Abstract
BackgroundThe cyanobacterium Anabaena PCC 7120#11 has been genetically engineered to act as a delivery vehicle for Bacillus thuringiensis subspecies israelensis mosquitocidal toxins. To address ecological concerns about releasing this genetically engineered microorganism into the environment for mosquito larva control, the persistence and ecological impacts of PCC 7120#11 was evaluated using multi-species, standardized aquatic microcosms.MethodsThe microcosms were set up as described in ASTM E1366-02 (Standard Practice for Standardized Aquatic Microcosms: Fresh Water), with a few modifications. The treatment group microcosms were inoculated with PCC 7120#11 and key water quality parameters and non-target effects were compared between the treatment and control groups over a period of 35 days.ResultsPCC 7120#11 decreased from a concentration of 4.50 × 106 cells/ml (at inoculation) to 1.32 × 103 cells/ml after 4 weeks and larvicidal activity against third instar larvae of Anopheles arabiensis was only evident for two weeks after treatment. Both treatment and the interaction of treatment and time had a significant effect on nitrate, phosphate and photosynthetic microorganism concentrations. Treatment with PCC 7120#11 caused a temporary spike in ammonia in the microcosms a week after treatment, but the concentrations were well below acute and chronic criteria values for ammonia in freshwater ecosystems. Cyprinotus vidua concentrations were not significantly different between PCC 7120#11 and control microcosms. In PCC 7120#11 microcosms, Daphnia pulex concentrations were significantly lower than control concentrations between days 18 and 25. By the end of the experiment, none of the measured variables were significantly different between the treatment groups.ConclusionsThe standard aquatic microcosm experiments provided more data on the ecological impacts of PCC 7120#11 than single-organism assessments would have. On the basis of the relatively minor, short-term effects that PCC 7120#11 had on water quality parameters and non-target invertebrates, further evaluation of PCC 7120#11 for use in integrated vector management is warranted.
Highlights
The cyanobacterium Anabaena PCC 7120#11 has been genetically engineered to act as a delivery vehicle for Bacillus thuringiensis subspecies israelensis mosquitocidal toxins
As part of an assessment of the usefulness of PCC 7120#11 in integrated vector management (IVM), we evaluated the effects of PCC 7120#11 on a target organism (An. arabiensis) and ecotoxicology test organisms using the standardized aquatic microcosm (SAM) system
For each of the evaluated responses, the concentration curves for the control and PCC 7120#11 microcosms were similar in shape (Figs. 1, 2 and 3), but for some responses there were significant interactions of treatment (PCC 7120#11 or control) and time
Summary
The cyanobacterium Anabaena PCC 7120#11 has been genetically engineered to act as a delivery vehicle for Bacillus thuringiensis subspecies israelensis mosquitocidal toxins. To address ecological concerns about releasing this genetically engineered microorganism into the environment for mosquito larva control, the persistence and ecological impacts of PCC 7120#11 was evaluated using multi-species, standardized aquatic microcosms. Bacillus thuringiensis subspecies israelensis (Bti) is a spore-forming, aerobic, gram-positive bacterium that produces crystalline inclusions that contain Cry (crystal) or Cyt (cytolytic) proteins that are toxic to nematoceran larvae [1]. In an attempt to overcome the limitations of Bti as a larvicidal agent, microorganisms have been genetically engineered with the aim of producing Bti-based control agents that persist longer in the environment [8, 11]
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