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. 2019 Dec 6:10:2738.
doi: 10.3389/fmicb.2019.02738. eCollection 2019.

Microbial Composition and Variability of Natural Marine Planktonic and Biofouling Communities From the Bay of Bengal

Angelina G Angelova  1 , Gregory A Ellis  2 , Hemantha W Wijesekera  3 , Gary J Vora  2
Affiliations

Microbial Composition and Variability of Natural Marine Planktonic and Biofouling Communities From the Bay of Bengal

Angelina G Angelova et al. Front Microbiol. .

Abstract

The Bay of Bengal (BoB) is the largest bay in the world and presents a unique marine environment that is subjected to severe weather, a distinct hydrographic regime and a large anthropogenic footprint. Despite these features and the BoB's overall economic significance, this ecosystem and its microbiome remain among the most underexplored in the world. In this study, amplicon-based microbial profiling was used to assess the bacterial, archaeal, and micro-eukaryotic content of unperturbed planktonic and biofilm/biofouling communities within the BoB. Planktonic microbial communities were collected during the Southwest monsoon season from surface (2 m), subsurface (75 m), and deep-sea (1000 m) waters from six south-central BoB locations and were compared to concomitant mature biofouling communities from photic-zone subsurface moorings (∼75 m). The results demonstrated vertical stratification of all planktonic communities with geographic variations disappearing in the deep-sea environment. Planktonic microbial diversity was found to be driven by different members of the community, with the most dominant phylotypes driving the diversity of the photic zone and rarer species playing a more influential role within the deep-sea. Geographic variability was not observed in the co-located biofouling microbiomes, but community composition and variability was found to be driven by depth and the presence of macro-fouling and photosynthetic organisms. Overall, these results provide much needed baselines for longitudinal assessments that can be used to monitor the health and evolution of this dynamic and critically important marine environment.

Keywords: marine biofilm; microbiome; microfouling; planktonic; rRNA.

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Figures

FIGURE 1
FIGURE 1
Geographic map of the BoB with hydrographic characteristics. (A) Geographic map including salinity gradient. Sampling sites are indicated with yellow dots and labeled NRL1–NRL6. Picture reference: http://podaac.jpl.nasa.gov/SeaSurfaceSalinity/Aquarius. (B) PCA ordination plot based on BoB physicochemical characteristics (including oxygen, fluorescence, salinity, temperature, nitrate, nitrite, and orthophosphate content) in August 2015. PC1 explains 51% of variations in physicochemical characteristics and clearly separates deep-sea water (3.DS) from surface and subsurface water (1.SF and 2.SS). (C) A boxplot of observed values for physicochemical characteristics of water column in August 2015. Observed values (where available), include temperature [Temp (°C)], salinity [Sal (PSU)], oxygen [O2 (mg/L)], fluorescence (Flu), nitrate [NO3 (ppm)], nitrite [NO2 (ppm)], and orthophosphate [PO43+ (ppm)], grouped per examined water layers: surface (red), subsurface (green), and deep-sea (blue). Pairs for comparison of values between layers as well as the significance of this comparison is also indicated (black horizontal bars and stars, respectively). Nitrate, nitrite, and phosphorous content for deep-sea water were not measured.
FIGURE 2
FIGURE 2
Planktonic microbial profiles for each BoB water layer, based on 16S and 18S rRNA gene amplicons and visualized with Krona Tools. (A) Photic zone, surface layer, 1.SS at ∼2 m depth. (B) Photic zone subsurface layer, 2.SS, at ∼75 m depth. (C) Aphotic zone, deep-sea layer, 3.DS at ∼1000 m depth. Taxonomic groups were assigned and represented to deepest taxonomic level possible.
FIGURE 3
FIGURE 3
Physical and chemical factors influencing BoB photic planktonic microbial communities. (A) Pearson correlation heatmap for the top 30 most abundant taxonomic classes and environmental variables per layer. Stars represent significance of correlation. (B) Circle correlation plot, where relationships between phylotypes (blue) and environmental factors (red) are presented in terms of radial distances and their cosine angles (González et al., 2012; Rohart et al., 2017). Sharp and obtuse angles between variables represent positive and negative correlations, respectively, while perpendicularity presents no correlation. Strength of correlations is represented by distance from the radial origin.
FIGURE 4
FIGURE 4
Beta diversity analyses of BoB biofilm communities and microbial response to environmental variables. (A) nMDS ordination plot of square root transformed Bray–Curtis dissimilarity matrix produced from photic zone subsurface biofilm communities (n = 31). (B) Circular correlation plot of BoB biofilm microbial community members (blue) at each site and depth and corresponding environmental variables (red) presented in terms of radial distances and their cosine angles (González et al., 2012; Rohart et al., 2017). (C) nMDS plot of square root transformed Bray–Curtis dissimilarity matrix produced from 12 selected biofilms. Arrows present core phylotypes (significance > 0.05) that best explain the biotic structure with length representing the strength of the correlation. Gradient represents sample diversity based on Inverse Simpson values.
FIGURE 5
FIGURE 5
Differential abundance analysis (DESeq2) between clusters of biofilm samples, exploring and ranking the taxonomic classes that were most significantly different between clusters. A larger fold change is indicative of enrichment within each group.
FIGURE 6
FIGURE 6
Phenotypes of selected samples along with the profiles of their top 25 most abundant species from the collected biofilms. Macrofouling organisms observed were not examined in this study. Taxonomy was presented to the deepest assigned rank.
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