Evaluating use of ferricyanide-mediated respiration bioassays to quantify stimulatory and inhibitory effects on Escherichia coli populations.
A number of recent studies have utilised ferricyanide as a respiratory mediator for microbial-based assays for determining water quality parameters such as biochemical oxygen demand (BOD) and toxicity. The majority of assays published to date obtain a result by determining the difference in ferrocyanide accumulation between a test sample and one or more control samples. However, a validation of the relationship between ferrocyanide accumulation and standard measures of cell density or viability has not yet been performed. To this end, a rapid microbially catalysed ferricyanide-mediated respiration (FM-RES) assay was compared with standard plate count (SPC) and spectrophotometer (OD(600)) measurements on a growing batch culture of Escherichia coli. Good agreement was observed between all techniques, with predictable deviations noted in different phases of the growth curves. Standardised FM-RES assays showed excellent correlations with the SPC method under controlled conditions, indicating that short-term changes in microbial activity are due to a change in per-cell respiration, rather than changes in cell numbers. The FM-RES assay was then used to observe the changes in the respiration of E. coli induced by the addition of a glucose-glutamic acid (GGA) mixture, 3,5-dichlorophenol (3,5-DCP) and Ag(+) in various combinations and concentrations. Stimulation of respiration was pronounced in the presence of GGA while both 3,5-DCP and, in particular, Ag(+) demonstrated inhibitory respiratory effects. The results highlight the validity and suitability of ferricyanide-mediated respiration bioassays, with appropriate modification, to monitor either stimulatory effects on microbial populations, such as occurs with BOD, or inhibitory effects, such as occurs with toxicity assays.
Catterall
Kylie
K
Gold Coast Water, PO Box 5042, Gold Coast Mail Centre, QLD 9729, Australia.
Robertson
David
D
Teasdale
Peter R
PR
Welsh
David T
DT
John
Richard
R
D018407:Bacterial Physiological Phenomena; D015374:Biosensing Techniques / Q000379:methods*; D002733:Chlorophenols / Q000032:analysis / Q000378:metabolism; D004926:Escherichia coli / Q000254:growth & development / Q000378:metabolism*; D005292:Ferricyanides / Q000378:metabolism*; D018698:Glutamic Acid / Q000032:analysis / Q000378:metabolism; D008826:Microbial Sensitivity Tests / Q000379:methods*; D010100:Oxygen / Q000378:metabolism*; D012834:Silver / Q000032:analysis / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism*
D002733:Chlorophenols; D005292:Ferricyanides; D014874:Water Pollutants, Chemical; D018698:Glutamic Acid; D012834:Silver; C116190:3,5-dichlorophenol; D010100:Oxygen