What is PMF?
PMF is the incorporation of new genes into plants, permanently or transiently, to produce proteins and essentially making them biodegradable single-use bioreactors. So why use plants instead of giant stainless-steel bioreactors? Well, plants have quite a few advantages.
- They are inherently safe because no human pathogens grow in plants.
- There is no need for sterile growth conditions as plants can use their own immune systems to fend off disease.
- Many of the methods used to incorporate genetic material into plants can be scaled to thousands of acres.
- The desired protein production can be achieved within 4-8 weeks or sometimes 3-5 days after inserting the appropriate DNA sequence.
- Capital expenditure is much lower. It’s been estimated that the capital cost of a 60,000L S1 safety level greenhouse can be built for 25-55% of the cost of a similar bioreactor facility.
- They are sustainable, many side streams can be extracted, and any remains are biodegradable.
Some major disadvantages are:
- Low productivity due to the larger size of plant cells vs bacteria (10,000x) and typical mammalian cells (1,000x). This results in relatively lower numbers of protein producing cell units per kilogram of tissue or litre of medium.
- High downstream processing costs, as generally the plant cells need to be broken open to extract the target molecule vs excretion of the target molecule into the growth medium in many other systems.
- The danger of genetic material “escaping” into related or even unrelated plants and ending up in food crops.
How can we mitigate the disadvantages?
- Using non-food/feed crops such as tobacco may limit the risk of gene transfer to food crops and reduce the chances of contamination.
- Using transient expression where the bacteria used to infect the plant are modified and not the plant DNA. This reduces the risk of contamination, which can be reduced further by production in contained facilities.
- New plant breeding techniques like CRISPR-cas can dramatically improve plant growth rates and increase yields.
- The use of vertical farming to address the low productivity and genetic contamination issues.