Microbial degradation of petroleum hydrocarbons: an environmental perspective.

Mechanistic implications of plastic degradation

Biodegradation of poly(vinyl alcohol) based materials

D. HADAD, S. GERESH AND A. SIVAN. 2005. Aim: To select a polyethylene-degrading micro-organism and to study the factors affecting its biodegrading activity. Methods and Results: A thermophilic bacterium Brevibaccillus borstelensis strain 707 (isolated from soil) utilized branched low-density polyethylene as the sole carbon source and degraded it. Incubation of polyethylene with B. borstelensis (30 days, 50� C) reduced its gravimetric and molecular weights by 11 and 30% respectively. Brevibaccillus borstelensis also degraded polyethylene in the presence of mannitol. Biodegradation of u.v. photo-oxidized polyethylene increased with increasing irradiation time. Fourier Transform Infra-Red (FTIR) analysis of photooxidized polyethylene revealed a reduction in carbonyl groups after incubation with the bacteria. Conclusions: This study demonstrates that polyethylene – considered to be inert – can be biodegraded if the right microbial strain is isolated. Enrichment culture methods were effective for isolating a thermophilic bacterium capable of utilizing polyethylene as the sole carbon and energy source. Maximal biodegradation was obtained in combination with photo-oxidation, which showed that carbonyl residues formed by photo-oxidation play a role in biodegradation. Brevibaccillus borstelensis also degraded the CH2 backbone of nonirradiated polyethylene. Significance and Impact of the Study: Biodegradation of polyethylene by a single bacterial strain contributes to our understanding of the process and the factors affecting polyethylene biodegradation.

Biodegradation of polyethylene by the thermophilic bacterium Brevibacillus borstelensis.

Much of the early work on the microbial utilization of petroleum hydrocarbons, conducted in the 1950s and 1960s, was done with the goal of using hydrocarbons as substrates for producing microbial biomass (Shennan, 1984; Champagnat, 1964; Champagnat and Llewelyn, 1962; Cooney et al., 1980; Ballerini, 1978). Petroleum was viewed as an inexpensive carbon source and single cell protein (microbial biomass) was considered as a possible solution to the perceived impending world food shortage for the predicted global population explosion. Applied studies focused on optimizing microbial growth on low- to middle-molecular-weight hydrocarbons. These studies developed fermentor designs for large-scale single cell protein production with agitation and aeration systems that permitted high rates of microbial growth on soluble and highly emulsified hydrocarbon substrates. High-speed impellers (>800 rpm) were used to mix the hydrocarbon substrates and high rates of forced aeration with baffles within the fermentors were used to supply the molecular oxygen necessary for the microbial utilization of hydrocarbons (Hatch, 1975; Prokop and Sobotka, 1975). Optimized microbial growth in these fermentors consumes as much as 100,000 g hydrocarbon/m3 per day (Kanazawa, 1975).

Hydrocarbon Biodegradation and Oil Spill Bioremediation

Mono-, di-, tri-, and tetraethylene glycols and polyethylene glycols (PEG) with molecular weight up to 20,000 were degraded by soil microorganisms. A strain of Pseudomonas aeruginosa able to use a PEG of average molecular weight 20,000 was isolated from soil. Washed cells oxidized mono and tetraethylene glycols, but O2 consumption was not detectable when such cells were incubated for short periods with PEG 20,000. However, the bacteria excreted an enzyme which converted low- and high-molecular-weight PEG to a product utilized by washed P. aeruginosa cells. Gas chromatography of the supernatant of a culture grown on PEG 20,000 revealed the presence of a compound co-chromatographing with diethylene glycol. A metabolite formed from PEG 20,000 by the extracellular enzyme preparation was identified as ethylene glycol by combined gas chromatography-mass spectrometry.

Microbial degradation of polyethylene glycols.

Measurements of biological O2 demand showed that normal alkanes containing up to 44 carbon atoms were metabolized by microorganisms.

J. R. Haines

Papers

Microbial degradation of polyethylene glycols.

Microbial degradation of high-molecular-weight alkanes.