17
carbon-rich structure, so finding the exact mechanism of its mineralization through
biological means would be revolutionary to the fermentation industry (Wierckx
et al. 2015). In recent years, a number of microbes have been isolated and identified
which are capable of degrading recalcitrant plastic material. They are potential candidates for the development of biocatalytic strategies for plastic recycling processes,
by which valuable raw materials can be recovered and produced from the carbon in
plastic in an environmentally friendly sustainable way (Urbanek et al. 2018).
However, the effect of this technology on reducing waste is often compared with
incineration and recycling methods.
Yoshida et al. (2016) reported two enzymes (polyethylene terephthalate and
mono-2-hydroxyethyl terephthalate) involved in the process of converting polyethylene terephthalate into harmless products, mono-2-hydroxyethyl terephthalate,
terephthalic acid, and ethylene glycol, where terephthalic acid is ingested by the cell
through the terephthalic acid transporter, where it is catabolized by dehydrogenases
and hydrogenases for cellular metabolism. Other investigations are also going on
the transformation of waste plastic into alternative fuel oil or gas through catalytic
pyrolysis; however, this method is proved to lack stable products and to be uneconomical (Panda et al. 2010). Since, research on biodegradation studies has progressed and enables researchers to work toward the unknown and unmapped side of
the biodegradation mechanism. However, it is only possible if there is proper waste
collection and separation of different types of plastic waste for further processing
because depolymerized products of different plastic will vary. It will be an ecofriendly approach for reducing plastic waste as well as a solution to distressing situations due to plastic waste generation (Wei and Zimmermanm 2017).
1.6 Standards of Biodegradation Testing Methods
With rising plastic waste in the environment, several views and reports have been
proposed for the biodegradation of plastics. However, many inadequacies in studies
lack uniformity for productive output, necessitating the development of a directed
standard testing method for biodegradation studies. Biodegradation studies are a
broad and interdisciplinary area where chemistry, microbiology, biochemistry,
molecular biology, bioinformatics, and ecology should be considered for building
eminent parameters in the area.
Several microorganisms have been screened for plastic biodegradation using
various analytical techniques such as molecular weight, topography, tensile strength,
and gravimetric and functional group indexes. Current biodegradation analysis
methods lack adequacy, such as biofilm formation, surface oxidation, or brittlement.
Certainly, adherence of microorganisms indicates their affinity toward the substrate
(Balasubramanian et al. 2010; Kumari et al. 2019); however, this does not necessarily indicate biodegradation. It could be abiotic factors that lead to structural and
morphological changes but not biodegradation of microorganisms. Also, we cannot
be sure about the survival of microbes for the complete duration of the test. Initially,
1 Microbial Degradation of Plastics and Its Biotechnological Advancement
carbon-rich structure, so finding the exact mechanism of its mineralization through
biological means would be revolutionary to the fermentation industry (Wierckx
et al. 2015). In recent years, a number of microbes have been isolated and identified
which are capable of degrading recalcitrant plastic material. They are potential candidates for the development of biocatalytic strategies for plastic recycling processes,
by which valuable raw materials can be recovered and produced from the carbon in
plastic in an environmentally friendly sustainable way (Urbanek et al. 2018).
However, the effect of this technology on reducing waste is often compared with
incineration and recycling methods.
Yoshida et al. (2016) reported two enzymes (polyethylene terephthalate and
mono-2-hydroxyethyl terephthalate) involved in the process of converting polyethylene terephthalate into harmless products, mono-2-hydroxyethyl terephthalate,
terephthalic acid, and ethylene glycol, where terephthalic acid is ingested by the cell
through the terephthalic acid transporter, where it is catabolized by dehydrogenases
and hydrogenases for cellular metabolism. Other investigations are also going on
the transformation of waste plastic into alternative fuel oil or gas through catalytic
pyrolysis; however, this method is proved to lack stable products and to be uneconomical (Panda et al. 2010). Since, research on biodegradation studies has progressed and enables researchers to work toward the unknown and unmapped side of
the biodegradation mechanism. However, it is only possible if there is proper waste
collection and separation of different types of plastic waste for further processing
because depolymerized products of different plastic will vary. It will be an ecofriendly approach for reducing plastic waste as well as a solution to distressing situations due to plastic waste generation (Wei and Zimmermanm 2017).
1.6 Standards of Biodegradation Testing Methods
With rising plastic waste in the environment, several views and reports have been
proposed for the biodegradation of plastics. However, many inadequacies in studies
lack uniformity for productive output, necessitating the development of a directed
standard testing method for biodegradation studies. Biodegradation studies are a
broad and interdisciplinary area where chemistry, microbiology, biochemistry,
molecular biology, bioinformatics, and ecology should be considered for building
eminent parameters in the area.
Several microorganisms have been screened for plastic biodegradation using
various analytical techniques such as molecular weight, topography, tensile strength,
and gravimetric and functional group indexes. Current biodegradation analysis
methods lack adequacy, such as biofilm formation, surface oxidation, or brittlement.
Certainly, adherence of microorganisms indicates their affinity toward the substrate
(Balasubramanian et al. 2010; Kumari et al. 2019); however, this does not necessarily indicate biodegradation. It could be abiotic factors that lead to structural and
morphological changes but not biodegradation of microorganisms. Also, we cannot
be sure about the survival of microbes for the complete duration of the test. Initially,
1 Microbial Degradation of Plastics and Its Biotechnological Advancement