Publications

3843

ABSTRACT The recently described bacterium “ Candidatus Methylomirabilis oxyfera” couples the oxidation of the important greenhouse gas methane to the reduction of nitrite. The ecological significance of “ Ca . Methylomirabilis oxyfera” is still underexplored, as our ability to identify the presence of this bacterium is thus far limited to DNA-based techniques. Here, we investigated the lipid composition of “ Ca . Methylomirabilis oxyfera” to identify new, gene-independent biomarkers for the environmental detection of this bacterium. Multiple “ Ca . Methylomirabilis oxyfera” enrichment cultures were investigated. In all cultures, the lipid profile was dominated up to 46% by the fatty acid (FA) 10-methylhexadecanoic acid (10MeC 16:0 ). Furthermore, a unique FA was identified that has not been reported elsewhere: the monounsaturated 10-methylhexadecenoic acid with a double bond at the Δ7 position (10MeC 16:1Δ7 ), which comprised up to 10% of the total FA profile. We propose that the typical branched fatty acids 10MeC 16:0 and 10MeC 16:1Δ7 are key and characteristic components of the lipid profile of “ Ca . Methylomirabilis oxyfera.” The successful detection of these fatty acids in a peatland from which one of the enrichment cultures originated supports the potential of these unique lipids as biomarkers for the process of nitrite-dependent methane oxidation in the environment.

ABSTRACT Ammonia-oxidizing archaea (AOA) typically predominate over ammonia-oxidizing bacteria in marine sediments. We herein present the draft genome sequence of an ammonia-oxidizing archaeon, “ Candidatus Nitrosopumilus sediminis” AR2, which was enriched in culture from a marine sediment obtained off Svalbard, within the Arctic Circle. The typical genes involved in archaeal ammonia oxidation and carbon fixation necessary for chemolithoautotrophic growth were observed. Interestingly, the AR2 genome sequence was revealed to possess, uniquely among cultivated AOA from marine environments, a capability for urea utilization.

ABSTRACT Ammonia-oxidizing archaea (AOA) are ubiquitous in various marine environments and play important roles in the global nitrogen and carbon cycles. We here present a high-quality draft genome sequence of an ammonia-oxidizing archaeon, “ Candidatus Nitrosopumilus koreensis” AR1, which was found to dominate an ammonia-oxidizing enrichment culture in marine sediment off Svalbard, the Arctic Circle. Despite a significant number of nonoverlapping genes (ca. 30%), similarities of this strain to “ Candidatus Nitrosopumilus maritimus” were revealed by core genes for archaeal ammonia oxidation and carbon fixation, G+C content, and extensive synteny conservation.

Secondary metabolites are ubiquitous in bacteria, but by definition, they are thought to be nonessential. Highly toxic secondary metabolites such as patellazoles have been isolated from marine tunicates, where their exceptional potency and abundance implies a role in chemical defense, but their biological source is unknown. Here, we describe the association of the tunicate Lissoclinum patella with a symbiotic α-proteobacterium, Candidatus Endolissoclinum faulkneri, and present chemical and biological evidence that the bacterium synthesizes patellazoles. We sequenced and assembled the complete Ca . E. faulkneri genome, directly from metagenomic DNA obtained from the tunicate, where it accounted for 0.6% of sequence data. We show that the large patellazoles biosynthetic pathway is maintained, whereas the remainder of the genome is undergoing extensive streamlining to eliminate unneeded genes. The preservation of this pathway in streamlined bacteria demonstrates that secondary metabolism is an essential component of the symbiotic interaction.

Plants of Convolvulus arvensis exhibiting symptoms of undersized leaves, shoot proliferation and yellowing, collectively defined as bindweed yellows, were sampled in different regions of Europe and assessed for phytoplasma infection by PCR amplification using phytoplasma universal rRNA operon primer pairs. Positive results were obtained for all diseased plants. RFLP analysis of amplicons comprising the16S rRNA gene alone or the16S rRNA gene and 16-23S intergenic spacer region indicated that the detected phytoplasmas were distinguishable from all other previously described rRNA gene sequences. Analysis of 16S rRNA gene sequences derived from seven selected phytoplasma strains (BY-S57/11, BY-S62/11, BY-I1015, BY-I1016, BY-BH1, BY-BH2 and BY-G) showed that they were nearly identical (99.9–100 % gene sequence similarity) but shared less than 97.5 % similarity with comparable sequences of other phytoplasmas. Thus, BY phytoplasmas represent a new taxon whose closest relatives are stolbur phytoplasma strains and ‘ Candidatus Phytoplasma fragariae ’ with which they share 97.2 % and 97.1 % 16S rRNA gene sequence similarity, respectively. Phylogenetic analysis of 16S rRNA gene sequences confirmed that bindweed yellows phytoplasma strains collectively represent a distinct lineage within the phytoplasma clade and share a common ancestor with previously published or proposed ‘Candidatus Phytoplasma’ taxa within a major branch including aster yellows and stolbur phytoplasmas. On the basis of unique 16S rRNA gene sequences and biological properties that include a single host plant species and a geographical distribution limited to parts of Europe, the bindweed yellows (BY) phytoplasmas represent a coherent but discrete taxon, ‘Candidatus Phytoplasma convolvuli’, with strain BY-S57/11 (GenBank accession no. JN833705) as the reference strain.