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Bacterioplankton Communities in Dissolved Organic Carbon-Rich Amazonian Black Water

journal contribution
posted on 2025-03-20, 06:20 authored by Francois-Etienne Sylvain, Sidki Bouslama, Aleicia HollandAleicia Holland, Nicolas Leroux, Pierre-Luc Mercier, Adalberto Luis Val, Nicolas Derome

Abstract:

The Amazon River basin sustains dramatic hydrochemical gradients defined by three water types: white, clear, and black waters. In black water, important loads of allochthonous humic dissolved organic matter (DOM) result from the bacterioplankton degradation of plant lignin. However, the bacterial taxa involved in this process remain unknown, since Amazonian bacterioplankton has been poorly studied. Its characterization could lead to a better understanding of the carbon cycle in one of the Earth’s most productive hydrological systems. Our study characterized the taxonomic structure and functions of Amazonian bacterioplankton to better understand the interplay between this community and humic DOM. We conducted a field sampling campaign comprising 15 sites distributed across the three main Amazonian water types (representing a gradient of humic DOM), and a 16S rRNA metabarcoding analysis based on bacterioplankton DNA and RNA extracts. Bacterioplankton functions were inferred using 16S rRNA data in combination with a tailored functional database from 90 Amazonian basin shotgun metagenomes from the literature. We discovered that the relative abundances of fluorescent DOM fractions (humic-, fulvic-, and protein-like) were major drivers of bacterioplankton structure. We identified 36 genera for which the relative abundance was significantly correlated with humic DOM. The strongest correlations were found in the Polynucleobacter, Methylobacterium, and Acinetobacter genera, three low abundant but omnipresent taxa that possessed several genes involved in the main steps of the b-aryl ether enzymatic degradation pathway of diaryl humic DOM residues. Overall, this study identified key taxa with DOM degradation genomic potential, the involvement of which in allochthonous Amazonian carbon transformation and sequestration merits further investigation.

IMPORTANCE:

The Amazon basin discharge carries an important load of terrestrially derived dissolved organic matter (DOM) to the ocean. The bacterioplankton from this basin potentially plays important roles in transforming this allochthonous carbon, which has consequences on marine primary productivity and global carbon sequestration. However, the structure and function of Amazonian bacterioplanktonic communities remain poorly studied, and their interactions with DOM are unresolved. In this study, we (i) sampled bacterioplankton in all the main Amazon tributaries, (ii) combined information from the taxonomic structure and functional repertory of Amazonian bacterioplankton communities to understand their dynamics, (iii) identified the main physicochemical parameters shaping bacterioplanktonic communities among a set of .30 measured environmental parameters, and (iv) characterized how bacterioplankton structure varies according to the relative abundance of humic compounds, a by-product from the bacterial degradation process of allochthonous DOM.

Funding

This work was supported by the National Geographic Society, Natural Sciences and Engineering Research Council of Canada (NSERC), MITACS, and Ressources Aquatiques Quebec through travel and field work grants (F.-E.S.). This study was also supported in part by a NSERC Discovery grant (N.D.), the Instituto Nacional de Ciencia e Tecnologia de Adaptacoes da Biota Aquatica da Amazpnia (INCT ADAPTA) project (A.L.V.), a Canada-Brazil Awards Joint Research Project (N.D. and A.L.V.), and by funds from Conselho Nacional de Desenvolvimento Cientifico e Technologico (CNPq), Fundacao de Amparo a Pesquisa do Estado do Amazonas (FAPEAM), and Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES).

History

Publication Date

2023-05-18

Journal

Microbiology spectrum

Volume

11

Issue

3

Pagination

17p.

Publisher

American Society for Microbiology

ISSN

2165-0497

Rights Statement

© 2023 Sylvain et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license: https://creativecommons.org/licenses/by/4.0

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