Developing the sugarcane biofactory for high value biomaterials

Abstract

The world is now in the age of Biotechnology. The tools of biotechnology are impacting everything from modern medicine and the pharmaceutical industry, through to the energy and agriculture sectors and the manufacturing, automotive and fuel industries. This "biotech revolution" has come as we approach a crucial time for petrochemical industries. Political instability in the Middle East, and the ever increasing demand for crude oil coming from China and India, are putting a strain on the world's ability to produce adequate amounts of inexpensive crude oil. The result of this has been an escalation in crude oil prices. Governments and corporate sectors are developing the strategic plans necessary to gradually wean themselves from their petroleum dependency. The combination of the biotech revolution, the economic impact caused by the increasing cost of crude oil, combined with the planning and investment of government, corporate and private sectors in biological solutions to this problem is creating a new economy, a Bio-based or BioEconomy. This new economy will be based on carbohydrates. Brazil and the USA are leading this charge. Brazil is using sugars from sugarcane as the carbohydrate for their biorefineries to make ethanol and a small amount of bioplastics. The USA is using the sugars in corn starch to make ethanol and a range of bioplastics. Around the world people are looking at the biomass of our agriculture and forestry sectors as a potential cheap, abundant and renewable source of sugars for the biorefineries of the future. Sugarcane (Saccharum spp. hybrids) has the potential to be a key crop in the developing BioEconomy. It is the second fastest growing tropical grass, produces a large biomass, partitions carbon into sucrose at up to 42% of the dry weight of the stalk, has a mobile pool of hexose sugars through most of its life cycle, is vegetatively propagated due to the difficulty in producing seeds, and can be harvested multiple times before replanting. We have successfully engineered sugarcane using the tools of modern biotechnology to function as a biofactory producing two different bioplastics and an alternative sugar. We have transformed sugarcane with 3 genes from a bacterium, Ralstonia eutropha, that encode the genetic pathway for poly-3-hydroxybutyrate (PHB). In the best line, PHB accumulated at 2.5% of leaf dry weight (DW). Sugarcane was also evaluated as a production platform for p-hydroxybenzoic acid (pHBA) using two different bacterial genes, one from Escherichia coli, and the other from Pseudomonas fluorescens. Each of these genes modify a different existing biochemical pathway in sugarcane. In the best line, a glycosylated form of pHBA accumulated in the leaf and stem tissue at 7.3% and 1.5% DW, respectively. Lastly, we have used a single gene from apple (Malus domestica) to engineer sugarcane to make the alternative sugar sorbitol. The best line contained sorbitol at 12% DW in leaves and 1 % DW in stems. Brazil's example of establishing biorefineries at sugar mills to produce biofuel and bioplastics and our examples of engineering sugarcane to make new bioplastics and alternative sugars demonstrate that this crop not only has the potential but already is playing an important role in the growing BioEconomy