Microbial Array for Risk Assessment (MARA): a new multi-species technology for environmental eco-toxicology testing
Posted: Wednesday 29th April 2009
Traditionally, “assessment” of the impact of environmental toxicants has been via extrapolation of chemical analysis of the medium in question; be it air, water, soil, sewage, landfill leachates, or living surfaces. While this provides interested parties with useful or even essential chemical analytical data it provides no information on the effect of these toxicants on living systems or the biosphere.
Historically, for toxicity testing of products developed for human use (e.g. a skin care product) animal testing was often the method of choice. However such testing had and still has, huge cost and ethical considerations and restraints. True “environmental samples”, on the other hand, such as effluents or soil extracts, have been monitored for toxicity using bioassays which involve higher organisms such as daphnia, fish eggs and other invertebrates. Assays involving microorganisms were largely confined to algae until the event of microbial based test systems such as Microtox® were developed. Microtox® and other luminescence based equivalents measure the effect of any potential toxicant present on the light output of a single luminous bacterial species such as Vibrio fischeri. This has the benefit of being a rapid and sensitive test, and this and similar tests have gained widespread acceptance as useful tools in monitoring environmental toxicity.
However such tests centre around the response of a single species and focus within the organism on a single genotypic feature - the Lux operon; thus a perhaps legitimate criticism is that as such they can be considered to be genetically narrow.
NCIMB based in Aberdeen, Scotland has further developed the concept of microbial arrays together with the Karolinska Institute in Sweden and with funding support from the Scottish Enterprise SMART award and dti EUREKA scheme. These awards have allowed NCIMB to extend the potential usefulness of such arrays by adding a multi-species dimension, thus presenting a more diverse population of microorganisms to perform the risk assessment.
The Microbial Assay for Risk Assessment (MARA) test developed out of the NCIMB public collection (the UK’s major repository for environmental bacteria), comprises of 11 different microbial species and includes a yeast and a spread of genetically diverse bacteria from the alpha, beta and gamma proteobacteria. These 11 species are freeze dried in situ in a 96 well micro-titre plate. When resuscitated, dilutions of the sample being tested are incubated and the plate is then scanned and read using proprietary software. Based on patterns of growth inhibition (manifested by reduced pellet formation and azo dye reduction in each well), a Microbial Toxic Concentration (MTC) is calculated.
Unlike single species tests such as Microtox®, MARA provides 11 different datasets on the sample under test and the software calculates both MTC values for each strain as well as a mean MTC for the complete array. Data accumulated from each test forms a “toxic fingerprint” unique to each sample and this can be particularly useful when regular monitoring of a system such as a factory effluent. In such industrial environments, a change in toxic profile is a useful early warning of process change, a consequence of which may have an undesirable environmental impact requiring urgent detailed chemical analysis or even process shutdown.
The potential for the MARA concept is enormous and NCIMB have further products in the pipeline currently undergoing in house evaluation for specialised market segments – these include a rapid luminescent array (LumiMARA) for water testing using both marine and freshwater isolates, and a specialised array of dermal isolates; both commensal and pathogenic, for the skin care sector (DermaMARA). With the potential to embrace many other commercial applications NCIMB is working with partners to develop MARA array systems for applications such as disinfectant testing incorporating strains which are industrial standards; the impact of nanoparticles in the environment, and custom designed arrays for client specific applications.
