Synthesis, properties and uses of bacterial storage lipid granules as naturally occurring nanoparticles Nicholas Thomson, a David Summers b and Easan Sivaniah * a Received 13th January 2010, Accepted 6th April 2010 DOI: 10.1039/b927559b Bacterial storage lipids including poly(hydroxyalkanoates), triacylglycerols and wax esters are biodegradable materials with applications in food production, household goods, cosmetics, packaging and medicine. They are produced as a carbon and energy store by a wide range of species, and are accumulated in cytoplasmic granules. Various proteins are known to associate with these granules, thereby presenting the opportunity to functionalise their surfaces and to create biotechnologically applicable biobeads with the potential to replace existing colloidal systems for protein purification, drug delivery and enzyme immobilisation. This review summarises the production of such structures, and considers the methods available to adjust the physical properties of the granules to make them suitable for novel applications. Introduction A large and diverse array of bacteria is known to produce and store lipid compounds within their cytoplasm in the form of insoluble granules. Bacterial production of these substances has the potential to ease the pressure on farmland and food supply chains, replace costly and (possibly) ethically questionable products derived from animals and reduce the economic and environmental costs of production by utilising waste streams from other industries. Bacteria are also more amenable to the tailoring of the properties of their lipid products by techniques such as altering feedstock composition and genetic engineering. 1,2 In recent years interest has grown in the use of lipid granules themselves for biotechnological purposes such as protein purifi- cation, antibody display and enzyme immobilisation. In this respect, the isolated granules may be approached in the same way as other colloidal particles that have been used for such purposes for many years. 3–5 However, the composite structure of lipid inclusions and their formation inside living cells add both a degree of complexity and the opportunity for more sophisti- cated designs. Therefore, an in-depth understanding of all aspects of these structures is crucial to allow their potential to be realised. This review examines how storage lipids are produced by bacteria, the process of creating granular structures from them and the potential biotechnological applications for which they may be useful. To appreciate the interaction of different factors that affect bacterial storage lipid composition, quantity and uses, one must examine the interfaces between biochemistry, genetics, medicine, colloid and polymer physics, and microbiology. Prevalence and functions of bacterial storage lipids Bacterial storage lipids are generally accumulated under condi- tions of nutrient imbalance, frequently to well over 50% of the cell dry weight. 6 They are inherently osmotically inert and water insoluble. This, combined with their superior energy density a Cavendish Laboratory, University of Cambridge, Cambridge, UK. E-mail: es10009@cam.ac.uk; Fax: +44 (0)1223 337000; Tel: +44 (0)1223 337267 b Genetics Department, University of Cambridge, Cambridge, UK. E-mail: dks11@hermes.cam.ac.uk; Fax: +44 (0)1223 333992; Tel: +44 (0)1223 333991 Nicholas Thomson Nicholas Thomson completed his BSc in Biotechnology with Management from Edinburgh University in 2007. He is now a PhD student under Dr Easan Sivaniah in the Physics Depart- ment of Cambridge University. His research, in collaboration with Dr David Summers, focuses on utilising a novel protein expression system for the production of poly- hydroxyalkanoates. David Summers David Summers’ research is in the fundamental cellular processes of site-specific recom- bination and cell cycle control in bacteria. His laboratory is involved in the commercialisa- tion of discoveries arising from its basic research programme. A substantial part of this work has involved the development of the Quiescent Cell Expression System, a novel bacterial cell factory for the expression of recombinant proteins in non- growing Escherichia coli. This journal is ª The Royal Society of Chemistry 2010 Soft Matter , 2010, 6, 4045–4057 | 4045 REVIEW www.rsc.org/softmatter | Soft Matter Published on 05 May 2010. Downloaded by Rikagaku Kenkyu-Sho on 04/12/2014 04:33:50. View Article Online / Journal Homepage / Table of Contents for this issue