A New Microbial Contact Assay for Marine Sediments (7 pp)

Abstract

Dedicated to Prof. Dr. Ulrich Forstner on his 65th birthday The number of microbiological contact tests for marine sediments is low, although microorganisms enable a rapid screening and monitoring of sediment quality and a high resolution of hazard assessment. As no single biotest can provide reliable answers concerning the potential hazard of environmental samples, a combination of bioassays needs to be applied to serve this purpose. In order to cover as many potential effects as possible, test organisms should have different sensitivities; assays should cover different exposure pathways, and measure the effect on various physiological functions. 3 different Vibrio species (V. proteolyticus, V. natriegens, V. gazogenes) were tested for their suitability as test organisms in a contact assay on the basis of their activity, sensitivity and their spectrum of salinity tolerance. As a test endpoint, dehydrogenase activity over an incubation time of 2 hours (~ 3 generations) was chosen, quantified by resazurine reduction. The test was miniaturized to 96 well plates, including a dilution series, and quality criteria were established. The assay was then tested on natural sediments from a contaminated site in the Lubeck Bight. Vibrio proteolyticus proved to be the best suited test organism out of those tested for this bioassay. The miniaturized test system revealed a coefficient of variation of positive controls in 16 tests of 17.8 %. Its application to contaminated sediments from the Lubeck Bight showed a good differentiation of samples from different depths and zones, which reflected the general contamination pattern and capping activities in that area. The miniaturized test system that has been developed for V. proteolyticus is suited to assess toxic effects of brackish and marine sediments. Due to an increased number of replicates and an extensive sediment dilution series, the degree of certainty of hazard assessment is elevated. The integration of this sediment contact assay as a complementary test in a microbiological test battery is recommended.