PROTISTAN COMMUNITIES IN AQUIFERS - A REVIEW

Eukaryotic microorganisms (protists) are a very important component of microbial communities inhabiting groundwater aquifers. This is not un expected when one considers that many protists feed heterotrophically, ,by means of either phagotrophy (bacterivory) or osmotrophy. Protistan numbers are usually low (<10(2) per g dw of aquifer material) in pris tine, uncontaminated aquifers but may increase by several orders of ma gnitude in aquifers subject to organic pollution. small flagellates (t ypically 2-3(5) mu n in size in situ) are by far the dominant protists in aquifers, although amoebae and occasionally ciliates may also be p resent in much lower numbers. Although a wealth of new taxonomic infor mation is waiting to be brought to light, interest in the identity of aquifer protists is not exclusively academic. If verified, the followi ng hypotheses may prove to be important towards our understanding of t he functioning of microbial communities in aquifers: (1) Differences i n swimming behavior between species of flagellates lead to feeding het erogeneity and niche differentiation, implying that bacterivorous flag ellates graze on different subsets of the bacterial community, and the refore play different roles in controlling bacterial densities. (2) Ba cterivorous flagellates grazing on bacteria capable of degrading organ ic compounds have an indirect effect on the overall rates of biodegrad ation.