Peter R. Hawkins

rRNA Sequences and Evolutionary Relationships among Toxic and Nontoxic Cyanobacteria of the Genus Microcystis

A primary-structure analysis of the 16S rRNA gene was performed with 10 strains representing five described and one unidentified species of the genus Microcystis. The phylogenies determined illustrate the evolutionary affiliations among Microcystis strains, other cyanobacteria, and related plastids and bacteria. A cluster of 10 strains that included hepatotoxic isolates identified as Microcystis aeruginosa formed a monophyletic group. However, the genus Microcystis appeared to be polyphyletic and contained two strains that clustered with unicellular cyanobacteria belonging to the genus Synechococcus. The clustering of related Microcystis strains, including strains involved in the production of the cyclic peptide toxin microcystin, was consistent with cell morphology, gas vacuolation, and the low G + C contents of the genomes. The Microcystis lineage was also distinct from the lineage containing the unicellular genus Synechocystis and the filamentous, heterocyst-forming genus Nostoc. The secondary structure of a Microcystis 16S rRNA molecule was determined, and genus-specific sequence signatures were used to design primers that permitted identification of the potentially toxic cyanobacteria belonging to the genus Microcystis via DNA amplification.

Isolation and toxicity of Cylindrospermopsis raciborskii from an ornamental lake

In Australia, the tropical/subtropical cyanobacterium Cylindrospermopsis raciborskii forms substantial blooms in some drinking water supply reservoirs, rivers and recreational water bodies during the warmer months of the year. This paper describes the isolation, culture and toxicity characterisation of Cylindrospermopsis from a water bloom in a small lake in NSW, Australia. The cyanobacterium grew as straight trichomes terminating with a characteristic heterocyst. The toxic alkaloid cylindrospermopsin was separated and identified by high-performance liquid chromatography at a concentration of 5.5 mg/g dry cells, 0.026 pg/cell. Intraperitoneal injection of sonicated cells caused liver, kidney, intestinal and lung damage, with an LD50 of 52 mg cells/kg mouse body weight at 24 hr, and 32 mg/kg at 7 days. The 24 hr mouse toxicity is not consistent with previous studies using pure cylindrospermopsin, and is suggestive of other toxic compounds in this isolate.

Hepatic and renal toxicity of the blue–green alga (cyanobacterium) Cylindrospermopsis raciborskii in male Swiss albino mice

When administered to mice, either orally or intraperitoneally, extracts of the cyanobacterium Cylindrospermopsis raciborskii strain AWT 205 induced dose‐dependent liver and kidney damage. Liver damage was generally centrilobular, becoming more severe and generalized as the dose increased. Damaged hepatocytes were characterized by increased cellular vacuolation, intercellular spaces, and darker nuclear and cytoplasmic staining. Kidney damage was characterized by a reduction in the number of erythrocytes in the glomerulus and an increase in the space around the glomerulus, increased diameter of the tubule lumina, proximal tubule epithelial necrosis, and the presence of proteinaceous material in the distal tubules. Transmission electron microscopy of the same tissue revealed epithelial cell necrosis in the proximal tubules, suggesting the material accumulating in the distal tubules was in part cell debris from this necrosis. The nature, location, and time course of histological damage were similar for oral and intraperitoneal administration, with maximum damage being observed 2–3 days after treatment. The LD50 (24 h) for intraperitoneally administered Cylindrospermopsis preparations ranged from 50 to 110 mg dry weight of lysed cells per kilogram, whereas the LD50 (7 days) ranged between 20 and 65 mg/kg depending upon the batch examined. In contrast, oral administration of 1400 mg/kg, while inducing clear histological damage, was not fatal to any of the animals used in the study. The extent of comparative severity of damage to the liver and kidneys caused by different batches of Cylindrospermopsis of similar cylindrospermopsin content varied considerably, implying the presence of more than one toxin. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 143–150, 1999

Specific Amplification and Restriction Polymorphisms of the Cyanobacterial rRNA Operon Spacer Region

Summary Forty-two strains of cyanobacteria commonly associated with toxic bloom events and representing 10 cyanobacterial genera were examined by RFLP analysis of the PCR amplified 16S-23S rRNA gene internal transcribed spacer (ITS). A total of 97 different DNA profiles were generated by the application of 8 restriction endonucleases to digest the PCR products. The length of the PCR products obtained for strains assigned to the same genus seemed to be a useful taxonomic character and could probably be used for rapid identification. Nine characteristic amplification products delineated the 10 genera studied. Intrageneric strain differentiation was provided by restriction digest profiles which, when combined for each strain, resulted in 27 distinct genotypes. Specific amplification of cyanobacterial strains from mixed populations and environmental samples containing algae and heterotrophic bacteria was possible due to the use of a cyanobacteria specific 16S rRNA gene-directed PCR primer. The genetic relatedness observed between the taxa studied coincided with the taxonomic identification of the studied strains, particularly within the genera Anabaena and Microcystis.

Genotypes of Cryptosporidium from Sydney water catchment areas

Aims:  Currently cryptosporidiosis represents the major public health concern of water utilities in developed nations and increasingly, new species and genotypes of Cryptosporidium are being identified in which the infectivity for humans is not clear. The complicated epidemiology of Cryptosporidium and the fact that the majority of species and genotypes of Cryptosporidium cannot be distinguished morphologically makes the assessment of public health risk difficult if oocysts are detected in the raw water supplies. The aim of this study was to use molecular tools to identify sources of Cryptosporidium from the Warragamba catchment area of Sydney, Australia.

16S Ribosomal RNA Gene Sequence and Phylogeny of Toxic Microcystis sp. (Cyanobacteria)

The toxigenic and bloom-forming cyanobacterial genus Microcystis contains several ill-defined species. The 16S rDNA for two strains of toxic M. aeruginosa were sequenced and compared to available cyanobacterial, bacterial, and chloroplast 16S rRNA gene information. Phylogeny and the validity of a molecular taxonomy for the genus Microcystis is presented.

The Risk of Cryptosporidium to Sydney's Drinking Water Supply

Publisher Summary To protect the quality of drinking water in Sydney, the Sydney Water Corporation (SWC) and the recently created Sydney Catchment Authority (SCA) have adopted a catchment to customer risk management approach after the Cryptosporidium water crisis in 1998. In Sydney such an approach involves close collaboration with the New South Wales Department of Health (NSW Health), as well as the consortia managing several of Sydneys large water filtration plants (WFPs) under Build-Own-Operate (BOO) contracts. This chapter presents a paper, which aims to provide an update of the main actions that have been taken since the water crisis in Sydney in 1998. These updates need to be in: the catchments, water treatment plants, distribution system, and analytical laboratories for Cryptosporidium analysis.