Complete Genome Sequence of Celeribacter baekdonensis Strain LH4, a Thiosulfate-Oxidizing Alphaproteobacterial Isolate from Gulf of Mexico Continental Slope Sediments.

We report here the closed genome sequences of Celeribacter baekdonensis strain LH4 and five unnamed plasmids obtained through PacBio sequencing with 99.99% consensus concordance. The genomes contained several distinctive features not found in other published Celeribacter genomes, including the potential to aerobically degrade styrene and other phenolic compounds.

Metatranscriptomic analysis of diminutive Thiomargarita-like bacteria ("Candidatus Thiopilula" spp.) from abyssal cold seeps of the Barbados Accretionary Prism.

Large sulfur-oxidizing bacteria in the family Beggiatoaceae are important players in the global sulfur cycle. This group contains members of the well-known genera Beggiatoa, Thioploca, and Thiomargarita but also recently identified and relatively unknown candidate taxa, including "Candidatus Thiopilula" spp. and "Ca. Thiophysa" spp. We discovered a population of "Ca. Thiopilula" spp. colonizing cold seeps near Barbados at a ∼4.7-km water depth. The Barbados population consists of spherical cells that are morphologically similar to Thiomargarita spp., with elemental sulfur inclusions and a central vacuole, but have much smaller cell diameters (5 to 40 µm). Metatranscriptomic analysis revealed that when exposed to anoxic sulfidic conditions, Barbados "Ca. Thiopilula" organisms expressed genes for the oxidation of elemental sulfur and the reduction of nitrogenous compounds, consistent with their vacuolated morphology and intracellular sulfur storage capability. Metatranscriptomic analysis further revealed that anaerobic methane-oxidizing and sulfate-reducing organisms were active in the sediment, which likely provided reduced sulfur substrates for "Ca. Thiopilula" and other sulfur-oxidizing microorganisms in the community. The novel observations of "Ca. Thiopilula" and associated organisms reported here expand our knowledge of the globally distributed and ecologically successful Beggiatoaceae group and thus offer insight into the composition and ecology of deep cold seep microbial communities.

Dimorphism in methane seep-dwelling ecotypes of the largest known bacteria.

We present evidence for a dimorphic life cycle in the vacuolate sulfide-oxidizing bacteria that appears to involve the attachment of a spherical Thiomargarita-like cell to the exteriors of invertebrate integuments and other benthic substrates at methane seeps. The attached cell elongates to produce a stalk-like form before budding off spherical daughter cells resembling free-living Thiomargarita that are abundant in surrounding sulfidic seep sediments. The relationship between the attached parent cell and free-living daughter cell is reminiscent of the dimorphic life modes of the prosthecate Alphaproteobacteria, but on a grand scale, with individual elongate cells reaching nearly a millimeter in length. Abundant growth of attached Thiomargarita-like bacteria on the integuments of gastropods and other seep fauna provides not only a novel ecological niche for these giant bacteria, but also for animals that may benefit from epibiont colonization.