Influence of protozoan grazing on contaminant biodegradation

Abstract

The influence of protozoan grazing on biodegradation rates in samples from contaminated aquifer sediment was evaluated under aerobic and anaerobic conditions. Predator–prey biomass ratios suggested that protozoan grazing might be influencing bacterial populations. Experiments under aerobic conditions were conducted with a sediment extract fed with BTEX and treated with protozoan inhibitors (cycloheximide, neutral red, amphotericin‐B). After 10 days, BTEX losses were enhanced in the presence of protozoan inhibitors, suggesting that reduced protozoan grazing enhanced the rate of BTEX biodegradation. In tests conducted in macrocosms under anaerobic conditions, treatments included benzaldehyde (carbon substrate), benzaldehyde+cycloheximide, a live control (no carbon), and an abiotic control. In both the benzaldehyde‐only and benzaldehyde+cycloheximide treatments, repeated benzaldehyde additions resulted in an increase in the total fermenter population from 103 to 105 cells (g sediment)−1 and in the Fe‐reducing population from 101 to 105 cells g−1. However, the protozoan population remained at about 20 cells g−1 in the sediment with no cycloheximide, and there was no difference in benzaldehyde biodegradation in the presence and absence of cycloheximide, suggesting that predation was not a significant control on anaerobic benzaldehyde biotransformation.

Review: Microbial biocenoses in pristine aquifers and an assessment of investigative methods

“…Microorganisms also influence the hydraulic properties of aquifers. For example, heterotrophic bacteria contribute to the initial karstification of carbonate rocks by generating CO 2 (Gabrovsek et al 2000); biofilms may partly clog the pore spaces, while protozoans and microinvertebrates graze on these biofilms (DeLeo and Baveye 1997; Kota et al 1999). To some degree, specific micro-and macroorganisms or the entire biocenoses allow to conclude on the groundwater quality.…”

Distribution patterns of attached and suspended bacteria in pristine and contaminated shallow aquifers studied with an in situ sediment exposure microcosm

“…Kinner et al 1993, Sinclair et al 1993. Grazing on attached bacteria was proved to be an effective feeding mode for benthic protists (Starink et al 1994, Eisenmann et al 1998, and both stimulating and inhibiting effects of protozoan grazing upon the sediment bacterial community have been found (DeLeo & Baveye 1997, Kinner et al 1998, Kota et al 1999. Although bacterial communities in pristine aquifers seem to be bottom-up controlled, top-down effects from protists and meio-and macroorganisms grazing on attached bacteria may occur to a certain extent and become more important with a switch from oligotrophic to nutrient-rich conditions.…”

Meiofauna reduces bacterial mineralization of naphthalene in marine sediment

“…To our knowledge, the effect from meiofauna on PAH mineralization has not been studied previously but studies on the effects of protozoans on degradation of contaminants have been conducted (Rogerson and Berger, 1983;Kota et al, 1999;Tso and Taghon, 2006). In these studies, protozoans had a stimulatory effect on the bacterial degradation of contaminants, possibly by increasing the turnover of nutrients.…”