The microbial degradation of polyethylene glycols

The work described in this thesis was undertaken to elucidate the metabo­lic pathways by which oligo- and polymeric glycols are degraded by micro organisms. From a variety of microorganisms isolated by elective culture on minimal medium containing either ethylene glycol (EG), diethylene glycol (DEG) or polyethylene glycol 400 (PEG 400), three pure cultures, designated Z, R and 0, were selected for further study. Strain R showed a marked prefer­ence for utilising oligomeric glycols (2-4 EO groups) while strain 0 grew best on the polymeric materials (6-25 EO groups); strain Z utilised EG exclusively. The partial degradation of PEG 200 by strains R and 0 was studied in some detail and the specificity of these isolates for growth within a particular molecular weight range confirmed. Those components of the mixture that were not utilised were converted into acidic derivatives which accumulated in the medium. Cell-extracts of EG-grown strains Z and R contained a glycol dehydrogenase which resembled in several characteristics the methanol dehydrogenase of methylotrophic bacteria in that it had a high pH optimum, an in vitro requirement for phenazine methosulphate (PMS) as an artificial carrier, was activated by NH^ and had a molecular weight in the region of 120000. This enzyme which catalysed the conversion of ethylene glycol to glycol- aldehyde also attacked DEG, triethylene+ glycol (TEG) and a number of primary and secondary alcohols. A NAD -linked aldehyde dehydrogenase, glycollate oxidase (located in the particulate fraction) and enzymes involved in the metabolism of glycollate to pyruvate, in particular glyoxylate carboligase, tartronate semialdehyde reductase and glycerate kinase, were demonstrated in the soluble fraction of extracts of strain Z grown on EG and of strain R grown on EG, DEG or TEG. These enzymes were significantly absent (with the exception of aldehyde dehydrogenase) in succinate-grown cells. This is consistent with oxidation of EG and possibly DEG and TEG by way of the glycerate pathway. The metabolic control of EG-metabolism in strains Z and R was examined but because the appropriately blocked mutants were not isolated, identi­fication of the specific inducers was not possible. Preliminary results suggested that successive inductive events regulate the synthesis of enzymes which convert EG into 2-phosphoglycerate. Evidence was obtained to implicate an active transport system for ethylene glycol uptake in strains Z and R, which recognised oligomeric but not polymeric glycols. The high Ks value calculated suggested that EG is an unnatural substrate of a glycerol or alkanol transport system. Oxidation of polymeric glycols but not EG or the oligomeric glycols was effected by PMS-supplemented extracts of strain 0 grown on PEG 400. The immediate product(s) of PEG oxidation were not identified but are probably carboxylated derivatives.