Evan Stephens, Juliane Wolf, Melanie Oey, Eugene Zhang, Ben Hankamer and Ian L. Ross

Abstract An advanced understanding of the genetics of microalgae and the availability of molecular biology tools are both critical to the development of advanced strains, which offer efficiency advantages for primary production, and more specifically in the context of production for biocrude and renewable energy. Consequently, we outline the current state of the art in microalgal molecular biology including the available genome sequences, molecular techniques and toolkits, amenable strains for transformation of nuclear and plastid genomes, and the control of transgenes at both transcriptional and translational levels. We also examine some strategies for improvement of expression and regulation. We suggest the primary strategies in strain improvement that are most relevant to biocrude applications; briefly illustrate the process of photosynthesis to enable identification of targets for improvement of net photosynthetic conversion efficiency in mass cultivation; and further discuss how improvement of metabolic systems may also be achieved and benefit production models. Finally, we acknowledge the aspects of prudent risk assessment and consequent regulation that are developing and how our knowledge of natural algae in existing ecosystems, and GM work in conventional agriculture both contribute lessons to these discussions. We conclude that if properly managed, these developments provide significant potential for increasing global capacity for renewable fuel production from microalgae and that these developments could also have benefits for other applications.

E. Stephens • J. Wolf • M. Oey • E. Zhang • B. Hankamer • I. L. Ross (H)

Institute for Molecular Bioscience, The University of Queensland, Queensland, Australia e-mail: i. ross@imb. uq. edu. au

E. Stephens • J. Wolf • B. Hankamer • I. L. Ross

Solar Biofuels Research Centre, The University of Queensland, Queensland, Australia

© Springer International Publishing Switzerland 2015 191

N. R. Moheimani et al. (eds.), Biomass and Biofuels from Microalgae,

Biofuel and Biorefinery Technologies 2, DOI 10.1007/978-3-319-16640-7_11

11.1 Introduction

The Need for Strain Improvement While microalgae are a proven and promising platform for the production of high-value products, their greatest potential arguably lies in their ability to capture solar energy and convert it to chemical energy in the form of high energy density fuel feedstocks with low net carbon emissions. The importance of this is highlighted by the fact that * 80 % of global energy demand is supplied in the form of fuels, while only *20 % is utilised as electricity (BP 2014; Stephens et al. 2013b). Consequently, there is a great need for renewable fuel production systems that have an economic and energetically positive return on investment (ROI), and microalgae are one of the very few options for making this a reality at scale.

Thermochemical processing of whole biomass to biocrude is a promising area of research and current commercialisation. At first glance this processing strategy does appear to promise increased yields, since in addition to lipids, other organic mol­ecules such as proteins, starch and cellulose can be converted. It may also address some of the conventional cost/energy bottlenecks, particularly as complete dewa­tering and cell disruption are not needed. But it must also be considered that, in contrast to the extraction of a relatively homogenous product such as TAGs and neutral lipids, the resultant output product from hydrothermal liquefaction (HTL) can vary in quality from a type I kerogen (a complex carbonaceous organic com­pound) (Speight 2006) to a higher grade biocrude, equivalent to the best petroleum crudes. The quality of the output depends upon the efficiency of the HTL process as well as the composition of the initial biomass. While the upgrading of kerogen to biocrude can be a much simpler process than lipid extraction from microalgae biomass, it remains an economic and energetic cost in the process. Thus, the technology can be streamlined partly by the development of microalgal production strains that have a more desirable composition for HTL processing and conse­quently improve the quality of biocrude output. The marketability of the biocrude product to fuel producers depends upon specific quality criteria including high carbon and hydrogen content and low oxygen, nitrogen and sulphur levels. Other qualitative considerations include acyl chain lengths and saturation, as well as finer points related to fuel standards. To achieve such standards and ultimately obtain a biocrude product that is comparable to conventional petroleum crude, HTL kero — gens and oils can require fractionation to a higher grade product. This additional process step results in material losses and increased energy costs which offset some of the anticipated benefit of this production strategy. This poses a significant operational loss unless the residual fraction can be efficiently recycled back to production (e. g. through strategies such as anaerobic digestion or gasification) or otherwise contributes to cost recovery and energy balance.

Strain development through the use of molecular biology has greater flexibility than conventional breeding and strain development techniques. This may translate to increases in overall productivity (greater volumes to process) and greater carbon density (higher grade biocrude output) and so is of importance for advancing this production strategy. Knowledge of algal genetics is not yet as sophisticated as other model systems. The ability to engineer algal biology is correspondingly limited at present, but is growing rapidly. Here, we discuss the ongoing development of molecular research for greater understanding of microalgae systems. In particular, we summarise the increasing set of available molecular techniques (Sect. 11.2), their application to microalgae technologies (Sect. 11.3) and the establishment of prudent regulatory systems to ensure these systems become environmentally responsible and socially accepted (Sect. 11.4).