Biogeography and biodiversity in sulfide structures of active and inactive vents at deep-sea hydrothermal fields of the Southern Mariana Trough

Abstract

The abundance, diversity, activity, and composition of microbial communities in sulfide structures both of active and inactive vents were investigated by culture-independent methods. These sulfide structures were collected at four hydrothermal fields, both on- and off-axis of the back-arc spreading center of the Southern Mariana Trough. The microbial abundance and activity in the samples were determined by analyzing total organic content, enzymatic activity, and copy number of the 16S rRNA gene. To assess the diversity and composition of the microbial communities, 16S rRNA gene clone libraries including bacterial and archaeal phylotypes were constructed from the sulfide structures. Despite the differences in the geological settings among the sampling points, phylotypes related to the Epsilonproteobacteria and cultured hyperthermophilic archaea were abundant in the libraries from the samples of active vents. In contrast, the relative abundance of these phylotypes was extremely low in the libraries from the samples of inactive vents. These results suggest that the composition of microbial communities within sulfide structures dramatically changes depending on the degree of hydrothermal activity, which was supported by statistical analyses. Comparative analyses suggest that the abundance, activity and diversity of microbial communities within sulfide structures of inactive vents are likely to be comparable to or higher than those in active vent structures, even though the microbial community composition is different between these two types of vents. The microbial community compositions in the sulfide structures of inactive vents were similar to those in seafloor basaltic rocks rather than those in marine sediments or the sulfide structures of active vents, suggesting that the microbial community compositions on the seafloor may be constrained by the available energy sources. Our findings provide helpful information for understanding the biogeography, biodiversity and microbial ecosystems in marine environments.

FIG. 1.

Organic contents, enzymatic activity and stable carbon isotopic ratios. (A) Total nitrogen (TN, wt%) and total organic carbon (TOC, wt%) in each part of the samples. (B) Stable carbon isotopic ratio (δ¹³C value, ‰ versus PDB) of the organic matter and enzymatic activities. Error bars (n = 3) of enzymatic activities are also shown.

FIG. 2.

Composition of the microbial communities based on the 16S rRNA clone libraries constructed from each subsample of sulfide structures using the prokaryote-universal primer set. The relative abundances of the detected clones belonging to each taxonomic group are shown. The total clone number in each library is shown in parentheses.

FIG. 3.

Comparison of microbial communities in the SMT by UniFrac. (A) Jackknife environment cluster analysis and (B) principal coordinates analysis are shown. Jackknife values (higher than 50%) based on 100 permutations are shown at branch points. Legends for the symbols are shown in the inset box in panel B.

FIG. 4.

Venn diagrams comparing the estimated Chao1 species richness found in the communities. Comparisons between the active vent samples (AFhm, AAcs, APbsc, and APcsc, total number of sequences: n = 889) and the inactive vent samples (IPltc and IYdc, n = 415) (A), between the AAcs and IPltc samples (B), among the subsamples of the AAcs sample (C), and among the subsamples of the IPltc sample (D) are shown. The number within these areas indicates the Chao1 species richness estimates.

FIG. 5.

Principal coordinates analysis for epsilonproteobacterial populations in various marine environments. Two graphs show the comparison based on the hydrothermal activity (left) and water depth (right), respectively, which are performed using the same data set. The identification of the sampling areas are indicated with each letter and number in the left graph (see Table S2 in the supplemental material for details): A, Antarctic continental shelf; B, Juan de Fuca Ridge; C, Baltic Sea; D, Mediterranean; E, Black Sea; F, Saanich Inlet; G, Central Arctic Ocean; H, Central Indian Ridge; I, East Pacific Rise 13°N; J and K, East Pacific Rise 9°N; L, French Atlantic coast; M, Guaymas basin; N, Gulf of Mexico; O, Gulf of Papua; P, Harbor of Milazzo; Q, Mid-Atlantic Ridge; R, Japanese bays; S, Kermadec Arc; T, Loihi Seamount; U, Manus Basin; V, Mid-Okinawa Trough; W and 6, Coasts of USA; X, Nankai Trough; Y, North Sea; Z, Ushuaia; 1, Pacific Antarctic Ridge; 2, Southern Okinawa Trough; 3, Suiyo Seamount; 4, Taketomi Island; 5, Tasmania; 7, TOTO; and 8 and 9, the present study of the SMT.

FIG. 6.

Comparison of microbial communities among marine environments by principal coordinates analysis. The identification for the sampling areas are indicated with each letter in the graph: A and E, Japan Trench; B, Suruga bay, Japan; C, Ryukyu Trench; D, Izu-Bonin Trench; F, Iheya North, mid-Okinawa Trough; G, Kairei field, Central Indian Ridge; H, Guaymas basin; I, Mertz Glacier Polynya of Antarctic continental shelf; J, Hornsund off the coast of Spitsbergen, Arctic Ocean; K, Rainbow site, Mid-Atlantic Ridge; L, 9°N, East Pacific Rise; M, Juan de Fuca Ridge; N, the coast of the Southern North Sea, Belgium; O, Y site, SMT (IYdc sample); P, Pika site, SMT (IPItc sample); and Q, Pika site, SMT (APcsc sample). The sample type for A, B, C, D, E, I, J, and N is cold marine sediment; that for F, G, O, and P is sulfide structure of inactive vents; that for H and K is hydrothermal sediment; that for L and M is seafloor basaltic rock; that for Q is sulfide structure of active vents as a reference. Legends for the symbols are shown in the box. See Table S3 in the supplemental material for details.