N2-fixing
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Crocosphaera is a major dinitrogen (N2)-fixing microorganism, providing bioavailable nitrogen (N) to marine ecosystems. The N2-fixing enzyme nitrogenase is deactivated by oxygen (O2), which is abundant in marine environments. Using a cellular scale model of Crocosphaera sp. and laboratory data, we quantify the role of three O2 management strategies by Crocosphaera sp.: size adjustment, reduced O2 diffusivity, and respiratory protection. Our model predicts that Crocosphaera cells increase their size under high O2 Using transmission electron microscopy, we show that starch granules and thylakoid membranes are located near the cytoplasmic membranes, forming a barrier for O2 The model indicates a critical role for respiration in protecting the rate of N2 fixation. Moreover, the rise in respiration rates and the decline in ambient O2 with temperature strengthen this mechanism in warmer water, providing a physiological rationale for the observed niche of Crocosphaera at temperatures exceeding 20°C. Our new measurements of the sensitivity to light intensity show that the rate of N2 fixation reaches saturation at a lower light intensity (∼100 μmol m-2 s-1) than photosynthesis and that both are similarly inhibited by light intensities of >500 μmol m-2 s-1 This suggests an explanation for the maximum population of Crocosphaera occurring slightly below the ocean surface.IMPORTANCECrocosphaera is one of the major N2-fixing microorganisms in the open ocean. On a global scale, the process of N2 fixation is important in balancing the N budget, but the factors governing the rate of N2 fixation remain poorly resolved. Here, we combine a mechanistic model and both previous and present laboratory studies of Crocosphaera to quantify how chemical factors such as C, N, Fe, and O2 and physical factors such as temperature and light affect N2 fixation. Our study shows that Crocosphaera combines multiple mechanisms to reduce intracellular O2 to protect the O2-sensitive N2-fixing enzyme. Our model, however, indicates that these protections are insufficient at low temperature due to reduced respiration and the rate of N2 fixation becomes severely limited. This provides a physiological explanation for why the geographic distribution of Crocosphaera is confined to the warm low-latitude ocean.
- MeSH
- fixace dusíku * MeSH
- kyslík metabolismus MeSH
- sinice cytologie metabolismus účinky záření MeSH
- škrob metabolismus MeSH
- světlo * MeSH
- teplota * MeSH
- transmisní elektronová mikroskopie MeSH
- tylakoidy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
BACKGROUND AND AIMS: Rootless carnivorous plants of the genus Utricularia are important components of many standing waters worldwide, as well as suitable model organisms for studying plant-microbe interactions. In this study, an investigation was made of the importance of microbial dinitrogen (N2) fixation in the N acquisition of four aquatic Utricularia species and another aquatic carnivorous plant, Aldrovanda vesiculosa. METHODS: 16S rRNA amplicon sequencing was used to assess the presence of micro-organisms with known ability to fix N2. Next-generation sequencing provided information on the expression of N2 fixation-associated genes. N2 fixation rates were measured following (15)N2-labelling and were used to calculate the plant assimilation rate of microbially fixed N2. KEY RESULTS: Utricularia traps were confirmed as primary sites of N2 fixation, with up to 16 % of the plant-associated microbial community consisting of bacteria capable of fixing N2. Of these, rhizobia were the most abundant group. Nitrogen fixation rates increased with increasing shoot age, but never exceeded 1·3 μmol N g(-1) d. mass d(-1). Plant assimilation rates of fixed N2 were detectable and significant, but this fraction formed less than 1 % of daily plant N gain. Although trap fluid provides conditions favourable for microbial N2 fixation, levels of nif gene transcription comprised <0·01 % of the total prokaryotic transcripts. CONCLUSIONS: It is hypothesized that the reason for limited N2 fixation in aquatic Utricularia, despite the large potential capacity, is the high concentration of NH4-N (2·0-4·3 mg L(-1)) in the trap fluid. Resulting from fast turnover of organic detritus, it probably inhibits N2 fixation in most of the microorganisms present. Nitrogen fixation is not expected to contribute significantly to N nutrition of aquatic carnivorous plants under their typical growth conditions; however, on an annual basis the plant-microbe system can supply nitrogen in the order of hundreds of mg m(-2) into the nutrient-limited littoral zone, where it may thus represent an important N source.
- MeSH
- amoniové sloučeniny analýza MeSH
- Bacteria genetika izolace a purifikace metabolismus MeSH
- bakteriální RNA chemie genetika MeSH
- Droseraceae metabolismus mikrobiologie MeSH
- dusík metabolismus MeSH
- ekologie MeSH
- ekosystém MeSH
- fixace dusíku * MeSH
- izotopy dusíku MeSH
- Magnoliopsida metabolismus mikrobiologie MeSH
- molekulární sekvence - údaje MeSH
- RNA ribozomální 16S chemie genetika MeSH
- sekvence nukleotidů MeSH
- sekvenční analýza RNA MeSH
- voda metabolismus MeSH
- výhonky rostlin metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
Trichodesmium is an important dinitrogen (N2)-fixing cyanobacterium in marine ecosystems. Recent nucleic acid analyses indicate that Trichodesmium colonies with their diverse epibionts support various nitrogen (N) transformations beyond N2 fixation. However, rates of these transformations and concentration gradients of N compounds in Trichodesmium colonies remain largely unresolved. We combined isotope-tracer incubations, micro-profiling and numeric modelling to explore carbon fixation, N cycling processes as well as oxygen, ammonium and nitrate concentration gradients in individual field-sampled Trichodesmium colonies. Colonies were net-autotrophic, with carbon and N2 fixation occurring mostly during the day. Ten percent of the fixed N was released as ammonium after 12-h incubations. Nitrification was not detectable but nitrate consumption was high when nitrate was added. The consumed nitrate was partly reduced to ammonium, while denitrification was insignificant. Thus, the potential N transformation network was characterised by fixed N gain and recycling processes rather than denitrification. Oxygen concentrations within colonies were ~60-200% air-saturation. Moreover, our modelling predicted steep concentration gradients, with up to 6-fold higher ammonium concentrations, and nitrate depletion in the colony centre compared to the ambient seawater. These gradients created a chemically heterogeneous microenvironment, presumably facilitating diverse microbial metabolisms in millimetre-sized Trichodesmium colonies.
- MeSH
- amoniové sloučeniny metabolismus MeSH
- autotrofní procesy MeSH
- denitrifikace MeSH
- dusičnany metabolismus MeSH
- dusík metabolismus MeSH
- fixace dusíku MeSH
- koloběh dusíku MeSH
- koloběh uhlíku MeSH
- kyslík metabolismus MeSH
- mořská voda mikrobiologie MeSH
- nitrifikace MeSH
- oxid uhličitý metabolismus MeSH
- Trichodesmium metabolismus MeSH
- uhlík metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
Nitrogen fixation and assimilation processes are vital to the functioning of any ecosystem. Nevertheless, studying these processes using 15N-based stable isotope probing was so far limited because of technical challenges related to the relative rarity of nitrogen in nucleic acids and proteins compared to carbon, and because of its absence in lipids. However, the recent adoption of high-throughput sequencing and statistical modelling methods to SIP studies increased the sensitivity of the method and enabled overcoming some of the challenges. This chapter describes in detail how to perform DNA- and RNA-SIP using 15N.
- MeSH
- bakteriální RNA chemie genetika izolace a purifikace metabolismus MeSH
- bakterie fixující dusík genetika metabolismus MeSH
- centrifugace - gradient hustoty MeSH
- DNA bakterií chemie genetika izolace a purifikace metabolismus MeSH
- fixace dusíku genetika fyziologie MeSH
- izotopové značení metody MeSH
- izotopy dusíku metabolismus MeSH
- vysoce účinné nukleotidové sekvenování MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats.
A survey of the ecological variability within 52 populations of Schoenoplectus californicus (C.A. Mey.) Soják across its distributional range revealed that it is commonly found in nitrogen (N) limited areas, but rarely in phosphorus limited soils. We explored the hypothesis that S. californicus supplements its nitrogen demand by bacterial N2-fixation processes associated with its roots and rhizomes. We estimated N2-fixation of diazotrophs associated with plant rhizomes and roots from several locations throughout the species' range and conducted an experiment growing plants in zero, low, and high N additions. Nitrogenase activity in rhizomes and roots was measured using the acetylene reduction assay. The presence of diazotrophs was verified by the detection of the nifH gene. Nitrogenase activity was restricted to rhizomes and roots and it was two orders of magnitude higher in the latter plant organs (81 and 2032 nmol C2H4 g DW-1 d-1, respectively). Correspondingly, 40x more nifH gene copies were found on roots compared to rhizomes. The proportion of the nifH gene copies in total bacterial DNA was positively correlated with the nitrogenase activity. In the experiment, the contribution of fixed N to the plant N content ranged from 13.8% to 32.5% among clones from different locations. These are relatively high values for a non-cultivated plant and justify future research on the link between N-fixing bacteria and S. californicus production.
- MeSH
- bakteriální proteiny metabolismus MeSH
- distribuce rostlin MeSH
- druhová specificita MeSH
- dusík chemie metabolismus MeSH
- fixace dusíku * MeSH
- fosfor chemie metabolismus MeSH
- kořeny rostlin metabolismus MeSH
- mokřady * MeSH
- nitrogenasa metabolismus MeSH
- oddenek metabolismus mikrobiologie MeSH
- oxidoreduktasy metabolismus MeSH
- půda chemie MeSH
- rostlinné proteiny metabolismus MeSH
- šáchorovité metabolismus mikrobiologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Jižní Amerika MeSH
- Severní Amerika MeSH
The N2-fixing cyanobacterium Trichodesmium is an important player in the oceanic nitrogen and carbon cycles. Trichodesmium occurs both as single trichomes and as colonies containing hundreds of trichomes. In this review, we explore the benefits and disadvantages of colony formation, considering physical, chemical, and biological effects from nanometer to kilometer scale. Showing that all major life challenges are affected by colony formation, we claim that Trichodesmium's ecological success is tightly linked to its colonial lifestyle. Microbial interactions in the microbiome, chemical gradients within the colony, interactions with particles, and elevated mobility in the water column shape a highly dynamic microenvironment. We postulate that these dynamics are key to the resilience of Trichodesmium and other colony formers in our changing environment.
- MeSH
- fixace dusíku MeSH
- oceány a moře MeSH
- sinice * MeSH
- sociální chování MeSH
- Trichodesmium * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
- Geografické názvy
- oceány a moře MeSH
The systematics of single-celled cyanobacteria represents a major challenge due to morphological convergence and application of various taxonomic concepts. The genus Cyanothece is one of the most problematic cases, as the name has been applied to oval-shaped coccoid cyanobacteria lacking sheaths with little regard to their phylogenetic position and details of morphology and ultrastructure. Hereby we analyze an extensive set of complementary genetic and phenotypic evidence to disentangle the relationships among these cyanobacteria. We provide diagnostic characters to separate the known genera Cyanothece, Gloeothece, and Aphanothece, and provide a valid description for Crocosphaera gen. nov. We describe two new genera, Rippkaea and Zehria, to characterize two distinct phylogenetic lineages outside the previously known genera. We further describe 13 new species in total including Cyanothece svehlovae, Gloeothece aequatorialis, G. aurea, G. bryophila, G. citriformis, G. reniformis, Gloeothece tonkinensis, G. verrucosa, Crocosphaera watsonii, C. subtropica, C. chwakensis, Rippkaea orientalis, and Zehria floridana to recognize the intrageneric diversity as rendered by polyphasic analysis. We discuss the close relationship of free-living cyanobacteria from the Crocosphaera lineage to nitrogen-fixing endosymbionts of marine algae. The current study includes several experimental strains (Crocosphaera and "Cyanothece") important for the study of diazotrophy and the global oceanic nitrogen cycle, and provides evidence suggesting ancestral N2 -fixing capability in the chroococcalean lineage.
- MeSH
- Cyanothece * MeSH
- fixace dusíku MeSH
- fylogeneze MeSH
- oceány a moře MeSH
- RNA ribozomální 16S MeSH
- sinice * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- oceány a moře MeSH
Crocosphaera watsonii is a unicellular N2-fixing (diazotrophic) cyanobacterium observed in tropical and subtropical oligotrophic oceans. As a diazotroph, it can be a source of bioavailable nitrogen (N) to the microbial community in N-limited environments, and this may fuel primary production in the regions where it occurs. Crocosphaera watsonii has been the subject of intense study, both in culture and in field populations. Here, we summarize the current understanding of the phylogenetic and physiological diversity of C. watsonii, its distribution, and its ecological niche. Analysis of the relationships among the individual Crocosphaera species and related free-living and symbiotic lineages of diazotrophs based on the nifH gene have shown that the C. watsonii group holds a basal position and that its sequence is more similar to Rippkaea and Zehria than to other Crocosphaera species. This finding warrants further scrutiny to determine if the placement is related to a horizontal gene transfer event. Here, the nifH UCYN-B gene copy number from a recent synthesis effort was used as a proxy for relative C. watsonii abundance to examine patterns of C. watsonii distribution as a function of environmental factors, like iron and phosphorus concentration, and complimented with a synthesis of C. watsonii physiology. Furthermore, we have summarized the current knowledge of C. watsonii with regards to N2 fixation, photosynthesis, and quantitative modeling of physiology. Because N availability can limit primary production, C. watsonii is widely recognized for its importance to carbon and N cycling in ocean ecosystems, and we conclude this review by highlighting important topics for further research on this important species.
- MeSH
- fixace dusíku * MeSH
- fylogeneze * MeSH
- sinice * genetika metabolismus fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
Na I. chirurgické klinice VFN 1. LF UK v Praze se bariatrickou chirurgií zabýváme již od roku 1983, kdy v letech 1983-1986 byly prováděny vertikální gastroplastiky, mezi lety 1986-1993 byly prováděny neadjustabilní bandáže žaludku laparotomicky. Od roku 1993, kdy jsme jako první na světě provedli gastrickou bandáž (GB) laparoskopicky, ji provádíme standardně touto metodou. V letech 1993-1998 jsme na I. chirurgické klinice VFN 1. LF UK V Praze laparoskopicky provedli 517 GB pro morbidní obezitu, kdy body mass index (BMI) byl 34-49 kg/m2. V naší skupině bylo 449 žen a 59 mužů. Nejčastější pozdní komplikací v našem souboru morbidně obézních nemocných, kterým byla naložena laparoskopicky neadjustabilní gastrická bandáž, bylo v 5,1 % zvětšení proximálního pouche nad gastrickou bandáží roztažením (dUatací) jeho stěny nebo podklouznutím (slippage) přední stěny pod bandáží proximálně, následně s poruchou evakuace žaludku a zvracením. Pokusili jsme se snížili výskyt účinnost navržené fixace neadjustabilní gastrické bandáže manžetou, provedli jsme v letech 1998-1999 prospektivní randomizovanou studii na souboru 80 morbidně obézních nemocných, rozdělených do experimentální skupiny nl-GB+M s manžetou a do kontrolní skupiny n2-GB-M bez manžety. Sledovali jsme jednak výskyt zmíněné komplikace a jednak změnu velikosti objemu pouche nad GB za 1 rok. Z endoskopického měření velikosti pouche nad GB po operaci a za 1 rok jsme zjistili, že ve skupině nl-GB+M došlo k průměrnému zvětšení objemu pouche o 14,6 ml, to je na 124 % původní velikosti, kdežto u skupiny n2-GB-M došlo k průměrnému zvětšení objemu pouche o 33,6 ml, to je na 154,1 % původní velikosti (p < 0,001). Na základě získaných výsledků a s vědomím toho, že se jedná o soubor malých čísel, si dovolujeme vyslovit domněnku, že navržená modifikace ve smyslu fixace neadjustabilní gastrické bandáže manžetou vytvořenou z přední stěny žaludku může snížit výskyt komplikace podklouznutí (slippage) přední stěny žaludku proximálně nad bandáž.
We have been concerned with bariatric surgery at the First Surgical Clinic of th General Faculty Hospital, First Medical Faculty, Charles University Prague since 1983. In 1983-1986 vertical gastroplasties were made. between 1986 and 1993 non-adjustable gastric bands were provided by the laparotómie approach. Since 1993 when we were the first to implement a gastí-ic band operation (GB) by the laparoscopic route, this method is used as the standard method. In 1993-1998 we made at the First Surgical Clinic 517 laparoscopic GB operation on account of morbid obesity in patients with a body mass index of 34-49 kg/m2. The group comprised 449 women and 59 men. The most frequent late complication in our group of morbidly obese patients who had a laparoscopically administered GB was in 5.1 % enlargement of the proximal pouch above the GB by dilatation of its wall or slippage of the anterior wall proximally under the GB with a subsequent disorder of gastric evacuation and vomiting. We tried to reduce the incidence of this complication by fixing the GB by a cuff made from the anterior gastric wall. To test the effectiveness of the suggested fixation of the non-adjustable GB by a cuff we implemented in 1998-1999 a prospective randomized study in a group of 80 morbidly obese patients divided into experimental group nl-GB+C with the cuff and a control eroun n2-GB-C without a cuff. We investigated the incidence of the mentioned complication and the changed volume of the pouch above the GB after one year. Endoscopic assessment of the size of the pouch above the GB after surgery and after one year revealed that in group nl-GB+C the mean increase of the pouch volume was 14.6 ml, i.e. 124 % of the original size, while in group n2-GB-C the mean increase of the volume was 33.6 ml, i.e. 154.1 % of the original size (p < 0.001). Based on the assembled results and aware of the fact that small groups were involved, we should like to express the assumption that the suggested modification, i.e. fixation of a non-adjustable GB by a cuff made from the anterior gastric wall can reduce the incidence of the complication of slippage of the anterior gastric wall proximally above the bandage.
