NEW DILUTION METHOD IN MICROTITER-PLATES FOR ENUMERATION AND ENRICHMENT OF COPIOTROPHIC AND OLIGOTROPHIC BACTERIA

A new microtiter-plate dilution method was applied during the expediti on ANTARKTIS-XI/2 with RV ''Polarstern'' to determine the distribution of copiotrophic and oligotrophic bacteria in the water columns at pol ar fronts. Twofold serial dilutions were performed with an eight-chann el Electrapette in 96-wells plates by mixing 150 mu l of seawater with 150 mu l of copiotrophic or oligotrophic Trypticase-Broth, three time s per well. After incubation of about 6 months at 2 degrees C, turbidi ties were measured with an eight-channel photometer at 405 nm and comb inations of positive test results for three consecutive dilutions chos en and compared with a Most Probable Number table, calculated for 8 re plicates and twofold serial dilutions. Densities of 12 to 661 cells/ml for copiotrophs, and 1 to 39 cells/ml for oligotrophs were found. Col ony Forming Units on copiotrophic Trypticase-Agar were between 6 and 8 47/ml, which is in the same ranee as determined with the MPN method.