methylohalidivorans DSM 14336T (pMeth_A285) as well as the RepC-8 type plasmid of Phaeobacter daeponensis DSM23529T (pDaep_A276). Table 6 Integrated Microbial Genome Ceritinib 1032900-25-6 (IMG) locus tags of P. caeruleus DSM 24564T genes for the initiation of replication, toxin/antitoxin modules and two representatives of type IV secretion systems (T4SS) that are required for conjugation. The locus tags are … Several strains affiliated with the Roseobacter clade show a high potential to produce secondary metabolites [51]. Pigmentation of cells is often related with secondary metabolite production [61]. We assume that the characteristic blue color of P. caeruleus is attributed to the production of the blue pigment indigoidine. In the closely related and blue-colored Phaeobacter sp.

strain Y4I indigoidine is produced via a non-ribosomal peptide synthase (NRPS)-based biosynthetic pathway encoded by the gene cluster igiBCDFE [62]. In strain Y4I indigoidine production is correlated with pleiotrophic effects, such as motility, resistance to hydrogen peroxide, surface colonization and inhibition of Vibrio fischeri. A cluster analysis revealed that the P. caeruleus plasmid pCaer_B246 contains a homologous igiBCDFE gene cluster (Caer_4407 – Caer_4412). Thus it seems likely that P. caeruleus can also produce the antimicrobial secondary metabolite indigoidine via its NRPS cluster. Therefore, indigoidine could be the pigment responsible for the blue color and P. caeruleus could have inhibitory effects on other bacteria. Mutants in either of the two LuxIR systems in Phaeobacter sp.

strain Y4I are lacking the indigoidine production, therefore, quorum sensing seems to play a role in its biosynthesis [62]. A correlation between quorum sensing and pigmentation and antimicrobial effects is already known for members of the Roseobacter clade. The LuxIR-type quorum sensing system of P. inhibens DSM 17395 (originally deposited as P. gallaeciensis DSM 17395; Buddruhs et al., unpublished) regulates N-acyl homoserine lactones production which co-occurs with the strains AV-951 dark pigmentation and antibiotic activity [63]. The P. caeruleus DSM 24564T chromosome cCaer_A3521 has a luxIR gene cluster (Caer_1365 – Caer_1371) which shows strong homology to the mentioned LuxIR-type cluster of P. inhibens DSM 17395 and strain Y4I, thus pigmentation and putative inhibitory effects could be regulated via quorum sensing. Besides these luxIR genes, five other luxIR clusters are encoded in the genome of strain DSM 24564T which could play an important role in cell-cell signaling. Recently siderophore production was shown for P. inhibens DSM 17395 [64].