A novel electroporation procedure for highly efficient transformation of Lipomyces starkeyi

Microbial lipids produced by oleaginous microorganisms as raw materials for the production of oleochemicals and biodiesel are sustainable while avoiding competition with food products. The oleaginous yeast Lipomyces starkeyi is an excellent lipid producer with a great industrial potential that is suitable as a valuable host to improve lipid production through genetic engineering modifications. However, genetic tools, including effective transformation methods, for L. starkeyi are insufficient for improvement of lipid production and analysis of lipid production mechanisms. We previously developed a polyethylene glycol (PEG)-mediated spheroplast transformation method that significantly improved the homologous recombination efficiency of L. starkeyi strain ∆lslig4. Although other transformation methods, including lithium acetate (LiAc)-mediated transformation and Agrobacterium tumefaciens-mediated transformation, have been reported, a more efficient and convenient transformation method for L. starkeyi is desired. In this study, we developed a novel electroporation transformation method that was first applied for integration of drug-resistance gene markers into the genome of L. starkeyi strain ∆lslig4 at the 18S ribosomal DNA locus of a multiple-copy gene, which yielded approximately 60 transformants/μg of DNA. Optimization of five parameters (i.e., cell growth phase, cell density, osmotic stabilizers, pretreatment agents, and electric conditions) enhanced the efficiency of transformation to approximately 1.5 × 10⁴ transformants/μg of DNA. As compared with those of LiAc-mediated transformation and PEG-mediated spheroplast transformation, the efficiency of the proposed transformation method was increased by about 111- and 7-fold, respectively. Additionally, the transformation efficiency of our proposed electroporation method targeting a single-copy gene locus yielded 273 transformants/μg of DNA. To our knowledge, this is the first report of a successful electroporation method to accelerate analysis of lipid production by L. starkeyi.