General information

Pseudomonas spp.

Pseudomonas spp. are cosmopolitan organisms found in a multitude of habitats including soil, organic matter, water, the rhizosphere, plants and animals, including mammals. The vast array of metabolites produced includes CLPs of which close to 100 have been individually documented to varying extent. Like for Bacillus CLPs, one defining property that Ps-CLPs have in common, due to the presence of a fatty acid tail, is their surface tension lowering properties, designating them as biosurfactants (Fechtner et al., 2011). As more Ps-CLPs were isolated, specific families or “groups” were defined with chemically similar Ps-CLPs and named for a particular prototype Ps-CLP as shown in Figure 1. These include the viscosin (Groupé et al., 1951), orfamide (Gross et al., 2007; Ma et al., 2016a), amphisin (Sorensen et al., 2001), syringomycin (Segre et al., 1989), syringopeptin (Ballio et al., 1991), and tolaasin groups (Rainey et al., 1991; Bassarello et al., 2004). New CLPs are continuously found in numerous environments, and can be assigned to an existing group (D’Aes et al., 2014; Weisshoff et al., 2014; Johnston et al., 2015; Michelsen et al., 2015a; Zachow et al., 2015; Ma et al., 2016a; Gotze et al., 2017) or constitute a new group, such as the recently discovered bananamides, (Nguyen et al., 2016) and xantholysins (Li et al., 2013). Finally, a variety of Ps-CLP have not yet formally been classified as a group (Figure 1) but can be treated as such, if the oligopeptide length is used as criterion. These include the entolysins (Vallet-Gely et al., 2010), putisolvins (Kuiper et al., 2003), pseudofactins (Janek et al., 2010), syringopeptins (Ballio et al., 1991), corpeptin (Emanuele et al., 1998), and fuscopeptins (Ballio et al., 1996). With about 100 unique Ps-CLPs distributed over 14 groups characterized so far, the chance for rediscovery is obviously increasing, yet the expectation is that not all Ps-CLP groups have been uncovered so far (Nguyen et al., 2016). With so many unique Ps-CLP described and to avoid confusion, we will indicate the individual CLP group members with the first letter of the group name between brackets, unless the CLP name is the same as the group name. For example, WLIP, a CLP of the viscosin group will be designated as WLIP-(V), while tensin, a CLP of the amphisin group will be denominated as tensin-(A).

Biological synthesis

Cyclic lipodepsipeptides are produced by NRPSs, protein complexes consisting of large multi-domain modules. Current understanding of the processes involved is well developed, as collected in the excellent review from Sussmuth and Mainz (2017). Additionally, Roongsawang et al. (2010) reported a clear summary on the genomics of the NRPS of Pseudomonas spp. per lipopeptide-producer. Often, a single biosynthetic NRPS cluster produces more than one CLP due to an assumed flexibility of some adenylation domains that are responsible for amino acid recognition. This results in the production of so-called minors that differ in the identity of a single amino acid, in addition to the major compound. It is unclear whether the minors represent a functional role.