Authors: Vipin Chandra Kaliaa,b* , Subhasree Raya,b
aMicrobial Biotechnology and Genomics, CSIR - Institute of Genomics and Integrative Biology (IGIB), Delhi University Campus, Mall Road, Delhi-110007.
bAcademy of Scientific & Innovative Research (AcSIR), 2, Rafi Marg, Anusandhan Bhawan, New Delhi- 110001.
Plastics are one of the most widely used synthetic chemical products. They are important components of our daily life. A major issue related to the plastics is their non-biodegradable nature, which makes their disposal a cause of worry for Environmentalists and Health Managers. An alternative is to look for biodegradable plastics. There are “synthetic” bioplastics, which are prepared by mixing chemicals and biological compounds, but the degradation is limited by the contribution made by the biomatter. In contrast, microbes under certain stressed environmental conditions can metabolize carbon compounds in to polyhydroxyalkanoates (PHAs), which are completely degradable natural bioplastics.
The potential alternatives to non-biodegradable plastics
“Synthetic” Biodegradable Plastics
- Polylactic acid (PLA): PLA is a biodegradable aliphatic polyester, which can be produced from cane sugar or corn starch, tapioca starch. Here, bacterial fermentation results in the production of lactic acid, which is then polymerized into PLA. It gets naturally degraded in soil although the susceptibility to get degraded is lower compared to other aliphatic polyesters such as poly(ε-caprolactone (PCL).
- Polybutylene succinate (PBS): It involves esterification of succinic acid (produced by microbial fermentation of renewable sources) with 1,4-butanediol resulting in the formation of oligomers of PBS.
- Polytrimethylene terephthalate (PTT): The process for producing PTT involves condensation polymerization of 1,3-propanediol (produced by bacterial conversion of glycerol rich biodiesel industry effluent), and terephthalic acid or dimethyl-terephthalate.
- Starch and Cellulose based Bioplastics: Biomass from vegetable oil, corn, pea starch, banana peels, and tapioca are added to chemicals.
· PolyHydroxyAlkanoates (PHAs)
Microbes have the unique ability to withstand stress conditions by diverting their metabolic routes. Microbes under normal conditions metabolize organic carbon (C) compounds through Tri-carboxylic acid cycle to generate energy. However, in the presence of excess of C and limitations of minerals such as N, K, O, Mg, etc., TCA cycle is cut short and terminates in the production of poly-3-hydroxybutyrate (PHB). PHB has physico-chemical properties quite similar to petroleum based polypropylene. There are other possibilities of incorporating different fatty acids and supplements leading to the production of biopolymers with different compositions including co-polymers. These variations are grouped as Polyhydroxyalkanoates (PHAs). PHBs are brittle in nature, whereas PHAs are more ductile and less elastic than plastics. PHAs have wider applications, the best being their use as implants in Medical Industry.
The limits of degradation
The term “synthetic” Biodegradable Plastics is misleading as the limit of biodegradation is regulated by the quantity of biological matter. Biological component may constitute only up to 30% of the final product. In contrast, PHAs can be termed as true Bioplastics, as these are synthesized by biological routes from renewable materials. Their complete degradation is also executed through enzymes: PHA depolymerase.
PHAs are the true bioplastics.
1. Cai L, Yuan MQ, Liu F, Jian J, Chen GQ (2009) Enhanced production of medium-chain-length polyhydroxyalkanoates (PHA) by PHA depolymerase knockout mutant of Pseudomonas putida KT2442. Bioresour Technol 100:2265-2270. doi: 10.1016/j.biortech.2008.11.020
2. Chen GQ, Wu Q (2005) The application of polyhydroxyalkanoates as tissue engineering materials. Biomaterials 26:6565-6578. doi: 10.1016/j.biomaterials.2005.04.036
3. Kalia VC, Chauhan A, Bhattacharyya G (2003). Genomic databases yield novel bioplastic producers. Nat Biotechnol 21:845-846. doi:10.1038/nbt0803-845
4. Kalia VC, Prakash J, Koul S (2016) Biorefinery for glycerol rich biodiesel industry waste. Indian J Microbiol. 56:113-125. doi: 10.1007/s12088-016-0583-7
5. Kalia VC, Raizada N, Sonakya V (2000). Bioplastics. J Sci Industrial Res 59: 433-445.
6. Kumar P, Mehariya S, Ray S, Mishra A, Kalia VC (2015) Biodiesel industry waste: a potential source of bioenergy and biopolymers. Indian J Microbiol 55:1-7. doi: 10.1007/s12088-014-0509-1
7. Kumar P, Mehariya S, Ray S, Mishra A, Kalia VC (2015) Biotechnology in aid of biodiesel industry effluent (glycerol): biofuels and bioplastics. In: Microbial Factories (Ed. Kalia VC). Springer, New Delhi, pp 105-119. doi: 10.1007/978-81-322-2598-0
8. Kumar P, Patel SKS, Lee JK, Kalia VC (2013) Extending the limits of Bacillus for novel biotechnological applications. Biotechnol Adv 31:1543-1561. doi: 10.1016/j.biotechadv.2013. 08.007
9. Kumar P, Ray S, Patel SKS, Lee JK, Kalia VC (2015) Bioconversion of crude glycerol to polyhydroxyalkanoate by Bacillus thuringiensis under non-limiting nitrogen conditions. Int J Biol Macromol 78:9-16. doi: 10.1016/j.ijbiomac.2015.03.046
10. Kumar P, Singh M, Mehariya S, Patel SKS, Lee JK, Kalia VC (2014) Ecobiotechnological approach for exploiting the abilities of Bacillus to produce co-polymer of polyhydroxyalkanoate. Indian J Microbiol 54:1-7. doi: 10.1007/s12088-014-0457-9
11. Kumar T, Singh M, Purohit HJ, Kalia VC (2009) Potential of Bacillus sp. to produce polyhydroxybutyrate from biowaste. J Appl Microbiol 106:2017-2023. doi: 10.1111/j.1365-2672.2009. 04160.x
12. Magdouli S, Brar SK, Blais JF, Tyagi RD (2015) How to direct the fatty acid biosynthesis towards polyhydroxyalkanoates production? Biomass and Bioenergy 74:268-279. doi: 10.1016/j.biombioe.2014.12.017
13. Patel SKS, Kumar P, Singh S, Lee JK, Kalia VC (2015) Integrative approach for hydrogen and polyhydroxybutyrate production. In Microbial factories waste treatment (Ed. Kalia VC). Springer, New Delhi, pp 73-85. doi: 10.1007/978-81-322-2598- 0_5
14. Patel SKS, Kumar P, Singh S, Lee JK, Kalia VC (2015) Integrative approach to produce hydrogen and polyhydroxybutyrate from biowaste using defined bacterial cultures. Bioresour Technol 176:136-141. doi: 10.1016/j.biortech.2014.11.029
15. Patel SKS, Lee JK, Kalia VC (2016) Integrative approach for producing hydrogen and polyhydroxyalkanoate from mixed wastes of biological origin. Indian J Microbiol 56:293-300. doi: 10.1007/s12088-016-0595-3
16. Raut S, Raut S, Sharma M, Srivastav C, Adhikari B, Sen SK (2015) Enhancing degradation of low density polyethylene films by Curvularia lunata SG1 using particle swarm optimization strategy. Indian J Microbiol 55: 258-268. doi: 10.1007/s12088-015-0522-z.
17. Ray S, Kalia VC (2016) Microbial cometabolism and polyhydroxyalkanoate co-polymers. Indian J Microbiol. doi: 10.1007/s12088-016-0622-4.
18. Reddy CSK, Ghai R, Rashmi, Kalia VC (2003) Polyhydroxyalkanoates: an overview. Bioresour Technol 87:137-146. doi: 10.1016/S0960-8524(02)00212-2
19. Singh M, Kumar P, Patel SKS, Kalia VC (2013) Production of polyhydroxyalkanoate co-polymer by Bacillus thuringiensis. Indian J Microbiol 53:77-83. doi: 10.1007/s12088-012-0294-7
20. Singh M, Kumar P, Ray S, Kalia VC (2015) Challenges and opportunities for the customizing polyhydroxyalkanoates. Indian J Microbiol 55:235-249. doi: 10.1007/s12088-015-0528-6
21. Singh M, Patel SKS, Kalia VC (2009) Bacillus subtilis as potential producer for polyhydroxyalkanoates. Microb Cell Fact 8:38. doi: 10.1186/1475-2859-8-38
About Author / Additional Info:
Researchers in Microbial Biotechnology and Genomics at CSIR-IGIB, Delhi.