Browsing by Author "Ininbergs, Karolina"
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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 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 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.