Free-living bacterial communities associated with tubeworm (Ridgeia piscesae) aggregations in contrasting diffuse flow hydrothermal vent habitats at the Main Endeavour Field, Juan de Fuca Ridge

Abstract

We systematically studied free-living bacterial diversity within aggregations of the vestimentiferan tubeworm Ridgeia piscesae sampled from two contrasting flow regimes (High Flow and Low Flow) in the Endeavour Hydrothermal Vents Marine Protected Area (MPA) on the Juan de Fuca Ridge (Northeast Pacific). Eight samples of particulate detritus were recovered from paired tubeworm grabs from four vent sites. Most sequences (454 tag and Sanger methods) were affiliated to the Epsilonproteobacteria, and the sulfur-oxidizing genus Sulfurovum was dominant in all samples. Gammaproteobacteria were also detected, mainly in Low Flow sequence libraries, and were affiliated with known methanotrophs and decomposers. The cooccurrence of sulfur reducers from the Deltaproteobacteria and the Epsilonproteobacteria suggests internal sulfur cycling within these habitats. Other phyla detected included Bacteroidetes, Actinobacteria, Chloroflexi, Firmicutes, Planctomycetes, Verrucomicrobia, and Deinococcus-Thermus. Statistically significant relationships between sequence library composition and habitat type suggest a predictable pattern for High Flow and Low Flow environments. Most sequences significantly more represented in High Flow libraries were related to sulfur and hydrogen oxidizers, while mainly heterotrophic groups were more represented in Low Flow libraries. Differences in temperature, available energy for metabolism, and stability between High Flow and Low Flow habitats potentially explain their distinct bacterial communities.

Figure 1

Map of the northeast Pacific (modified from Bourbonnais et al. 2012) showing the location of the Endeavour Segment on the Juan de Fuca Ridge, as well as the major vent fields of this segment. The sample collection sites are in blue. (MEF = Main Endeavour vent field).

Figure 2

Examples of typical sampling sites. (A) High Flow environment inhabited by the short-fat phenotype of Ridgeia piscesae. The shimmering indicates the presence of hydrothermal fluid venting through the aggregation tubeworms. (Note their white tube and bright-red healthy-looking branchial plume.) (B) Low Flow envi-ronment inhabited by the long-skinny phenotype of R. piscesae. No shimmering is visible. (Note their brown-orange color of the tube and the reduced branchial plume.)

Figure 3

Relative abundance of (A) the major taxonomic groups and (B) the genera detected within the class Epsilonproteobacteria in the eight clone libraries constructed from 454 tag sequencing. Genera that did not reach 1% of the relative abundance of at least one library and unidentified operational taxonomic units (OTU)s were grouped under the category “Other and Unclassified”.

Figure 4

Relative abundance of (A) the phyla (the phylum Proteobacteria, which dominated all clone libraries, was divided into the four classes detected) and (B) species confidently identified within the class Epsilonproteobacteria in the eight clone libraries constructed from Sanger sequencing.

Figure 5

Rarefaction analysis of the libraries created from 454 tag sequencing showing the richness of each clone library at the 97% similarity level.

Figure 6

Hierarchical clustering analysis showing the similarity of the libraries constructed from 454 tag sequencing to each other using the Morisita–Horn calculator of dissimilarity. The scale bar represents the estimated divergence between the libraries.

Figure 7

Nonmetric multidimensional scaling (NMDS) 2D similarity plot showing the distance between the libraries constructed from 454 tag sequencing based on the Morisita–Horn calculator of dissimilarity.

Figure 8

Relative abundance of the significantly differently represented operational taxonomic units (OTU)s (P < 0.05) in (A) High Flow phyla, (B) Low Flow phyla, (C) High Flow Proteobacteria and (D) Low Flow Proteobacteria.