Exploring the Biosynthesis of Unsaturated Fatty Acids in Bacillus cereus ATCC 14579 and Functional Characterization of Novel Acyl-Lipid Desaturases

Abstract

ABSTRACTAt low temperatures,Bacillus cereussynthesizes large amounts of unsaturated fatty acids (UFAs) with double bonds in positions Δ5 and Δ10, as well as Δ5,10 diunsaturated fatty acids. Through sequence homology searches, we identified two open reading frames (ORFs) encoding a putative Δ5 desaturase and a fatty acid acyl-lipid desaturase in theB. cereusATCC 14579 genome, and these were named BC2983 and BC0400, respectively. Functional characterization of ORFs BC2983 and BC0400 by means of heterologous expression inBacillus subtilisconfirmed that they both encode acyl-lipid desaturases that use phospholipids as the substrates and have Δ5 and Δ10 desaturase activities. Thus, these ORFs were correspondingly nameddesA(Δ5 desaturase) anddesB(Δ10 desaturase). We established that DesA utilizes ferredoxin and flavodoxins (Flds) as electron donors for the desaturation reaction, while DesB preferably employs Flds. In addition, increased amounts of UFAs were found whenB. subtilisexpressingB. cereusdesaturases was subjected to a cold shock treatment, indicating that the activity or the expression of these enzymes is upregulated in response to a decrease in growth temperature. This represents the first work reporting the functional characterization of fatty acid desaturases fromB. cereus.