Browsing by Author "Bergman, Birgitta"
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Item Biological N2-fixation on Mangrove Pneumatophores: Preliminary Observations and Perspectives(2002) Lugomela, Charles; Bergman, BirgittaItem Cyanobacterial Diversity and Nitrogen Fixation in Coastal Areas around Zanzibar, Tanzania(Schweizerbart, 2001) Lugomela, Charles; Bergman, Birgitta; Waterbury, J.Cyanobacterial diversity and nitrogen fixation were examined in coastal areas around Zanzibar, Tanzania. Samplings were performed intermittently from June 1997 to October, 1999 from plankton, intertidal and subtidal microbial mats as well as from epiphytes on seagrasses and seaweeds. A total of 21 cyanobacterial genera comprising 50 species are described, out of which 64% were filamentous non-heterocystous forms, 24% heterocystous forms and 12% unicellular forms. Non-heterocystous Oscillatoria spp. dominated the microbial mats and epiphytic habitats, and the like-wise non-heterocystous Trichodesmium spp. were the most abundant cyanobacteria in net samples. Fourteen of the species identified were analyzed for the ability to fix dinitrogen using the acetylene reduction assay and eleven species showed nitrogenase activity. Six of these species were also subjected to immuno-blotting. The presence of a nitrogenase (Fe-protein) protein with an average molecular weight of 36 kDa was detected. The results suggest higher cyanobacterial diversity in the area investigated than previously reported and indicate that the capacity to fix molecular nitrogen is present in a number of species that are often prominent in these habitats. It is therefore concluded that cyanobacteria may have an important role and may contribute to new N-production in coastal areas of Tanzania.Item Diurnal Expression of Hetr and Diazocyte Development in the Filamentous Non-Heterocystous Cyanobacterium Trichodesmium Erythraeum(2003) El-Shehawy, Rehab; Lugomela, Charles; Ernst, A.; Bergman, BirgittaThe marine non-heterocystous cyanobacterium Trichodesmium fixes atmospheric N2 aerobically in light. In situ immunolocalization/light microscopy of NifH revealed that lighter, non-granulated cell regions observed correspond to the nitrogenase-containing diazocyte clusters in Trichodesmium IMS101. The number of diazocyte clusters per trichome varied from 0 to 4 depending on trichome length. The constant percentage of diazocytes (approx. 15 %) in cultured strains and five natural populations suggests a developmentally regulated differentiation process. Real-time RT-PCR showed that ntcA, encoding the global nitrogen regulator in cyanobacteria, and hetR, the key regulatory gene in heterocyst differentiation, are both constitutively expressed during a 12 h/12 h light/dark cycle. hetR in addition showed a distinct peak in the dark (close to midnight) while nifH expression commenced 6–8 h later. The expression of all three genes was negatively affected by addition of ammonia. Some early heterocyst differentiation genes were also identified in the genome of Trichodesmium. The data suggest that hetR and ntcA may be required for development and function of diazocytes in Trichodesmium.Item Epiphytic Cyanobacteria of the Seagrass Cymodocea Rotundata: Diversity, Diel Nifh Expression and Nitrogenase Activity(Wiley, 2013-05) Hamisi, Mariam; Diez, Beatriz; Lyimo, Thomas J.; Ininbergs, Karolina; Bergman, BirgittaEpiphytic cyanobacteria of the seagrass Cymodocearotundata: diversity, diel nifH expression andnitrogenase activityMariam Hamisi,1* Beatriz Díez,2†Thomas Lyimo,3Karolina Ininbergs2and Birgitta Bergman21College of Natural & Mathematical Sciences, TheUniversity of Dodoma, P.O. Box 338, Dodoma,Tanzania.2Department of Ecology, Environment and PlantSciences, Stockholm University, Lilla Frescati, SE-10691 Stockholm, Sweden.3Department of Molecular Biology & Biotechnology, Dares Salaam University, P.O. Box 35179, Dar es Salaam,Tanzania.SummarySeagrasses are photoautotrophic, ecologically im-portant components of many globally widespreadcoastal ecosystems, in which combined nitrogen maylimit their production. We examined the biodiversityand diazotrophic capacity of microbial epiphytesassociated with the phyllosphere of the seagrassCymodocea rotundata of the Western Indian Ocean.Light microscopy, 16S rRNA and nifH gene analysisrevealed the dominance of cyanobacteria in the epi-phytic microbial community. Most phylotypes wererelated to free-living uncultured benthic cyanobacte-ria, while some to cyanobacterial endosymbionts ofmarine diatoms. Novel and potentially diazotrophicspecies, some of known pantropical distribution,were also discovered. Significant diel nitrogenaseactivities (acetylene reduction assay) were recorded(up to 358 ⫾ 232 nmol C2H4g-1of seagrass FW h-1).The nifH gene expression patterns showed that het-erocystous phylotypes may be the dominant diazo-trophs during the day and non-heterocystous atnight. These data show that C. rotundata is colonizedby diverse diazotrophic cyanobacteria species andsuggest that these may be beneficial partners ofItem Nitrogen Fixation by Epiphytic and Epibenthic Diazotrophs Associated with Seagrass Meadows along the Tanzanian Coast, Western Indian Ocean. Aquat Microb Ecol(2009-09) Hamisi, Mariam; Lyimo, Thomas J.; Muruke, M . H. S.; Bergman, BirgittaSeasonal, diurnal, and age-dependent variations in nitrogen fixation (nitrogenase activity) by epiphytic diazotrophs colonizing the seagrasses Halodule uninervis, Cymodocea rotundata, Thalassodendron ciliatum, and Thalassia hemprichii, and by epibenthic diazotrophs associated with seagrass-vegetated and nonvegetated sediments, were estimated at 2 sites along the Tanzanian coast, Western Indian Ocean. Acetylene reduction-gas chromatography showed that nitrogenase activity values were significantly higher (p = 0.0004) at the site with low nutrient levels (Mjimwema) than at the site with higher nutrient levels (Ocean Road). The nitrogenase activity ranged from 10 to 192 nmol N g(-1) h(-1) for H. uninervis, 7 to 80 nmol N g(-1) h(-1) for C. rotundata, 10 to 75 nmol N g(-1)h(-1) for Thalassia hemprichii, and from 4 to 61 nmol N g(-1) h(-1) for Thalassodendron ciliatum. Nitrogenase activity values in sediments covered by seagrasses were significantly higher than in surrounding nonvegetated sediments (t = 4.021, p = 0.0005). Significant variations in nitrogenase activity were apparent depending on leaf age and season, with highest activity being found in mid-aged leaves during the northeastern monsoon (NEM), and in older leaves during the southeastern monsoon (SEM). Daytime nitrogenase activity was appreciable on above-ground seagrass parts, while rhizosphere activity peaked at night-time. Collectively our data show that diazotrophs (cyanobacteria and other bacteria) are associated with seagrasses (leaves and roots), and potentially constitute an integral part of the ecosystem. They show highly dynamic nitrogenase activity and a succession in seagrass colonization, and we concluded that their presence may contribute to the productivity of the seagrass beds.Item Reevaluation of the Nitrogen Fixation Behavior in the Marine Non-Heterocystous Cyanobacterium Lyngbya Majuscula.(Wiley, 2003) Lundgren, Pernilla; Ininbergs, Karolina; Lugomela, Charles; Söderbäck, Erik; Bergman, BirgittaLyngbya majuscula Harvey ex Gomont is a common marine cyanobacterium in tropical and subtropical near-shore waters. A few reports have indicated that L. majuscula fixes nitrogen only in the light. Because this feature is uncommon among non-heterocystous cyanobacteria, we attempted a reevaluation. Nitrogenase activity, regulation, and localization were examined over diel cycles on natural populations of L. majuscula growing in subtidal zones off Zanzibar in the western Indian Ocean. The data show that L. majuscula fixed nitrogen and synthesized nitrogenase in all cells during the dark phase of a diel cycle. During the light phase, nitrogenase was degraded to undetectable levels.Item Trichodesmium Has Cells Specialized for Nitrogen Fixation but Lacks Heterocysts(Springer Link, 1997) Bergman, Birgitta; Fredriksson, C.; Janson, S.; Carpenter, Edward; Paerl, Hans; Lugomela, CharlesTwo features make research on the marine cyanobacterium Trichodesmium of particular relevance. The first, relates to its common occurrence and important role in a global perspective. Although Trichodesmium is restricted to coastal habitats and open oceans with temperatures above about 18–20°C, it is probably quantitatively one of the most common cyanobacterium in nature. Recent estimates also indicate that it supports the pelagic zone of the oligotrophic oceans with considerable amounts of fixed nitrogen (Carpenter & Romans 1991). Furthermore, Trichodesmium is unique in that it fixes nitrogen aerobically in light, a feature only known from cyanobacteria differentiating heterocysts, a specific cell type for the oxygen sensitive nitrogen-fixing enzyme nitrogenase.Item Trichodesmium in Coastal Waters of Tanzania: Diversity, Seasonality, Nitrogen and Carbon Fixation(Springer Link, 2002) Lugomela, Charles; Lyimo, Thomas J.; Bryceson, Ian; Semesi, Adelaida K.; Bergman, BirgittaSeasonal distribution, nitrogen fixation and primary productivity of Trichodesmium species were intermittently studied in the coastal waters of Tanzania. Samples were collected in 1975/6, 1980, 1993/4, 1994/5 and 1998/9. Four colony forming species were found, i.e. T. erythraeum, T. tenue, T. thiebautii and one unidentified Trichodesmium sp. while T. contortum was rarely encountered, and only as individual trichomes. T. erythraeum was most abundant, although other Trichodesmiumspecies dominated during particular periods of the year. The occurrence of Trichodesmium showed a consistent seasonal pattern. High Trichodesmium biomass was promoted by the NE monsoon (December–April) while it was low or absent during the SE monsoon (June–October). The biomass was highest at the surface especially during calm weather periods. The NE monsoon was characterized by elevated rainfall, temperature and nitrate concentrations while salinity, light intensity and turbidity tended to decrease. Phosphate concentrations did not show systematic variations with season. The rate of nitrogen fixation by Trichodesmium species in surface waters was 1.8 1.6 pmol N trichome–1 h–1 giving an average N2 fixation of 42.7 mmol N m–3y–1. The mean rate of carbon fixation was 1.15 0.3 ng C trichomes–1 h–1 in the upper 5 m depth. It is estimated that Trichodesmium contributes about 0.03–20% of the total CO2 fixation in the coastal surface waters during the SE and NE monsoon, respectively.Item Variability in Diazotrophy and Cyanobacterial Diversity in a Tropical Intertidal Lagoon(2008) Ininbergs, Karolina; Diez, Beatriz; Lugomela, Charles; Seppala, Susanna; Borg, Agneta J.; Bergman, BirgittaBenthic nitrogen fixation has been estimated to contribute 15 Tg N year1to themarine nitrogen budget. With benthic marine nitrogen fixation being largelyoverlooked in more recent surveys, a refocus on benthic diazotrophy wasconsidered important. Variations in nitrogenase activity (acetylene reduction-gaschromatography) in a tropical lagoon in the western Indian Ocean (Zanzibar,Tanzania) were monitored over a 3-year period (2003–2005) and related tocyanobacterial and diazotrophic microbial diversity using a polyphasic approach.Different nitrogenase activity patterns were discerned, with the predominantpattern being high daytime activities combined with low nighttime activities.Analyses of the morphological and 16S rRNA gene diversity among cyanobacteriarevealed filamentous nonheterocystous (Oscillatoriales) and unicellular (Chroo-coccales) representatives to be predominant. Analyses of the nifH gene diversityshowed that the major phylotypes belonged to noncyanobacterial prokaryotes.However, as shown by cyanobacterial selective nifH-denaturing gradient gelelectrophoresis analysis, cyanobacterial nifH gene sequences were present at allsites. Several nifH and 16S rRNA gene phylotypes were related to unculturedcyanobacteria or bacteria of geographically distant habitats, stressing the wide-spread occurrence of still poorly characterized microorganisms in tropical benthicmarine communities.