Optimal Mutagen Doses for Emiliania huxleyi

Emiliania huxleyi (E. huxleyi) is one of the most prominent coccolithophores. Given favorable conditions, E. huxleyi blooms can reach sizes exceeding 100,000km², with densities of 10⁷ cells per L (Olson & Strom 2002).

With increasing demand and limited supply of fossil fuels, it has become increasingly popular to look toward alternative renewable fuel sources. E. Huxleyi store energy predominately as uniquely structured polyunsaturated long chain (C_37-39) alkenes, alkenones and alkenoates (abbreviated as PULCAs) (Eltgroth et al 2005). Unlike the stored energy of macroalgae and higher order plants, triacylglycerols (TAGs), PULCAs provide a similar composition to native petroleum crude oils (Yamane 2013), which offers a more cost effective and higher yielding extraction process (Wu et al 1999). A number of factors have been shown to influence the alkenone content of E. huxleyi, such as nitrogen deficiency, phosphate limitation (Li et al 2014), and temperature (Shiraiwa et al 2005). For these reasons E. huxleyi has the potential to be an attractive system for algal biofuel.

The broad and long-term objective of our research is to elucidate the alkenone biosynthesis pathway in E. Huxleyi, using random mutagenesis techniques. We propose to use UV light and methylmethane sulfonate (MMS) to create a mutant population, from which clones unable to synthesize alkenones will be selected. Identifying genes whose specific mutations underlie the loss-of-function phenotype will then reveal genes of interest. The aim of this research was to determine the UV and MMS dose response rates for E. huxleyi to ascertain optimal doses defined as a 50% survival rate for each of the two mutagens. Preliminary data indicate that E. huxleyi appear to be highly sensitive to UV mutagenesis, with an LD₅₀ of 0.57mJ/cm² for the calcifying strain M217 and 0.96mJ/cm² for the non-calcifying strain CCMP1516. Both calcifying and non-calcifying strains exhibit similar LD₅₀ values for MMS at 1-2% (v/v).