Microbial degradation of polyethers

• Published in: Applied microbiology and biotechnology 2002, Vol.58 (1), p.30-38
• Main Author: Kawai, F
• Format: Article
• Language: English
• Subjects: acetaldehyde; Acids; Aerobiosis; Alcohol; alcohol dehydrogenase; Alcohols; aldehyde dehydrogenase; Anaerobic bacteria; Anaerobiosis; Bacteria; Bacteria - enzymology; Bacteria - metabolism; biodegradation; Biodegradation of pollutants; Biological and medical sciences; Biotechnology; brown-rot fungi; carbon; Carboxylic acids; cytoplasm; Dehydrogenase; Dehydrogenases; dehydrogenation; diglycolic acid; enantiomers; Environment and pollution; Enzymes; Ethers - chemistry; Ethers - metabolism; flavoproteins; Fundamental and applied biological sciences. Psychology; glycolic acid; glyoxylic acid; horses; Industrial applications and implications. Economical aspects; iron; liver; Metabolism; Microbial degradation; Molecular weight; oxidants; oxidation; Oxidation-Reduction; Oxidizing agents; polyethers; Polyethylene glycol; Polyethylene Glycols - chemistry; Polyethylene Glycols - metabolism; Polymers; Polymers - chemistry; Polymers - metabolism; polypropylenes; propanediol dehydratase; Propylene Glycols - chemistry; Propylene Glycols - metabolism; Pseudomonas stutzeri; reducing agents; Stenotrophomonas maltophilia; substrate specificity; toxicity
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-001-0850-2

This paper summarizes studies on microbial degradation of polyethers. Polyethers are aerobically metabolized through common mechanisms (oxidation of terminal alcohol groups followed by terminal ether cleavage), well-characterized examples being found with polyethylene glycol (PEG). First the polymer is oxidized to carboxylated PEG by alcohol and aldehyde dehydrogenases and then the terminal ether bond is cleaved to yield the depolymerized PEG by one glycol unit. Most probably PEG is anaerobically metabolized through one step which is catalyzed by PEG acetaldehyde lyase, analogous to diol dehydratase. Whether aerobically or anaerobically, the free OH group is necessary for metabolization of PEG. PEG with a molecular weight of up to 20,000 was metabolized either in the periplasmic space (Pseudomonas stutzeri and sphingomonads) or in the cytoplasm (anaerobic bacteria), which suggests the transport of large PEG through the outer and inner membranes of Gram-negative bacterial cells. Membrane-bound PEG dehydrogenase (PEG-DH) with high activity towards PEG 6,000 and 20,000 was purified from PEG-utilizing sphingomonads. Sequencing of PEG-DH revealed that the enzyme belongs to the group of GMC flavoproteins, FAD being the cofactor for the enzyme. On the other hand, alcohol dehydrogenases purified from other bacteria that cannot grow on PEG oxidized PEG. Cytoplasmic NAD-dependent alcohol dehydrogenases with high specificity towards ether-alcohol compound, either crude or purified, showed appreciable activity towards PEG 400 or 600. Liver alcohol dehydrogenase (equine) also oxidized PEG homologs, which might cause fatal toxic syndrome in vivo by carboxylating PEG together with aldehyde dehydrogenase when PEG was absorbed. An ether bond-cleaving enzyme was detected in PEG-utilizing bacteria and purified as diglycolic acid (DGA) dehydrogenase from a PEG-utilizing consortium. The enzyme oxidized glycolic acid, glyoxylic acid, as well as PEG-carboxylic acid and DGA. Similarly, dehydrogenation on polypropylene glycol (PPG) and polytetramethylene glycol (PTMG) was suggested with cell-free extracts of PPG and PTMG-utilizing bacteria, respectively. PPG commercially available is atactic and includes many structural (primary and secondary alcohol groups) and optical (derived from pendant methyl groups on the carbon backbone) isomers. Whether PPG dehydrogenase (PPG-DH) has wide stereo- and enantioselective substrate specificity towards PPG isomers or not must await further puri