A Parasitic Arsenic Cycle That Shuttles Energy from Phytoplankton to Heterotrophic Bacterioplankton

ABSTRACT In many regions of the world oceans, phytoplankton face the problem of discriminating between phosphate, an essential nutrient, and arsenate, a toxic analogue. Many phytoplankton, including the most abundant phytoplankton group known, Prochlorococcus, detoxify arsenate (AsV) by reduction to...

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Auteurs principaux: Stephen J. Giovannoni, Kimberly H. Halsey, Jimmy Saw, Omran Muslin, Christopher P. Suffridge, Jing Sun, Chih-Ping Lee, Eric R. Moore, Ben Temperton, Stephen E. Noell
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Publié: American Society for Microbiology 2019
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spelling oai:doaj.org-article:b4d34f574ddc4a0ab48e070813d9871f2021-11-15T15:55:24ZA Parasitic Arsenic Cycle That Shuttles Energy from Phytoplankton to Heterotrophic Bacterioplankton10.1128/mBio.00246-192150-7511https://doaj.org/article/b4d34f574ddc4a0ab48e070813d9871f2019-04-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.00246-19https://doaj.org/toc/2150-7511ABSTRACT In many regions of the world oceans, phytoplankton face the problem of discriminating between phosphate, an essential nutrient, and arsenate, a toxic analogue. Many phytoplankton, including the most abundant phytoplankton group known, Prochlorococcus, detoxify arsenate (AsV) by reduction to arsenite (AsIII), followed by methylation and excretion of the methylated arsenic products. We synthesized [14C]dimethyl arsenate (DMA) and used it to show that cultured Pelagibacter strain HTCC7211 (SAR11) cells oxidize the methyl group carbons of DMA, producing 14CO2 and ATP. We measured [14C]DMA oxidation rates in the P-depleted surface waters of the Sargasso Sea, a subtropical ocean gyre. [14C]DMA was oxidized to 14CO2 by Sargasso Sea plankton communities at a rate that would cause turnover of the estimated DMA standing stock every 8.1 days. SAR11 strain HTCC7211, which was isolated from the Sargasso Sea, has a pair of arsenate resistance genes and was resistant to arsenate, showing no growth inhibition at As/P ratios of >65:1. Across the global oceans, there was a strong inverse relationship between the frequency of the arsenate reductase (LMWPc_ArsC) in Pelagibacter genomes and phosphate concentrations. We propose that the demethylation of methylated arsenic compounds by Pelagibacter and possibly other bacterioplankton, coupled with arsenate resistance, results in the transfer of energy from phytoplankton to bacteria. We dub this a parasitic cycle because the release of arsenate by Pelagibacter in principle creates a positive-feedback loop that forces phytoplankton to continually regenerate arsenate detoxification products, producing a flow of energy to P-limited ocean regions. IMPORTANCE In vast, warm regions of the oceans, phytoplankton face the problem of arsenic poisoning. Arsenate is toxic because it is chemically similar to phosphate, a scarce nutrient that phytoplankton cells need for growth. Many phytoplankton, including the commonest phytoplankton type in warm oceans, Prochlorococcus, detoxify arsenate by adding methyl groups. Here we show that the most abundant non-photosynthetic plankton in the oceans, SAR11 bacteria, remove the methyl groups, releasing poisonous forms of arsenic back into the water. We postulate that the methylation and demethylation of arsenic compounds creates a cycle in which the phytoplankton can never get ahead and must continually transfer energy to the SAR11 bacteria. We dub this a parasitic process and suggest that it might help explain why SAR11 bacteria are so successful, surpassing all other plankton in their numbers. Field experiments were done in the Sargasso Sea, a subtropical ocean gyre that is sometimes called an ocean desert because, throughout much of the year, there is not enough phosphorous in the water to support large blooms of phytoplankton. Ocean deserts are expanding as the oceans absorb heat and grow warmer.Stephen J. GiovannoniKimberly H. HalseyJimmy SawOmran MuslinChristopher P. SuffridgeJing SunChih-Ping LeeEric R. MooreBen TempertonStephen E. NoellAmerican Society for MicrobiologyarticleSAR11arsenicoceanMicrobiologyQR1-502ENmBio, Vol 10, Iss 2 (2019)
institution DOAJ
collection DOAJ
language EN
topic SAR11
arsenic
ocean
Microbiology
QR1-502
spellingShingle SAR11
arsenic
ocean
Microbiology
QR1-502
Stephen J. Giovannoni
Kimberly H. Halsey
Jimmy Saw
Omran Muslin
Christopher P. Suffridge
Jing Sun
Chih-Ping Lee
Eric R. Moore
Ben Temperton
Stephen E. Noell
A Parasitic Arsenic Cycle That Shuttles Energy from Phytoplankton to Heterotrophic Bacterioplankton
description ABSTRACT In many regions of the world oceans, phytoplankton face the problem of discriminating between phosphate, an essential nutrient, and arsenate, a toxic analogue. Many phytoplankton, including the most abundant phytoplankton group known, Prochlorococcus, detoxify arsenate (AsV) by reduction to arsenite (AsIII), followed by methylation and excretion of the methylated arsenic products. We synthesized [14C]dimethyl arsenate (DMA) and used it to show that cultured Pelagibacter strain HTCC7211 (SAR11) cells oxidize the methyl group carbons of DMA, producing 14CO2 and ATP. We measured [14C]DMA oxidation rates in the P-depleted surface waters of the Sargasso Sea, a subtropical ocean gyre. [14C]DMA was oxidized to 14CO2 by Sargasso Sea plankton communities at a rate that would cause turnover of the estimated DMA standing stock every 8.1 days. SAR11 strain HTCC7211, which was isolated from the Sargasso Sea, has a pair of arsenate resistance genes and was resistant to arsenate, showing no growth inhibition at As/P ratios of >65:1. Across the global oceans, there was a strong inverse relationship between the frequency of the arsenate reductase (LMWPc_ArsC) in Pelagibacter genomes and phosphate concentrations. We propose that the demethylation of methylated arsenic compounds by Pelagibacter and possibly other bacterioplankton, coupled with arsenate resistance, results in the transfer of energy from phytoplankton to bacteria. We dub this a parasitic cycle because the release of arsenate by Pelagibacter in principle creates a positive-feedback loop that forces phytoplankton to continually regenerate arsenate detoxification products, producing a flow of energy to P-limited ocean regions. IMPORTANCE In vast, warm regions of the oceans, phytoplankton face the problem of arsenic poisoning. Arsenate is toxic because it is chemically similar to phosphate, a scarce nutrient that phytoplankton cells need for growth. Many phytoplankton, including the commonest phytoplankton type in warm oceans, Prochlorococcus, detoxify arsenate by adding methyl groups. Here we show that the most abundant non-photosynthetic plankton in the oceans, SAR11 bacteria, remove the methyl groups, releasing poisonous forms of arsenic back into the water. We postulate that the methylation and demethylation of arsenic compounds creates a cycle in which the phytoplankton can never get ahead and must continually transfer energy to the SAR11 bacteria. We dub this a parasitic process and suggest that it might help explain why SAR11 bacteria are so successful, surpassing all other plankton in their numbers. Field experiments were done in the Sargasso Sea, a subtropical ocean gyre that is sometimes called an ocean desert because, throughout much of the year, there is not enough phosphorous in the water to support large blooms of phytoplankton. Ocean deserts are expanding as the oceans absorb heat and grow warmer.
format article
author Stephen J. Giovannoni
Kimberly H. Halsey
Jimmy Saw
Omran Muslin
Christopher P. Suffridge
Jing Sun
Chih-Ping Lee
Eric R. Moore
Ben Temperton
Stephen E. Noell
author_facet Stephen J. Giovannoni
Kimberly H. Halsey
Jimmy Saw
Omran Muslin
Christopher P. Suffridge
Jing Sun
Chih-Ping Lee
Eric R. Moore
Ben Temperton
Stephen E. Noell
author_sort Stephen J. Giovannoni
title A Parasitic Arsenic Cycle That Shuttles Energy from Phytoplankton to Heterotrophic Bacterioplankton
title_short A Parasitic Arsenic Cycle That Shuttles Energy from Phytoplankton to Heterotrophic Bacterioplankton
title_full A Parasitic Arsenic Cycle That Shuttles Energy from Phytoplankton to Heterotrophic Bacterioplankton
title_fullStr A Parasitic Arsenic Cycle That Shuttles Energy from Phytoplankton to Heterotrophic Bacterioplankton
title_full_unstemmed A Parasitic Arsenic Cycle That Shuttles Energy from Phytoplankton to Heterotrophic Bacterioplankton
title_sort parasitic arsenic cycle that shuttles energy from phytoplankton to heterotrophic bacterioplankton
publisher American Society for Microbiology
publishDate 2019
url https://doaj.org/article/b4d34f574ddc4a0ab48e070813d9871f
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