102
7 Bioremediation of Plastics and Polythene in Marine Water
Table 7.2
Plastic-degrading enzyme with source.
Sr. no.
Type of plastic
Enzyme
Source of enzyme
References
1.
Polyethylene (PE)
Laccase
Rhodococcus ruber
[28]
Alkane hydroxylase
Pseudomonas sp. E4
strain
[29]
2.
Polyethylene
terephthalate (PET)
Cutinase
[30]
Lipase
Carboxylesterase
PETase
Ideonella sakaiensis
[24]
3.
Polyurethane (PU)
PueB Lipase
Pseudomonas
chlororaphis
[31]
Cutinase
Thermobifida
[32]
4.
Polyamide
Cyclic dimer hydroxylase
[33]
6-Aminohexanoate
aminotransferase
Arthrobacter sp.
Semialdehyde
dehydrogenase
Manganese-dependent
peroxidase
White-rot fungus
[34]
7.6
Mechanism of Biodegradation
7.6.1
Formation of Biofilm
The foremost step toward the biodegradation of plastic is the attachment of microbial
cells to the surface of the polymer, forming a film. There are various factors which
may affect the formation of a biofilm as follows:
1. Biotic factor: biotic factors include nutritional source and formation of the film.
2. Abiotic factor: abiotic factors include the topography of polymer, presence of
oxygen, chemical characteristics such as temperature, pH, salinity, chemical char-
acteristics, and hydrophobicity, and surface roughness.
Various forces act on the microbial cells which initiate the process. One of which
being nutritional deficiency, which leaves plastic as only nutrient sources and hence
facilitates the adherence of the cell. The adherence was the initial physical interac-
tion between the cells and the substrate, which cause an irreversible attachment of
the cell. These attachment forces are responsible and determine the properties of
biofilm hence form.
The formation of an initial layer of biofilm over the surface of the polymer is very
crucial and deciding step. This layer determines the degradation efficiency. Chem-
ical properties of biofilm, such as surface modification of the polymer structure of
biofilm, all of these factors have an ultimate impact on the growth of subsequent