DOCSLIB.ORG

Resource Limitation Affects Productivity and Heterocyst Formation in Nitrogen-Fixing Cyanobacteria

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Resource Limitation Affects Productivity and Heterocyst Formation in Nitrogen-Fixing Cyanobacteria Resource limitation affects productivity and heterocyst formation in nitrogen-fixing cyanobacteria Hansen Johnson Semester in Environmental Science, Marine Biological Laboratory, Woods Hole, MA Bates College, Lewiston, ME Mentors: Ed Rastetter and Zoe Cardon December 2011 Keywords: Resource optimization, substitutable resource, cyanobacteria, heterocyst, Anabaena, Abstract Cyanobacteria, of the species Anabaena circinalis, were used as model organisms to test several ideas pertaining to the concept of substitutable resource optimization. These cyanobacteria can acquire nitrogen through fixation or assimilation of nitrate. Fixation requires the presence of heterocysts, which are specialized cells that are energetically expensive to make, while assimilation is only possible when nitrate is available in sufficient concentrations. The primary goals of this study were to compare Anabaena growth and heterocyst development over a nitrogen and phosphorus gradient as well as determine if substitutable resource acquisition strategies can differentially affect the environment. A regression design was used to establish growth solutions with a nitrogen gradient from 0.3 to 300.3 mg/L nitrate and a phosphorus gradient from 0.035 to 70 mg/L phosphate. Samples were incubated for 14 days before being analyzed for chlorophyll a concentration, dry biomass, heterocyst density, filament length, 13-C and 15-N isotope fractionation, pH, and alkalinity. The phosphorus gradient had no significant effect on any treatment. Chlorophyll a concentration, filament length, and pH all agreed that optimal growth occurred at 30 mg/L nitrate. Heterocyst density showed that heterocysts only formed below 10 mg/L nitrate, and this concentration indicated the point at which the Anabaena switched between fixing nitrogen and assimilating nitrate. These two processes had differential effects on the environment as nitrate assimilation generated alkalinity while nitrogen fixation did not. Because nitrate assimilation generated alkalinity, the total pool of dissolved inorganic carbon actually increased as available nitrogen increased. Introduction Plants have evolved impressive strategies of compensating for conditions across the globe in which the relative availability of essential resources often vary by more than two orders of magnitude (Chapin et al 1987). The plants, and other organisms, that are confronted with this variation survive by allocating their effort to acquire the resources necessary to maximize growth and production in a process called resource optimization. This concept has developed over the last thirty years and has been substantiated by both field and modeled observations and experimentation (Rastetter et al 2001). Further study has revealed that organisms often have two or more strategies that can be substituted for one another to fulfill the same resource requirement. Strategic allocation of resources of this kind is more specifically referred to as substitutable resource optimization (Tilman 1982; Rastetter forthcoming). Nitrogen-fixing cyanobacteria, often referred to as perfect producers for their unique ability to both fix nitrogen and perform oxygenic photosynthesis, consistently choose among three sources of nitrogen; they can either fix nitrogen gas from the atmosphere or acquire nitrate or ammonium in their environment (Kumar et al 2010). Cyanobacteria have specialized cells called heterocysts that enable nitrogen fixation. These thick-walled, anoxic cells have the ability to form and break down depending on environmental conditions (Mariscal and Flores 2010). Depending on availability, some species of cyanobacteria can also either take up carbon dioxide or bicarbonate as substitutable sources of carbon (Gundersen and Mountain 1973). The pathways that cyanobacteria choose to acquire these substitutable nutrients affects both the organism and its environment. 2 One would intuitively believe that cyanobacteria’s ability to obtain the same resource through multiple pathways would allow it to dominate many systems (Vitousek and Howarth 1991). Dierber and Scheinkman (1987) found nitrogen fixation by cyanobacteria often does play an important role in nitrogen cycling, providing close to half of all nitrogen inputs to a freshwater lake in Florida. Cyanobacteria also receive a lot of publicity for the dense and often destructive blooms that occur periodically under the right circumstances. Blooms can form thick mats that consume oxygen, block light, and even emit strong neurotoxins in addition to other effects on the environment (Smith 1990; Lehtimaki et al 1997; Paerl et al 2001). Despite the adaptability and periodic dominance of cyanobacteria, a blue-green carpet does not cover our world’s oceans. Each resource acquisition pathway has certain tradeoffs associated with it (Rastetter forthcoming; Rastetter et al 2001). For example, the formation and maintenance of heterocysts and their component parts makes nitrogen fixation an energetically costly process (Kumar et al 2010). However, this process theoretically becomes beneficial when nitrate and ammonia are so rare that the organism will save energy by fixing its own nitrogen rather than exploit the small amount of nitrogen available from its surroundings (Vitousek et al 2002; Rastetter et al 2001). Heterocysts demand energy that the organism would have otherwise dedicated to growth or reproduction. As a consequence of this redistribution of resources, changes in the productivity of cyanobacteria with and without heterocysts should indicate the relative cost of nitrogen fixation. I designed an experiment to test this concept of substitutable resource optimization in the nitrogen-fixing cyanobacteria Anabaena. My primary goal was to understand how biomass and productivity changed over a nutrient gradient and connect any variation in biomass back to tradeoffs associated with heterocyst formation. Aldea et al (2008) pointed out that heterocysts depend heavily on their neighboring cells for carbon and provide nitrogen in return. This is not unlike the symbiosis between nitrogen fixing Rhizobium and legumes in which the energetic demands of the bacteria actually restrict the growth of the plant (Ryle et al 1979). My hypothesis was that the presence of heterocysts would cause a significant reduction in productivity because of the added costs associated with nitrogen fixation. I wanted to better understand what nutrient concentrations trigger heterocyst formation as well as the nature of the transition from possessing heterocysts to lacking them and vice versa. Ogawa and Carr (1969) found that Anabaena exposed to nitrate, ammonium, and atmospheric nitrogen formed heterocysts with different densities. They did not, however, monitor heterocyst density over a concentration gradient. Mickelson et al (1966) monitored heterocyst density over a nitrogen gradient but did not carry out the experiment until heterocysts disappeared completely. I expanded on their work by creating a large enough gradient to capture the transition to and away from the presence of heterocysts. I believed that the cost of nitrogen fixation would cause the transition to take place rapidly and at a fairly low nitrogen concentration. My third and final goal was to investigate how the resource acquisition strategies implemented by the cyanobacteria would alter their environment. I did not entirely know what to expect, as this aspect of cyanobacterial life is poorly documented. Brewer and Goldman (1976) demonstrated that nitrate assimilation by phytoplankton has the capacity to increase alkalinity while nitrogen fixation does not. Gundersen and Mountain (1973) also mentioned that bicarbonate uptake by nitrifying bacteria can have a slight but significant effect on alkalinity. Many more environmental effects result from the formation of dense blooms but these are more difficult to recreate and study in culture (Pearl et al 2001). I hoped that this study would increase 3 our understanding of substitutable resource optimization in cyanobacteria and how different resource acquisition strategies alter the organism and its environment. Methods Preparing liquid culture Anabaena circinalis in liquid culture was supplied by the Connecticut Valley Biological Supply Company (model L 111LS). The cyanobacteria were sterilely transferred to four 250 mL flasks containing sterile BG11 growth solution (Stanier et al 1971) and bubbled in a growth chamber (Conviron Model No. PGW36DE) for ten days. All sterile work was done in a laminar flow hood (Labconco Model No. 3612504). All the cultures were exposed to between 27+/-5 uE of light for 16 hours per day at a temperature of 25° C. Carbon dioxide levels were slightly elevated in the chamber and fairly constant at 495 ppm. After the ten day period I chose the flask with the least contamination, determined visually and by microscope, and used it to inoculate liquid cultures that varied in the relative availability of nitrogen and phosphorus. I used a regression design to achieve the desired gradients of nitrogen and phosphorus (Table 1). I made a large batch of BG11 without adding any nitrogen, in the form of NaNO3, or phosphorus, in the form of K2HPO4. I divided this batch into 12 one litre bottles, each containing 800 mL of solution. To half of the bottles I added NaNO3 to yield approximate concentrations of 0, 6, 30, 60, 300 and 600 mg/L nitrogen from nitrate (designated as N1 through N6). A small amount of ammonium, present in ferric ammonium citrate, contributed around 0.3 mg/L of nitrogen to every
Load more

Recommended publications
  • Periodic and Coordinated Gene Expression Between a Diazotroph and Its Diatom Host
    The ISME Journal (2019) 13:118–131 https://doi.org/10.1038/s41396-018-0262-2 ARTICLE Periodic and coordinated gene expression between a diazotroph and its diatom host 1 1,2 1 3 4 Matthew J. Harke ● Kyle R. Frischkorn ● Sheean T. Haley ● Frank O. Aylward ● Jonathan P. Zehr ● Sonya T. Dyhrman1,2 Received: 11 April 2018 / Revised: 28 June 2018 / Accepted: 28 July 2018 / Published online: 16 August 2018 © International Society for Microbial Ecology 2018 Abstract In the surface ocean, light fuels photosynthetic carbon fixation of phytoplankton, playing a critical role in ecosystem processes including carbon export to the deep sea. In oligotrophic oceans, diatom–diazotroph associations (DDAs) play a keystone role in ecosystem function because diazotrophs can provide otherwise scarce biologically available nitrogen to the diatom host, fueling growth and subsequent carbon sequestration. Despite their importance, relatively little is known about the nature of these associations in situ. Here we used metatranscriptomic sequencing of surface samples from the North Pacific Subtropical Gyre (NPSG) to reconstruct patterns of gene expression for the diazotrophic symbiont Richelia and we – 1234567890();,: 1234567890();,: examined how these patterns were integrated with those of the diatom host over day night transitions. Richelia exhibited significant diel signals for genes related to photosynthesis, N2 fixation, and resource acquisition, among other processes. N2 fixation genes were significantly co-expressed with host nitrogen uptake and metabolism, as well as potential genes involved in carbon transport, which may underpin the exchange of nitrogen and carbon within this association. Patterns of expression suggested cell division was integrated between the host and symbiont across the diel cycle.
    [Show full text]
  • Characterization of a Gene Controlling Heterocyst Differentiation in the Cyanobacterium Anabaena 7120
    Downloaded from genesdev.cshlp.org on September 25, 2021 - Published by Cold Spring Harbor Laboratory Press Characterization of a gene controlling heterocyst differentiation in the cyanobacterium Anabaena 7120 William J. Buikema and Robert Haselkorn Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637 USA Anabaena 7120 mutant 216 fails to differentiate heterocysts. We previously identified a 2.4-kb wild-type DNA fragment able to complement this mutant. We show here that the sequence of this fragment contains a single open reading frame [hetR), encoding a 299-amino-acid protein. Conjugation of deletion subclones of this fragment into strain 216 showed that the /ieti?-coding region is both necessary and sufficient for complementation of the Het~ phenotype. The mutation in 216 is located at nucleotide 535 in the betR gene, converting a serine at position 179 in the wild-type protein to an asparagine in the mutant. Interruption of the hetR gene in wild-type cells results in a mutant phenotype identical to that of 216. Both 216 and wild-type cells containing wild-type hetR on a plasmid display increased frequency of heterocysts, even on media containing fixed nitrogen. These results suggest that hetR encodes a product that is not only essential for but also controls heterocyst development. This putative regulatory protein lacks known structural motifs characteristic of transcription factors and probably acts at a level one or more steps removed from its target genes. [Key Words: Cyanobacteria; heterocyst; nitrogen fixation; Anabaena 7120; regulation; development] Received December 7, 1990; accepted December 28, 1990. Cyanobacteria are a diverse family of prokaryotes that Wolk 1973; Haselkorn 1978; Stewart 1980; Wolk 1982; carry out oxygenic photosynthesis similar to green Carr 1983; Bohme and Haselkorn 1988).
    [Show full text]
  • Cyanobacterial Heterocysts
    Downloaded from http://cshperspectives.cshlp.org/ on September 25, 2021 - Published by Cold Spring Harbor Laboratory Press Cyanobacterial Heterocysts Krithika Kumar2, Rodrigo A. Mella-Herrera1,2, and James W. Golden1 1Division of Biological Sciences, University of California-San Diego, La Jolla, California 92093 2Department of Biology, Texas A&M University, College Station, Texas 77843 Correspondence: [email protected] Many multicellular cyanobacteria produce specialized nitrogen-fixing heterocysts. During diazotrophic growth of the model organism Anabaena (Nostoc) sp. strain PCC 7120, a regulated developmental pattern of single heterocysts separated by about 10 to 20 photosyn- thetic vegetative cells is maintained along filaments. Heterocyst structure and metabolic activity function together to accommodate the oxygen-sensitive process of nitrogen fixation. This article focuses on recent research on heterocyst development, including morphogen- esis, transport of molecules between cells in a filament, differential gene expression, and pattern formation. rganisms composed of multiple differenti- Filaments are composed of only two cell types Oated cell types can possess structures, func- and these are arrayed in a one-dimensional tions, and behaviors that are more diverse and pattern similar to beads on a string (Figs. 1 efficient than those of unicellular organisms. and 2). Among multicellular prokaryotes, heterocyst- Many cyanobacterial species are capable of forming cyanobacteria offer an excellent model nitrogen fixation. However, oxygenic
    [Show full text]
  • Understanding the Physiology of Heterocyst and Nitrogen Fixation in Cyanobacteria Or Blue-Green Algae
    Nature and Science, 6(1), 2008, ISSN: 1545-0740, [email protected] Understanding the Physiology of Heterocyst and Nitrogen Fixation in Cyanobacteria or Blue-Green Algae. Dr. Pankaj Sah* *Department of Botany, Kumaun University, Nainital–263002 (Uttarakhand State), India. Email: [email protected] Abstract: Ever since the man started thinking about his origin and evolution, he has sought answer on scientific facts and findings. In nature there are certain tiny microscopic blue-green algae or Cyanobacteria that have immense importance from many aspects ranging primarily from Nitrogen Fixation to the most coveted query – the origin of animal life on this planet. This paper is a peer review into the various physiological aspects of the nitrogen fixation and simultaneous Oxygen evolving mechanisms of blue- green algae. This paper makes the understanding of cyanobacterial nitrogen fixation in the Heterocyst easy, and also links the evolution of free Oxygen (g) from the splitting of water by its vegetative cells and ultimately, the role of Cyanobacteria in altering the primitive earth’s reducing atmosphere into present day oxygenating and thus making animal life possible on earth. [Nature and Science. 2008;6(1):28-33]. ISSN: 1545-0740. Key Words: Cyanobacteria; Blue-Green Algae; Heterocyst; Nitrogen Fixation. Introduction: The blue-green algae or Cyanobacteria are the most primitive form of algae under plant kingdom. These are basically a type of autotrophic bacteria, which are prokaryotic in their cellular structure. These are called as blue-green algae because they contain the photosynthetic pigments- c phycocyanin (dominant pigment), c phycoerythryin, and chlorophyll a, which are responsible for their characteristic blue-green colour.
    [Show full text]
  • Regulatory Rnas in Photosynthetic Cyanobacteria Matthias Kopf and Wolfgang R
    FEMS Microbiology Reviews, fuv017, 39, 2015, 301–315 doi: 10.1093/femsre/fuv017 Review Article REVIEW ARTICLE Regulatory RNAs in photosynthetic cyanobacteria Matthias Kopf and Wolfgang R. Hess∗ Faculty of Biology, Institute of Biology III, University of Freiburg, D-79104 Freiburg, Germany ∗ Corresponding author: Faculty of Biology, Institute of Biology III, University of Freiburg, Schanzlestr.¨ 1, D-79104 Freiburg, Germany. Tel: +49-761-203-2796; Fax: +49-761-203-2745; E-mail: [email protected] One sentence summary: Hundreds of potentially regulatory small RNAs (sRNAs) have been identified in model cyanobacteria and, despite recent significant progress, their functional characterization is substantial work and continues to provide surprising insights of general interest. Editor: Emmanuelle Charpentier ABSTRACT Regulatory RNAs play versatile roles in bacteria in the coordination of gene expression during various physiological processes, especially during stress adaptation. Photosynthetic bacteria use sunlight as their major energy source. Therefore, they are particularly vulnerable to the damaging effects of excess light or UV irradiation. In addition, like all bacteria, photosynthetic bacteria must adapt to limiting nutrient concentrations and abiotic and biotic stress factors. Transcriptome analyses have identified hundreds of potential regulatory small RNAs (sRNAs) in model cyanobacteria such as Synechocystis sp. PCC 6803 or Anabaena sp. PCC 7120, and in environmentally relevant genera such as Trichodesmium, Synechococcus and Prochlorococcus. Some sRNAs have been shown to actually contain μORFs and encode short proteins. Examples include the 40-amino-acid product of the sml0013 gene, which encodes the NdhP subunit of the NDH1 complex. In contrast, the functional characterization of the non-coding sRNA PsrR1 revealed that the 131 nt long sRNA controls photosynthetic functions by targeting multiple mRNAs, providing a paradigm for sRNA functions in photosynthetic bacteria.
    [Show full text]
  • Isolation, Growth, and Nitrogen Fixation Rates of the Hemiaulus-Richelia (Diatom-Cyanobacterium) Symbiosis in Culture
    Isolation, growth, and nitrogen fixation rates of the Hemiaulus-Richelia (diatom-cyanobacterium) symbiosis in culture Amy E. Pyle1, Allison M. Johnson2 and Tracy A. Villareal1 1 Department of Marine Science and Marine Science Institute, The University of Texas at Austin, Port Aransas, TX, USA 2 St. Olaf College, Northfield, MN, USA ABSTRACT Nitrogen fixers (diazotrophs) are often an important nitrogen source to phytoplankton nutrient budgets in N-limited marine environments. Diazotrophic symbioses between cyanobacteria and diatoms can dominate nitrogen-fixation regionally, particularly in major river plumes and in open ocean mesoscale blooms. This study reports the successful isolation and growth in monocultures of multiple strains of a diatom-cyanobacteria symbiosis from the Gulf of Mexico using a modified artificial seawater medium. We document the influence of light and nutrients on nitrogen fixation and growth rates of the host diatom Hemiaulus hauckii Grunow together with its diazotrophic endosymbiont Richelia intracellularis Schmidt, as well as less complete results on the Hemiaulus membranaceus- R. intracellularis symbiosis. The symbioses rates reported here are for the joint diatom-cyanobacteria unit. Symbiont diazotrophy was sufficient to support both the host diatom and cyanobacteria symbionts, and the entire symbiosis replicated and grew without added nitrogen. Maximum growth rates of multiple strains of H. hauckii symbioses in N-free medium with N2 as the sole N source were − 0.74–0.93 div d 1. Growth rates followed light saturation kinetics in H. hauckii – −2 −1 Submitted 28 April 2020 symbioses with a growth compensation light intensity (EC)of7 16 µmol m s and − − Accepted 16 September 2020 saturation light level (E )of84–110 µmol m 2s 1.
    [Show full text]
  • Cyanobacterial Genome Evolution Subsequent to Domestication by a Plant (Azolla)
    Cyanobacterial genome evolution subsequent to domestication by a plant ( A z o l l a ) John Larsson Cyanobacterial genome evolution subsequent to domestication by a plant (Azolla) John Larsson ©John Larsson, Stockholm 2011 ISBN 978-91-7447-313-1 Printed in Sweden by Universitetsservice, US-AB, Stockholm 2011 Distributor: Department of Botany, Stockholm University To Emma, my family, and all my friends. Abstract Cyanobacteria are an ancient and globally distributed group of photosynthetic prokaryotes including species capable of fixing atmospheric dinitrogen (N2) into biologically available ammonia via the enzyme complex nitrogenase. The ability to form symbiotic interactions with eukaryotic hosts is a notable feature of cyanobacteria and one which, via an ancient endosymbiotic event, led to the evolution of chloroplasts and eventually to the plant dominated biosphere of the globe. Some cyanobacteria are still symbiotically competent and form symbiotic associations with eukaryotes ranging from unicellular organisms to complex plants. Among contemporary plant-cyanobacteria associations, the symbiosis formed between the small fast-growing aquatic fern Azolla and its cyanobacterial symbiont (cyanobiont), harboured in specialized cavities in each Azolla leaf, is the only one which is perpetual and in which the cyanobiont has lost its free-living capacity, suggesting a long-lasting co- evolution between the two partners. In this study, the genome of the cyanobiont in Azolla filiculoides was sequenced to completion and analysed. The results revealed that the genome is in an eroding state, evidenced by a high proportion of pseudogenes and transposable elements. Loss of function was most predominant in genetic categories related to uptake and metabolism of nutrients, response to environmental stimuli and in the DNA maintenance machinery.
    [Show full text]
  • The Nitrogen Stress-Repressed Srna Nsrr1 Regulates Expression of All1871, a Gene Required for Diazotrophic Growth in Nostoc Sp
    life Article The Nitrogen Stress-Repressed sRNA NsrR1 Regulates Expression of all1871, a Gene Required for Diazotrophic Growth in Nostoc sp. PCC 7120 Isidro Álvarez-Escribano, Manuel Brenes-Álvarez , Elvira Olmedo-Verd, Agustín Vioque and Alicia M. Muro-Pastor * Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, 41092 Sevilla, Spain; [email protected] (I.Á.-E.); [email protected] (M.B.-Á.); [email protected] (E.O.-V.); [email protected] (A.V.) * Correspondence: [email protected]; Tel.: +34-954489521 Received: 25 March 2020; Accepted: 27 April 2020; Published: 29 April 2020 Abstract: Small regulatory RNAs (sRNAs) are post-transcriptional regulators of bacterial gene expression. In cyanobacteria, the responses to nitrogen availability, that are mostly controlled at the transcriptional level by NtcA, involve also at least two small RNAs, namely NsiR4 (nitrogen stress-induced RNA 4) and NsrR1 (nitrogen stress-repressed RNA 1). Prediction of possible mRNA targets regulated by NsrR1 in Nostoc sp. PCC 7120 allowed, in addition to previously described nblA, the identification of all1871, a nitrogen-regulated gene encoding a protein of unknown function that we describe here as required for growth at the expense of atmospheric nitrogen (N2). We show that transcription of all1871 is induced upon nitrogen step-down independently of NtcA. All1871 accumulation is repressed by NsrR1 and its expression is stronger in heterocysts, specialized cells devoted to N2 fixation. We demonstrate specific interaction between NsrR1 and the 50 untranslated region (UTR) of the all1871 mRNA, that leads to decreased expression of all1871. Because transcription of NsrR1 is partially repressed by NtcA, post-transcriptional regulation by NsrR1 would constitute an indirect way of NtcA-mediated regulation of all1871.
    [Show full text]
  • The Evolutionary Diversification of Cyanobacteria: Molecular–Phylogenetic and Paleontological Perspectives
    The evolutionary diversification of cyanobacteria: Molecular–phylogenetic and paleontological perspectives Akiko Tomitani†‡, Andrew H. Knoll§¶, Colleen M. Cavanaugh§, and Terufumi Ohno† †The Kyoto University Museum, Kyoto University, Yoshida-honmachi, Sakyo, Kyoto 606-8501, Japan; and §Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138 Contributed by Andrew H. Knoll, February 6, 2006 Cyanobacteria have played a significant role in Earth history as (Stigonematales), vegetative cells can differentiate into morpho- primary producers and the ultimate source of atmospheric oxygen. logically and ultrastructurally distinct heterocysts, cells that To date, however, how and when the group diversified has specialize in nitrogen fixation under aerobic conditions (8), or remained unclear. Here, we combine molecular phylogenetic and akinetes, resting cells that survive environmental stresses such as paleontological studies to elucidate the pattern and timing of early cold and desiccation (9), depending on growth conditions. In cyanobacterial diversification. 16S rRNA, rbcL, and hetR genes were addition, filaments of subsection V have complicated branching sequenced from 20 cyanobacterial strains distributed among 16 patterns. Their developmental variety and complexity are thus genera, with particular care taken to represent the known diversity among the most highly developed in prokaryotes. of filamentous taxa. Unlike most other bacteria, some filamentous The geologic record offers some clues
    [Show full text]
  • Seasonal Dynamics of the Endosymbiotic, Nitrogen-Fixing Cyanobacterium Richelia Intracellularis in the Eastern Mediterranean Sea
    The ISME Journal (2008) 2, 911–923 & 2008 International Society for Microbial Ecology All rights reserved 1751-7362/08 $30.00 www.nature.com/ismej ORIGINAL ARTICLE Seasonal dynamics of the endosymbiotic, nitrogen-fixing cyanobacterium Richelia intracellularis in the eastern Mediterranean Sea Edo Bar Zeev1, Tali Yogev1, Dikla Man-Aharonovich2, Nurit Kress3, Barak Herut3, Oded Be´ja`2 and Ilana Berman-Frank1 1Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat Gan, Israel; 2Faculty of Biology, Technion-Israel Institute of Technology, Haifa, Israel and 3Israel Oceanographic and Limnological Research, National Institute of Oceanography, Haifa, Israel Biological nitrogen fixation has been suggested as an important source of nitrogen for the ultra- oligotrophic waters of the Levantine Basin of the Mediterranean Sea. In this study, we identify and characterize the spatial and temporal distribution of the N-fixing (diazotrophic) cyanobacterium Richelia intracellularis. R. intracellularis is usually found as an endosymbiont within diatoms such as Rhizosolenia spp and Hemiaulus spp. and is an important diazotroph in marine tropical oceans. In this study, two stations off the Mediterranean coast of Israel were sampled monthly during 2005–2007. R. intracellularis was identified by microscopy and by reverse transcribed-PCR which confirmed a 98.8% identity with known nifH sequences of R. intracellularis from around the world. The diatom–diazotroph associations were found throughout the year peaking during autumn (October–November) at both stations. Abundance of R. intracellularis ranged from 10 to 55 À1 heterocysts l and correlated positively with the dissolved Si(OH)4/(NO3 þ NO2) ratio in surface waters. Although the rates of nitrogen fixation were very low, averaging B1.1 nmol N lÀ1 dayÀ1 for the R.
    [Show full text]
  • Effect of Mercury on the Growth and Biochemical Behavior of Nostoc Muscorum and Anabaena Variabilis
    Int J Pharma Bio Sci 2019 July; 10(3): (B) 11-21 Original Research Article Microbiology International Journal of Pharma and Bio Sciences ISSN 0975-6299 EFFECT OF MERCURY ON THE GROWTH AND BIOCHEMICAL BEHAVIOR OF NOSTOC MUSCORUM AND ANABAENA VARIABILIS YOGESH NEGI1, SUNIL SHARMA2, BARIHUN THYRNIANG3, FRANKIE J. LALOO3 AND SAMRAT ADHIKARI4* 1Senior Research Fellow, Advanced Level Biotech Hub Facility, Department of Biotechnology, St. Edmund’s College Shillong-793003, Meghalaya, India 2Research Associate, Advanced Level Biotech Hub Facility, Department of Biotechnology, St. Edmund’s College Shillong-793003, Meghalaya, India 3UG Student, Department of Biotechnology, St. Edmund’s College, Shillong-793003, Meghalaya, India 4*Associate Professor, Head, Department of Biotechnology, Coordinator, Advanced Level Biotech Hub Facility, St. Edmund’s College, Shillong-793003, Meghalaya, India ABSTRACT Cyanobacteria are a highly diversified group of photosynthetic organisms which can be exploited as a potential candidate for bioremediation processes. The present study evaluates the toxic effect of a heavy metal, mercury (Hg2+ (II)), on the growth and biochemical aspects of Nostoc muscorum and Anabaena variabilis. The results depicted negative effects of Hg2+ on cyanobacteria by hampering normal growth and physiological activities. The treated cells showed diminishing growth pattern and decrease in the photosynthetic pigments. Significant decline was also revealed in the biomass and lipid content. The LC50 value of Hg was determined to be 0.6µM for both the cultures. Activity of the enzymes involve in nitrogen metabolism such as Glutamine Synthetase (GS), Nitrate Reductase (NR) and Nitrite Reductase (NIR) were studied and showed reduced activity. This decreased activity also correlates with the reduction in the heterocyst frequency as obtained in the results.
    [Show full text]
  • Cyanobacterial-Plant Symbioses
    Symbiosis, 14 (1992) 61-81 61 Balaban, Philadelphia/Rehovot Review article Cyanobacterial-Plant Symbioses BIRGITTA BERGMAN, AMAR N. RAI, CHRISTINA JOHANSSON and ERIK SODERBACK Department of Botany, Stockholm University, S-106 91, Stockholm, Sweden Tel. ( 46) 8 16 37 51, Fax ( 46) 8 16 55 25 Received February 27, 1992; Accepted March 26, 1992 Abstract Diazotrophic cyanobacteria form symbioses with representatives from several plant divisions, but for unknown reasons, only one or a few plant groups in each division are involved. Representatives are found among lower plants, such as algae (diatoms), fungi (lichens), bryophytes and ferns, as well as among higher plants, such as the gymnosperm cycad and the angiosperm Gunnera. Thus, the host plants constitute a highly heterogenic group with apparently little in com• mon besides being capable of using a nitrogen-fixing cyanobacterium to support their total need of nitrogen. In contrast, it appears that the cyanobacterial gen• era involved are limited and almost exclusively of a filamentous non-branching type capable of differentiating heterocysts. The purpose of this paper is to sum• marize some aspects of our current knowledge of cyanobacterial-plant symbioses with emphasis on bryophytes, Azolla and Gunnera. For a more comprehensive review the reader is referred to Rai (1990a). Keywords: cyanobacteria, symbiosis, N2-fixation, infection process, N-assimilation, heterocysts 1. The Host Plants Bryophytes In the division Bryophyta only six genera (out of a total of about 340) are documented to harbor cyanobacteria endophytically (Table 1; Rodgers and Stewart, 1977; Meeks, 1990). These are Blasia, Cavicularia, Anihoceros, 0334-5114/92 /$03.50 @1992 Balaban 62 B.
    [Show full text]