Thomas Butler: Could algae solve 21st century problems?

What are the problems to address in society with microalgae?

Transitioning from a petroleum to a bio-based, circular economy is essential in the near future to combat climate change, minimise energy consumption, reduce chemical inputs and waste, in conjunction with providing alternative sustainable products.  Microalgae have great potential as a cell factory containing lipids, proteins, pigments, carbohydrates, minerals, and vitamins.  Even though electrified-road transport offers a potential alternative to diesel, for shipping and aviation industries substitutes to diesel and kerosene are required.  Microalgae can offer the potential for biodiesel production and have the highest areal oil yields (up to 75 % of the cell is oil) and they have been explored for alternatives to kerosene.  Microalgae have a high protein content and they are suitable for humans, animals, or for aquaculture feed.  Two specific fatty acids, docasahexaneoic acid/DHA (responsible for brain development) and eicosapentaenoic acid/EPA (cardiovascular benefits) offer great potential as vegan alternatives to oily fish such as salmon and offer the same health benefits.  Microalgae can also offer potential for cosmetics, bioplastics, antibiotics, vaccines, and recently have been explored as a possible anti-retroviral against HIV.

Since the 1970s the main driver for microalgal research was for biofuels but the emphasis has shifted over the past decade.  Markets have transitioned towards high value products such as pigments and cosmetics; Spirulina (Arthrospira) for phycocyanin (used as a food colourant e.g. blue smarties), Haematococcus lacustris for astaxanthin (which I mentioned in the Halloween episode – why salmon are red), and Dunaliella salina for β-carotene (food colouration).  However, there is a requirement for bulk products such as protein to emerge into the market.  For this the cost of microalgae needs to be reduced.  It has been hypothesised that microalgal biomass can be produced at 5 euros/kg but for obtaining products this cost is much higher as the microalgal biomass has to be harvested (microalgae are typically 95 % water), the cell walls disrupted, and the product extracted which adds significant cost to the process.  One solution to the high cost of microalgal production is to adopt a biorefinery approach, something which I have explored during my PhD.  A biorefinery is where multiple products are produced from the biomass that add value to the process compared with a single product alone, theoretically the highest value product should be the main product.

Why choose the diatom Phaeodactylum tricornutum of all the microalgae?

Phaeodactylum tricornutum is a microalgal diatom that utilises carbon as carbon dioxide and bicarbonate and has the potential for bio-based manufacturing.  Compared with plants it has a high doubling time (up to 12 h for a single doubling in biomass), it can grow using seawater, reducing the requirement for freshwater, and it can use wastewater and flue gases (waste from power stations) for growth.  It can accumulate a wide variety of natural products including oil, the fatty acids EPA and DHA, the carbohydrate chrysolaminarin (antioxidant) and the pigment fucoxanthin (nutraceutical for weight loss).  In addition the genome has been sequenced and a molecular toolbox has been developed enabling the production of genetically engineered products of interest such as bioplastics, recombinant proteins (such as antibodies against Hepatitis B) and triterpenoids (antimicrobial and anti-tumour activities).  

What is my PhD and what have I been working on?

I have been working on developing P. tricornutum as a biorefinery platform adding value to the biomass with the aim of minimising chemical inputs and the waste which is produced.  I would like to thank The Engineering and Physical Sciences Research Council (EPSRC) and my supervisor Dr Raman Vaidyanathan for the opportunity. 

During my PhD I have been determining which products are the highest value and aiming to maximise these products (fucoxanthin and EPA) whilst characterising the remainder of the biomass which could be sold as bulk products (protein and carbohydrate) for aquaculture or animal feed.  During the cultivation stages it is important to understand the physiology of the cell.  Three key elements are carbon, nitrate, and phosphate and these need to be moitored to avoid limiting conditions.  In addition, microalgae do not live alone and there is a microbial consortium which can often be found.  Some of these bacteria can be friends (providing vitamins and carbon dioxide to the culture) and some can be foe (leading to culture crashes).  More work is required on characterisation of these bacteria, and understanding how to control the population, which is what I have been working towards. 

During my PhD I have conducted work in the laboratory, and at pilot scale cultivating microalgae in the UK and also the Netherlands.  Taking your research from the laboratory to pilot scale presents a series of challenges to overcome, mainly engineering, but also biological such as contamination from pests such as single celled protozoa (see below). 

I have also been addressing the downstream side (harvesting and extraction); exploring a bio-based flocculant to replace toxic aluminium (can cause neurodegenerative disease) which is used in industry and this bio-based flocculant can harvest the biomass in 10 minutes (normally 1 to >10 h is required in industry).  This wet biomass can be directly cell disrupted and extracted without the need for drying the biomass (added cost) which is something our research group has been working on.  For targeting the bottlenecks in the process a great deal of method development was required which was a long journey.