It’s a well-known fact that if you want to make paper, somewhere along the line you need to chop down a tree. With millions of tonnes of paper being produced annually, this really adds up to a lot of trees. Of course many companies now are well aware of ways to harvest trees sustainably – whether it is chopping trees in moderation, or replanting as they go – but sustainable deforestation doesn’t always equate to sustainable paper-making.
Paper is primarily made from cellulose and the cellulose in trees is locked up in a complex network with other polymers including lignin and hemicelluloses (both of which are waste products to the paper industry). This sums to less than a third of the tree being turned into paper. In an ideal world these waste products would be recycled and used for other purposes, but in reality much of this is used for burning as fuel or put into landfill.
Cellulose is not only crucial for paper manufacturing but is also widely used in other industries such as food, textiles and cosmetics. In the past decade many microbiologists have tried to find a more sustainable method for producing cellulose – after all, it isn’t just plants that make this incredibly important biopolymer. We’ve known for a long time bacteria will generate cellulose in order to form biofilms (an extracellular polymeric matrix that helps the cells aggregate and attach to a surface). At first glance it seems like a viable solution: the bacteria will happily grow their own weight in cellulose under the right conditions and all they need for this is an acidic medium with plenty of sugar. Probing a little deeper uncovers the fact that nobody is doing this and not because of legislation on GMOs or a lack of infrastructure – it’s a much simpler reason.
Whilst it may sound like growing your own weight in cellulose is an impressive feat, when you only weigh a fraction of a nanogram it simply isn’t enough. The maximum yield of biocellulose (that is, cellulose produced by microorganisms rather than plants) is at at less than a gram per litre. So it would entail hundreds of litres of growing cells just to get one square metre of office paper – not exactly an inspiring statistic.
As we move into the spring of 2016 several pieces of research are starting to push back these limitations. The detail that known biocellulose-producing bacteria readily synthesise the polymer under acidic, high sugar conditions led to a simple yet effective method for finding a species with a higher biocellulose production. In nature, there is an abundant and common place that is both acidic and rich in sugar: fruit. Recently, a group of scientists in Malaysia have attempted to take on the task of finding this ‘holy grail’ of biocellulose production. The tropical climate allows for the growth of many citrus fruits as well as many other familiar acidic fruits such as pineapples and mangoes. By isolating the bacteria from different fruit samples, and screening for cellulose production the researchers identified several new strains of cellulose producers, and managed to identify strains with almost double the production of the previous record holder.
Granted, a doubling of a very small number still gives us a very small number, but there are two things to bear in mind with this finding. One is that we haven’t nearly begun to identify all the biocellulose producers on the planet and the other is that the strain of bacterium is just one factor at work when it comes to making biocellulose. Without getting too bogged down in the details (you can find those here) it turns out that the medium which was previously seen as ideal for biocellulose production may not be the best bet. New studies have pointed out that whilst the standard medium used to grow cellulose is a good all-rounder, a tailored medium to the specific organism can bring about almost ten times the biocellulose production. This pulls down our ‘hundreds of litres per square metre’ to ‘tens of litres per square metre’ – a much more reasonable number.
Does this mean that in the not so distant future our newspapers, books and flyers are all going to be made from a bacterial source rather than a plant? It’s hard to say at this point and certainly more research needs to be done, but 2016 definitely looks bright for biocellulose, and hopefully a slightly greener future.
Robert G Millar (University of Warwick)
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