Mobile genetic elements Genomic diversification of bacteria is known to be driven by phage-mediated horizontal gene Tofacitinib transfer. Prophage-like structures are found in many (marine) bacteria [45,46]. In strain DSM 23566T, 58 genes were annotated as phage genes. This number is distinctly higher than those in the phylogenetically related Phaeobacter and Leisingera species (Figure 1; 8 �C 38 phage genes) and in other Roseobacter clade bacteria [47]. Analysis of the genome of strain DSM 23566T with PHAST [48] revealed eight prophage regions, two of which were intact, another four of which were questionable and two that were incomplete (Table 5). These prophage regions constituted nearly 5% of the bacterial chromosome (cArct_4215).

One of the intact prophage regions (7) is likely a Mu-like phage, since many of the coding sequences (mostly corresponding to Phaar_02143 – Phaar_02190) yielded hits with Rhodobacter phage RcapMu (“type”:”entrez-nucleotide”,”attrs”:”text”:”NC_016165″,”term_id”:”356870838″,”term_text”:”NC_016165″NC_016165), Enterobacteria phage Mu (“type”:”entrez-nucleotide”,”attrs”:”text”:”NC_000929″,”term_id”:”9633494″,”term_text”:”NC_000929″NC_000929) and Burkholderia phage BcepMu (“type”:”entrez-nucleotide”,”attrs”:”text”:”NC_005882″,”term_id”:”48696910″,”term_text”:”NC_005882″NC_005882). The incomplete prophage region 3 also had hits to Mu-like phages. Mu-like phages are known to pack and transfer flanking host DNA in addition to their own genome and are found in Rhodobacter capsulatus, although they are more common in Gammaproteobacteria [49].

Table 5 Prophage regions in the genome of P. arcticus DSM 23566T cArct_4215, GC% = 59.10%, length = 4,215,469 bp? The other intact prophage region (region 4 in Table 5) strongly resembles a GTA (gene transfer agent) since it contains a major capsid protein (PhaarD_01806) that is similar (64%, e=0 [42,43]) to the highly conserved major capsid protein (g5) of R. capsulatus GTA [50,51]. These phage-like entities contain and transfer random fragments of bacterial host genomic DNA and are found in most Alphaproteobacteria, especially in the Rhodobacterales [50]. The occurrence of all these prophage-like structures together with the absence of a CRISPR system (i.e. an antiphage defense system [52]) suggests that phages may be important for genomic diversification within the Phaeobacter group. Secondary metabolism In contrast to its relative P. gallaeciensis, which is known for the production of the antibiotic tropodithietic acid (TDA) [39], no homologs of Cilengitide TDA production genes tdaBCEF were found in strain DSM 23566T.