substrate range that does not allow the enzyme to cleave 2HEAA, which may be the case in strain K1, may prevent these strains from metabolizing 2HEAA and result in their inability to grow on 1,4-dioxane.…”

Bioaugmentation for treatment of full-scale diethylene glycol monobutyl ether (DGBE) wastewater by Serratia sp. BDG-2

“…Many screened strains or acclimated microbial consortia are shown significant abilities of degradating recalcitrant or toxic organics in laboratory [28,13,27], but have to face up to the risk of failure inducing by inhospitable actual conditions in full-scale facilities.…”