Ideonella sakaiensis- Plastic eating bacteria

Today the use of plastic and the pollutants has been the global threat. It has created an impact on the terrestrial as well as the marine ecosystem. Though the use of plastic has to comfort our living style, the lack of proper management has created pollution in nature. Recently, researchers from Japan have isolated the plastic-eating bacterium which is known as “Ideonella sakaiensis“

Ideonella sakaiensis

In 2016, it was identified by the Kyoto Institute of Technology and Kenji Miyamoto of Keio University in Japan.
It can use plastic poly (ethylene terephthalate) (PET) as a sole source of carbon and energy.
It was isolated from the sediment sample outside of the plastic bottle recycling facility.
PET is made from ethylene glycol and dimethyltryptamine (DMT)
Both of these constituents are made from crude oil.
Ideonella sakaiensis is able to break down into its two constituents.

Image Source: Wikipedia and Depositphotos

**Scientific Classification of Ideonella sakaiensis– Plastic eating bacteria**

Domain: Bacteria
Phylum: Proteobacteria
Class: Betaproteobacteria
Order: Burkholderiales
Family: Comamonadaceae
Genus: Ideonella
Species: sakaiensis

**Characteristics of Ideonella sakaiensis– Plastic eating bacteria**

Gram-negative
Aerobic
Rod-shaped
Non-spore forming
Motile
Having single flagellum
Catalase positive
Oxidase positive
pH 5.5-9.0 (optimum 7-7.5)
Temperature 15-42 °C (optimum 30-37 °C)
shown to grow on PET surface in a community with I. sakaiensis cells with the help of thin appendages
The G+C content of genomic DNA was 70.4 mol%
Strain: 201-F6
no growth with 3% (w/v) NaCl or at 45 °C

Colony characteristics

circular, smooth, non-pigmented or creamy, raised, translucent, the entire margin of 0.5-1.0 mm in diameter after incubation at 30°C on NBRC no.802 agar medium for 2 days

Enzymes

PETase or PET hydrolase

Hydrolyze the ester bonds in PET into mono (2-hydroxyethyl) terephthalic acid (MHET)

MHETase

It is a lipid-anchored MHET hydrolase enzyme present on the cells outer membrane
Hydrolyze the MHET into two monomeric constituents

Mode of action

PETase converts PET into mono-(2-hydroxyethyl) terephthalate acid (MHET), terephthalate (TPA), and bis (2-hydroxyethyl) TPA (PHET). Then MHETase converts MHET into ethylene glycol and TPA. Then the products can be easily broken by other micro-organisms with CO2 and water as the final result.

Applications

Degradation of PET plastics
Effective for recycling and bioremediation

Limitations

Ideonella sakaiensis breaks only PET. Other kinds of plastic like polyethylene, polypropylene, and PVC do exist in nature.

Challenges

The process is so slow. It takes about 6 weeks at 30°C to fully degrade a thumb-nail sized piece of PET.
For industrial purposes, there are a number of practical problems

Future

Despite the limitations and challenges, we can hope that with the use of genetic engineering such enzymes may be manipulated and its production can be done on large scale. Further research may be done regarding the enzymes for the degradation of plastic other than PET.

References

https://en.m.wikipedia.org/wiki/Ideonella_sakaiensis
https://www.dtu.dk/english/news/2019/09/eng
https://www.microbiologyresearch.org/content/journal/ijsem/10.1099

Sources

3% – https://www.ncbi.nlm.nih.gov/pubmed/27045688
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1% – https://www.heise.de/forum/heise-online/News-Kommentare/Verbessertes-Bakterien-Enzym-verdaut-Plastikflaschen/In-was-wird-das-PET-recyclet/posting-32226220/show/
1% – https://www.encyclopedia.com/science-and-technology/biology-and-genetics/genetics-and-genetic-engineering/genetic-engineering
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