Review on the current status of polymer degradation: a microbial approach

TL;DR: The occurrence and distribution of microbes that are involved in the degradation of both natural and synthetic polymers are described and it seems that biological agents and their metabolic enzymes can be exploited as a potent tool for polymer degradation.

Abstract: Inertness and the indiscriminate use of synthetic polymers leading to increased land and water pollution are of great concern. Plastic is the most useful synthetic polymer, employed in wide range of applications viz. the packaging industries, agriculture, household practices, etc. Unpredicted use of synthetic polymers is leading towards the accumulation of increased solid waste in the natural environment. This affects the natural system and creates various environmental hazards. Plastics are seen as an environmental threat because they are difficult to degrade. This review describes the occurrence and distribution of microbes that are involved in the degradation of both natural and synthetic polymers. Much interest is generated by the degradation of existing plastics using microorganisms. It seems that biological agents and their metabolic enzymes can be exploited as a potent tool for polymer degradation. Bacterial and fungal species are the most abundant biological agents found in nature and have distinct degradation abilities for natural and synthetic polymers. Among the huge microbial population associated with polymer degradation, Pseudomonas aeruginosa, Pseudomonas stutzeri, Streptomyces badius, Streptomyces setonii, Rhodococcus ruber, Comamonas acidovorans, Clostridium thermocellum and Butyrivibrio fibrisolvens are the dominant bacterial species. Similarly, Aspergillus niger, Aspergillus flavus, Fusarium lini, Pycnoporus cinnabarinus and Mucor rouxii are prevalent fungal species.

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Pathak and Navneet
Bioresour. Bioprocess. (2017) 4:15
DOI 10.1186/s40643-017-0145-9
REVIEW
Review onthe current status ofpolymer
degradation: a microbial approach
Vinay Mohan Pathak
*
and Navneet
Abstract
Inertness and the indiscriminate use of synthetic polymers leading to increased land and water pollution are of
great concern. Plastic is the most useful synthetic polymer, employed in wide range of applications viz. the packag-
ing industries, agriculture, household practices, etc. Unpredicted use of synthetic polymers is leading towards the
accumulation of increased solid waste in the natural environment. This affects the natural system and creates vari-
ous environmental hazards. Plastics are seen as an environmental threat because they are difficult to degrade. This
review describes the occurrence and distribution of microbes that are involved in the degradation of both natural and
synthetic polymers. Much interest is generated by the degradation of existing plastics using microorganisms. It seems
that biological agents and their metabolic enzymes can be exploited as a potent tool for polymer degradation. Bacte-
rial and fungal species are the most abundant biological agents found in nature and have distinct degradation abili-
ties for natural and synthetic polymers. Among the huge microbial population associated with polymer degradation,
Pseudomonas aeruginosa, Pseudomonas stutzeri, Streptomyces badius, Streptomyces setonii, Rhodococcus ruber, Coma-
monas acidovorans, Clostridium thermocellum and Butyrivibrio fibrisolvens are the dominant bacterial species. Similarly,
Aspergillus niger, Aspergillus flavus, Fusarium lini, Pycnoporus cinnabarinus and Mucor rouxii are prevalent fungal species.
Keywords: Polymer, Microbial degradation, Bacteria, Fungi, Natural polymers, Synthetic polymers, Polysaccharide,
Hydrolytic enzyme, Pollution, Organic pollutants, Waste management, Biofilm, Surfactants, LDPE, Aerobic degradation,
Anaerobic degradation, UV irradiation, Manmade compound, Plastic waste, SEM, Sturm test, FT-IR
© The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
(
http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,
provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license,
and indicate if changes were made.
Background
Developments in science and technology, especially over
the last 2 decades, have led to the production of a num
-
ber of synthetic polymers worldwide. e polymers are
chains of monomers linked together by chemical bonds.
Polymers such as lignin, starch, chitin, etc., are present in
the environment naturally. Nowadays, synthetic polymers
are used in several industries, of which packaging appli
-
cation covers 30% of plastic use throughout the world
(Shah et al.
2008b; Dey et al. 2012; Kumar et al. 2011).
In the nineteenth and twentieth centuries plastic played
a revolutionary role in the packaging industries. ere
-
after, approaches to transportation were changed with
the introduction of carrying bags made of polyethylene
(Nerland etal.
2014). Synthetic polymers are widely used
because of their durability and low cost, but disposal of
packaging material has emerged as a challenge for solid
waste management, and it is a major source of pollution
(Song et al.
2009; Dey et al. 2012). Now such types of
synthetic compounds have become a nuisance affecting
natural resources like water quality and soil fertility by
contaminating them (Bhatnagar and Kumari
2013; Ojo
2007; Arutchelvi etal. 2008). In the 1990s, plastic waste
was found to have tripled and is continuously increas
-
ing in the marine environment (Moore
2008). e level
of debris materials increased markedly from 1990 to 1995
on Bird Island of South Georgia; similarly, the garbage
amount doubled in the coastline area of the UK during
1994–1998 (Walker etal.
1997; Barnes 2002). It was esti
-
mated that neuston plastic increased ten-fold between
1970 and 1980 in Japan (Moore
2008). e total demand
for plastic was 107 million tons in 1993, which increased
to 146 million tons in 2000. e growth rate of the plas
-
tic industry in Pakistan is 15% per annum (Shah et al.
Open Access
*Correspondence: vinaymohanpathak@gmail.com
Department of Botany and Microbiology, Gurukul Kangri University,
Haridwar, Uttarakhand 249-404, India

Page 2 of 31
Pathak and Navneet
Bioresour. Bioprocess. (2017) 4:15
2008b). Plastic waste is being generated rapidly world-
wide. e UK, China and India contribute 1 million tons,
4.5 million tons and 16 million tons, respectively (Kumar
etal.
2011). India generates around 10 thousand tons of
plastic waste (Puri et al.
2013). e annual production
of plastic was estimated as 57 million tons in Europe in
2012. Polyethylene is one of the common forms of plas
-
tic compared to others (polyvinyl chloride, polypropyl-
ene, etc.) (Nerland et al.
2014). Plastic materials have
become versatile, competitive and reliable substitutes for
traditionally used metal, leather and wood materials in
the past 5 decades because of their toughness, flexibility
and physical properties (Sivan
2011; Singh and Sharma
2008). Durability and undesirable accumulation of syn
-
thetic polymers are major threats to the environment.
Plastic waste recycling has largly unsuccessful outcomes;
of the over 1 trillion plastic bags dumped per annum in
the US, only 5% are recycled. Apparently, waste manage
-
ment (bioremediation) is one of the ways to reduce the
adverse effects and can serve as a potential tool (Shah
etal.
2008b; Ojo 2007; Ali etal. 2014).
In-vitro degradation of synthetic polymers is a time-
consuming process (Schink et al.
1992; Bhatnagar and
Kumari
2013). Production of synthetic polymers, espe
-
cially polyethylene (140 million tons per annum), is caus-
ing problems with the waste management, and their
consumption is increasing day by day at a rate of 12% per
annum (Kumar etal.
2011; Sivan 2011; Shah etal. 2008b;
Koutny etal.
2006).
Plastic waste in the form of litter enters running water
in different ways according to nature and ultimately
contaminates the marine environment (Obradors and
Aguilar
1991). e proliferation rate of plastic materials
is very fast, and the marine environment is affected by
such wastes throughout the world. Plastic waste causes
eight intricate problems in the marine environment:
(1) plastic trash pollutes, (2) plastic entangles marine
life, (3) ingestion of plastic items, (4) biodegradation of
petroleum-based plastic polymers is time-consuming,
(5) broken plastic and its pellets disturb the food web, (6)
interference with sediment inhabitants, (7) marine litter
destroying the primary habitat of new emerging life and
(8) marine plastic litter causes major damage to vessels.
In a 1970s study on 247 plankton samples in the Atlantic
Ocean, 62% of the samples found plastic matter. Similarly,
in the North Atlantic during the 1960s–1990s sampling of
plankton showed a considerable increase of microscopic
plastics in the marine environment (Moore
2008).
Distribution ofdierent types ofpolymers
Polymers are made up from non-renewable as well as
renewable feedstock. ese polymers are well known
for their diverse applications in industries, domestic
appliances, transportation, construction, shelters, storage
and packaging practices. Such polymers are differentiated
according to their chemical nature, structural arrange
-
ment, physical properties and applications as shown in
Table
1 (Shah etal. 2008b; Dey etal. 2012; Kumar etal.
2011; Smith 2005).
Natural polymers
Natural polymers are found abundantly in nature in the
forms of biopolymers and dry material of plants as shown
in Table
2 (Leschine 1995). e constitution of the plant
cell wall differs with the composition of the lignocellu
-
losic biomass (cellulose, hemicellulose and lignin), which
provides strength (Premraj and Doble
2005). Lignocellu
-
loses play a critical role in developing plant biomass, in
which cellulose, hemicellulose and lignin are the major
building blocks of the natural polymer (Perez etal.
2002).
Synthetic polymers
Plastics are manmade compounds that consist of a long
chain of polymeric molecules and unusual bonds, with
excessive molecular mass and halogen substitutions.
Nowadays plastic manufacturing involves different inor
-
ganic and organic materials, including carbon, hydrogen,
chloride, oxygen, nitrogen, coal and natural gases (Shah
etal.
2008b). e most widely used polymers contribut
-
ing to plastic waste are low-density polyethylene (LDPE),
high-density polyethylene (HDPE), polyvinyl chloride,
polystyrene and polypropylene with 23, 17.3, 10.7, 12.3
and 18.5%, respectively, and the remaining 9.7% of other
types of polymer (Puri etal.
2013). e polymer produc
-
tion in 2012 was estimated as polyethylene 30% (LLDPE
and LDPE 18%, HDPE 12%), polypropylene 19%, polyvi
-
nyl chloride 11%, polystyrene 7%, polyethylene tereph-
thalate 7% and polyurethanes 7% worldwide (Nerland
et al.
2014). e sales distribution and amount in per
-
centage of synthetic polymer consumed in North Amer-
ica during 1995 and 2004 are shown in Table
3 and Fig.1,
respectively (Summers
1996; Zheng and Yanful 2005).
Standards forpolymer degradation
Literature and information on biodegradable products
are organized by the US government, with the help of the
Biodegradable Products Institute (BPI). BPI is an organi
-
zation that deals with academia, industry and government
bodies that encourage recycling of polymeric materials
(biodegradable). Production of the biodegradable poly
-
mer involves the addition of starch and plant fiber extract.
BPI provides matter to the ASTM (American Society for
Testing and Materials) for assembling ASTM standards
(ASTM D6400, D6866). ese are the principle databases
of degradation used to supervise industry. e logo for the
compostable product was introduced by the USCC (US

Page 3 of 31
Pathak and Navneet
Bioresour. Bioprocess. (2017) 4:15
Table 1 Types ofpolymer (Averous andPollet 2012; Babul etal. 2013)
Type ofpolymer Structure R group Structure T
m
(°C) Application References
Bio-based polymers
Poly (3-hydroxyvalerate)
(PHV)
Homo-polymer Ethyl
118 Industrial, drug delivery (Averous and Pollet 2012; Liu et al. 2014; Ojumu
et al. 2004; Turesin et al. 2000; Bonartsev et al.
2007)
Poly (3-hydroxybutyrate)
(PHB)
Homo-polymer Methyl
168–182 Pharmaceutical and drug
delivery
(Averous and Pollet 2012; Liu et al. 2014; Velde and
Kiekens 2002; Nurbas and Kutsal 2004; Ojumu
et al. 2004; Jirage et al. 2011; Turesin et al. 2000)
Poly (3-hydroxyoctade-
canoate) (PHOd)
Homo-polymer Penta decanoyl
54–55 Medicine area (Averous and Pollet 2012; Guo et al. 2013; Dhar
et al. 2008; Giudicianni et al. 2013; Bonilla and
Perilla 2011)
Poly (3-hydroxyoctanoate)
(PHO)
Homo-polymer Pentyl
40–60 Medical applications (Averous and Pollet 2012; Souza 2013; Basnett
et al. 2012; Liu et al. 2011; Basnett et al. 2013)
Poly (3-hydroxydecanoate)
(PHD)
Homo-polymer Heptyl
54 Fiber industry (Averous and Pollet 2012; Werner et al. 2014; Song
et al. 1998; Rameshwari and Meenakshisunda-
ram 2014)
Poly (3-hydroxybutyrate-
co-3-hydroxyhexanoate)
(PHBH
x
)
Co-polymer Methyl, with propyl
10%HH×120 Medical applications (Babul et al. 2013; Averous and Pollet 2012; Chang
et al. 2014; Coen and Dehority 1970; Xie et al.
2009)
Poly (hydroxybutyrate-co-
hydroxyvalerate) (PHBV)
Co-polymer Methyl with ethyl
165–175 Pharmaceutical (drug
delivery)
(Nerland et al. 2014; Gerard et al. 2014; Nwachkwu
et al. 2010; Hatakka 2005; Danis et al. 2015;
Zembouai et al. 2014)
Synthetic polymers
Polyethylene Homo-polymer Hydrogen
140–143 In wires (as insulating
matter), bags
(Tobin 2010; Nakayama et al. 1991; Menon et al.
2010; Petre et al. 1999)
Polyvinyl chloride Homo-polymer Chorine [–CH
2
–CHCl–]
n
115–245 Leather, pipe, bottles (Wilkes et al.
2005; Summers 2008; Summers 1996;
Menon et al. 2010)
Polypropylene Homo-polymer Methyl
165 Fabric material, carpets (Ruiyun et al. 1994; Tripathi 2002; Mccallum et al.
2007; Yam 2009; Perez et al. 2014; Menon et al.
2010; Petre et al. 1999)
Polyethylene terephthalate Homo-polymer Carboxyl and hydroxyl
280 Packaging applications,
bottles, food wrappers,
pipes
(Zheng and Yanful 2005; Perez et al. 2002; Liu et al.
2011; Jeffrie 1994; Kwon et al. 2009)
Polyurethane Hetero-polymer Isocyanate and polyol
400 Fibers, foams, paints, coat-
ing, packaging
(Zheng and Yanful 2005; Slade et al. 1964; Zafar
2013; Zembouai et al. 2014)

Page 4 of 31
Pathak and Navneet
Bioresour. Bioprocess. (2017) 4:15
Table 1 continued
Type ofpolymer Structure R group Structure T
m
(°C) Application References
Polystyrene Homo-polymer Phenyl
240 Cups, containers,
pharmaceutical, plates,
cosmetics
(Zheng and Yanful, 2005; Sharma et al. 2000; Flavel
et al. 2006; Nakayama et al. 1991; Carvalheiro
et al. 2008; Mcalpine et al. 2001)
Polycarbonate Homo-polymer Carbonate
52–150 Heat-resistant coating,
optical instruments and
automotives
(Sweileh et al. 2010; Koutsos 2009; Jeon and Baek
2010; Cheah and Cook 2003; Akola and Jones
2003; Scheller and Ulvskov 2010; Takanashi et al.
1982)
Nylon Homo-polymer Amide
190, 276 Fiber manufacturing (Leja and Lewandowicz 2010a, b; Chao and
Hovatter 1987; Wan et al. 1995; Kubokawa and
Hatakeyama 2002; Hasegawa and Mikuni 2014)

Page 5 of 31
Pathak and Navneet
Bioresour. Bioprocess. (2017) 4:15
Composting Council) and BPI, shown in Fig.
2 (Kolybaba
et al.
2003; http://www2.congreso.gob.pe/sicr/cendocbib/
con2_uibd.nsf/4EF8A31F2BF5D3480525772A0053CD80/$
FILE/Ensayo_biodegradables_pl%C3%A1sticos_by.pdf
).
Diversity ofpolymer degradation
Living organisms are involved in the breakdown of plas-
tic material, and consequently the recycled form reverses
back to the environment. Anaerobic microbial degra
-
dation releases greenhouse gas (methane) in landfills,
which increases global warming. Aerobic conditions are
essential for fungal degradation while bacterial degrada
-
tion proceeds in aerobic as well as anaerobic conditions
(Kumar etal.
2011; Chandra and Rustgi 1998). Plastic can
be reduced in an eco-friendly manner with the help of soil
bacteria and proper water availability. Decomposition of
the polymer depends on its chemical composition, which
supports the growth of microorganisms in the form of
nutrient sources. e starch-based polymer is favorable
for microbial attack, and hydrolytic enzymes act on the
polymer matrix to reduce their weight. Polymer made
from starch or flax fiber shows greater biodegradability
as compared to other synthetic polymers. Microorgan
-
isms also play an important role in the degradation of
petroleum-based polymers. Petroleum-based polymers
such as polyolefins are degraded through photo-degrada
-
tion (Kumar etal.
2011; Sen and Raut 2015).
Emerging technology is continuously involved in
improving the processing of biopolymers by using an
additive (benzophenone) during their construction.
Additives play a significant role in the chemical process
during photo-degradation. Such amendments affect their
thermal sensitivity and UV-absorbing capacities. Chemi
-
cally sensitive polymers have a better biodegradabil-
ity rate compared to other polymers. Similarly, thermal
Table 2 Types ofbio-based polymers (Babul etal.
2013; Averous andPollet 2012)
Microorganism based Biotechnology based Agro-based
Polyhydroxyalkanoates (mcl-PHA,
PHB, PHB-co-V)
Polylactides, PBS, PE, PTT, PPP Polysaccharides and lipids (starch,
cellulose, alginates)
Proteins–animal proteins (casein, whey,
colagen/gelatin), plant protein (zein,
soya, gluten)
Table 3 Plastic sales in North America, 1995 (Summers
1996)
Type ofpolymer Billions ofpounds
LDPE/LLDPE 14–16
PVC 12–14
HDPE 12–14
PP 10–12
PS 6–7
Polyester 4
PC <2
Fig. 1 Percentage distribution of synthetic polymer (PP polypropyl-
ene, HDPE high-density polyethylene, PVC polyvinyl chloride, LLDPE
linear low-density polyethylene, LDPE low-density polyethylene, PS
polystyrene, thermoplastics and others) sales in North America in
2004 (Zheng and Yanful 2005)
Fig. 2 Symbol representing biodegradable grade compostable
polymers (http://www2.congreso.gob.pe/sicr/cendocbib/con2_uibd.
nsf/4EF8A31F2BF5D3480525772A0053CD80/$FILE/Ensayo_biode-
gradables_pl%C3%A1sticos_by.pdf)