Filtration-induced release of dissolved free amino acids:application to cultures of marine protozoa

Abstract

We examined effects of filtration on measuring dissolved free amino acids (DFAA) in cultures of bacterivorous marine flagellates Paraphysomonas imperforata and ciliates Uronema sp. Based on comparisons of several filtration techniques, we found that syringe filtration using Acrodiscs (Gelman Sciences) did not cause an artificial increase of DFAA for cultures of both species. Filtration caused release of DFAA from Uronema sp, when cells collected on the filter surface of the Acrodiscs were exposed to air. Filtration with GF/F glass fiber filters (Whatman) also caused release of DFAA from Uronema sp., leading to overestimation of DFAA concentrations by a factor of 1.7. These results indicate that Acrodiscs with syringe filtration can be used to collect DFAA samples from cultures of protozoa and probably of other microorganisms and from natural aquatic environments.