They may combine an affinity for sulfated polysaccharides and other polymeric carbon molecules [10, 11] produced by their eukaryote hosts with a resistance to eukaryote chemical defense molecules. The resulting competitive advantage over other bacterial groups that are utilizing the same kind of substrates, for example the Bacteroidetes [35] might be one of the keys to the success of planctomycetes in a wide variety of environments on earth. Our results show differences between the ABT737 different sampling times (February, July and September), in planctomycete abundance, OTU composition and diversity. For example, in February there is a relatively low abundance of planctomycetes (Figure 1) compared

to July and September. This may be linked to Selleckchem eFT-508 the

age of the kelp tissue, as the kelp lamina is older in February compared to in July SC79 and September due to the seasonal growth cycle of the kelp. Aging of the kelp tissue could be associated with lowered antibacterial chemical defense by the kelp, as the old kelp lamina is to be shed soon after February, and does therefore not need to be defended against microbial colonization. Without the presence of chemical defense substances, the planctomycetes could loose their competitive advantage over other bacterial groups, explaining their lower abundance in February. The senescence of the kelp tissue as it ages could also cause the appearance of new niches involved in degradation of different kelp constituents, thereby enabling the more diverse planctomycete communities that are observed in February compared to July and September (Table 1, Figure 6). Among the different planctomycete lineages that are represented on the kelp, the lineage defined as “”RB1″” in this study appears to be the most abundant, accounting for a majority of the clones at all sampling times (Figure 4). The high abundance of

RB1 planctomycetes may thus be the cause of the observed dominance of planctomycetes on kelp surfaces (Figs. 1 this website and 2). Their high abundance implies a lifestyle that makes them particularly successful on kelp surfaces. Yet the lineage also includes reference sequences from a variety of other marine habitats, indicating that RB1 is not a kelp-specific lineage. The RB1 and RB2 lineages, defined in this study, are clearly related to the “”Pirellulae”", a lineage including the genera Pirellula, Rhodopirellula and Blastopirellula (formerly all included in the genus Pirellula). Yet our phylogenetic analyses did not place them reliably with any of the described genera, indicated by the bootstrap support for the relevant branches in Figure 4. There are no sequences of cultured strains within the RB1 and RB2 lineages available in the databases. Another uncultured lineage, the so-called OM190 planctomycetes (Silva taxonomy) is also represented by clones from kelp surfaces at all sampling times, yet in low numbers.