Effect of Growth Conditions and Staining Procedure upon the Subsurface Transport and Attachment Behaviors of a Groundwater Protist

Abstract

The transport and attachment behaviors of Spumella guttula (Kent), a nanoflagellate (protist) found in contaminated and uncontaminated aquifer sediments in Cape Cod, Mass., were assessed in flowthrough and static columns and in a field injection-and-recovery transport experiment involving an array of multilevel samplers. Transport of S. guttula harvested from low-nutrient (10 mg of dissolved organic carbon per liter), slightly acidic, granular (porous) growth media was compared to earlier observations involving nanoflagellates grown in a traditional high-nutrient liquid broth. In contrast to the highly retarded (retardation factor of ϳ3) subsurface transport previously reported for S. guttula, the peak concentration of porous-medium-grown S. guttula traveled concomitantly with that of a conservative (bromide) tracer. About one-third of the porousmedium-grown nanoflagellates added to the aquifer were transported at least 2.8 m downgradient, compared to only ϳ2% of the broth-grown nanoflagellates. Flowthrough column studies revealed that a vital (hydroethidine [HE]) staining procedure resulted in considerably less attachment (more transport) of S. guttula in aquifer sediments than did a staining-and-fixation procedure involving 4,6-diamidino-2-phenylindole (DAPI) and glutaraldehyde. The calculated collision efficiency (ϳ10 ؊2 for porous-medium-grown, DAPI-stained nanoflagellates) was comparable to that observed earlier for the indigenous community of unattached groundwater bacteria that serve as prey. The attachment of HE-labeled S. guttula onto aquifer sediment grains was independent of pH (over the range from pH 3 to 9) suggesting a primary attachment mechanism that may be fundamentally different from that of their prey bacteria, which exhibit sharp decreases in fractional attachment with increasing pH. The high degree of mobility of S. guttula in the aquifer sediments has important ecological implications for the protistan community within the temporally changing plume of organic contaminants in the Cape Cod aquifer.Recent findings regarding the role of protists in natural attenuation of organically contaminated aquifers 20; N. E. Kinner, R. W. Harvey, D. M. Shay, D. W. Metge, and, A. Warren, submitted for publication), in groundwater quality (25,36,37,41), and in controlling the flux of unattached bacteria in flowthrough column studies (5, 19) are leading to an increasing interest in their subsurface mobility. Although a number of recent studies examined the transport potential of oocysts of the obligate protozoan pathogen Cryptosporidium parvum through saturated porous media in laboratory microcosms (2, 9), little is known about the transport potential of protists that are indigenous to aquifers. In 1991, the groundwater nanoflagellate Spumella guttula (Kent) (18) was used in a small-scale injection-and-recovery study (12) involving a sandy, treated-sewage-contaminated aquifer. The contaminated aquifer harbors a large (up to 10 5 /g [dry weight] [gdw]) (17) and diverse (29, 30) protistan community, dominated ...

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