MEPS 147:295-300 (1997)  -  doi:10.3354/meps147295

A microbial biosensor consisting of an oxygen microelectrode with microbial cells immobilized in polyvinyl alcohol attached to the tip is described. Since the oxygen consumption of the immobilized cells is dependent on the oxidation of assimilable carbon, the biosensor allows the estimation of available dissolved organic carbon (ADOC) in sediment profiles on a microscale. Only that fraction of the ADOC can be detected which is actually respired by the test organisms. Since the biosensor works only in oxic sediments, oxygen has to be measured separately. Calibration was achieved in mineral salt medium of different oxygen content using different concentrations of carbon (glucose, acetate). The 90% response time of the biosensor was about 10 s; within 1.5 min a plateau was reached, indicating that the diffusion of oxygen from the sample was in equilibrium with the oxygen consumption of the cells. Measurements with immobilized yeast cells revealed that within the diffusive boundary layer, concentrations of ADOC increased, reaching maximum values immediately below the sediment surface. Less than 0.1% of the total organic carbon (TOC) was immediately available for microbial metabolism. Based on respiration calculated from measurements by oxygen microelectrodes in the dark, the average turnover time of ADOC within the upper 1 mm of the sediment was in the range of 50 min.

Oxygen microelectrode · Biosensor · Immobilization · Dissolved organic carbon · Sediment