Porous underwater chamber (PUC) for in‐situ determination of nutrient and pollutant bioavailability to microorganisms

Abstract

Physical (e.g., temperature and light) and biogeochemical (e.g., cycling) parameters are known to affect bioavailability and toxicity of nutrients and pollutants to microorganisms. A system that would allow exposure of selected microorganisms to in situ conditions could provide relevant and novel evaluations of bioavailability. A simple and low cost 37 mL porous underwater chamber (PUC), in which test microorganisms are exposed to field conditions, is presented. The PUC is a thin, acrylic cylinder with polycarbonate membranes on each side, providing an optimal (75 cm2) exchange with the external solution. Regardless of the membrane pore size (0.4 and 5 µm), the PUC required 10 h to equilibrate with the external solution, close to the theoretical time determined for the diffusion of a model compound, the Suwannee River fulvic acid. For in situ use, the PUCs can be filled with filtered water to minimize the equilibration time. The system was validated in 20 to 60 L artificial freshwater by evaluating (1) Cd bioaccumulation by the microalga Chlamydomonas reinhardtii and (2) iron bioavailability to a cyanobacterial bioreporter in comparison with conventional bottle assays. The use of the PUC resulted in no significant differences in Cd uptake fluxes or iron bioavailability. Field experiments undertaken on Lake Erie demonstrated that the PUCs could be used to evaluate the contribution of particulate iron to iron bioavailability. Because the PUCs might not correctly reflect bioavailability for substances at low concentrations with high biouptake fluxes, a critical discussion with respect on the rate‐limiting steps of the device is presented. Several considerations that might facilitate the appropriate use of the PUCs are given.

Assessing triclosan-induced ecological and trans-generational effects in natural phytoplankton communities: a trait-based field method

“…The ideal mesocosm would maintain test populations in natural conditions with their complex and fluctuating environment (de la Broise and Palenik 2007;Hassler et al 2008), and dialysis bags have been used in the past to culture various microorganisms including phytoplankton and to assay the effects of pollutants on phytoplankton in nature (see Powers et al 1976).…”

A Novel In Situ Tool for the Exposure and Analysis of Microorganisms in Natural Aquatic Systems

“…Previous reports on such in situ exposures, under controlled conditions, are scarce (e.g., (11)). Traditionally, transplant experiments have been performed with plants (e.g., (20), for moss), invertebrates (e.g., (21), for mussels), and vertebrates (e.g., (22), for fish).…”

Cyanobacterial Bioreporters as Sensors of Nutrient Availability

“…Further, whereas chemical measures of total DFe can provide an estimate of the potential for Fe limitation, DFe need not be synonymous with bioavailable Fe. Some forms of PFe appear to be bioavailable [35,44] whereas some Fe associated with the operationally-defined dissolved phase (<0.45 mm) is not immediately available for uptake [58]. The complex chemical speciation of Fe in aquatic systems and the uncertainties associated with biological assimilation of Fe species make it difficult to ascertain the fractions of chemically detectable Fe that are readily available to phytoplankton.…”

“…While the use of Fe-responsive bioreporters has offered some evidence of transient Fe deficiency in the Great Lakes (e.g., [9,62]), it is not widespread [35,46]. A new approach whereby the bioreporter is contained in a porous underwater chamber (PUC) during incubation with unfiltered water [44] promises to offer insight into the biological cycling of Fe by regenerative processes such as grazing and viral lysis which may provide 30-80% of the algal Fe demand in surface seawater [62].…”

“…PCC 7002 [17]. Despite the fact that these strains are not particularly ecologically relevant with respect to most oligotrophic aquatic environments, these prototype strains afforded an opportunity to demonstrate the feasibility in using reporters in both freshwater [9,18,35,38,41,[44][45][46] and marine samples [17].…”