(2001) showed that the reaction is dependent on the presence of membrane

fractions of recombinant E. coli carrying B. subtilis pgsBCA genes. No γ-PGA was produced if cytosolic or other extracellular fractions were used in the in vitro assay, indicating that a membrane this website association was required. The enzyme complex remains attached to the cell membrane while γ-PGA is secreted by the cell. The PgsA protein can function as a γ-PGA transporter, indicating an important role in the elongation of the γ-PGA polymer (Ashiuchi et al., 2001). The production of γ-PGA was repressed by the sporulation-specific transcription factor Spo0A. Even though the pgsBCA operon is highly regulated, γ-PGA is not essential for cell growth and biofilm formation (Branda et al., 2006). The sequences of pgsBCA genes have been found to be similar to those of the ywsC and ywtAB genes of B. subtilis 168 (Urushibata et al., 2002). As described, the synthesis of γ-PGA requires energy, posing an interesting

question: what is the advantage to the cell? Stanley & Lazazzera (2005) proposed that γ-PGA is involved in biofilm formation to enhance cell–surface interactions through salt bridges (e.g. Ca2+ or Mg2+) as intermediaries between negative-charged cell surfaces. The in vitro production of γ-PGA could also be activated during biofilm formation in response to an increase in the salinity and osmolarity of the medium resulting from evaporation of Proteasome inhibition water during a long duration of incubation. In B. anthracis the production of γ-PGA results in the formation of a capsule and is correlated to the virulence of the strain (Candela & Fouet, 2006). However, in spite of some detailed studies, the specific role of γ-PGA in natural environments needs to be further clarified and investigations are needed to assess the presence of other sorptive EPS. The third category of EPS includes surface-active lipopeptides, such as surfactin, which are among the most-studied molecules produced by B. subtilis (Flemming et al., 2007). On the basis of the structural relationships,

lipopeptides have been classified into three groups: the surfactin group, the iturin group and the plipastatin–fengycin group (Tsuge et al., 2001) (Fig. 1). Although these surfactants are not large polymeric compounds, they play a very important also role in solubilizing substrates that otherwise would be inaccessible to the bacteria (Neu, 1996; Sutherland, 2001b). Synthesis of lipopeptides does not occur on ribosomes, but is catalyzed by large complex peptide synthetases protein structures (Lin et al., 1999). Even though surfactants exist in nature in both low- and high-molecular-weight forms, only the low-molecular-weight forms are found in B. subtilis (Ron & Rosenberg, 2001). The lipopeptide surfactins are the most important surfactants studied in B. subtilis (Fig. 1).