Under the Microscope (Part 2): Food, Fuel and Medicine

Using microbial biotechnology in our food, fuel and pharmaceutical industries:

Microscopic image of an isolated micro-organism – Image Credit: https://www.shutterstock.com/image-illustration/microorganism-bacteria-isolated-microscopic-world-724091662

In a previous post, I highlighted the potential advantages and limitations facing the biofuel industry. In aiming to produce biofuel in high quantities and on land without competing against food crop cultivation, the last decade has seen considerable attention being given to the possibility of using microalgae for biofuel production. Microalgae are capable of tolerating a wide variety of pH ranges, temperatures, light intensities, etc, and their ability to generate large quantities of triglycerides relative to their cell volume makes them an attractive means by which biodiesel can be produced.

Research has consistently shown that microalgae typically alter their lipid biosynthetic pathways to generate higher cellular levels of triglycerides when starved of nutrients such as nitrogen. Cultivation of microalgae for triglyceride production typically takes place within either an open raceway pond, or a closed system photo-bioreactor (as highlighted below).

Microalgae Photobioreactor used to cultivate microalgae for biofuel production – Image Credit: https://en.wikipedia.org/wiki/Photobioreactor

This unique aspect of algae cellular biochemistry can also be exploited genetically, whereby algae can be genetically modified to have certain enzymes involved in lipid biosynthesis over-expressed to increase their cellular lipid content for biofuel production. Using CRISPR-Cas9, scientists at Exxonmobil in 2017 were able to selectively target and knock-out the regulatory gene ZnCys Nannochloropsis gaditana. The result was an increase in cellular lipid content from 20% to 55%.

Biofuel production using micro-organisms is not solely confined to microalgae, with other notable examples including Clostridium bacteria in “ABE” (Acetone, Butanol, Ethanol) fermentation. This process involves the anaerobic bacterial fermentation of a carbohydrate (typically glucose) by Clostridium leading to the production of Acetone, n-Butanol and Ethanol (with a ratio of 3:6:1 of Acetone, n-Butanol and Ethanol respectively). Researchers have also begun utilising CRISPR-Cas9 in bacterial strains such as E. coli to enhance n-Butanol production, as was the case in 2019 when Abedelaal et al, used CRISPR-Cas9 to successfully introduce DNA encoding enzymes required in the n-Butanol synthesis pathway into E. coli.

However, microbial biofuels aren’t in the clear just yet. Numerous economic analyses show the costs of executing these operations on a larger commercial scale are currently too high to be feasible. This sadly, has been realised at the expense of several biofuel companies, notably Sapphire Energy which despite having raised over $100 million in investment, have scaled back their algal biofuel production owing to high operation costs and are exploring alternative means by which algae maybe biotechnologically exploited.

The current limited capacity has prompted research into exploring other means by which microalgae may be commercially exploited. One of which is through utilising microalgae to express high value products for use in the food and nutraceutical industries. The marine alga Phaeodactylum tricornutum is known to accumulate Omega-3 long chain polyunsaturated fatty acid (LC-PUFA) and Eicosapentaenoic acid (EPA) and as a result, is considered to be a model organism for the production of Omega-3 supplements (which themselves provide a variety of dietary and health benefits e.g. as a supplement to improve liver function in people suffering with non-alcoholic fatty liver disease).

Phaeodactylum tricornutum – Image Credit: https://en.wikipedia.org/wiki/Phaeodactylum_tricornutum

Recently researchers have been able to genetically modify P. tricornutum to over-express genes involved in the lipid biosynthetic pathway. The result was a significant increase in the cellular content of desired Omega-3 fatty acids. This offers a promising alternative to marine fish (which currently serve as our main source of dietary Omega-3), as depleting stocks of wild fish and pollution of marine environments is forcing us to search for alternative means by which these supplements can be sourced.

Over the last century, we have often taken medication to prevent infection from micro-organisms. Ironically, some of these same micro-organisms may now hold the key to developing and producing high value products which have the potential for use as future therapeutic interventions. The use of E. coli is one such example. The simple genome of E. coli makes it an ideal candidate for the production and expression of high value products for use as pharmaceuticals. A notable example being to produce insulin to treat Diabetes mellitus.

Human insulin has been used to treat diabetes since the 1980’s with E. coli having served as the primary cell factory for its production. In this process, the gene for insulin is selected and inserted into a plasmid which is taken up by E. coli. Once the E. coli have sufficiently multiplied the insulin is then harvested and purified for use in medicine.

Schematic of recombinant insulin production in E. coli – Image Credit: http://www.scielo.br/scielo.php?pid=S1517-83822016000500051&script=sci_arttext

There are however disadvantages with using E. coli for production, such loss of plasmid property and improper protein refolding. Recent research into looking at alternative micro-organisms for use has revealed the yeast Saccharomyces cerevisiae to be more advantageous at producing recombinant insulin compared with E. coli on accounts of it producing proteins which are properly refolded and unlike E. coli produced insulin, making them more appropriate for use. Although using yeast for the production of such medicine is not as widespread, the research shows us that the ability to use micro-organisms to produce proteins needed for valuable medicines is very promising indeed!

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