Rational strain improvement for surfactin production: enhancing the yield and generating novel structures

Abstract

Surfactin, one of the most powerful microbial surfactants, is a lipopeptide-type biosurfactant which combines interesting physicochemical properties and biological activities. However, the high cost caused by its low productivity largely limits the commercial application of surfactin. Hence, many engineered bacterium have also been used to enhance surfactin biosynthesis. This review briefly summarizes the mechanism of surfactin biosynthesis, highlighting the synthesis pathway of N-terminally attached fatty acids, and outlines the main genetic engineering strategies for improving the yield and generating novel structures of surfactin, including promoter engineering, enhancing efflux systems, modifying the transcriptional regulatory genes of surfactin synthase (srfA), genomics and transcriptomics analysis, non ribosomal peptide synthetase (NRPS) domain and combinatorial biosynthesis. Finally, we discuss the future prospects of the research on surfactin.

Keywords: Biosynthesis; Branched chain fatty acids; NRPS; Structure; Surfactin.

Fig. 1

Chemical structure of surfactins [32]

Fig. 2

The biosynthesis pathways of branched-chain amino acids participating in surfactin biosynthesis. a Branched-chain amino acid biosynthesis module, represented by light grey panel. ilvA, l-threonine dehydratase; ilvBN, acetohydroxy acid synthase I; ilvGM, acetohydroxy acid synthase II; ilvIH, acetohydroxy acid synthase III; ilvC, acetohydroxy acid isomeroreductase; ilvD, dihydroxy acid dehydratase; leuACDB: leuA, 2-isopropylmate synthase; leuCD, isopropylmalate isomerase; leuB, 3-isopropylmalate dehydrogenase; EMP, Embden–Meyerhof–Parnas pathway, marked with deep gray panel; ilvE, branched chain amino acid aminotransferase; phdABCD, pyruvate dehydrogenase; accABCD, acetyl-CoA carboxylase. b Biosynthesis of branched-chain fatty acids and CoA-activated 3-hydroxy long chain fatty acids, represented by light orange panel. fabD, malonyl-CoA:ACP transacylase; FabH, β-ketoacyl-ACP synthases; Branched-chain α-keto acid dehydrogenase complex marked with deep gray panel; Ptb, butyryl coenzyme A transferase; Bcd, l-leucine dehydrogenase; Buk, butyrate kinase; LpdV, 2-oxoisovalerate dehydrogenase; BkdAA, 2-oxoisovalerate dehydrogenase; BkdAB, 2-oxoisovalerate dehydrogenase; BkdB, 2-oxoisovalerate dehydrogenase; YbdT, fatty acid beta-hydroxylating cytochrome P450 enzyme; LcfA and LcfB, long-chain fatty acid-CoA ligases. FAB, fatty acid biosynthesis. The degradation pathway of l-isoleucine was marked with green panels; the degradation pathway of l-valine was marked with purple panels; the degradation pathway of l-leucine was marked with orange panels. c Nonribosomal peptide synthetase synthesis module. A, adenylation domain, represented by amino acids in red colour; PCP, peptidyl carrier protein domains, shown in green colour; C, condensation domain, shown in gray colour; E, epimerization domain, shown in purple colour; TE, thioesterase domain, shown in orange colour

Fig. 3

The schematic model for the regulation of the transcription of the srfA operon network involved in two extracellular signaling peptide-mediated quorum sensing in B. subtilis. T-bars indicate the negative effects on DNA binding or protein interactions. Bent arrow represents the promoter. ‘P’ in the circle represents the phosphoryl group

Fig. 4

The general regulatory network of surfactin synthesis. Refer to Wu et al. [33], with minor modifications