Today the world is facing problem related to spread of plastic all around us which cause infection and pollution. PET {poly(ethylene terephthalate)} is extensively used throughout the world. PET is made from petroleum and is widely used in textile industries and plastic bottles. Most of the PET product simply end up by land filling and never enter the recycling process. About 56 million ton of PET was produce worldwide in 2013 alone. Currently the only PET products being recycled are bottles, but the amount of recycled account are just 37% of the total production volume of PET bottle i.e. 6.13 million tons. Currently the chemical method is being used to recycle PET waste, which is quite energy consuming process and shows only assimilation of PET waste. Various microorganisms have also been reported to assimilate PET waste. However, assimilation is not the final solution of this problem as it is only a partial degradation. Recently, a novel microorganism Ideonella sakaiensis strain 201-F6 has been identified which uses PET as an energy resource and is able to produce environment friendly bi products such as ethylene glycol and terephthalic acid. Scientists also discovered two enzymes (PETase and MHETase) produced by the strain 201-F6 which hydrolyze PET. Based on the property of PETase and MHETase it is now understood that the strain 201-F6 is capable to use PET as its major energy source and convert it into easily degradable components.

1. Bacterial Degradation Of
Plastic
By
Shivam Saini
Shirin Akhtar
Saksham Saxena
Dr. Gajendra B. Singh
Department of Biotechnology
National conference on “Bio resources
as a key to value added products”

2. What is Plastic ?
 Plastic are typically organic polymers of high molecular
mass, but they often contain other substances.
 They are usually synthetic, most commonly derived from
petrochemical but many are partially natural.
 The first fully synthetic plastic was Bakelite ,invented in New
York in 1907 by Leo Baekeland.

3. •POLYETHYLENE TEREPTHALATE (PET) : Carbonate drinks, bottles,
peanut butter jars, plastic film, microwavable packaging.
•POLYETHYLENE (PE) : Wide range of inexpensive uses including
supermarket bags, plastic bottles.
•POLYLVINYL CHLORIDE (PVC) : Plumbing pipes and guttering, shower
curtains, window frames, flooring.
•LOW DENSITY POLYETHYLENE (LDPE) : Outdoor furniture, siding,
floor tiles, shower curtains, clamshell packaging.
•POLYCARBONATE (PC) : Compact Disk, Eye Glasses, riot shield,
security windows, traffic light, lenses.
Types of Plastic

4. World Plastic Production

5. Polyethylene terephthalate
 Polyethylene terephthalate, commonly abbreviated PET, is the most
common thermoplastic polymer resin of the polyester family.
 It is used in fibers for clothing, containers for liquids and foods.
 The majority of the world's PET production is for synthetic fibers (in
excess of 60%), with bottle production accounting for about 30% of
global demand in the context of textile applications.
 PET is referred to by its common name, polyester, whereas the
acronym PET is generally used in relation to packaging.
 Polyester makes up about 18% of world polymer production and is the
fourth-most produced polymer; polyethylene (PE), polypropylene (PP)
and polyvinyl chloride (PVC) are first, second and third, respectively.
 PET consists of polymerized units of the monomer ethylene
terephthalate, with repeating (C10H8O4) units.

7. PET was patented in 1941 by John Rex Whinfield, James Tennant
Dickson and their employer the Calico Printers'
Association of Manchester, England. E. I. DuPont de Nemoursin
Delaware, USA, first used the trademark Mylar in June 1951 and
received registration of it in 1952. It is still the best-known name
used for polyester film. The current owner of the trademark is
DuPont Teijin Films US, a partnership with a Japanese company
The PET bottle was patented in 1973 by Nathaniel Wyeth.
History

8. Uses of PET
 Because PET is an excellent water and moisture barrier material,
plastic bottles made from PET are widely used for soft drinks.
 For certain specialty bottles, such as those designated for beer
containment
 PET sandwiches an additional polyvinyl alcohol (PVOH) layer to
further reduce its oxygen permeability.
 PET is also used as a substrate in thin film solar cells.
 Terylene is also spliced into bell rope tops to help prevent wear
on the ropes as they pass through the ceiling.

9. Physical Properties
PET in its natural state is a colorless, semi-crystalline resin. Based
on how it is processed, PET can be semi-rigid to rigid, and it is very
lightweight. It makes a good gas and fair moisture barrier, as well
as a good barrier to alcohol and solvents. It is strong and impact-
resistant. PET becomes white when exposed to chloroform and
also certain other chemicals such as toluene.

10. Production
Polyethylene terephthalate is produced from ethylene
glycol and dimethyl terephthalate (C6H4(CO2CH3)2) or terephthalic
acid.
The former is a transesterification reaction, whereas the latter is
an esterification reaction.

11. Degradation
PET is subjected to various types of degradations during processing.
The main degradations that can occur are hydrolytic, and probably
most important, thermal oxidation. When PET degrades, several
things happen: discoloration, chain scissions resulting in reduced
molecular weight, formation of acetaldehyde, and cross-links ("gel"
or "fish-eye" formation). Discoloration is due to the formation of
various chromophoric systems following prolonged thermal
treatment at elevated temperatures. This becomes a problem when
the optical requirements of the polymer are very high, such as in
packaging applications. The thermal and thermo oxidative
degradation results in poor processibility characteristics and
performance of the material.

12. Biodegradation
Ideonella sakaiensis is a bacterium from
the genus Ideonella and family Comamonadaceae capable
of breaking down PET plastic which was isolated from outside
a plastic bottle recycling facility.

13. Discovery of Bacteria
Ideonella sakaiensis was identified in 2016 by a team of researchers
from Kyoto Institute of Technology and Keio University, after
collecting samples of PET debris in a search for bacteria which relied
on the plastic for carbon growth. The bacterium was observed to
utilize two distinct enzymes that reacted with water to break down
PET plastics into terephthalic acid and ethylene glycol, substances
which on their own pose no threat to the environment.

14. Mechanism of PETase and MHETase
c
=
o
-o
o
cH2-cH2-o-c
=
n
c-o
=
oo
-c
=
H+ OH-
H+ OH-
CH2-CH2-O
PET
PETase
MHET
MHETase
Ethylene glycol Terephthalic acid

15. Impact
The discovery of Ideonella sakaiensis has potential importance for
the recycling process of PET plastics. Prior to discovery of the
bacterium, the only known consumers of PET were a small number
of fungi including Pestalotiopsis microspora, and knowledge of the
new species has spurred discussion about biodegradation as a
method of recycling. The bacterium can currently break down a thin
film of PET in a little over six weeks, so it is thought that any
prospective applications in mass recycling programs will have to be
preceded by enhancement of its abilities through genetic
modification.

16. Conclusion
Compare with chemical Process PET degradation using
microorganisms and enzymes consumes less energy
and environmentally friendly option. We believe that
the present research results bring us closer to
achieving an ideal model for PET recycling, so long as
we are able to enhance the activity level and stability of
these newly discovered microbial enzymes.

17. Reference
Yoshida, S., Hiraga, K., Talehana, T., Taniguchi, I., Yamaji, H., Maeda, Y.,
Toyohara, K., Miyamoto, K., Kimura, Y., Oda, K. (2016) “A bacterium that
degrades and assimilates poly(ethylene terephthalate)”, Science, Vol.
351:6278, 1196-1199.
The new plastic economy : Rethinking the future of plastic (World economic
Forum) : January 2016
Tokiwa, Y., Calabia, B.P., Ugwu, C.U., Aiba, S. (2009) “Biodegradability of
Plastics”, International Journal of molecular Sciences, Vol. 10, 3722-3742.