Abstract
BackgroundBacteria belonging to Planctomycetes display several unique morphological and genetic features and are found in a wide variety of habitats on earth. Their ecological roles in these habitats are still poorly understood. Planctomycetes have previously been detected throughout the year on surfaces of the kelp Laminaria hyperborea from southwestern Norway. We aimed to make a detailed investigation of the abundance and phylogenetic diversity of planctomycetes inhabiting these kelp surfaces.ResultsPlanctomycetes accounted for 51-53% of the bacterial biofilm cells in July and September and 24% in February according to fluorescence in situ hybridization (FISH) results. Several separate planctomycetes lineages within Pirellulae, Planctomyces and OM190 were represented in 16S rRNA gene clone libraries and the most abundant clones belonged to yet uncultured lineages. In contrast to the abundance, the diversity of the planctomycete populations increased from July to February and was probably influenced by the aging of the kelp tissue. One planctomycete strain that was closely related to Rhodopirellula baltica was isolated using selective cultivation techniques.ConclusionsBiofilms on surfaces of L. hyperborea display an even higher proportion of planctomycetes compared to other investigated planctomycete-rich habitats such as open water, sandy sediments and peat bogs. The findings agree well with the hypothesis of the role of planctomycetes as degraders of sulfated polymeric carbon in the marine environment as kelps produce such substances. In addition, the abundant planctomycete populations on kelp surfaces and in association with other eukaryotes suggest that coexistence with eukaryotes may be a key feature of many planctomycete lifestyles.
Highlights
Bacteria belonging to Planctomycetes display several unique morphological and genetic features and are found in a wide variety of habitats on earth
Abundance of planctomycetes in kelp surface biofilms Quantification of planctomycetes in samples from July 2007, February 2007 and September 2008 using fluorescence in situ hybridization (FISH) showed that they make up a large part of the kelp surface biofilm community in all three sampling occasions
Inspection of the cloned 16S rRNA gene sequences revealed that the Pir1223 target sequence was present in all clones except those belonging to the OM190 lineage suggesting that the specificity of this probe needs to be reevaluated
Summary
Bacteria belonging to Planctomycetes display several unique morphological and genetic features and are found in a wide variety of habitats on earth. Their ecological roles in these habitats are still poorly understood. Bacteria belonging to the phylum Planctomycetes have revealed several remarkable features that set them apart from other bacteria. Their cryptic morphology led early microbiologists to mistake them for fungi, and the discovery of their cell compartmentalization, featuring membrane bounded organelles, raised fundamental questions about the evolution of eukaryotes [1,2]. Results from several studies suggest that planctomycetes favor a biofilm lifestyle, adhering to surfaces in aquatic environments including marine sediments [6]
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