Response of marine bacterial community composition to iron additions in three iron-limited regimes (original) (raw)
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Journal of Experimental Marine Biology and Ecology, 2007
While it has been shown that phytoplankton productivity and community structure are influenced by the availability of Fe in several high nutrient-low chlorophyll (HNLC) regions of the world's oceans, the influence of Fe on the bacterial community remains unresolved. Therefore, we sampled water from the Peruvian upwelling region of the equatorial Pacific Ocean and examined how bacterial community structure changes with Fe additions (1.5 nM, 0.5 nM above ambient) and sequestration, which was accomplished by additions of the fungal siderophore desferrioxamine B (DFB) (1.0 nM, 5.0 nM). We hypothesized that either 1) the bacterial communities are generally Fe-limited and thus show positive responses to Fe addition; or 2) that bacteria form the equivalent of response groups and show a limited number of responses to Fe addition; or else 3) that the bacterial communities show no response to Fe addition. Using Terminal Restriction Fragment Length Polymorphism analysis, we found that the eubacterial community changed in response to Fe. Whereas the overall community shows little abundance and richness responses to Fe availability, bacteria can be arranged into response groups showing divergent responses to Fe addition. With validated cluster analysis, we found that the bacterial community consisted of four response groups. One group showed strong positive responses to increasing Fe availability, while another group showed strong negative responses. The abundance patterns of the final two groups showed no response to alterations in Fe availability, although one persisted at a high abundances and the other a low abundance. These results reveal that it may be difficult to describe a singular bacterial community response to changes in Fe availability, and that understanding the influence of Fe on bacteria dynamics may require an understanding of the different responses of individual sub-groups of bacteria within the microbial community.
Marine bacteria and biogeochemical cycling of iron in the oceans
Fems Microbiology Ecology, 1999
Prokaryotic microbes play a critical role in oceanic Fe cycling. They contain most of the biogenic Fe in offshore waters and are responsible for a large portion of the Fe uptake by the plankton community. In the subarctic North Pacific, surface populations of heterotrophic species assimilate more than 50% of the dissolved Fe and thus compete directly with phytoplankton for this limiting resource. In oligotrophic tropical and subtropical waters, photosynthetic bacteria become more important in Fe cycling as the number of unicellular cyanobacteria increases and the nitrogen-fixing Trichodesmium, which contains most of the biogenic Fe in the mixed layer, becomes abundant. Like their terrestrial counterparts, heterotrophic and phototrophic marine bacteria produce Fe-binding siderophores that are involved in Fe acquisition. Evidence exists that bacteria may modify Fe chemistry in the sea through the production of these ligands and thereby play a significant role in regulating production of eukaryotic phytoplankton. z
Deep Sea Research Part II: Topical Studies in Oceanography, 2009
Little is known about the effects of iron enrichment in high-nutrient, low chlorophyll (HNLC) waters on the community composition of heterotrophic bacteria, which are crucial to nutrient recycling and microbial food webs. Using denaturing gradient gel electrophoresis (DGGE) of 16S rDNA fragments, we investigated the heterotrophic eubacterial community composition in surface waters during an in situ iron enrichment experiment (SEEDS-II) in the western subarctic Pacific during the summer of 2004. DGGE fingerprints representing the community composition of eubacteria differed inside and outside the iron-enriched patch. Sequencing of DGGE bands revealed that at least five phylotypes of α-proteobacteria including Roseobacter, Cytophaga-Flavobacteria-Bacteroides (CFB), γ-proteobacteria, and Actinobacteria occurred in almost all samples from the iron-enriched patch. Diatoms did not bloom during SEEDS-II, but the eubacterial composition in the iron-enriched patch was similar to that in diatom blooms observed previously. Although dissolved organic carbon DOC accumulation was not detected in surface waters during SEEDS-II, growth of the Roseobacter clade might have been particularly stimulated after iron additions. Two identified phylotypes of CFB were closely related to the genus Saprospira, whose algicidal activity might degrade the phytoplankton assemblages increased by iron enrichment. These results suggest that the responses of heterotrophic bacteria to iron enrichment could differ among phylotypes during SEEDS-II.
Limnology and Oceanography, 2011
We investigated the contribution of distinct bacterial groups to bulk abundance and leucine incorporation during a spring phytoplankton bloom induced by natural iron fertilization in the Southern Ocean (Kerguelen Ocean and Plateau Compared Study, January-February 2005). Oligonucleotide probes were designed to target five operational taxonomic units (OTUs) at a narrow phylogenetic level ($ 99% identity of the 16S ribosomal ribonucleic acid [rRNA] gene). During the peak of the phytoplankton bloom, the Roseobacter groups NAC11-7 and RCA, the OTUs SAR92 belonging to Gammaproteobacteria, and the Bacteroidetes OTU Agg58 dominated bulk abundance and leucine incorporation. These four OTUs disappeared with the decline of the bloom, when the cosmopolitan groups SAR11 and SAR86 became dominant. In high-nutrient, low-chlorophyll waters and at a site characterized by transient high phytoplankton biomass, the SAR11 and SAR86 clusters and a Polaribacter OTU dominated abundance and leucine incorporation in the upper 100 m. Our results demonstrate that a few distinct bacterial groups identified on a relatively narrow phylogenetic level account for 47% to 82% of bulk abundance and leucine incorporation during the spring phytoplankton bloom in the naturally fertilized region off Kerguelen. The major role of these bacterial groups in carbon cycling in response to natural iron fertilization in the Southern Ocean suggests they could play an important role in the coupling of the biogeochemical cycles of carbon and iron.
Response of bacterioplankton to iron fertilization in the Southern Ocean
Limnology and Oceanography, 2004
We studied the bacterial response to Fe fertilization over 3 weeks during the second iron-enrichment experiment (EisenEx) in the Southern Ocean. Bacterial abundance in the Fe-fertilized patch increased over the first 12 d following Fe release and remained about twice as high as outside the Fe-fertilized patch until the end of the experiment. Bacterial production peaked a few days after each of the three Fe releases inside the Fe-fertilized patch, reaching rates two to three times higher than outside the patch. Besides the peaks in leucine and thymidine incorporation following Fe release, bacterial production was not significantly higher inside the patch than outside, suggesting direct limitation of bacterial growth by Fe. Bacterial aminopeptidase activity roughly followed the increase in bacterial abundance, whereas cell-specific ␣and -glucosidase were higher inside the Fe-fertilized patch. The diversity of -glucosidases was determined by capillary electrophoresis zymography. The different -glucosidases showed much higher activity levels inside the patch than in the surrounding waters, and three additional -glucosidases constituting ϳ55% of the total -glucosidase activity were present inside the Fe-fertilized patch from day 9 onward. No major changes in response to Fe fertilization were detected in the phylogenetic composition of the bacterioplankton community, as determined by 16S rDNA fingerprinting, indicating a remarkable adaptation of the bacterioplankton community to episodic iron inputs. This stability on the phylogenetic level is contrasted by the dramatic qualitative and quantitative changes in ectoenzymatic activity.
Response of bacterioplankton to iron fertilization of the Southern Ocean, Antarctica
Frontiers in Microbiology, 2015
Ocean iron fertilization is an approach to increase CO 2 sequestration. The Indo-German iron fertilization experiment "LOHAFEX" was carried out in the Southern Ocean surrounding Antarctica in 2009 to monitor changes in bacterial community structure following iron fertilization-induced phytoplankton bloom of the seawater from different depths. 16S rRNA gene libraries were constructed using metagenomic DNA from seawater prior to and after iron fertilization and the clones were sequenced for identification of the major bacterial groups present and for phylogenetic analyses. A total of 4439 clones of 16S rRNA genes from ten 16S rRNA gene libraries were sequenced. More than 97.35% of the sequences represented four bacterial lineages i.e. Alphaproteobacteria, Gammaproteobacteria, Bacteroidetes, and Firmicutes and confirmed their role in scavenging of phytoplankton blooms induced following iron fertilization. The present study demonstrates the response of Firmicutes due to Iron fertilization which was not observed in previous southern ocean Iron fertilization studies. In addition, this study identifies three unique phylogenetic clusters LOHAFEX Cluster 1 (affiliated to Bacteroidetes), 2, and 3 (affiliated to Firmicutes) which were not detected in any of the earlier studies on iron fertilization. The relative abundance of these clusters in response to iron fertilization was different. The increase in abundance of LOHAFEX Cluster 2 and Papillibacter sp. another dominant Firmicutes may imply a role in phytoplankton degradation. Disappearance of LOHAFEX Cluster 3 and other bacterial genera after iron fertilization may imply conditions not conducive for their survival. It is hypothesized that heterotrophic bacterial abundance in the Southern Ocean would depend on their ability to utilize algal exudates, decaying algal biomass and other nutrients thus resulting in a dynamic bacterial succession of distinct genera.
The heterotrophic bacterial response during the Southern Ocean Iron Experiment (SOFeX)
Limnology and Oceanography, 2004
We studied heterotrophic bacterial dynamics as part of the Southern Ocean Iron Experiment (SOFeX), January-February 2002. Two phytoplankton blooms were monitored following infusions with iron sulfate (FeSO 4 ). The first bloom was initiated north of the Antarctic Polar Front Zone (APFZ) in silica-poor waters (North Patch) and was observed sporadically over 42 d, whereas the second was south of the APFZ in silica-rich waters (South Patch) and was continuously observed for 30 d. In both experiments, iron additions resulted in increased chlorophyll a (Chl a), particulate organic matter (POC ϩ PN), and a drawdown of inorganic nutrients. Heterotrophic bacteria responded by increasing their abundance (110% and 60% increases in bacterial abundance in the North and South Patch, respectively, relative to nonenriched waters). Thymidine (TdR) and leucine (Leu) incorporation rates in the North Patch increased by 400% and 120%, respectively, with more modest increases in the South Patch (80% and 70%, respectively). In the South Patch, bacterial production (BP) was significantly correlated with net particulate primary production (PP) and Chl a. Bacterial abundance was also significantly correlated with Chl a. Net bacterial accumulation rate in the South Patch was 0.02 d Ϫ1 over 17 d, excluding physical dilution by mixing with water outside the South Patch. The evidence suggests that bacterial growth during Southern Ocean Iron Experiment (SOFeX) was limited by labile carbon rather than by iron. Despite the close association of BP to PP, BP remained a small fraction of PP (Ͻ10%).
Progress in Oceanography, 2005
To verify the hypothesis that the growth of phytoplankton in the Western Subarctic Gyre (WSG), which is located in the northwest subarctic PaciWc, is suppressed by low iron (Fe) availability, an in situ Fe fertilization experiment was carried out in the summer of 2001. Changes over time in the abundance and community structure of phytoplankton were examined inside and outside an Fe patch using phytoplankton pigment markers analyzed by high-performance liquid chromatography (HPLC) and Xow cytometry (FCM). In addition, the abundance of heterotrophic bacteria was also investigated by FCM. The chlorophyll a concentration was initially ca. 0.9 g l ¡1 in the surface mixed layer where diatoms and chlorophyll b-containing green algae (prasinophytes and chlorophytes) were predominant in the chlorophyll biomass. After the iron enrichment, the chlorophyll a concentration increased up to 9.1 g l ¡1 in the upper 10 m inside the Fe patch on Day 13. At the same time, the concentration of fucoxanthin (a diatom marker) increased 45-fold in the Fe patch, and diatoms accounted for a maximum 69% of the chlorophyll biomass. This result was consistent with a microscopic observation showing that the diatom Chaetoceros debilis had bloomed inside the Fe patch. However, chlorophyllide a concentrations also increased in the Fe patch with time, and reached a maximum of 2.2 g l ¡1 at 5 m depth on Day 13, suggesting that a marked abundance of senescent algal cells existed at the end of the experiment. The concentration of peridinin (a dinoXagellate marker) also reached a maximum 24-fold, and dinoXagellates had contributed signiWcantly (>15%) to the chlorophyll biomass inside the Fe patch by the end of the experiment. Concentrations (K. Suzuki).
Limnology and Oceanography, 2014
The response of heterotrophic bacteria in a mesoscale iron (Fe) enrichment was measured in the northeast subarctic Pacific Ocean in July 2002. Addition of FeSO 4 increased the dissolved Fe concentration in the fertilized patch to 2-3 nmol L 21 and triggered an increase in concentration of Fe(III)-binding ligands that complexed all of the dissolved Fe. Two to three days later, leucine incorporation rate and specific growth rate of bacteria doubled. Physiological markers of bacterial Fe nutritional state varied during the experiment as the microbial community assimilated the added Fe. Cellular uptake rate of an iron-siderophore complex, 55 Fe-ferrioxamine B (FB), increased twofold to fourfold over background values and then declined by day 4.5. The fastest rate of Fe-FB uptake on day 2.5 coincided roughly with a transient increase in outer-membrane, 55 Fe-FB-binding protein(s) in bacteria and with the peak in ligand concentration. Maximum potential uptake rate of inorganic Fe (V max) was 8 zmol Fe bacterium 21 h 21 prior to Fe enrichment and then decreased by a factor of four within 2.5 d of fertilizing the patch as bacteria became Fe sufficient. V max gradually increased by day 6.5 as the bacterial community re-entered iron deficiency. Similar changes in growth and Fe uptake kinetics were observed after a second Fe addition. Heterotrophic bacteria in the subarctic Pacific were Fe-deficient and responded directly to Fe addition by up-regulating pathways for Fe-siderophore acquisition and assimilating complexed Fe. The observation that increases in Fe uptake pathways and production were synchronous is consistent with the hypothesis that bacterial growth was directly limited by Fe.