Kirsten Heimann

ABSTRACT Commercially viable carbon–neutral biodiesel production from microalgae has potential for replacing depleting petroleum diesel. The process of biodiesel production from microalgae involves harvesting, drying and extraction of lipids which are energy- and cost-intensive processes. The development of effective large-scale lipid extraction processes which overcome the complexity of microalgae cell structure is considered one of the most vital requirements for commercial production. Thus the aim of this work was to investigate suitable extraction methods with optimised conditions to progress opportunities for sustainable microalgal biodiesel production. In this study, the green microalgal species consortium, Tarong polyculture was used to investigate lipid extraction with hexane (solvent) under high pressure and variable temperature and biomass moisture conditions using an Accelerated Solvent Extraction (ASE) method. The performance of high pressure solvent extraction was examined over a range of different process and sample conditions (dry biomass to water ratios (DBWRs): 100%, 75%, 50% and 25% and temperatures from 70 to 120 °C, process time 5–15 min). Maximum total lipid yields were achieved at 50% and 75% sample dryness at temperatures of 90–120 °C. We show that individual fatty acids (Palmitic acid C16:0; Stearic acid C18:0; Oleic acid C18:1; Linolenic acid C18:3) extraction optima are influenced by temperature and sample dryness, consequently affecting microalgal biodiesel quality parameters. Higher heating values and kinematic viscosity were compliant with biodiesel quality standards under all extraction conditions used. Our results indicate that biodiesel quality can be positively manipulated by selecting process extraction conditions that favour extraction of saturated and mono-unsaturated fatty acids over optimal extraction conditions for polyunsaturated fatty acids, yielding positive effects on cetane number and iodine values. Exceeding biodiesel standards for these two parameters opens blending opportunities with biodiesels that fall outside the minimal cetane and maximal iodine values.

Despite their ecological importance, very little is known about the taxonomy and ecology of benthic diatoms in coral-reef ecosystems. Diatom densities and community compositions were investigated in three distinct regions of the Great Barrier Reef (GBR): (a) Wet Tropics (WT), (b) Princess Charlotte Bay (PCB), and (c) the Outer Shelf (OS). About 209 taxa were observed in the GBR sediments

Pyrocystis lunula is a unicellular, marine, photoautotrophic, bioluminescent dinoflagellate. This organism is used in the Lumitox® bioassay with inhibition of bioluminescence re-establishment as the endpoint. Experiments determined if acute changes in pH, salinity, or temperature had an effect on the organisms’ ability to re-establish bioluminescence, or on the bioassay's potential to detect sodium dodecyl sulfate (SDS) and copper toxicity. The

Confocal microscopy was used to study the intracellular localisation of a series of inert polypyridylruthenium(ii) complexes with three eukaryotic cells lines - baby hamster kidney (BHK), human embryonic kidney (HEK-293) and liver carcinoma (Hep-G2). Co-staining experiments with the DNA-selective dye DAPI demonstrated that the di-, tri- and tetra-nuclear polypyridylruthenium(ii) complexes that are linked by the bis[4(4'-methyl-2,2'-bipyridyl)]-1,12-dodecane bridging ligand ("bb12") showed a high degree of selectivity for the nucleus of the eukaryotic cells. Additional co-localisation experiments with the general nucleic acid stain SYTO 9 indicated that the ruthenium complexes showed a considerable preference for the RNA-rich nucleolus, rather than chromosomal DNA. No significant differences were observed in the intracellular localisation between the ΔΔ and ΛΛ enantiomers of the dinuclear complex. Cytotoxicity assays carried out over 72 hours indicated that the ruthenium complexes, particularly the tri- and tetra-nuclear species, were significantly toxic to the eukaryotic cells. However, when the activity of the least cytotoxic compound (the ΔΔ enantiomer of the dinuclear species) was determined over a 24 hour period, the results indicated that the ruthenium complex was approximately a 100-fold less toxic to liver and kidney cells than to Gram positive bacteria. Circular dichroism (CD) spectroscopy was used to examine the effect of the ΔΔ and ΛΛ enantiomers of the dinuclear complex on the solution conformations of RNA and DNA. The CD experiments indicated that the RNA maintained the A-type conformation, and the DNA the B-type structure, upon binding by the ruthenium complexes.

ABSTRACT Tropical N2-fixing cyanobacteria offer an attractive alternative for production of biomass and bioproducts with potentially low cultivation and harvesting costs. The present study evaluated the biomass productivity of the N2-fixing cyanobacterium Tolypothrix sp. NQAIF319 grown in nitrogen-free medium in outdoor suspension and biofilm prototype cultivation systems in tropical Australia (Queensland). One-week cycles yielded maximum biomass productivities—estimated based on ground area occupied by single systems— of 45–49 g dry weight m−2 day−1 (suspension) and 1.0– 1.2 g dry weight m−2 day−1 (biofilm) with minimal biological contamination (Tolypothrix sp. biomass representing 94–98% of the photosynthetic community). Moderate productivities of the pigments phycocyanin/phycoerythrin (0.1–2.8 g m−2 day−1), fatty acids (0.1–2.0 g m−2 day−1), and nitrogen stored in the biomass (0.1–5.9 g m−2 day−1) were reached in biofilm and suspension systems, respectively, opening avenues for production of low-value commodities with potentially big markets (nitrogen-rich biofertilizers and aquaculture feed) and higher-value chemicals (phycobiliproteins and fatty acids). Simulated multi-system arrangements yielded theoretical overall areal productivities four to six times lower than those in single systems thus highlighting the need for future tests fine-tuning inter-system separation to minimize shadowing while maximizing the efficiency in land use in larger-scale production plants. Biofilm and self-flocculated biomass showed 80-fold and 53-fold reduced extracellular-water contents compared to suspension cultures, respectively, which will need to be considered for techno-economic and water/carbon footprint evaluation of each of the possible bioproduct synthesis pathways. In conclusion, the flexible and simple prototypes developed together with the good properties of Tolypothrix sp. represent a promising platform for low-cost production of cyanobacterial bioproducts in tropical regions using low nitrogen-containing water sources.