Degradation of plastics causing pollution using bacteria for improvement of freshwater fish cultivation

Abstract

Plastics are defying the natural cycle as most plastic items can take more than 400 years to decompose since they are characteristically inert and resistant to microbial attacks. Worldwide, researchers came up with the data in 2017 that mankind has contributed to approximately 8.3 billion tons of plastic, and thus, the annual plastic production is supposedly going to triple by the year 2050. On the other side, freshwater aquaculture system has been shrinking rapidly because of indiscriminate use of plastics generated from on-growing urbanization coupled with industrialization. When plastics are disposed without future consideration, it becomes the major cause of the outbreak of water pollution, causing depletion in the level of underground water sources and thus increasing the danger level for aquatic–marine life. Most critically, plastics, like polyvinyl chloride, or PVC, are extremely toxic for natural health as well as the environment because they release considerable amount of mercury, dioxins, and phthalates, which could choke health to hazards. Against this background, implementation of a particular bacteria in order to clean plastic debris adds a path-breaking tool to bioremediation. A bacterium called “Ideonella sakaiensis” is solely responsible for completely degrading polyethylene terephthalate, or PET, within a period of 6 weeks. While sequencing the genome of this bacterium to find the main biochemical contributors to the pathway of the PET hydrolytic activity, an enzyme known as PETase came into picture which is secreted by this bacterium. The enzyme creates an intermediate compound called MHET, which is absorbed by the cell and further hydrolyzed by a second enzyme. This second enzyme called MHET hydrolase eventually converts MHET into two environmentally benign monomers such as terephthalic acid and ethylene glycol. The organism then uses these obtained monomers to facilitate its growth in this process. In order to investigate harmful effects of plastic-polluted water on aquatic life after introduction of Ideonella sakaiensis, biochemical oxygen demand (BOD), dissolved oxygen content (D02), carbon dioxide content, ammonia and sulfur values have also been estimated before and after introduction of Ideonella sakaiensis. E.coli formations were used as indicators of bacterial pollution, if any, in the tank. Average temperature (67.3 °F), pH level (7.38), alkalinity (67.3 mg/L), and dissolve oxygen level (4.12 mg/L) have been found suitable for sustainable aquaculture practices. Percentage of ammonia (0.003) and nitrate (0.207) is also not congenial for good fish production. However, the presence of Escherichia coli (E.coli) inside the tank may be enough to state that the water present has been contaminated either by some domestic sewage or by plastics.