Protistan communities in aquifers: a review

Abstract

Eukaryotic microorganisms (protists) are a very important component of microbial communities inhabiting groundwater aquifers. This is not unexpected 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 pristine, uncontaminated aquifers but may increase by several orders of magnitude in aquifers subject to organic pollution. Small flagellates (typically 2-3(5) microns in size in situ) are by far the dominant protists in aquifers, although amoebae and occasionally ciliates may also be present in much lower numbers. Although a wealth of new taxonomic information is waiting to be brought to light, interest in the identity of aquifer protists is not exclusively academic. If verified, the following hypotheses may prove to be important towards our understanding of the functioning of microbial communities in aquifers: (1) Differences in swimming behavior between species of flagellates lead to feeding heterogeneity and niche differentiation, implying that bacterivorous flagellates graze on different subsets of the bacterial community, and therefore play different roles in controlling bacterial densities. (2) Bacterivorous flagellates grazing on bacteria capable of degrading organic compounds have an indirect effect on the overall rates of biodegradation.

Degradation of trace concentrations of the persistent groundwater pollutant 2,6-dichlorobenzamide (BAM) in bioaugmented rapid sand filters

“…We observed a rapid increase in protozoan cell density following inoculation of up to 10 4 /cm 3 . Small bacterivorous flagellates, the most abundant group of protozoa in the filters, have previously been shown to dominate in groundwater aquifers although amoebae and ciliates may also be present (Novarino et al, 1997). Assuming that 10e100 bacteria are consumed per flagellate per hour (Sherr et al, 1983;Weisse, 1990), protozoa may cause a loss of 10 6 -10 7 /cm 3 bacteria per day in the top of the filters.…”

Springs of the Alps – Sensitive Ecosystems to Environmental Change: From Biodiversity Assessments to Long-term Studies

“…Protoza -especially ciliates -were studied to some extent in groundwater and mosses -one of the most important substrates in springs -and, for these habitats, even review papers are available (Novarino et al, 1997;Foissner, 2000, respectively). Spring protozoa, however, do not seem to have received much attention so far (Cleven & Su¨ss, 2006), with the partial exception of thermal and mineral springs (e.g.…”

A tiered framework for assessing groundwater ecosystem health

“…2006). The majority of microbes are sparsely dispersed as single cells or small colonies attached to sediment surfaces, providing a food source for invertebrates (Novarino et al, 1997;Humphreys, 2006). Generally less than 1% of available sediment surfaces are colonized by bacteria (Griebler et al, 2002;Anneser et al, 2010), with healthy, undisturbed aquifers tending to have very low microbial diversity and activity relative to surface waters (Griebler & Lueders, 2009), due mainly to naturally low concentrations of nutrients, carbon and oxygen (Gounot, 1994).…”