In vitro degradation of low-density polyethylene by new bacteria from larvae of the greater wax moth, Galleria mellonella.

Three bacterial species isolated from whole body extracts of the greater wax moth larvae, Galleria mellonella, were evaluated for their ability to utilize low-density polyethylene (LDPE) as a sole carbon source in vitro. These bacteria were identified as Lysinibacillus fusiformis, Bacillus aryabhattai, and Microbacterium oxydans. Their ability to biodegrade LDPE was assessed by growth curves, cell biomass production, polyethylene (PE) weight loss, and the presence of LDPE hydrolysis products in the growth media. Consortia of these bacteria with three other bacteria previously shown to degrade LDPE (Cupriavidus necator H16, Pseudomonas putida LS46, and Pseudomonas putida IRN22) were also tested. Growth curves of the bacteria utilizing LDPE as a sole carbon source revealed a peak in cell density after 24 h. Cell densities declined by 48 h but slowly increased again to different extents, depending on the bacteria. Incubation of LDPE with bacteria isolated from greater wax moth larvae had significant effects on bacterial cell mass production and weight loss of LDPE in PE-containing media. The bacterial consortia were better able to degrade LDPE than were the individual species alone. Gas chromatographic analyses revealed the presence of linear alkanes and other unknown putative LDPE hydrolysis products in some of bacterial culture media.

Microbial degradation of low-density polyethylene and synthesis of polyhydroxyalkanoate polymers.

We have characterized the ability of eight bacterial strains to utilize powdered low-density polyethylene (LDPE) plastic (untreated and without any additives) as a sole carbon source. Cell mass production on LDPE-containing medium after 21 days of incubation varied between 0.083 ± 0.015 g/L cell dry mass (cdm) for Micrococcus luteus IRN20 and 0.39 ± 0.036 g/L for Cupriavidus necator H16. The percent decrease in LDPE mass ranged from 18.9% ± 0.72% for M. luteus IRN20 to 33.7% ± 1.2% for C. necator H16. Linear alkane hydrolysis products from LDPE degradation were detected in the culture media, and the carbon chain lengths of the hydrolysis products detected varied, depending on the species of bacteria. We also determined that C. necator H16 produced short-chain-length polyhydroxyalkanoate biopolymers, while Pseudomonas putida LS46 and Acinetobacter pittii IRN19 produced medium-chain-length biopolymers while growing on polyethylene powder. Cupriavidus necator H16 accumulated poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-V) polymers to 3.18% ± 0.4% of cdm. The monomer composition of the PHB-V was 94.9% ± 0.61% 3-hydroxybutyrate and 5.03% ± 0.56% 3-hydroxyvalerate. This is the first report that provides direct evidence for simultaneous bioconversion of LDPE plastic to biodegradable polyhydroxyalkanoate polymers.