CSIRO PUBLISHING Review www.publish.csiro.au/journals/ajc Aust. J. Chem. 2005, 58, 237–245 Ferricyanide-Mediated Microbial Reactions for Environmental Monitoring Kristy Morris, A Huijun Zhao, A and Richard John A,B A School of Environmental andApplied Sciences, Griffith University, Gold Coast Campus, Gold Coast QLD 9726, Australia. B Corresponding author. Email: r.john@griffith.edu.au The ability of microorganisms to use ferricyanide as an alternative electron acceptor for respiratory processes has been known for nearly 100 years. More recently, the use of ferricyanide-mediated bioreactions for environmental monitoring has received much attention. This paper reviews the recent developments of these mediated microbial processes for rapid biochemical oxygen demand analysis and direct toxicity assessment during the past five years. The ability of eukaryotic microorganisms to use ferricyanide as an alternative electron acceptor for a range of applications is also described. Manuscript received: 2 February 2005. Final version: 3 March 2005. Introduction The ability of microorganisms to use redox mediators as alter- native electron acceptors for metabolic processes has been exploited widely for clinical and environmental applications over the past few decades. Redox mediators such as the fer- ricyanide ion can replace oxygen as the terminal electron acceptor in the respiratory pathway of heterotrophic micro- organisms, and are ultimately reduced. Because these media- tors are typically coloured and/or electroactive, quantification of the reduced form of the mediator can be accomplished Richard John obtained his Ph.D. (1993) from the University ofWollongong,Australia, dealing with the chemical and electrochem- ical properties of heterocyclic conducting polymers. Fellowships from the Royal Society and theAustralian Research Council allowed him to carry out post-doctoral studies at Oxford University and at the University ofWollongong. In 1996 he was appointed as a lecturer at Griffith University. From 2000–2004 he was the elected Chair of the Electrochemistry Division of the Royal Australian Chemical Institute. His research interests include the development of new analytical methodologies for environmental and clinical analysis, the electrochemistry of new materials, and the education and communication of science. He has published over 50 international peer-reviewed research articles as well as several book chapters and two patents. Kristy Morris is a Ph.D. student at Griffith University, who has just submitted her thesis for examination. Her research studies have focussed on the development of a rapid assay for biochemical oxygen demand employing ferricyanide-mediated microbial reactions. She has so far co-authored five papers in this area. Kristy is currently pursuing post-doctoral opportunities in the USA. Huijun Zhao is an electrochemist, having obtained his Ph.D. in 1994 from the University ofWollongong. He currently holds an Associate Professor position at Griffith University. His research activities include electromembrane separations, energy storage materials/secondary batteries, photocatalysis, biosensing techniques, and on-line environmental analytical methods. He has published in excess of 50 papers in international peer-reviewed journals as well as several patents in these fields. by optical and/or electrochemical methods to quantify the amount of microbial activity.The latter method, in particular, has provided a simple, rapid, and inexpensive way to measure a wide variety of microbial metabolic processes. While redox-mediated microbial processes have been known for nearly 100 years, the last decade has seen a resurgence in interest in these mediated bioreactions. In par- ticular, the use of the ferricyanide ion coupled with microbial processes for environmental monitoring has been the focus of many recent studies. This paper provides a summary © CSIRO 2005 10.1071/CH05038 0004-9425/05/040237