Limits...
Microbe biogeography tracks water masses in a dynamic oceanic frontal system

View Article: PubMed Central - PubMed

ABSTRACT

Dispersal limitation, not just environmental selection, plays an important role in microbial biogeography. The distance–decay relationship is thought to be weak in habitats where dispersal is high, such as in the pelagic environment, where ocean currents facilitate microbial dispersal. Most studies of microbial community composition to date have observed little geographical heterogeneity on a regional scale (100 km). We present a study of microbial communities across a dynamic frontal zone in the southwest Indian Ocean and investigate the spatial structure of the microbes with respect to the different water masses separated by these fronts. We collected 153 samples of free-living microorganisms from five seamounts located along a gradient from subtropical to subantarctic waters and across three depth layers: (i) the sub-surface chlorophyll maximum (approx. 40 m), (ii) the bottom of the euphotic zone (approx. 200 m), and (iii) the benthic boundary layer (300–2000 m). Diversity and abundance of microbial operational taxonomic units (OTUs) were assessed by amplification and sequencing of the 16S rRNA gene on an Illumina MiSeq platform. Multivariate analyses showed that microbial communities were structured more strongly by depth than by latitude, with similar phyla occurring within each depth stratum across seamounts. The deep layer was homogeneous across the entire survey area, corresponding to the spread of Antarctic intermediate water. However, within both the sub-surface layer and the intermediate depth stratum there was evidence for OTU turnover across fronts. The microbiome of these layers appears to be divided into three distinct biological regimes corresponding to the subantarctic surface water, the convergence zone and subtropical. We show that microbial biogeography across depth and latitudinal gradients is linked to the water masses the microbes persist in, resulting in regional patterns of microbial biogeography that correspond to the regional scale physical oceanography.

No MeSH data available.


Related in: MedlinePlus

Temperature and salinity of water masses on SWIR seamounts. The points represent the clusters from the multivariate regression tree analysis. STSW is subtropical surface water, SICW is south Indian central water, SASW is colder subantarctic surface water, and AAIW is Antarctic intermediated water. The t/s properties showed a sub-surface salinity minimum (A). At the base of the fairly well-mixed surface layer, strong stratification marked the transition to a salinity maximum of 34.7–34.8 associated with a temperature maximum (B). At about 250 m an inflection in the t/s curve marked interleaving and small-scale minima and maxima in temperature and salinity (C). The segment C–B points to the end member of the STSW. C–D marks the area below the inflection point and points to the AAIW.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5383857&req=5

RSOS170033F5: Temperature and salinity of water masses on SWIR seamounts. The points represent the clusters from the multivariate regression tree analysis. STSW is subtropical surface water, SICW is south Indian central water, SASW is colder subantarctic surface water, and AAIW is Antarctic intermediated water. The t/s properties showed a sub-surface salinity minimum (A). At the base of the fairly well-mixed surface layer, strong stratification marked the transition to a salinity maximum of 34.7–34.8 associated with a temperature maximum (B). At about 250 m an inflection in the t/s curve marked interleaving and small-scale minima and maxima in temperature and salinity (C). The segment C–B points to the end member of the STSW. C–D marks the area below the inflection point and points to the AAIW.

Mentions: Microbial communities of corresponding depth layers in the north (Atlantis), convergence zone (Melville and Middle of What) and south (Coral) have similar abundant microorganisms at the order and phyla level, indicating adaptation to habitat rather than location for similar types of organisms. However, at an OTU level, the microbial communities show quite large differences between each location based on rank abundance and the MRT (figures 3 and 4). The MRT groups all deep seamount samples into one cluster, while separating out the surface and middle layer of Coral into two clusters, and the surface layer of Atlantis into another. As seen in the rank abundance, the surface layer on Coral is dominated by a Synechococcus OTU, which also dominates Melville and Middle of What, while Atlantis is dominated by Prochlorococcus. Both Synechococcus and Prochlorococcus have been shown in Djurhuus et al. [29] to be the dominant cyanobacteria at the surface of these seamounts. Interestingly, Prochlorococcus and Synechococcus are indicator species of the surface and middle layer, respectively, of the convergence zone seamounts distinguishing the different strata with their niche adaptations to high-light and low-light conditions. Photosynthetically available radiation is a major driver of primary producers, which will influence the surface communities, due to the strong environmental factor as seen on Coral, Melville, Middle of What and Sapmer (figures 5 and 6) [11].Figure 5.


Microbe biogeography tracks water masses in a dynamic oceanic frontal system
Temperature and salinity of water masses on SWIR seamounts. The points represent the clusters from the multivariate regression tree analysis. STSW is subtropical surface water, SICW is south Indian central water, SASW is colder subantarctic surface water, and AAIW is Antarctic intermediated water. The t/s properties showed a sub-surface salinity minimum (A). At the base of the fairly well-mixed surface layer, strong stratification marked the transition to a salinity maximum of 34.7–34.8 associated with a temperature maximum (B). At about 250 m an inflection in the t/s curve marked interleaving and small-scale minima and maxima in temperature and salinity (C). The segment C–B points to the end member of the STSW. C–D marks the area below the inflection point and points to the AAIW.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383857&req=5

RSOS170033F5: Temperature and salinity of water masses on SWIR seamounts. The points represent the clusters from the multivariate regression tree analysis. STSW is subtropical surface water, SICW is south Indian central water, SASW is colder subantarctic surface water, and AAIW is Antarctic intermediated water. The t/s properties showed a sub-surface salinity minimum (A). At the base of the fairly well-mixed surface layer, strong stratification marked the transition to a salinity maximum of 34.7–34.8 associated with a temperature maximum (B). At about 250 m an inflection in the t/s curve marked interleaving and small-scale minima and maxima in temperature and salinity (C). The segment C–B points to the end member of the STSW. C–D marks the area below the inflection point and points to the AAIW.
Mentions: Microbial communities of corresponding depth layers in the north (Atlantis), convergence zone (Melville and Middle of What) and south (Coral) have similar abundant microorganisms at the order and phyla level, indicating adaptation to habitat rather than location for similar types of organisms. However, at an OTU level, the microbial communities show quite large differences between each location based on rank abundance and the MRT (figures 3 and 4). The MRT groups all deep seamount samples into one cluster, while separating out the surface and middle layer of Coral into two clusters, and the surface layer of Atlantis into another. As seen in the rank abundance, the surface layer on Coral is dominated by a Synechococcus OTU, which also dominates Melville and Middle of What, while Atlantis is dominated by Prochlorococcus. Both Synechococcus and Prochlorococcus have been shown in Djurhuus et al. [29] to be the dominant cyanobacteria at the surface of these seamounts. Interestingly, Prochlorococcus and Synechococcus are indicator species of the surface and middle layer, respectively, of the convergence zone seamounts distinguishing the different strata with their niche adaptations to high-light and low-light conditions. Photosynthetically available radiation is a major driver of primary producers, which will influence the surface communities, due to the strong environmental factor as seen on Coral, Melville, Middle of What and Sapmer (figures 5 and 6) [11].Figure 5.

View Article: PubMed Central - PubMed

ABSTRACT

Dispersal limitation, not just environmental selection, plays an important role in microbial biogeography. The distance–decay relationship is thought to be weak in habitats where dispersal is high, such as in the pelagic environment, where ocean currents facilitate microbial dispersal. Most studies of microbial community composition to date have observed little geographical heterogeneity on a regional scale (100 km). We present a study of microbial communities across a dynamic frontal zone in the southwest Indian Ocean and investigate the spatial structure of the microbes with respect to the different water masses separated by these fronts. We collected 153 samples of free-living microorganisms from five seamounts located along a gradient from subtropical to subantarctic waters and across three depth layers: (i) the sub-surface chlorophyll maximum (approx. 40 m), (ii) the bottom of the euphotic zone (approx. 200 m), and (iii) the benthic boundary layer (300–2000 m). Diversity and abundance of microbial operational taxonomic units (OTUs) were assessed by amplification and sequencing of the 16S rRNA gene on an Illumina MiSeq platform. Multivariate analyses showed that microbial communities were structured more strongly by depth than by latitude, with similar phyla occurring within each depth stratum across seamounts. The deep layer was homogeneous across the entire survey area, corresponding to the spread of Antarctic intermediate water. However, within both the sub-surface layer and the intermediate depth stratum there was evidence for OTU turnover across fronts. The microbiome of these layers appears to be divided into three distinct biological regimes corresponding to the subantarctic surface water, the convergence zone and subtropical. We show that microbial biogeography across depth and latitudinal gradients is linked to the water masses the microbes persist in, resulting in regional patterns of microbial biogeography that correspond to the regional scale physical oceanography.

No MeSH data available.


Related in: MedlinePlus