Publications (9)21.64 Total impact
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Article: Similarity in microbial amino acid uptake in surface waters of the North and South Atlantic (sub-)tropical gyres
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ABSTRACT: The Earth's most extensive biomes – the oceanic subtropical gyres – are considered to be expanding with current surface ocean warming. Although it is well established that microbial communities control gyre biogeochemistry, comparisons of their metabolic activities between gyres are limited. In order to esti-mate metabolic activities including production of microbial communities, the uptake rates of amino acids leucine, methionine and tyrosine at ambient concentrations were estimated in surface waters of the Atlantic Ocean using radioisotopically labelled tracers. Data were acquired during six research cruises covering main oceanic provinces herein termed: North and South Atlantic Gyres, Bermuda Atlantic Time-series Study site (BATS), Equatorial region, and Mauritanian Upwelling (off Cape Blanc). Data were divided between provinces, the extents of which were identified by ocean colour data, in order to achieve provincial mean uptake rates. Leucine and methionine uptake rates did not differ between sampling peri-ods, and were comparable between the North and South subtropical gyres. Furthermore, variation in uptake rates measured throughout the two oligotrophic gyres, where sampling covered $4 Â 10 6 km 2 , was considerably lower than that measured within the Mauritanian Upwelling and Equatorial regions, and even at the BATS site. Tyrosine was generally the slowest of the amino acids to be taken up, however, it was assimilated faster than methionine within the Mauritanian Upwelling region. Thus, we propose that one value for leucine (12.6 ± 3.2 pmol L À1 h À1) and methionine (10.0 ± 3.3 pmol L À1 h À1) uptake could be applied to the oligotrophic subtropical gyres of the Atlantic Ocean. However, with the signifi-cantly lower uptake rates observed at the BATS site, we would not advise extrapolation to the Sargasso Sea.Progress In Oceanography 07/2011; 91:437-446. · 3.14 Impact Factor -
Article: Metaproteomic and metagenomic analyses of defined oceanic microbial populations using microwave cell fixation and flow cytometric sorting.
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ABSTRACT: A major obstacle in the molecular investigation of natural, especially oceanic, microbial cells is their adequate preservation for further land-based molecular analyses. Here, we examined the use of microwaves for cell fixation before high-speed flow cytometric sorting to define the metaproteomes and metagenomes of key microbial populations. The microwave fixation procedure was established using cultures of Synechococcus cyanobacteria, the photosynthetic eukaryote Micromonas pusilla and the gammaproteobacterium Halomonas variabilis. Shotgun proteomic analyses showed that the profile of microwave-fixed and -unfixed Synechococcus sp. WH8102 cells was the same, and hence proteome identification of microwave-fixed sorted cells by nanoLC-MS/MS is possible. Microwave-fixed flow-sorted Synechococcus cells can also be successfully used for whole-genome amplification and fosmid library construction. We then carried out successful metaproteomic and metagenomic analyses of microwave-fixed Synechococcus cells flow sorted from concentrates of microbial cells, collected in the North Atlantic Ocean. Thus, the microwave fixation procedure developed appears to be useful for molecular studies of microbial populations in aquatic ecosystems.FEMS Microbiology Ecology 10/2010; 74(1):10-8. · 3.41 Impact Factor -
Article: Diel rhythmicity in amino acid uptake by Prochlorococcus.
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ABSTRACT: The marine cyanobacterium Prochlorococcus, the most abundant phototrophic organism on Earth, numerically dominates the phytoplankton in nitrogen (N)-depleted oceanic gyres. Alongside inorganic N sources such as nitrite and ammonium, natural populations of this genus also acquire organic N, specifically amino acids. Here, we investigated using isotopic tracer and flow cytometric cell sorting techniques whether amino acid uptake by Prochlorococcus is subject to a diel rhythmicity, and if so, whether this was linked to a specific cell cycle stage. We observed, in contrast to diurnally similar methionine uptake rates by Synechococcus cells, obvious diurnal rhythms in methionine uptake by Prochlorococcus cells in the tropical Atlantic. These rhythms were confirmed using reproducible cyclostat experiments with a light-synchronized axenic Prochlorococcus (PCC9511 strain) culture and (35)S-methionine and (3)H-leucine tracers. Cells acquired the tracers at lower rates around dawn and higher rates around dusk despite >10(4) times higher concentration of ammonium in the medium, presumably because amino acids can be directly incorporated into protein. Leucine uptake rates by cells in the S+G(2) cell cycle stage were consistently 2.2 times higher than those of cells at the G(1) stage. Furthermore, S+G(2) cells upregulated amino acid uptake 3.5 times from dawn to dusk to boost protein synthesis prior to cell division. Because Prochlorococcus populations can account from 13% at midday to 42% at dusk of total microbial uptake of methionine and probably of other amino acids in N-depleted oceanic waters, this genus exerts diurnally variable, strong competitive pressure on other bacterioplankton populations.Environmental Microbiology 04/2008; 10(8):2124-31. · 5.84 Impact Factor -
Article: Light enhanced amino acid uptake by dominant bacterioplankton groups in surface waters of the Atlantic Ocean.
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ABSTRACT: (35)S-Methionine and (3)H-leucine bioassay tracer experiments were conducted on two meridional transatlantic cruises to assess whether dominant planktonic microorganisms use visible sunlight to enhance uptake of these organic molecules at ambient concentrations. The two numerically dominant groups of oceanic bacterioplankton were Prochlorococcus cyanobacteria and bacteria with low nucleic acid (LNA) content, comprising 60% SAR11-related cells. The results of flow cytometric sorting of labelled bacterioplankton cells showed that when incubated in the light, Prochlorococcus and LNA bacteria increased their uptake of amino acids on average by 50% and 23%, respectively, compared with those incubated in the dark. Amino acid uptake of Synechococcus cyanobacteria was also enhanced by visible light, but bacteria with high nucleic acid content showed no light stimulation. Additionally, differential uptake of the two amino acids by the Prochlorococcus and LNA cells was observed. The populations of these two types of cells on average completely accounted for the determined 22% light enhancement of amino acid uptake by the total bacterioplankton community, suggesting a plausible way of harnessing light energy for selectively transporting scarce nutrients that could explain the numerical dominance of these groups in situ.FEMS Microbiology Ecology 02/2008; 63(1):36-45. · 3.41 Impact Factor -
Article: Microbial control of phosphate in the nutrient-depleted North Atlantic subtropical gyre.
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ABSTRACT: Little is known about the dynamics of dissolved phosphate in oligotrophic areas of the world's oceans, where concentrations are typically in the nanomolar range. Here, we have budgeted phosphate uptake by the dominant microbial groups in order to assess the effect of the microbial control of this depleted nutrient in the North Atlantic gyre. Low concentrations (2.2 +/- 1.2 nM) and rapid microbial uptake (2.1 +/- 2.4 nM day(-1)) of bioavailable phosphate were repeatedly determined in surface waters of the North Atlantic oligotrophic gyre during spring and autumn research cruises, using a radiotracer dilution bioassay technique. Upper estimates of the concentration of bioavailable phosphate were 7-55% of the dissolved mineral phosphate suggesting that a considerable part of the chemically measured nanomolar phosphate was in a form unavailable for direct microbial uptake. A 1:1 relationship (r(2) = 0.96, P < 0.0001) was observed between the bioavailable total phosphate uptake and the phosphate uptake of all the flow sorted bacterioplankton cells, demonstrating that bacterioplankton were the main consumers of phosphate. Within the bacterioplankton a group of heterotrophic bacteria and Prochlorococcus phototrophic cyanobacteria, were the two major competing groups for bioavailable phosphate. These heterotrophic bacteria had low nucleic acid content and 60% of them comprised of SAR11 clade cells based on the results of fluorescence in situ hybridization. Each of the two competing bacterial groups was responsible for an average of 45% of the phosphate uptake, while Synechococcus cyanobacteria (7%) and picoplanktonic algae (0.3%) played minor roles in direct phosphate uptake. We have demonstrated that phosphate uptake in the oligotrophic gyre is rapid and dominated by two bacterial groups rather than by algae.Environmental Microbiology 09/2007; 9(8):2079-89. · 5.84 Impact Factor -
Article: Differential microbial uptake of dissolved amino acids and amino sugars in surface waters of the Atlantic Ocean
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ABSTRACT: Nitrogen bioavailability is considered to limit the productivity of oceanic oligotrophic gyres, the largest biomes on Earth. In order to assess the microbial requirement for small organic nitrogen molecules in these and other waters, the microbial uptake rates of amino acids (leucine, methionine and tyrosine) and amino sugars (glucosamine and N-acetyl-glucosamine) as well as glucose were compared using a bioassay technique of radiotracer dilution. The bioassays were carried out on four mid-Atlantic meridional transects spanning a latitudinal range from 60°N to 42°S. The mean concentrations of both bioavailable N-acetyl-glucosamine and glucose in the gyres were 1 nM, four times higher than the mean leucine concentration. Despite its lower concentration, the mean turnover time of leucine in the gyres of 15 h was 90 and 9 times shorter than the turnover time of N-acetyl-glucosamine and glucose, respectively. In addition, among amino acids, leucine was taken up in the gyres at a rate of 1.5 times faster than methionine and 2.5 times faster than tyrosine. Hence, oceanic bacterioplankton as a community showed a clear preference for amino acids, particularly leucine, compared with amino sugars. The preferential uptake of amino acids to sugars challenges the concept of microbial nitrogen or carbon limitation in the open ocean.Journal of Plankton Research. -
Article: Microbial control of phosphate in the nutrient-depleted North Atlantic subtropical gyre
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ABSTRACT: Little is known about the dynamics of dissolved phosphate in oligotrophic areas of the world's oceans, where concentrations are typically in the nanomolar range. Here, we have budgeted phosphate uptake by the dominant microbial groups in order to assess the effect of the microbial control of this depleted nutrient in the North Atlantic gyre. Low concentrations (2.2 ± 1.2 nM) and rapid microbial uptake (2.1 ± 2.4 nM day−1) of bioavailable phosphate were repeatedly determined in surface waters of the North Atlantic oligotrophic gyre during spring and autumn research cruises, using a radiotracer dilution bioassay technique. Upper estimates of the concentration of bioavailable phosphate were 7–55% of the dissolved mineral phosphate suggesting that a considerable part of the chemically measured nanomolar phosphate was in a form unavailable for direct microbial uptake. A 1:1 relationship (r2 = 0.96, P < 0.0001) was observed between the bioavailable total phosphate uptake and the phosphate uptake of all the flow sorted bacterioplankton cells, demonstrating that bacterioplankton were the main consumers of phosphate. Within the bacterioplankton a group of heterotrophic bacteria and Prochlorococcus phototrophic cyanobacteria, were the two major competing groups for bioavailable phosphate. These heterotrophic bacteria had low nucleic acid content and 60% of them comprised of SAR11 clade cells based on the results of fluorescence in situ hybridization. Each of the two competing bacterial groups was responsible for an average of 45% of the phosphate uptake, while Synechococcus cyanobacteria (7%) and picoplanktonic algae (0.3%) played minor roles in direct phosphate uptake. We have demonstrated that phosphate uptake in the oligotrophic gyre is rapid and dominated by two bacterial groups rather than by algae.Environmental microbiology. -
Article: SAR11 dominance among metabolically active low nucleic acid bacterioplankton in surface waters along an Atlantic Meridional Transect
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ABSTRACT: Low nucleic acid (LNA) bacterioplankton (sorted by flow cytometry) were characterised in surface water samples along a meridional transect from 48°N to 40° S across the Atlantic Ocean. The LNA bacterioplankton abundance and metabolic activity, assessed by their 35S-methionine uptake rate, were similar along the transect, representing 36 ± 6 and 36 ± 11% of total bacterioplankton, respectively. Fluorescence in situ hybridisation analysis of the flow-sorted cells revealed that the LNA bacterioplankton population was dominated (59 ± 4%) by and contained virtually all the identifiable SAR11 clade cells throughout the Atlantic Ocean. Therefore, the present study provides ecological characterisation of this flow-sorted group and suggests both phylogenetic and functional constancy of the LNA bacterioplankton at the basin-scale.Aquatic Microbial Ecology. -
Article: Seasonal dynamics of bacterioplankton community structure at a coastal station in the western English Channel
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ABSTRACT: An annual study of the bacterioplankton community structure was carried out at Stn L4 (50° 15'N, 04° 13'W) in the western English Channel between August 2003 and July 2004. Bacterioplankton abundance and community structure were assessed using flow cytometry and fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes, respectively. The Eubacteria domain dominated over the Archaea domain (<15%) at the highest phylogenetic level. The Sphingo-bacteria-Flavobacteria group of the Bacteroidetes phylum (SFB) numerically dominated in spring and early summer. The α-Proteobacteria dominated from late summer to winter. The SAR11 clade represented -13% of the microbial community throughout the year and accounted for up to 69% of α-Proteobacteria in late spring. Annually, γ-Proteobacteria were 2 or 3 times less abundant than the other groups and showed no obvious seasonal trend. The SAR86 cluster accounted for up to half of γ-Proteobacteria when it peaked in summer. Consequently, we found that community structure at higher taxonomic level did not change dramatically with season but lower level phylogenetic groups showed pronounced seasonal peaks.Aquatic Microbial Ecology.
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2008–2010
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National Oceanography Centre, Southampton
Southampton, ENG, United Kingdom
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