Biological nitrogen fixation is an energy-intensive process that contributes significantly toward supporting life on this planet. Among nitrogen-fixing organisms, cyanobacteria remain unrivaled in their ability to fuel the energetically expensive nitrogenase reaction with photosynthetically harnessed solar energy. In heterocystous cyanobacteria, light-driven, photosystem I (PSI)-mediated ATP synthesis plays a key role in propelling the nitrogenase reaction. Efficient light transfer to the photosystems relies on phycobilisomes (PBS), the major antenna protein complexes. PBS undergo degradation as a natural response to nitrogen starvation. Upon nitrogen availability, these proteins are resynthesized back to normal levels in vegetative cells, but their occurrence and function in heterocysts remain inconclusive. Anabaena 33047 is a heterocystous cyanobacterium that thrives under high light, harbors larger amounts of PBS in its heterocysts, and fixes nitrogen at higher rates compared to other heterocystous cyanobacteria. To assess the relationship between PBS in heterocysts and nitrogenase function, we engineered a strain that retains large amounts of the antenna proteins in its heterocysts. Intriguingly, under high light intensities, the engineered strain exhibited unusually high rates of nitrogenase activity compared to the wild type. Spectroscopic analysis revealed altered PSI kinetics in the mutant with increased cyclic electron flow around PSI, a route that contributes to ATP generation and nitrogenase activity in heterocysts. Retaining higher levels of PBS in heterocysts appears to be an effective strategy to enhance nitrogenase function in cyanobacteria that are equipped with the machinery to operate under high light intensities. IMPORTANCE The function of phycobilisomes, the large antenna protein complexes in heterocysts has long been debated. This study provides direct evidence of the involvement of these proteins in supporting nitrogenase activity in Anabaena 33047, a heterocystous cyanobacterium that has an affinity for high light intensities. This strain was previously known to be recalcitrant to genetic manipulation and, hence, despite its many appealing traits, remained largely unexplored. We developed a genetic modification system for this strain and generated a ΔnblA mutant that exhibited resistance to phycobilisome degradation upon nitrogen starvation. Physiological characterization of the strain indicated that PBS degradation is not essential for acclimation to nitrogen deficiency and retention of PBS is advantageous for nitrogenase function.
- Klíčová slova
- Cyanobacterium, cyclic electron flow, heterocyst, nitrogenase, photosystem I, phycobilisome,
- MeSH
- Anabaena chemie enzymologie genetika účinky záření MeSH
- bakteriální proteiny chemie genetika metabolismus MeSH
- fotosystém I - proteinový komplex chemie genetika metabolismus MeSH
- fykobilizomy chemie genetika metabolismus účinky záření MeSH
- kinetika MeSH
- nitrogenasa chemie genetika metabolismus MeSH
- regulace genové exprese u bakterií MeSH
- světlo MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Názvy látek
- bakteriální proteiny MeSH
- fotosystém I - proteinový komplex MeSH
- fykobilizomy MeSH
- nitrogenasa MeSH
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
- Názvy látek
- bakteriální proteiny MeSH
- dusík MeSH
- fosfor MeSH
- nitrogenasa MeSH
- nitrogenase reductase MeSH Prohlížeč
- oxidoreduktasy MeSH
- půda MeSH
- rostlinné proteiny 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.
- MeSH
- DNA bakterií genetika MeSH
- fixace dusíku fyziologie MeSH
- fylogeneze MeSH
- nitrogenasa metabolismus MeSH
- řeky MeSH
- RNA ribozomální 16S genetika MeSH
- sinice genetika izolace a purifikace fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- DNA bakterií MeSH
- nitrogenasa MeSH
- RNA ribozomální 16S MeSH
The well-developed biological soil crusts cover up to 40% of the soil surface in the alpine and subnival zones of the Tibetan Plateau, accounting for a vast area of Asia. We investigated the diversity and biomass of the phototrophic part (Cyanobacteria) of the microbial community inhabiting biological soil crusts and uncrusted soils in their surroundings on the elevation gradient of 5200-5900 m a.s.l. The influence of soil physico-chemical properties on phototrophs was studied. The ability of high-altitude phototrophs to fix molecular nitrogen was also determined under laboratory conditions. The biological soil crust phototroph community did not differ from that living in uncrusted soil in terms of the species composition, but the biomass is three-to-five times higher. An increasing trend in the cyanobacterial biomass from the biological soil crusts with elevation was observed, with the genera Nostoc spp., Microcoleus vaginatus and Phormidium spp. contributing to this increase. Based on the laboratory experiments, the highest nitrogenase activity was recorded in the middle elevations, and the rate of nitrogen fixation was not correlated with the cyanobacterial biomass.
- MeSH
- biodiverzita MeSH
- biomasa MeSH
- dusík metabolismus MeSH
- ekosystém * MeSH
- fixace dusíku MeSH
- nadmořská výška MeSH
- nitrogenasa metabolismus MeSH
- půda chemie MeSH
- půdní mikrobiologie * MeSH
- sinice klasifikace enzymologie fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- dusík MeSH
- nitrogenasa MeSH
- půda MeSH
The effect of UV-C radiation on thylakoid arrangement, chlorophyll-a and carotenoid content and nitrogenase activity of the cyanobacterium Microchaete sp. was studied. Chlorophyll-a and carotenoid content increased gradually up to 48 h of UV-C exposure but declined with longer exposures. Nitrogenase activity decreased moderately with 6 to 12 h exposure and decreased substantially afterwards. When cells exposed to UV-C for 12 to 24 h, grown under fluorescent light for 144 h, nitrogenase activity increased to levels greater than in the control cells. The exposure of UV-C treated cells to fluorescent light, however, did not result in recovery of pigment content. In Microchaete sp. cells treated with UV-C for 144 h, thylakoid membranes became dense, were aggregated into bundles, and were surrounded by spaces devoid of cytoplasm.
- MeSH
- biologické pigmenty metabolismus MeSH
- nitrogenasa metabolismus MeSH
- sinice enzymologie metabolismus účinky záření MeSH
- transmisní elektronová mikroskopie MeSH
- tylakoidy metabolismus MeSH
- ultrafialové záření * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- biologické pigmenty MeSH
- nitrogenasa MeSH
The potential for N(2) fixation by heterocystous cyanobacteria isolated from soils of different geographical areas was determined as nitrogenase activity (NA) using the acetylene reduction assay. Morphology of cyanobacteria had the largest influence on NA determined under light conditions. NA was generally higher in species lacking thick slime sheaths. The highest value (1446 nmol/h C(2)H(4) per g fresh biomass) was found in the strain of branched cyanobacterium Hassalia (A Has1) from the polar region. A quadratic relationship between NA and biomass was detected in the Tolypothrix group under light conditions. The decline of NA in dark relative to light conditions ranged from 37 to 100 % and differed among strains from distinct geographical areas. Unlike the NA of temperate and tropical strains, whose decline in dark relative to light was 24 and 17 %, respectively, the NA of polar strains declined to 1 % in the dark. This difference was explained by adaptation to different light conditions in temperate, tropical, and polar habitats. NA was not related to the frequency of heterocysts in strains of the colony-forming cyanobacterium Nostoc. Colony morphology and life cycle are therefore more important for NA then heterocyst frequency. NA values probably reflect the environmental conditions where the cyanobacterium was isolated and the physiological and morphological state of the strain.
- MeSH
- acetylen metabolismus MeSH
- fixace dusíku * MeSH
- nitrogenasa metabolismus MeSH
- půdní mikrobiologie * MeSH
- sinice klasifikace enzymologie fyziologie MeSH
- studené klima MeSH
- světlo * MeSH
- tma MeSH
- tropické klima MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- acetylen MeSH
- nitrogenasa MeSH
* As iron (Fe) deficiency is a main limiting factor of ocean productivity, its effects were investigated on interactions between photosynthesis and nitrogen fixation in the marine nonheterocystous diazotrophic cyanobacterium Trichodesmium IMS101. * Biophysical methods such as fluorescence kinetic microscopy, fast repetition rate (FRR) fluorimetry, and in vivo and in vitro spectroscopy of pigment composition were used, and nitrogenase activity and the abundance of key proteins were measured. * Fe limitation caused a fast down-regulation of nitrogenase activity and protein levels. By contrast, the abundance of Fe-requiring photosystem I (PSI) components remained constant. Total levels of phycobiliproteins remained unchanged according to single-cell in vivo spectra. However, the regular 16-kDa phycoerythrin band decreased and finally disappeared 16-20 d after initiation of Fe limitation, concomitant with the accumulation of a 20-kDa protein cross-reacting with the phycoerythrin antibody. Concurrently, nitrogenase expression and activity increased. Fe limitation dampened the daily cycle of photosystem II (PSII) activity characteristic of diazotrophic Trichodesmium cells. Further, it increased the number and prolonged the time period of occurrence of cells with elevated basic fluorescence (F(0)). Additionally, it increased the effective cross-section of PSII, probably as a result of enhanced coupling of phycobilisomes to PSII, and led to up-regulation of the Fe stress protein IsiA. * Trichodesmium survives short-term Fe limitation by selectively down-regulating nitrogen fixation while maintaining but re-arranging the photosynthetic apparatus.
- MeSH
- chlorofyl metabolismus MeSH
- down regulace MeSH
- fixace dusíku * MeSH
- fluorescenční mikroskopie MeSH
- fotosyntéza * MeSH
- fotosystém I - proteinový komplex metabolismus MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- fykobiliproteiny metabolismus MeSH
- fykoerythrin metabolismus MeSH
- karotenoidy metabolismus MeSH
- kinetika MeSH
- kultivační média MeSH
- nitrogenasa genetika metabolismus MeSH
- proliferace buněk MeSH
- sinice cytologie metabolismus MeSH
- western blotting MeSH
- železo metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- chlorofyl MeSH
- fotosystém I - proteinový komplex MeSH
- fotosystém II - proteinový komplex MeSH
- fykobiliproteiny MeSH
- fykoerythrin MeSH
- karotenoidy MeSH
- kultivační média MeSH
- nitrogenasa MeSH
- železo MeSH
Frequency of heterocytes and nitrogenase activity (NA) under light and dark cultivation conditions was determined in 12 cyanobacterial strains isolated from various soil habitats. In spite of a high variability, significant differences in NA among the strains were found in response of light and dark cultivation. Relatively high NA (9.9-15.3 micromol/h C2H4 per g fresh mass) under light conditions and basal NA after 12 h of dark cultivation were detected in Anabaena, Nodularia, Tolypothrix, and 1 of Cylindrospermum strains. On the other hand, significantly lower NA (0.76-5.4 micromol/h C2H4 per g fresh mass) was found under light conditions in Trichormus, Nostoc and another Cylindrospermum strain; the activity completely disappeared after 12 h of dark cultivation. NA values were not directly related to the frequency of the heterocytes. The total NA of cyanobacterial colony was found to be probably independent of the number and/or position of heterocytes. Remarkable differences in NA between strains isolated from cultivated fields and strains originating from natural or non-cultivated soils were found.
- MeSH
- nitrogenasa metabolismus MeSH
- půdní mikrobiologie * MeSH
- sinice enzymologie MeSH
- světlo MeSH
- tma MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
- Názvy látek
- nitrogenasa MeSH
An effect of various physico-chemical parameters on nitrogenase-catalyzed oxygen-free hydrogen production by Nostoc muscorum was demonstrated. More hydrogen was produced in the light than in the dark. Optimum temperature was 40 degrees C Various sugars increased hydrogen production whereas on easily metabolized nitrogen sources it was inhibited. The production was sensitive to salinity and Fe3+, Cu2+, Zn2+ and Ni2+ ions. Ultrastructural study revealed many electron-dense layers outside the cell-wall area that have not been observed earlier.
- MeSH
- dusík metabolismus MeSH
- elektronová mikroskopie MeSH
- kultivační média MeSH
- nitrogenasa metabolismus MeSH
- peroxid vodíku metabolismus MeSH
- sinice růst a vývoj metabolismus ultrastruktura MeSH
- světlo MeSH
- teplota MeSH
- uhlík metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- dusík MeSH
- kultivační média MeSH
- nitrogenasa MeSH
- peroxid vodíku MeSH
- uhlík MeSH
Selected flavonoids that are known as inducers and a suppressor of nodulation (nod) genes of the symbiotic bacterium Rhizobium leguminosarum bv. viciae were tested for their effect on symbiosis formation with garden pea as the host. A solid substrate was omitted from the hydroponic growing system in order to prevent losses of flavonoids due to adsorption and degradation. The presumed interaction of the tested flavonoids with nod genes has been verified for the genetic background of strain 128C30. A stimulatory effect of a nod gene inducer naringenin on symbiotic nodule number formed per plant 14 d after inoculation was detected at concentrations of 0.1 and 1 micro g ml(-1) nutrient solution. At 10 micro g ml(-1), the highest concentration tested, naringenin was already inhibitory. By contrast, nodulation was negatively affected by a nod gene suppressor, quercetin, at concentrations above 1 micro g ml(-1), as well as by another tested nod gene inducer, hesperetin. The deleterious effect of hesperetin might be due to its toxicity or to the toxicity of its degradation product(s) as indicated by the inhibition of root growth. Both the stimulatory effect of naringenin and the inhibitory effect of quercetin on nodule number were more pronounced at earlier stages of nodule development as revealed with specific staining of initial nodules. The lessening of the flavonoid impact during nodule development was ascribed to the plant autoregulatory mechanisms. Feedback regulation of nodule metabolism might also be responsible for the fact that the naringenin-conditioned increase in nodule number was not accompanied by any increase in nitrogenase activity. By contrast, the inhibitory action of quercetin and hesperetin on nodule number was associated with decreases in total nitrogenase activity. Naringenin also stimulated root hair curling (RHC) as one of the earliest nodulation responses at concentrations of 1 and 10 microg ml(-1), however, the same effect was exerted by the nod gene suppressor, quercetin, suggesting that feedback regulatory mechanisms control RHC in the range of nodulation-inhibiting high flavonoid concentrations. The comparison of the effect of the tested flavonoids in planta with nod gene activity response showed a two orders of magnitude shift to higher concentrations. This shift is explained by the absorption and degradation of flavonoids by both the symbionts during 3 d intervals between hydroponic solution changes. The losses were 99, 96.4, and 90% of the initial concentration of 10 micro g ml(-1) for naringenin, hesperetin, and quercetin, respectively.
- MeSH
- beta-galaktosidasa metabolismus MeSH
- flavanony * MeSH
- flavonoidy chemie farmakologie MeSH
- hesperidin chemie farmakologie MeSH
- hrách setý účinky léků růst a vývoj mikrobiologie MeSH
- hydroponie MeSH
- kořeny rostlin účinky léků růst a vývoj mikrobiologie MeSH
- nitrogenasa metabolismus MeSH
- quercetin chemie farmakologie MeSH
- Rhizobium leguminosarum účinky léků genetika růst a vývoj MeSH
- symbióza účinky léků MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- beta-galaktosidasa MeSH
- flavanony * MeSH
- flavonoidy MeSH
- hesperetin MeSH Prohlížeč
- hesperidin MeSH
- naringenin MeSH Prohlížeč
- nitrogenasa MeSH
- quercetin MeSH
