Biodegradation of Polyethylene by Bacillus sp. Indigenous to the Niger Delta Mangrove Swamp

Abstract

The ability of Bacillus mycoides and Bacillus subtilis (Bacillus species indigenous to the Niger Delta mangrove soil) to biodegrade polyethylene was studied. Low-density polyethylene (LDPE) and high-density polyethylene (HDPE) films were exposed outdoor for 24 weeks. The two isolates were able to grow on polyethylene (PE), forming visible biofilms. The plasmid pattern of the Bacillus species showed a similar pattern among the two Bacillus species, with one plasmid number and molecular weight around 25 kb, indicating a mega plasmid. The mean heterotrophic bacterial counts in the mangrove soil ranged between 2.81 x 10⁵ – 3.20 x 10⁸ CFU/g. The rate of degradation was determined by measurement of the residual weight of the PE films. Biodegradation in Erlenmeyer flasks by the bacteria after 60 days of incubation ranged between 8.41%-23.15%. Biodegradation was confirmed by Fourier-Transform Infrared (FTIR) spectroscopy, which showed introduction of carbonyl groups after natural weathering, which decreased after microbial treatment. Decrease in carbonyl index ranged between 10.5%-13.7%. The result showed that certain Bacillus sp. indigenous to the Niger Delta mangrove soil are capable of growing on PE films and biodegrade them, after an initial abiotic degradation.

Key words: Bacillus mycoides, Bacillus subtilis, biodegradation, carbonyl index, Natural weathering, Niger Delta mangrove.