Turbidity measurements in 96-wells microplates to determine the densities of copiotrophic and oligotrophic bacteria with the Most-Probable-Number-method during POLARSTERN cruise ANT-XI/2

A new microtiter-plate dilution method was applied during the expedition ANTARKTIS-XI/2 with RV Polarstern to determine the distribution of copiotrophic and oligotrophic bacteria in the water columns at polar fronts. Twofold serial dilutions were performed with an eight-channel Electrapette in 96-wells plates by mixing 150 µl of seawater with 150 µl of copiotrophic or olitrophic Trypticase-Broth, three times per well. After incubation of about 6 month at 2 °C, turbidities were measured with an eight-channel photometer at 405 nm and combinations of positive test results for three consecutive dilutions chosen and compared with a Most Probable Number table, calculated for 8 replicates and twofold serial dilutions. Densities of 12 to 661 cells/ml for copiotrophs, and 1 to 39 cells/ml for oligotrophs were found. Colony Forming Units on copiotrophic Trypticase-Agar were between 6 and 847 cells/ml, which is in the same range as determined with the MPN method.

(Table 1) Chloride concentrations in water obtained from observation wells on Helgoland Dune, North Sea

The hydrogeological conditions are unfavourable for a sufficient supply of drinking-water. The small size of the catchment area, the large hydraulic gradient inside the steep 'Buntsandstein'-cliff and the low geodetic level of the 'Dune Island' and the foreshore at the eastern foot of the cliff do not allow the formation and recharge of a sufficiently exploitable geodetic freshwater dome over the underlying saltwater. This means that until recently the provision of sufficient drinking-water for the island's inhabitants, for its garrison as well as for visiting ships was a problem. This problem has now been solved by the desalination of seawater.