Metatranscriptomic Analysis of Diminutive Thiomargarita-Like Bacteria (“Candidatus Thiopilula” spp.) from Abyssal Cold Seeps of the Barbados Accretionary Prism
ABSTRACT
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.