Fermentative degradation of polyethylene glycol by a strictly anaerobic, gram-negative, nonsporeforming bacterium, Pelobacter venetianus sp. nov

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Abstract
The synthetic polyether polyethylene glycol (PEG) with a MW of 20,000 was anaerobically degraded in enrichment cultures inoculated with mud of limnic and marine origins. Three strains (Gra PEG 1, Gra PEG 2 and Ko PEG 2) of rod-shaped, gram-negative, non-spore-forming, strictly anaerobic bacteria were isolated in mineral medium with PEG as the sole source of C and energy. All strains degraded dimers, oligomers and polymers of PEG up to a MW of 20,000 completely by fermentation to nearly equal amounts of acetate and ethanol. The monomer ethylene glycol was not degraded. An ethylene glycol fermenting anaerobe (strain Gra EG 12) isolated from the same enrichments was identified as Acetobacterium woodii. The PEG-fermenting strains did not excrete extracellular depolymerizing enzymes and were inhibited by ethylene glycol, probably owing to a blocking of the cellular uptake system. PEG, some PEG-containing nonionic detergents, 1,2-propanediol, 1,2-butanediol, glycerol and acetoin were the only growth substrates utilized of a broad variety of sugars, organic acids and alcohols. The isolates did not reduce sulfate, S, thiosulfate, or nitrate and were independent of growth factors. In coculture with A. woodii or Methanospirillum hungatei, PEG and ethanol were completely fermented to acetate (and methane). A marine isolate is described as the type strain of a new species, P. venetianus sp. nov. Its physiology and ecological significance, as well as the importance and possible mechanism an anaerobic polyether degradation, are discussed.