Due to the industrial revolution, many chemical compounds are synthesized, which are of great use for human being. But these are unknowns for the environment. Plastic is one of the few newly synthesized chemical compounds that utilize synthetic polymers like polyethylene, polyvinyl chloride, polystyrene in its manufacture. Plastics are widely used in world in daily life, all over the world. Properties of plastics:-

• Synthetic polymers are easily molded into different shapes.

• High durability and chemically resistant

• Neutral when in contact with food

• Non-reactive, when in contact with human body.

• Suitability for packaging



Apart from these advantages, there are certain drawbacks associated with the use of plastics such as:-

• Non-degradable hence accumulate in nature causing environmental problem.

• Run on non-renewable resources.

• Difficult to recycle

Increasing harmful effects of non-biodegradable compounds on the environment instigated scientists to focus on the development of such polymers that will easily biodegrade.



Approaches for production of biodegradable plastics:-

i) Direct use of renewable plant material. (Starch, cellulose etc.)

ii) Genetic engineering to produce more chemicals useful for bioplastic production.

iii) Genetic engineering of plants to directly produce biodegradable plastics such as polyhydroxyalkonates {PHA).



Plastics

Plastics may be either

a) Photobiodegradable

Photodegradable plastics have light sensitive groups that are inserted directly into the backbone of the polymers. This results in the production of non-degradable smaller fragments, that in turn weakens the material integrity.

b) semi- biodegradable and

Semi-biodegradable polymers can be degraded partially

Example of semi-biodegradable plastic can be made by blending starch and polyethylene.

c) 100%biodegradable

100% biodegradable are those which can be completely degraded. Examples include aliphatic polyesters, PHA (polyhydroxyalkonates) etc.



Techniques involved in the production of biodegradable polymers:-

1) Modification of existing material

2) Co-polymerization of known biodegradable materials by chemical means

3) Use of biopolymers for making plastic bags.

Semi-biodegradable plastic bags are manufactured by filling in the matrix of conventional polythene with starch. After the disposal of bags, microorganisms eat away starch, leaving behind the thin polythene film, which soon disintegrates.

Fertec and Warner Lambert, a United States and Italy based company are actively engaged in the development of fully biodegradable starch based plastics. Bioceta, the new cellulose diacetate-based biodegradable plastic has been developed by Rhone Poulenc's Belgium subsidiary, Tubiz Plastics. In contrast, the co-polymers of succinic acid, glycerol and polyethylene glycol are found to be 100% biodegradable when kept for 90 days in soil.



Bioplastics: - A replacement to currently available plastics is the use of genetically engineered biopolymers produced by the growth of micro-organisms or from plants. The materials used for production of bioplastics include poly β-hydroxy butyrate and polylactic acid. Polyhydroxyalkonates (PHA) are polyesters of various hydroxyalkonates that are synthesized and accumulated by numerous microbes as energy reserve. Polyhydroxybutyrate (PHB) is the most important among these. Many micro-organisms like Alcaligenes, Azotobacter, Bacillus, Nocardia etc., accumulate PHB as energy reserve material.



Production of PHA by genetically engineered plants

In industrial fermenter, the Biopol is produced by the bacterium that converts sugar into polymer. Scientists, for example in United States have recently developed a transgenic plant, which produces the biodegradable plastic directly. The plant used is Arabidopsis thaliana (commonly known as Wall Cress or Mouse-Ear Cress. Scientists inserted two foreign genes from Alcaligenes eutrophus bacteria, which produce PHB to the cress. Agrobacterium tumefaciens is used for the transfer of gene to cress plant. The main serious problem associated with this is that the plant becomes sick, possibly because new genes divert carbon away from the essential metabolites to PHB production.

It is also possible to genetically engineer the potatoes with an aim to produce and store plastics instead of starch in their tubers. Oilseed crops are the most important target for seed specific production of PHA because of the same origin from acetyl-CoA. Other crops, which can be used for the PHA production, are rapeseed, sunflower, soyabean etc.

But full scale, commercial development of transgenic PHA in crops is still in its infancy and will take more years for full establishment.



Production of PHA in genetically engineered bacteria

Now a days, PHA can also be produced by using genetically engineered bacteria. Recombinant E.Coli harboring the multicopy plasmid carrying Alcaligene eutrophus PHA biosynthesis gene is developed.

Advantages of using recombinant E.coli for PHA production are:-

i) A wider range of substrate availability e.g., lactose, sucrose, xylose etc.

ii) Engineered E.coli takes only 24 hours for the production of PHB while non-engineered ones take almost 3 days.

iii) Control of polydispersity index by modulating synthase activity.

iv) Natural PHA producers possess PHA depolymerase, which is responsible for its degradation while the genetically engineered E.coli lacks the enzyme.



To conclude, the biotechnology advancement in the development of biodegradable polymers clearly indicates our attitude towards the root cause of the problem rather than attacking on the symptoms and the side-effects. Therefore, we should now join hands together and aim for a biodegradable and eco-friendly environment. This will further open new arenas of success.



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Written by Shikha Sharma and Debasis Sahu