Variable growth responses of water thyme (Hydrilla verticillata) to whole-cell extracts of Cylindrospermopsis raciborskii.

Static-renewal ecotoxicity trials monitored growth of Hydrilla verticillata in conjunction with exposure to Cylindrospermopsis raciborskii whole-cell extracts containing the cyanotoxin cylindrospermopsin (CYN). Maximum exposure concentrations were 400 microg L(-1) CYN over 14 days. The responses of Hydrilla to the treatments were variable according to the toxin concentrations and lengths of exposure. Plant deaths, chlorosis, and necrosis were not recorded from treated plants. However, Hydrilla experienced significant growth stimulation and redistribution of plant resources in conjunction with exposure to the whole-cell extracts. Root production was particularly impacted. The results of this study imply that root production could aid in reducing C. raciborskii cell concentrations and CYN toxicity. Results of chlorophyll analyses differed, indicating that CYN in whole-cell extracts might exert complex effects on photosynthesis. This is the first study to describe the responses of an aquatic macrophyte following exposure to C. raciborskii whole-cell extracts containing the cyanotoxin cylindrospermopsin.

Multiple-organ toxicity resulting from cylindrospermopsin exposure in tadpoles of the cane toad (Bufo marinus).

Histological examinations were made of cane toad (Bufo marinus) tadpoles after exposure to freeze-thawed Cylindrospermopsis raciborskii whole cell extracts and live C. raciborskii cultures containing sublethal concentrations of the blue-green algal toxin, cylindrospermopsin (CYN). Toxin exposure resulted in tissue injuries to multiple organs, with particular severity noted in the liver, intestine, nephric ducts and gill epithelia. The extent of cellular damage was similar across trials exposing tadpoles to aqueous and cell-bound toxins, despite unequal toxin concentrations being present in each. It was concluded that the presence of cell-bound toxin, which may be directly ingested via grazing, plays a crucial role in the exertion of histological effects in B. marinus. This work provides baseline information regarding the ecotoxicity of CYN toward amphibians. The range of cellular effects noted in CYN-exposed tadpoles suggests that toxic C. raciborskii blooms could represent considerable health risks to amphibian populations and indicate potentially far-reaching ecological impacts of toxic C. raciborskii blooms.

Mortality and toxin bioaccumulation in Bufo marinus following exposure to Cylindrospermopsis raciborskii cell extracts and live cultures.

Cylindrospermopsis raciborskii is a cyanobacterium responsible for the production of the toxin, cylindrospermopsin (CYN). Tadpoles of the cane toad Bufo marinus were exposed to freeze-thawed whole cell extracts or live cultures of C. raciborskii containing maximum CYN concentrations of 400 microg L-1 or 232 microg L-1, respectively. Exposure to live culture treatment solutions resulted in up to 66% mortality of B. marinus, whereas tadpoles exposed to whole cell extracts containing similar toxin concentrations survived. Decreases in relative growth rates and time spent for swimming were recorded from tadpoles during both types of exposure regimes. Bioconcentration of CYN was not evident following exposure to whole cell extracts containing extracellular toxin. In contrast exposure to live cultures, which contained cell-bound toxin, resulted in maximum average tissue concentrations of 895 microg free-CYN kg-1 fresh weight. This is the first investigation of C. raciborskii exposure effects and toxin bioaccumulation in the developmental stages of an amphibian.

Influence of intracellular toxin concentrations on cylindrospermopsin bioaccumulation in a freshwater gastropod (Melanoides tuberculata).

Scant information is available regarding the bioaccumulation of cylindrospermopsin (CYN) in aquatic organisms, particularly in invertebrates. This study examined toxin bioconcentration and bioaccumulation in the aquatic snail, Melanoides tuberculata, following exposure to freeze-thawed whole cell extracts and a live Cylindrospermopsis raciborskii culture containing CYN. Both bioconcentration and bioaccumulation were evident, but exposure to toxin in the freeze-thawed solutions resulted in minor tissue contamination compared with that resulting from live C. raciborskii exposure. Thus, whilst CYN uptake resulted from both extracellular and intracellular exposures, the availability of intracellular toxin was critical in affecting tissue CYN values. M. tuberculata did not bioconcentrate CYN into the shell. Bioaccumulation of the analog deoxy-CYN was also recorded. Knowledge of intracellular toxin concentrations may be critical in evaluating the bioaccumulation, ecological and human health risks associated with contaminated systems.