3 results for Addison, Sarah Louise

  • ¹⁵N stable isotope probing of pulp and paper wastewaters

    Addison, Sarah Louise (2008)

    Masters thesis
    University of Waikato

    Stable isotope probing (SIP) is an established technique that can be applied to identify the metabolically active micro-organisms within a microbial population. The SIP method utilises an isotopically-labelled substrate and PCR techniques to discern the members of a microbial community that incorporate the isotope into their DNA or RNA. The current literature gap around using ¹⁵N isotopes with RNA-SIP offers real potential and advantages for targeting and identifying active members from mixed communities involved in global biogeochemical nitrogen cycling. This study specifically investigated whether nitrogen based compounds ncan be used as substrates in RNA-SIP methodologies and whether they can in turn be used to probe mixed community environments known to be actively fixing nitrogen. The nitrogen-limited systems targeted represented an ideal opportunity to assess the suitability of ¹⁵N-RNA-SIP approaches due to their known high nitrogen fixation rates. Identifying these nitrogen-fixing bacteria could provide a better representation analysis of the community, leading to an improved prediction on how to manage and optimise the treatment performance of target waste systems and to exploit the unique bioconversion properties of these types of organisms. Initially, the project undertook methodological proof of concept by using a soluble nitrogen source, ¹⁵NH₄Cl, to label the RNA of Novosphingobium nitrogenifigens and a mixed microbial community. Successful separation of the ¹⁴N- (control) and ¹⁵N-RNA was achieved for both pure and mixed communities using isopycnic caesium trifluoroacetate (CsTFA) gradients in an ultracentrifuge. The usefulness of this technique to identify active diazotrophs in real environmental samples was tested using a nitrogen-fixing community from a pulp and paper wastewater treatment system. After growing the mixed culture with ¹⁵N₂ as the sole nitrogen source, the labelled RNA was extracted and fractionated using isopycnic centrifugation in CsTFA gradients. The community composition of the active nitrogen-fixing community in the ¹⁵N₂ enriched fraction was analysed by establishing a 16S rRNA gene clone library containing over 200 members. These were analysed by comparison with published sequences and by phylogenetic analysis. It was found that the more isotopic label substrate incorporated, the further the buoyant density (BD) separation between ¹⁵N- and ¹⁴N-RNA. Novosphingobium nitrogenifigens gave an average BD shift of 0.03 + 0.004 g ml⁻¹ (95.0 atom % ¹⁵N) with ¹⁵NH₄Cl. For mixed communities the average BD shift was 0.02 + 0.004 g ml⁻¹ (80.0 atom % ¹⁵N) with 15NH4Cl and 0.013 + 0.002 g ml⁻¹ (32.6 atom % ¹⁵N) when using ¹⁵N₂. Clone library analysis of 16S rRNA genes present in the enriched ¹⁵N-RNA fraction of the mixed community was shown to consist of a diverse population of bacteria as indicated by a Shannon Weaver index value of >2.8. Three dominant genera (Aeromonas, Pseudomonas and Bacillus) were identified by comparison with published sequences and phylogenetic analysis. Many other groups not known as archetypal nitrogen-fixing bacteria were also identified, demonstrating that ¹⁵N₂-RNA-SIP provides a useful tool for the identification of important and previously unknown contributors to nitrogen fixation in a range of environments. Overall, this project has established that nitrogen based RNA-SIP is a powerful tool that can be used successfully and reproducibly with both pure and complex mixed microbial communities to study active diazotrophs in environmental samples.

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  • Identifying diazotrophs by incorporation of nitrogen from ¹⁵N₂ into RNA

    Addison, Sarah Louise; McDonald, Ian R.; Lloyd-Jones, Gareth (2010)

    Journal article
    University of Waikato

    The diversity and abundance of active diazotrophs was investigated in a New Zealand pulp and paper wastewater by enrichment with ¹⁵N₂. Purified ¹⁵N-RNA was analysed by reverse transcription, molecular cloning and sequence analysis of 16S rRNA to reveal a diverse community of bacteria as indicated by a Shannon Weaver Index value of > 2.8. The major class represented in the enriched culture were the γ-Proteobacteria at 85% with a secondary group of the phylum Firmicutes present at 8.2%, the remaining sequences were affiliated with the α- and β-Proteobacterial classes (1.4% and 4.3%, respectively). Three dominant genera, Aeromonas, Pseudomonas and Bacillus, were identified by comparison with published sequences and phylogenetic analysis. To confirm that representatives of the taxonomic groups identified from the active enriched nitrogen-fixing community were capable of fixing nitrogen Aeromonas and Pseudomonas species were cultivated and shown to possess nifH genes. In wastewater, fluorescence in situ hybridisation probing revealed that the dominant nitrogen-fixing population identified in this study were present in the population, but at lower levels. The population is, therefore, reliant on a small sub-population of diazotrophs to supply the community's nitrogen needs above that already present in the wastewater.

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  • Stable isotope probing: Technical considerations when resolving ¹⁵N-labeled RNA in gradients

    Addison, Sarah Louise; McDonald, Ian R.; Lloyd-Jones, Gareth (2010-01)

    Journal article
    University of Waikato

    RNA based stable isotope probing (SIP) facilitates the detection and identification of active members of microbial populations that are involved in the assimilation of an isotopically labeled compound. ¹⁵N-RNA-SIP is a new method that has been discussed in recent literature but has not yet been tested. Herein, we define the limitations to using ¹⁵N-labeled substrates for SIP and propose modifications to compensate for some of these shortcomings. We have used ¹⁵N-RNA-SIP as a tool for analysing mixed bacterial populations that use nitrogen substrates. After incubating mixed microbial communities with ¹⁵N-ammonium chloride or ¹⁵N₂ we assessed the fractionation resolution of ¹⁵N-RNA by isopycnic centrifugation in caesium trifluoroacetate (CsTFA) gradients. We found that the more isotopic label incorporated, the further the buoyant density (BD) separation between ¹⁵N- and ¹⁴N-RNA, however it was not possible to resolve the labeled from unlabeled RNA definitively through gradient fractionation. Terminal-restriction fragment length polymorphism (T-RFLP) analysis of the extracted RNA and fluorescent in situ hybridisation (FISH) analysis of the enrichment cultures provided some insight into the organisms involved in nitrogen fixation. This approach is not without its limitations and will require further developments to assess its applicability to other nitrogen-fixing environments.

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