Identification of the fatty alcohol oxidase FAO1 from Starmerella bombicola and improved novel glycolipids production in an FAO1 knockout mutant

Alkyl polyglucosides (APGs), which were first commercialized in the 1990s, are mild, non-ionic surfactants comprising fatty alcohols and glucose derived from recyclable starch. APGs have good properties as cleaners, foaming agents, and emulsifiers, and they do not undergo hydrolysis at an alkaline pH. In addition to their advantages over traditional synthetic surfactants, APGs are low-irritant surfactants that are nontoxic and easily degradable in the environment. Thus, APGs are considered to be environmentally friendly surfactants. Starmerella bombicola glycosylates long-chain omega or omega-1 hydroxy fatty acids, and it also directly glycosylates secondary alcohols. Although it is generally difficult to directly glycosylate primary alcohols, they are easily converted to the corresponding fatty acids by S. bombicola because of its strong alcohol oxidase activity. To redirect unconventional substrates toward APG synthesis, the long-chain alcohol oxidation pathway was blocked by knocking out the fatty alcohol oxidase gene. The complete sequence of the S. bombicola FAO1 gene (2046 bp) was cloned, and the obtained nucleotide sequence was used to construct a knockout cassette. An FAO1 knockout mutant with the correct genotype and phenotype was evaluated by fermentation on 1-tetradecanol. The mutant produced tetradecyl disaccharides and tetradecanediol tetrasaccharides. The APGs and diol polyglucosides (DPGs) production of the mutant was 27.3 g/L ((APGs + DPGs)/de novo sophorolipids ratio was about 15:1), while the parent strain did not produce APG or DPG. These data indicate that the substrates had been redirected toward novel glycolipids synthesis in the mutant.