Microbial Community Structure of Deep-sea Hydrothermal Vents on the Ultraslow Spreading Southwest Indian Ridge

Abstract

Southwest Indian Ridge (SWIR) is a typical oceanic ultraslow spreading ridge with intensive hydrothermal activities. The microbial communities in hydrothermal fields including primary producers to support the entire ecosystem by utilizing geochemical energy generated from rock-seawater interactions. Here we have examined the microbial community structures on four hydrothermal vents from SWIR, representing distinct characteristics in terms of temperature, pH and metal compositions, by using Illumina sequencing of the 16S small subunit ribosomal RNA (rRNA) genes, to correlate bacterial and archaeal populations with the nature of the vents influenced by ultraslow spreading features. Epsilon-, Gamma-, Alpha-, and Deltaproteobacteria and members of the phylum Bacteroidetes and Planctomycetes, as well as Thaumarchaeota, Woesearchaeota, and Euryarchaeota were dominant in all the samples. Both bacterial and archaeal community structures showed distinguished patterns compared to those in the fast-spreading East Pacific Ridge or the slow-spreading Mid-Atlantic Ridge as previously reported. Furthermore, within SWIR, the microbial communities are highly correlated with the local temperatures. For example, the sulfur-oxidizing bacteria were dominant within bacteria from low-temperature vents, but were not represented as the dominating group recovered from high temperature (over 300°C) venting chimneys in SWIR. Meanwhile, Thaumarchaeota, the ammonium oxidizing archaea, only showed high relative abundance of amplicons in the vents with high-temperature in SWIR. These findings provide insights on the microbial community in ultraslow spreading hydrothermal fields, and therefore assist us in the understanding of geochemical cycling therein.

Keywords: 16S ribosomal RNA; SWIR; hydrothermal vent; microbial community; ultraslow-spreading ridge.

Figure 1

Schematic location of the sampling sites and Longqi vent Field (red Pentagram) at SWIR. The map was created using python.

Figure 2

Taxonomic relative abundance of archaeal classes observed of chimney samples for Longqi vent field at SWIR. Bar charts show the Kingdom; Phylum distribution for taxonomically assigned tags that occurred more than 1,000 times.

Figure 3

Taxonomic relative abundance of Thaumarchaeota genera observed in chimney samples. DHVEG-6, Deep Sea Hydrothermal Vent Group 6. Groups in which no tags were sequenced are indicated with a red asterisk. Groups which were detected below1% are indicated with a blue oplus, between 1 and 2% are indicated with a diamond.

Figure 4

Taxonomic breakdown of bacterial 16S rRNA V4-region tags from each chimney sample. Pie Charts show Phylum; Class; Order distribution (The average relative abundance among samples is over 1%) for taxomomically assigned tags that occurred more than 1,000 times; the remaining tag sequences are grouped into “Other.”

Figure 5

Relative abundance of Gammaproteobacteria taxa observed in each chimney sample for Longqi field at SWIR. “others” represents the less abundant genera of Acinetobacter, Sedimenticola, Marinicella, Colwellia, Arenicellaceae, Marine methylotrophic Group 2, Coxiella, Granulosicoccus, and unclassified Gammaproteobacteria. Groups which were detected below1% are indicated with a blue oplus, between 1 and 2% are indicated with a blue diamond.

Figure 6

Relative abundance of Epsilonproteobacteria genera observed in each chimney samplefor Longqi field at SWIR. Groups which were detected below1% are indicated with a blue oplus, between 1 and 2% are indicated with a diamond.

Figure 7

Clustering analysis tree of the archaeal community structure of chimneys from SWIR, EPR and MAR. LS7 = Lucky Strike. Lucky Strike vent field located at MAR (Flores et al., 2011); CH7 = chimney sample from EPR, this study.

Figure 8

Clustering analysis tree of the bacterial community structure of chimneys from SWIR, EPR and MAR. LS7 = Lucky Strike. Lucky Strike vent field located at MAR (Flores et al., 2011); CH7 = Chimney sample from EPR, this study.