Lecture 7: Plastics from Plants

Question 1

advantages of plastics from plants:

Answer 1

• plants produce a lot of biomass
• biodegradable product
• renewable resource

Question 2

problems with plastics from plants:

Answer 2

• plastic is low value therefore the product myst be very cheap to be commercially viable
• previous productions of bioplastics has proven uneconomic

Question 3

types of plastics that can be made from plants:

Answer 3

Several different sorts of plastic can remade POLY-HYDROXYALKANOATES (PHA)

Question 4

Polyhydroxybutyrate (PHB) is synthesised as a storage polymer by the..

Answer 4

bacterium Ralstonia eutropha

Question 5

negative properties of polyhydroxybutyrate (PHB)

Answer 5

• brittle
• low melting point
• it thermally degrades just above its melting point which introduces problems when it is used to make products

Question 6

synthesis of polyhydroxybutyrate (PHB) synthesis in plants requires…

Answer 6

3 genes to be transferred from the bacterium to the plant, phbA, phbB, phcC

Question 7

polyhydroxybutyrate is a…. similar to…

Answer 7

biodegradable plastic with similar properties to polypropylene

Question 8

why isn’t polyhydroxybutyrate (PHB) commercially produced?

Answer 8

• not a commercially valuable product

- yields in plants are low

Question 9

lipid metabolism can be averted into PHB production by

Answer 9

introducing three genes

Question 10

transgenic plants expressing pub genes accumulate

Answer 10

PHB

-synthesis directed to chloroplast, normal site of starch synthesis

Question 11

transgenic plants expressing pub genes accumulate _____ BUT::

Answer 11

-yields are low,
-leaves are a poor atria for large scale production
-PHB is not a commercially suitable product
(brittle, stiff, difficult to work with )

Question 12

What plastic is related to polyhydroxybutyrate (PHB)

Answer 12

polyhydroxybutyrate-co-valerate (PHB-V) is a much more commercially useful product but plants DO NOT produce it

Question 13

using same pathway as PHB how can Polyhydroxybutyrate-co-valerate be produced?

Answer 13

for PHB (C4) lipid metabolism can be diverted by introducing three genes, PHB-V (C5) can be produced if significant quantities of propionyl CoA are present

Question 14

3 problems with producing PHB-V. PROBLEM 1:

Answer 14

1) phbA prooien won’t use propionyl coA as a substrate, so a second form of the enzyme Beta-ketothiolase gene (BktB) was isolated from Ralstonia eutropha

Question 15

3 problems with producing PHB-V. PROBLEM 2:

Answer 15

plants don’t contain enough propionyl-coA
Solution= increase flux into the pathway by increasing the amount of substrate 2-ketobutyrate. this was achieved by engineering the plants to contain threonine deaminase

Question 16

3 problems with producing PHB-V. PROBLEM 3:

Answer 16

plant threonine deaminase is inhibited by isoleucine, a metabolite of 2-ketobutyrate.
Solution: used a mutated form of threonine deaminase isolated from Eschericia coli. This only shows weak inhibition by isoleucine

Question 17

to make plant produce OHB-V, numerous steps are involved:

Answer 17

• pick a suitable plant - oil seed rape
• use promoters to direct synthesis to the seeds
• -ease of harvest
• -minimal impact on the rest of plant growth
• -high yield
• modify the coding regions so that the enzymes are made in the oil-storing plastids (leucoplasts)
• introduce genes which will synthesis PHB-V
• introduce genes to modify metabolism so that plenty of the correct substrates are produced

Question 18

is it economic? Use of green plants as industrial factories and commercial application of ‘green chemistry’ relies on

Answer 18

1) primary metabolic issues
2) cheap oil
3) plastic properties

Question 19

is it economic? PRIMARY METABOLIC ISSUES

Answer 19

• can the polymer be produced in plants at high enough concentrations for industrial extraction?
• can enough polymer production be maintained in plants over multiple generations?

Question 20

is it economic? CHEAP OIL

Answer 20

• limited global resource BUT massive scale production
• plastics derived from petrochemicals = inexpensive
• economics >important > environment credentials

Question 21

is it economic? PLASTIC PROPERTIES

Answer 21

-must be similar to petrochemicals competitors

Question 22

Biopol is PHB produced by

Answer 22

fermentation of plant sugars and oils

Question 23

long history of bioplastics science & production:

Answer 23

1941 onwards, long process.

-process requires investment from company for a long time

Question 24

metabolix (is a company) trilling bioplastic PRODUCING plants examples

Answer 24

• Camelina (brassica) in Canada. Achieved 10-20% PHAs in seed weight, but still not enough
• Switchgrasee in Massachusetts. Produced up to 3.7% leaf weight as PHB. Needed to be 5% too be economically viable
• Sugarcane in Australia

Question 25

life cycle assessment of plastics. Which is most sustainable? plastics from petrochemicals or plastics from plants?

Answer 25

• polyethylene (petroleum based) 47M joules energy
• bioplastic (fermentation method) 81M joules energy
• bioplastic (transgenic plants) ??? joules energy
• BUT for bioplastics must also consider agricultural inputs, fertiliser, water & land requirements.
• life cycles studies carried out- but assumptions of env friendly practises, not carried out properly!

Question 26

other areas of crop production where transgenic practices may be beneficial

Answer 26

> Pharmaceuticals:
-vitamin content (eg. golden rice)
–genetically altered to make beta-carotene, a pigment the body converts to vitamin A
-edible vaccines
–antigens expressed in plant tissues that elicit an immune response
-drugs
Inputs for the chemical industry

Question 27

advantages of edible vaccines:

Answer 27

• cost effective
• no need for refrigeration of the vaccine
• edible do not need to be infected
• several can be combined into one plants
• do not include heat killed pathogens

Question 28

problems with edible vaccines:

Answer 28

• controlling dosage (expression will vary in plants)
• vaccine fruit may be eaten by mistake
• escape of genes into wild relatives