Single bacterial strain capable of significant contribution to carbon cycling in the surface ocean

Bacterial growth, cell C, and DOC consumption of three treatments
TitleSingle bacterial strain capable of significant contribution to carbon cycling in the surface ocean
Publication TypeJournal Article
Year of Publication2014
AuthorsPedler BE, Aluwihare LI, Azam F
JournalProceedings of the National Academy of Sciences of the United States of America
Volume111
Pagination7202-7207
Date Published2014/07
Type of ArticleArticle
ISBN Number0027-8424
Accession NumberWOS:000336168100021
Keywordsalteromonas-macleodii; aquatic environments; california current ecosystem; CCE; communities; dissolved organic matter; dissolved organic-carbon; enzyme-activities; flow-cytometry; genetic diversity; marine biogeochemistry; marine-bacteria; microbial; microbial loop; ocean carbon cycle; pelagic; sargasso sea
Abstract

Marine dissolved organic carbon (DOC) encompasses one of the largest reservoirs of carbon on Earth. Heterotrophic bacteria are the primary biotic force regulating the fate of this material, yet the capacity of individual strains to significantly contribute to carbon cycling is unknown. Here we quantified the ability of a single Alteromonas strain [Alteromonas sp. strain Scripps Institution of Oceanography (AltSIO)] to drawdown ambient DOC in a coastal ecosystem. In three experiments, AltSIO alone consumed the entire pool of labile DOC, defined here as the quantity consumed by the submicron size fraction of ambient microbial assemblages within 5 d. These findings demonstrate that complete removal of the labile DOC pool in coastal surface seawater can be achieved by a single taxon. During long-term incubations (>1 y) testing semilabile DOC consumption, AltSIO entered dormancy but remained viable, while the diverse assemblages continued to consume carbon. Given that AltSIO is a large bacterium and thus subject to increased grazing pressure, we sought to determine the ecological relevance of this phenotype. Growth dynamics in natural seawater revealed that AltSIO rapidly outgrew the native bacteria, and despite intense grazing pressure, was never eliminated from the population. A survey in the California Current Ecosystem revealed that large bacteria (>= 40 fg C.cell(-1)) were persistent, accounting for up to 12% of total bacterial abundance and 24% of total bacterial biomass. We conclude that large, rapidly growing bacteria have the potential to disproportionately alter the fate of carbon in the mesotrophic ocean and play an important role in ecosystem function.

DOI10.1073/pnas.1401887111
Impact: 

"Together, these findings suggest that rarely dominant bacteria, otherwise intensely grazed or in a temporary survival state, may be responsible for a disproportionately large fraction of dissolved organic matter (DOM) recycling. Their outsized potential to influence the fate of carbon in the surface ocean suggests that rapidly growing large bacteria play an important role in ecosystem function and should be considered in global models of ocean carbon cycling."

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