Use of protoplasts from paired heterogenic bacterial species to detect tin contaminants: Prospects for biosensor development

Abstract

Two different bacteria gave different respiratory responses to the test analytes, tributyl tin (TBT) and cadmium as expressed by positive sigmoid responses by Halomonas sp. (slope, +1.71 [TBT]; +1.76 [Cd]) and negative sigmoid responses by Bacillus pumilis (slope, -1.06 [TBT]; -0.59 [Cd]). The EC50 values determined from Hill plots for the response of Halomonas sp. to the TBT and Cd were 1 and 8.5 mM, respectively, which were lower by a factor of 10 than the corresponding values for B. pumilis. With protoplasts of B. pumilis there was a major shift in the signal from sigmoid negative to positive with TBT (+1.35) but not Cd (-0.5), while the signals with the remaining protoplast-analyte combinations remained unchanged. For all four protoplast-analyte combinations the EC50 values were in the order of 10-100-fold lower than those for their whole cell counterparts. When other analytes were tested the protoplasts gave a similar response to tin as for TBT, but detected copper and 2,4-dichlorophenol with similar signal profiles to Cd and with lower sensitivity. The difference in signal and higher sensitivity of the two species protoplast system towards TBT/tin compared to the other analytes tested, suggests that it may feasible to develop this approach for the detection of tin residues.