Environmental Challenges (Apr 2021)
Biodegradation of polyethylene by the bacterium Pseudomonas aeruginosa in acidic aquatic microcosm and effect of the environmental temperature
Abstract
The main problem about plastic packaging after their use is the fate of the plastic waste disposed of into the environment. This study was carried out in aquatic microcosm and aimed at assessing the impact of the temperature of an acidic environment on the polyethylene degradation by the bacterium Pseudomonas aeruginosa, as well as the electrical conductivity of the medium and the temporal abundance dynamics of cells involved. Sterilized pieces of polyethylene of 0.08 g in weight were immersed in sterile mineral solutions of pH 5 in glass flasks containing P. aeruginosa cells at concentration adjusted to 186.103 CFU/100 µL. The whole was incubated at 7 °C, 23 °C, 37 °C and 44 °C for 10 days, 20 days and 30 days. Analysis after incubations showed that electrical conductivity which was 3386 µS/cm at the initial moment increased with an increase in incubation period. Its highest value 5476 µS/cm was noted at 44 °C after 30 days. The pH of solutions decreased. Its lowest value 4.11 was noted at 7 °C after 10 and 20 days. The apparent degradation rates of polyethylene fragments varied from 8.10−5 g/10days (at 7 °C and 23 °C) to 2.10−4 g/10days (at 44 °C). The highest percentage of weight loss of the polyethylene was 6.25% registered after 30 days at 44 °C. The apparent changing rates in cell abundance varied with variation in incubation temperature. It was positive under 7 °C and 23 °C reflecting relative cell growth, and negative under 37 °C and 44 °C reflecting relative cell inhibition. The highest relative apparent cell growth rate was 1.831 CFU/10days recorded at 23 °C and the highest relative apparent cell inhibition rate was 7.831 CFU/10days recorded at 44 °C. In solutions, the pH, electrical conductivity and the weight of the fragments varied significantly from one incubation temperature to another and from one incubation period to another (P<0.05). Cell abundances varied only from one incubation temperature to another (P <0.05). The biodegradation process of polyethylene by P. aeruginosa under various environmental conditions and the impact of the products released on cells remains incompletely understood.
