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Applied and Environmental Microbiology, November 2007, p. 7277-7282, Vol. 73, No. 22
0099-2240/07/$08.00+0     doi:10.1128/AEM.01206-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Impact of Zooplankton Grazing on the Excystation, Viability, and Infectivity of the Protozoan Pathogens Cryptosporidium parvum and Giardia lamblia{triangledown}

S. J. Connelly,1* E. A. Wolyniak,2 K. L. Dieter,1,{dagger} C. E. Williamson,1 and K. L. Jellison2

Department of Zoology, Miami University, Oxford, Ohio,1 Department of Civil and Environmental Engineering, Lehigh University, Bethlehem, Pennsylvania2

Received 30 May 2007/ Accepted 6 September 2007

Very little is known about the ability of the zooplankton grazer Daphnia pulicaria to reduce populations of Giardia lamblia cysts and Cryptosporidium parvum oocysts in surface waters. The potential for D. pulicaria to act as a biological filter of C. parvum and G. lamblia was tested under three grazing pressures (one, two, or four D. pulicaria grazers per 66 ml). (Oo)cysts (1 x 104 per 66 ml) were added to each grazing bottle along with the algal food Selenastrum capricornutum (6.6 x 104 cells per 66 ml) to stimulate normal grazing. Bottles were rotated (2 rpm) to prevent settling of (oo)cysts and algae for 24 h (a light:dark cycle of 16 h:8 h) at 20°C. The impact of D. pulicaria grazing on (oo)cysts was assessed by (i) (oo)cyst clearance rates, (ii) (oo)cyst viability, (iii) (oo)cyst excystation, and (iv) oocyst infectivity in cell culture. Two D. pulicaria grazers significantly decreased the total number of C. parvum oocysts by 52% and G. lamblia cysts by 44%. Furthermore, two D. pulicaria grazers significantly decreased C. parvum excystation and infectivity by 5% and 87%, respectively. Two D. pulicaria grazers significantly decreased the viability of G. lamblia cysts by 52%, but analysis of G. lamblia excystation was confounded by observed mechanical disruption of the cysts after grazing. No mechanical disruption of the C. parvum oocysts was observed, presumably due to their smaller size. The data provide strong evidence that zooplankton grazers have the potential to substantially decrease the population of infectious C. parvum and G. lamblia in freshwater ecosystems.

* Corresponding author. Mailing address: Department of Zoology, Miami University, 212 Pearson Hall, Oxford, OH 45056. Phone: (513) 529-3100. Fax: (513) 529-6900. E-mail: connelsj{at}muohio.edu

{triangledown} Published ahead of print on 14 September 2007.

{dagger} Present address: 21 8th Street NE, Washington, DC 20002.

Applied and Environmental Microbiology, November 2007, p. 7277-7282, Vol. 73, No. 22
0099-2240/07/$08.00+0     doi:10.1128/AEM.01206-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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