Agriculture Reference
In-Depth Information
peptide, called competence stimulating peptide (CSP), is a 17-amino acid peptide including a
double glycine motif in the leader sequence, which is cleaved by a proteolytic domain of the
associated ABC transporter (ComA) [Hui and Morrison, 1991, Havarstein
et al.
, 1995, Zhou
et al.
, 1995]. Phosphorylation of ComE results in a positive feedback by inducing the
comCDE
as well as the
comAB
operon, respectively. Furthermore, the regulator
comX
is
induced, which mediates expression of genes responsible for competence. Regulation of
competence using the
comABCDE
system is known to be a general mechanism in
streptococci. Besides competence regulation, there are more targets downstream of
comE
involved in environmental adaptations and production of virulence factors, i.e. biofilm
formation or bacteriocin production, respectively [Cvitkovitch
et al.
, 2003, Peterson
et al.
,
2004, Kreth
et al.
, 2006, 2007].
The soil organism
Bacillus subtilis
also uses QS to control competence development, as
well as for initiation of sporulation in a coupled regulation circuit [Grossmann, 1995,
Lazazzera and Grossman, 1998]. Uptake of DNA is carried out during the transition from
exponential growth phase to the stationary phase. Internalized DNA is assumed to serve as
depository of genetic material used in chromosome repair. Limitation of nutrients in the
environment leads to sporulation. Two autoinducing peptides are known to mediate these
events. First is the processed ComX peptide, which acts similarly to the CSP peptide in
streptococci by activating the
comP
/
comA
two component signaling system, resulting in the
expression of the activator ComK. ComK promotes transcription of the genes that are
required for competence development [Magnuson
et al.
, 1994, Solomon
et al.
, 1995, van
Sinderen
et al.
,
1995, Turgay
et al.
, 1997, 1998]. A dual role in sporulation as well as in
competence is connected to the second peptide, the CSF autoinducer (competence and
sporulation factor). In contrast to other autoinducers, the CSF peptide posseses both
extracellular and intracellular signaling roles, and is therefore imported into the cell [Solomon
et al.
, 1995, Lazazzera
et al.
, 1997]. Promotion of the competence development is mediated
under low concentrations of the CSF peptide inside the cell by indirectly increasing the
activity of the ComA response regulator. High intracellular concentrations prevent
competence development and trigger sporulation by acting on a different two-component
system [Perego
et al.
, 1994, Grossmann, 1995, Solomon
et al.
, 1995]. Thus,
B. subtilis
can
react in an appropriate manner in response to environmental changes, due to the fluctuations
in the internal CSF concentration.
Thiolactone peptides (Figure 1) constitute the best known class of AIPs, particularly
those regulating the production of virulence factors in the pathogenic bacteria
Staphylococcus
aureus
[Balaban and Novick, 1995, Ji
et al.
, 1995]. Staphylococcal AIPs vary in the primary
amino acid sequence but contain a conserved cysteine at position 5 [Chhabra
et al.
, 2005]. In
S. aureus
, AIP-I production and regulation rely upon the
agrBDCA
genes. The autoinducing
peptide is encoded by
agrD
, and a two-component sensor kinase-response regulator pair
(AgrC and AgrA) acts as a receptor [Ji
et al.
, 1995]. When the extracellular concentration of
the peptide signal accumulates to the minimal stimulatory level, the histidine sensor kinase
protein detects it and subsequently, the response regulator is phosphorylated on a conserved
aspartate residue. The phosphorylated response regulator activates the transcription of target
genes [Miller and Bassler, 2001].
S. aureus
strains are classified into four different groups
according to the specificity of their AIPs [Schauder and Bassler, 2001].
