Influence of protozoan grazing on contaminant biodegradation

The influence of protozoan grazing on biodegradation rates in samples from contaminated aquifer sediment was evaluated under aerobic and anaerobic con ditions. Predator-prey biomass ratios suggested that protozoan grazing migh t be influencing bacterial populations. Experiments under aerobic condition s were conducted with a sediment extract fed with BTEX and treated with pro tozoan inhibitors (cycloheximide, neutral red, amphotericin-B). After 10 da ys, BTEX losses were enhanced in the presence of protozoan inhibitors, sugg esting that reduced protozoan grazing enhanced the rate of BTEX biodegradat ion. In tests conducted in macrocosms under anaerobic conditions, treatment s included benzaldehyde (carbon substrate), benzaldehyde+cycloheximide, a l ive control (no carbon), and an abiotic control. In both the benzaldehyde-o nly and benzaldehyde+cycloheximide treatments, repeated benzaldehyde additi ons resulted in an increase in the total fermenter population from 10(3) to 10(5) cells (g sediment)(-1) and in the Fe-reducing population from 10(1) to 10(5) cells g(-1). However, the protozoan population remained at about 2 0 cells g(-1) in the sediment with no cycloheximide, and there was no diffe rence in benzaldehyde biodegradation in the presence and absence of cyclohe ximide, suggesting that predation was not a significant control on anaerobi c benzaldehyde biotransformation. (C) 1999 Published by Elsevier Science B. V. All rights reserved.