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Microbe biogeography tracks water masses in a dynamic oceanic frontal system

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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.


NMDS plot highlighting community differences between the three depth layers (shallow, 40–80 m; middle, ∼200m; deep, greater than 200 m). The ellipses represent the 99% confidence interval ellipses of the layer. MANOVA, multivariate analysis of variance; stress, 0.1225.
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RSOS170033F2: NMDS plot highlighting community differences between the three depth layers (shallow, 40–80 m; middle, ∼200m; deep, greater than 200 m). The ellipses represent the 99% confidence interval ellipses of the layer. MANOVA, multivariate analysis of variance; stress, 0.1225.

Mentions: However, the middle stratum showed higher richness than the shallow and deep strata (ANOVA, F3,92=2.123, p=0.039, electronic supplementary material, figure S2; table 2). The strata also exhibited differences in their microbial community composition, demonstrated by the NMDS (figure 2; MANOVA p<0.01) with clear separation between the depth strata. Gammaproteobacteria dominated all depth layers, but the shallow layer had a higher abundance of the photoautotrophic class Synechococcophycideae compared with the middle and deep layers. In addition, the classes Flavobacteriia and Acidimicrobiia were more abundant in the shallow layer. Thaumarchaeota and Deltaproteobacteria both increased from shallow to deep (electronic supplementary material, figure S3).Table 2.


Microbe biogeography tracks water masses in a dynamic oceanic frontal system
NMDS plot highlighting community differences between the three depth layers (shallow, 40–80 m; middle, ∼200m; deep, greater than 200 m). The ellipses represent the 99% confidence interval ellipses of the layer. MANOVA, multivariate analysis of variance; stress, 0.1225.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

RSOS170033F2: NMDS plot highlighting community differences between the three depth layers (shallow, 40–80 m; middle, ∼200m; deep, greater than 200 m). The ellipses represent the 99% confidence interval ellipses of the layer. MANOVA, multivariate analysis of variance; stress, 0.1225.
Mentions: However, the middle stratum showed higher richness than the shallow and deep strata (ANOVA, F3,92=2.123, p=0.039, electronic supplementary material, figure S2; table 2). The strata also exhibited differences in their microbial community composition, demonstrated by the NMDS (figure 2; MANOVA p<0.01) with clear separation between the depth strata. Gammaproteobacteria dominated all depth layers, but the shallow layer had a higher abundance of the photoautotrophic class Synechococcophycideae compared with the middle and deep layers. In addition, the classes Flavobacteriia and Acidimicrobiia were more abundant in the shallow layer. Thaumarchaeota and Deltaproteobacteria both increased from shallow to deep (electronic supplementary material, figure S3).Table 2.

View Article: PubMed Central - PubMed

ABSTRACT

Dispersal limitation, not just environmental selection, plays an important role in microbial biogeography. The distance&ndash;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&thinsp;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&thinsp;m), (ii) the bottom of the euphotic zone (approx. 200&thinsp;m), and (iii) the benthic boundary layer (300&ndash;2000&thinsp;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.