Abstract
The Archaea are a widely distributed group of prokaryotes that inhabit and thrive in many different environments. In the sea, they play key roles in various global biogeochemical processes. Here, in order to investigate the vertical profiles of archaeal community across a large geographic distance, the compositions of archaeal communities in seven seawater columns in the Pacific Ocean were investigated using high throughput 454 pyrosequencing of the 16S rRNA gene. The surface archaeal communities showed lower diversity and greater variability than those in the deeper layers. Two of the major archaeal phyla that displayed different depth preferences were Thaumarchaeota and Euryarchaeota. The majority of Thaumarchaeota belonged to Marine Group I (MGI), which had high relative abundance in deep water. In contrast, Euryarchaeota, which mainly consisted of Marine Group II (MGII) and III (MGIII), were dominant in the surface layer. Compared with MGI and MGII, MGIII were less abundant in seawater and generally absent from the surface water of the subarctic Pacific. In addition, niche separation in the MGI, MGII, and MGIII subgroups was also observed. For example, MGI.C and MGII.A (the major subgroups of MGI and MGII, respectively) displayed a strong negative correlation with each other. The highest level of archaeal diversity was found in the core of an oxygen minimum zone (OMZ) located off Costa Rica, which resulted from the co-occurrence of both anaerobic and aerobic archaea. For example, methanotrophic archaea ANME-2, methanogenic archaea and several sediment origin archaea, such as Marine Benthic Group A (MBGA) and Bathyarchaeota, were all detected at relatively high abundance in the OMZ. Together, our findings indicate that vertical heterogeneities along water columns and latitudinal differentiation in the surface waters are ubiquitous features of archaeal communities in the Pacific Ocean, and the OMZ off Costa Rica is an archaeal biodiversity hot-spot.
Highlights
The Archaea comprise one of the three domains of the living world, along with Bacteria and Eukarya (Woese and Fox, 1977; Woese et al, 1990)
The aims of this study were: (1) to reveal the vertical profiles of the archaeal communities across a large geographic distance to help us understand the spatial distribution and heterogeneity of archaea in the global ocean; (2) to test our hypothesis that on a global scale, the microbial community structures are more variable in the surface waters than they are in the deeper layers due to bigger changes in the physico-chemical environment occurring in the former; and (3) to investigate the archaeal diversity in the oxygen minimum zone (OMZ)
Stations South China Sea (SCS) and Subtropical Western Pacific (SWP) are located in the subtropical western Pacific Ocean, stations SEP1 and SEP2 are in the subtropical eastern Pacific Ocean, and stations Western Subarctic Pacific-Station 1 (WSP1), Western Subarctic Pacific-Station 2 (WSP2), and Western Subarctic Pacific-Station 3 (WSP3) are in the western subarctic Pacific Ocean (Figure 1)
Summary
The Archaea comprise one of the three domains of the living world, along with Bacteria and Eukarya (Woese and Fox, 1977; Woese et al, 1990). Basin Scale Variation of Archaeal Communities (DeLong et al, 1994) and in hot springs (Barns et al, 1994; Takai and Horikoshi, 1999) In these various different environments, the Archaea play important roles in the global biogeochemical cycles, via a number of processes including carbon assimilation, mineralization, and precipitation (Berg et al, 2010; Offre et al, 2013). As most marine planktonic archaea cannot be maintained in culture, DNA-based molecular methods, such as terminal restriction fragment length polymorphism (TRFLP; Moeseneder et al, 2001) and clone library analysis (Massana et al, 2000; Bano et al, 2004), have been widely applied to study archaeal diversity in marine environments These and other studies have revealed that in seawater, organisms from just two phyla make up the bulk of the archaeal communities. MGI are phylogenetically divided into four subgroups (I.A, I.B, I.C, and I.D), which display different distribution patterns and activities in the marine environment (Hugoni et al, 2013)
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