Table 1 Summary of regulators involved in the synthesis and efflux of surfactin in Bacillus

Transcription of the srfAA-AD operon

ComX, ComA-ComP

ComP responds to the extracellular peptide pheromone ComX, then undergoes autophosphorylation and subsequently interacts with ComA to form ComA -P, ComA-P activates transcription of the srfAA-AD

Positive

[24,25,26]

RapC, RapF, RapA4

Binding with ComA, then inhibits ComA-P and Psrf interaction

Negative

[27,28,29,30,31,32]

RapD, RapG, RapH, RapK

Overexpression of these Rap proteins inhibits srfAA-AD expression

Negative

[33,34,35,36]

Rap60, RapQ

Regulates ComA activity by forming a ternary complex with ComA and DNA and inhibit srfAA-AD expression

Negative

[37,38,39]

PhrC, PhrF, PhrG, PhrH, PhrK, Phr60, PhrQ, PhrA4

Inhibits the activity of their cognate Rap proteins

Positive

[27,28,29,30, 33,34,35, 37,38,39]

RsiX, SigX

Disruption of rsiX activates sigX, which increases rapD expression

Negative

[40]

RghR

Repress rapD, rapG, and rapH expression

Positive

[35]

PhoR-PhoP

Positively regulates surfactin production under low phosphorus conditions

Positive

[41,42,43,44]

DegU

DegU directly binds to the srfAA-AD promoter or indirectly regulates srfAA-AD expression by regulating other genes in undomesticated wild strain. Knock out of the degU gene enhances surfactin production

Negative

[45,46,47,48]

Spo0A

Global regulator initiates sporulation. Deletion of spo0A enhances surfactin synthesis

Negative

[49]

CodY

A global regulator that inhibits srfAA-AD transcription by competing with RNA polymerase binding sites in the srfAA-AD promoter region

Negative

[50]

Spx

Spx occupies overlapping sites in the αCTD region of RNA polymerase which inhibits the binding between ComA-P and RNA polymerase with the srfAA-AD promoter

Negative

[51, 52]

PerR

Competitively binding to the srfAA-AD promoter region bound by ComA-P

Negative

[53]

Branched chain fatty acid synthesis

AccA, AccB, AccC, AccD

Acetyl-CoA carboxylase (ACCase) complex, catalyzes the formation of malonyl-CoA from acetyl-CoA

Positive

[54]

YngH

ACCase subunit (biotin carboxylase II), could maintain Acetyl-CoA ACCase activity

Positive

[55]

FabD

Acyl carrier protein transacylase, converts Malonyl-CoA to malonyl-acyl carrier protein (ACP)

Positive

[56]

FabHB

β-ketoacyl-acyl carrier protein synthase III (FabHB) catalyzes the condensation of β-keto acyl-ACP from malonyl-ACP and branched α-ketoacyl CoA

Positive

[56]

LcfA, YhfL, YhfT, YngI

Fatty acyl-CoA ligases

Positive

[57,58,59,60]

Amino acid synthesis

YrpC, RacE, MurC

Associated with l-Glu consumption

Negative

[61, 62]

PyrB, PyrC

Participates in the branching pathway for l-Asp biosynthesis, catalyzes the formation of Uracil from l-Asp

Positive

[61]

bkdAA, bkdAB, lpdV

Involved in the l-Leu and l-Val metabolic pathways, alters the proportion of surfactin isoforms

Negative

[63, 64]

Surfactin secretion and immunity

YcxA, KrsE

Transport membrane proteins, YcxA and KrsE interact with the polar amino acid of surfactin

Positive

[65, 66]

YerP

Transport membrane protein and homologous to the resistance and cytokinesis family of PMF-dependent efflux pumps

Positive

[23]