## 2 Strain Selection  
Perhaps the key fundamental issue for any microalgae biorefinery is strain selection. Polycultures will inevitably give rise to lower value products; whereas monoculture, and the control over product quality that comes with it, will tend towards higher value products. A further advantage of monocultures is the ability to undertake extensive environmental optimisation for increased productivity and performance. In recent years, with the advent of genomic technologies, genetic manipulation has redefined the metabolic potential of microalgae by offering the ability to enhance existing, and even insert entirely new, strain properties [11]. Traditionally, bioprospecting was undertaken in oceans, ponds, rivers, and other aquatic reservoirs of interest to identify strains displaying desired characteristics--such as fast growth rate, robust growth, cheap/easy selection, metabolites of interest, etc. [12; 13; 14]--which were subsequently incorporated into industrial processes. Building upon this, random chemical mutagenesis was utilised on the variants of what have now become well established strains, in order to improve their productivity for one particular metabolite of interest or one improved trait [15; 16] and provide 'proprietary status', often to appease nervous investors. The results of laboratory scale exploits to optimise the induction of particular metabolites are often willfully extrapolated, but rarely achieved at commercial scale, especially over seasonal dynamics. Targeted genetic modification does, however, circumvent or mitigate against many of these problems, improving productivity by direct design or producing entirely new compounds or recombinant proteins with higher value [17; 18]. Yet, the challenges of microalgal growth remain: effective scale-up and processing in an economically viable way. It is no surprise that the bold claims made by some biologists regarding the production potential of their microalgal strains can perhaps only be matched by their equivalent engineering counterparts with their usually unsubstantiated claims (hidden behind a mask of protecting their intellectual property) that their latest iteration of an established and well-understood cultivation technology holds the key to productivity for every algae, for every process, in every location. The truth is actually quite straight-forward and simple: for a successful industrial process, the right biological platform will need to be integrated with the right engineering infrastructure in a bespoke manner determined by local environmental conditions, infrastructures, market demands, and budgets. For a microalgae bioreinery to be successful, all these factors will need to be considered from the outset. Thus, a paradox exists: while genetic modification offers a road to success for a biorefinery, the developmental costs involved may actually limit the options available to how a particular microalgae process could be industrialised and, thus, impede exploitation efforts. A narrow focus on a particular product (i.e., not a bioreinery with multiple products per se) may be advantageous only if it is of sufficient value. Multifunctionalisation perhaps offers the most interesting opportunity in this regard and is gaining increasing traction and interest [18; 19], providing multiple higher value products simultaneously and moving closer towards the successful refinery model of the oil industry. It is clear that the successful application of a biorefinery model requires significant thought and consideration prior to expenditure. Surprisingly, few microalgae strains are currently grown at commercially relevant industrial scale (Table 1). Arguably the greatest commercial successes are: _Haematococcus pluvialis_ for production of the red pigment and potent antioxidant, astaxanthin; _Dumaliella salina_ or _bardawil_ for \(\beta\)-carotene; the cyanobacteria _Arthrospira platensis_ or _maxima_ (known as _Spirulina_ sp.)