The cyanoprokaryota is a morphologically diverse group of prokaryotes, known to occur in almost all biotopes where they provide a significant contribution to the primary productivity of most aquatic ecosystems and indeed the biosphere. Despite their importance, there are very few comprehensive regional accounts of cyanoprokaryote biodiversity in the scientific literature, particularly from Australia’s tropical regions and niches including benthic and extreme environments. In terms of morphological and molecular data, one particularly understudied section of the cyanoprokaryota is the Oscillatoriales. The representatives of this group which contains the simplest, most diversified and most variable cyanoprokaryotes without heterocytes and akinetes. They are differentiated by features, which vary with environmental and culture conditions and as such may not be phylogenetically informative. This project addresses the paucity of floristic and ecological information on Australia’s freshwater cyanoprokaryota (cyanobacteria) by investigating the relatively neglected yet ecologically significant order, the Oscillatoriales.
The project has four major foci. Representatives of the Oscillatoriales are known from most biotopes, however their relationships to environmental conditions and their relative contribution to total microfloral diversity in a number of habitats is poorly understood. Similarly there have been relatively few studies published on the microfloral communities of Australian river systems and their relationship to environmental conditions and none of these have simultaneously measured the compositional structure of both planktonic and benthic littoral community assemblages, or compared influences on community structure at multiple scales. A study of the microfloral assemblages of two Australian dryland river systems was conducted comparing Cooper Creek, Lake Eyre Basin, and the Warrego River, Murray–Darling Basin. How algal biodiversity is partitioned across the landscape was explored and whether variation is greater spatially or temporally was examined. Despite the waterholes studied having characteristically high levels of abiogenic turbidity, a total of 186 planktonic microalgae, 253 benthic diatom and 62 macroalgal species were recorded. The phytoplankton communities were dominated by flagellated cryptophytes, euglenophytes and chlorophytes, the diatom communities by cosmopolitan taxa known to tolerate wide environmental conditions, and the macroalgal communities by filamentous cyanobacteria. In general the assemblage patterns were poorly correlated with the measured environmental variables. Phytoplankton and diatom assemblage patterns were weakly correlated with several waterhole geomorphic measures, whereas macroalgal assemblage patterns showed some association with variability in ionic concentration.
The benthic freshwater cyanoprokaryote, Lyngbya wollei (Farlow ex Gomont) Speziale and Dyck is a known producer of the potent neurotoxic saxitoxins in the southern United States where it is regarded as a nuisance species. A morphological, ecological and toxicological evaluation was conducted on two south-east Queensland populations of L. wollei to investigate the similarities of this species with those reported in the literature from the northern hemisphere. We found that both populations produced the potent cyanotoxin cylindrospermopsin (CYN) and deoxy-cylindrospermopsin (deoxy- CYN). This is the first report of the production of CYN and deoxy-CYN by L. wollei or any species of the Oscillatoriales.
Extensive surveys of all representative freshwater biotopes in north-eastern Australia were conducted, collecting new material for taxonomic determination. Using a morphometric and ecological approach, existing Australian records and new collections were re-evaluated in light of recent nomenclatural changes. Taxonomic descriptions, original illustrations, photomicrographs, and keys were developed to facilitate their identification. The resulting volume provides a phenotypic baseline for the identification of field populations of the non-heterocystous, filamentous cyanoprokaryotes from north-eastern Australia. This phenotypic and ecological characterisation of natural populations is necessary to further both ecological and systematic research. It is currently the only practical method for widespread recognition of cyanoprokaryote diversity from different regions and is the first methodological step towards a polyphasic evaluation. Of the 122 taxa from north-eastern Australia discussed, three are described as new species following the requirements of the International Code of Botanical Nomenclature.
Cyanoprokaryote composition of microbial mats from an alkaline thermal spring from tropical north-eastern Australia was assessed. A polyphasic approach was used which included phenotypic observation of morphological and ultrastructural features, and genotypic analysis using partial 16S-rRNA sequences. Two distinct mat structures were recognisable: flat horizontally spreading mats, and mats comprised of densely arranged, non-lithified gelatinous tentaculiform towers. This tentaculiform mat type dominated the site. Eight genera and ten species from three cyanobacterial orders were identified based on morphological characters. These represented taxa previously known as thermophiles from other continents. Two filamentous morphotypes which formed the majority of the biomass of the towers had ultrastructural characteristics of the family Pseudanabaenaceae with 4 – 6 parietal thylakoids arranged concentrically and parallel to the cell wall, and type B cell division. DNA extracts were made from sections of the tentaculiform towers and the microbial community analysed by 16S cyanobacteria-specific PCR and denaturing-gradient gel electrophoresis (DGGE). Individual bands were excised from the gel and sequencing demonstrated five significant bands. Collectively they were related to a number of cyanobacteria from thermal habitats. Generally the morphological/ultrastructural characteristics aligned with the molecular classification, however the dominant Leptolyngbya morphotype was shown to cluster closely with Oscillatoria amphigranulata, isolated from New Zealand hot springs, and the sub-dominant Leptolyngbya was a unique phylotype with only moderate similarity (96%) to a range of Leptolyngbya from Greenland. This is the first polyphasic evaluation of thermophilic cyanobacterial communities from the Australian continent.