We alter the growth environment to enhance the production of the molecules that we are interested in.
PROFESSOR YUSUF CHISTI
Biochemical engineer Professor Yusuf Chisti of Massey’s School of Engineering and Advanced Technology researches using microscopic organisms to produce a variety of useful and commercially valuable substances for diverse applications.
An example is a current research project using algae to produce oils. ‘Algae are what makes seawater, rivers and lakes green,’ Professor Chisti explains. ‘They are microscopic organisms that are suspended in water. They use carbon dioxide and light to grow by photosynthesis and produce various compounds.’ Algae naturally make many useful compounds, but often in quantities too small to be commercially viable. Professor Chisti is researching how to grow algae so that they accumulate high levels of the desired compounds.
‘We alter the growth environment to enhance the production of the molecules that we are interested in,’ he says. ‘We then extract the compounds from them for various uses, such as for nutritional supplementation and potential fuels such as biodiesel and ethanol, or food colourants, and colours that could go into cosmetics, lipsticks and various medical products.’
An example is fatty acids, which are important for brain development. Most infant-formula manufacturers now add docosahexaenoic acid and arachidonic acid, commonly known as DHA and ARA (omega-3 and omega-6). Certain algae are natural sources of these fatty acids, and fish contain high amounts of them not because they produce it themselves, but rather because of the algae in their food chain. Eicosapentaenoic acid (EPA) is another fatty acid with health benefits, found in fish and produced by algae.
‘Traditionally, DHA and EPA are extracted from fish oil, but the supply of wild fish is declining,’ says Professor Chisti. ‘Fish oil is also a complicated mixture of many different types of oils and purification of the chemical that you want from such a complex mixture tends to be difficult and expensive. So it might be easier to actually make specific oils in algae so that the mixture is less complicated and the purification is easier.’
Using microbes to produce compounds might be more sustainable, but it needs to be competitive in terms of the cost of production.
PROFESSOR YUSUF CHISTI
However, producing algae products on a commercial scale is not currently easy. ‘Algae are hard to grow. They don’t grow very rapidly and their final population tends to be small. They require nutrients of the kind that you supply to crops, such as nitrogen and phosphorus. They require carbon dioxide, light for photosynthesis, and these things are very hard for them to get in water, because even though there is a lot of sunlight, it doesn’t get very deep into water, especially when it is coloured dark green with a big population of algae.’
Very large areas are therefore required to grow algae commercially, and yields are low. Harvesting is another challenge, requiring very large quantities of water to harvest just a small amount of the biomass. ‘All this processing takes a lot of effort, money and energy,’ Professor Chisti says. ‘We are trying to come up with a newer method of separating the water from the algae. We are hoping to achieve this using chemicals called flocculants which make the algae coagulate so that the particles attach to each other and become bigger, and settle to the bottom of the culture vessel. You can then remove most of the water from the top, and concentrate the biomass using centrifugation or filtration, methods that would be too expensive to use unless a lot of the water was first removed by other means.’
Another approach to reduce the cost of production is to increase the quantity of the compound of interest that each algal cell produces, so that fewer cells have to be harvested to get a certain amount of the compound. ‘Methods of cultivation do affect how much of a target compound is produced in a given mass of cells, so we are trying to increase the yield per cell by manipulating the feed regimen through how much nitrogen we feed, when we feed it, how much phosphorous we feed and when it is fed.’
More work is required for commercial viability of microbial production of certain products, but the method has promise in terms of potentially being more sustainable for production of biofuels and other industrial chemicals. The key, says Professor Chisti, will be in finding ways to reduce costs. ‘Using microbes to produce compounds might be more sustainable, but it needs to be competitive in terms of the cost of production.’