No abstract

Cylindrospermopsis raciborskii is a toxic-bloom-forming cyanobacterium that is commonly found in tropical to subtropical climatic regions worldwide, but it is also recognized as a common component of cyanobacterial communities in temperate climates. Genetic profiles of C. raciborskii were examined in 19 cultured isolates originating from geographically diverse regions of Australia and represented by two distinct morphotypes. A 609-bp region of rpoC1, a DNA-dependent RNA polymerase gene, was amplified by PCR from these isolates with cyanobacterium-specific primers. Sequence analysis revealed that all isolates belonged to the same species, including morphotypes with straight or coiled trichomes. Additional rpoC1 gene sequences obtained for a range of cyanobacteria highlighted clustering of C. raciborskii with other heterocyst-producing cyanobacteria (orders Nostocales and Stigonematales). In contrast, randomly amplified polymorphic DNA and short tandemly repeated repetitive sequence profiles revealed a greater level of genetic heterogeneity among C. raciborskii isolates than did rpoC1 gene analysis, and unique band profiles were also found among each of the cyanobacterial genera examined. A PCR test targeting a region of the rpoC1 gene unique to C. raciborskii was developed for the specific identification of C. raciborskii from both purified genomic DNA and environmental samples. The PCR was evaluated with a number of cyanobacterial isolates, but a PCR-positive result was only achieved with C. raciborskii. This method provides an accurate alternative to traditional morphological identification of C. raciborskii.Cyanobacterial blooms have become an increasing worldwide problem in aquatic habitats such as lakes, rivers, estuaries, and oceans and in man-made water storage systems. These occurrences can be partially attributed to gradual eutrophication of waterways. Certain species of cyanobacteria produce toxins, and as a result, blooms create major threats to animal and human health, tourism, recreation, and aquaculture.

The applications of in vivo probes that can detect the fluorescence of cyanobacterial phycocyanin are emerging and widely used for cyanobacterial detection in source waters. The objectives of this project were to study the sources of interferences involved with the readings of five probes (three commercially available probes and two prototype probes) using laboratory cultures and field samples. To compare the direct readings of different probes, the probe readings were presented in the form of a biovolume equivalent of cyanobacteria. Inorganic turbidity and the presence of algal biomass interfered with probe readings. A correction factor was developed for the cyanobacteria probes using simultaneous chlorophyll a measurements. The field data demonstrate that the potential underestimation of cyanobacterial biomass that corresponds to alert levels is a major issue with the application of in vivo probes. These alert levels are used to trigger monitoring and management actions. This study shows that the correlation between a probe's reading and cell count is almost meaningless, and that the correlation to biovolume is a relevant option for management purposes. Results show that probe users should be fully aware of the sources of interferences when applying and interpreting the results. In addition, the authors offer a novel procedure that corrects for chlorophyll a interference.

Planktonic populations and benthic resting stages (akinetes) of the common bloom-forming cyanobacteria Anabaena circinalis Rabenhorst and Anabaena flos-aquae f. flos-aquae (Lyngb.) Komárek were monitored in the Murray River near Nildottie and in adjacent floodplain wetlands (lagoons) from 1995 to 1997, to determine the extent of sporulation and the contribution of recruitment from the sediments to seasonal development of blooms. Physical and chemical characteristics of the water in the river and the lagoons were examined in relation to the succession of key life-cycle stages and growth. The warm, shallow lagoons supported considerably higher populations of Anabaena in the summer than did the river, with correspondingly higher incidence of sporulation. Viable akinetes were abundant in the sediments of both the river channel and the lagoons, providing a potentially significant inoculum for cyanobacterial growth. The apparent germination of akinetes early in summer and immediately following sporulation in mid summer indicated a strategy for both initiation and maintenance of populations. A. circinalis also persisted as a planktonic population throughout winter. Germination is considered more likely to occur in the shallow lagoons than in the main channel, principally because of frequent resuspension of sediments containing resting stages to the euphotic zone or because of direct penetration of light to the sediments.