The application of viable count procedures for measuring viable cells in the various marine environments

Abstract

To investigate whether the use of direct viable count (DVC), quantitative viable count (qDVC), colony-forming units and the contribution of capsule-bearing bacteria to the total number of bacteria and esterase-active bacteria could be used to clearly differentiate viable cells in various trophic status of seawater. Hundred and four marine isolates from various marine environments in Turkey (Western Black Sea, northern part of the Sea of Marmara, Northern Aegean Sea and eastern part of the Sea of Marmara) were screened. Seawater samples were taken from the surface (the upper 0-30 cm) and deeper layers (from 5 to 500 m) of the sea at different time periods between February 2002 and June 2007. For the assessment of cell elongation, minor modifications were made on DVC procedure in order to optimize the concentration of yeast extract and incubation time for enumeration of bacteria in response to nutrient addition. The best results were obtained when the yeast extract was used at a final concentration of 250 mg l(-1) (at 35 degrees C 24 h incubation) for bacteria isolated from eutrophic areas and a final concentration of 50 mg l(-1) for those selected from oligotrophic areas. A positive correlation was found between the trophic level and the level of metabolically active bacteria. Among these methods, the bacterial number obtained by qDVC is higher than those gained by other methods. The results indicate that the qDVC procedure could easily differentiate between viable cells and dormant or dead cells. We suggest that this method may be applicable to detecting the level of metabolic potential of bacterial communities in marine environments. The study resulted in increased knowledge on the applicability of the qDVC method that arranges the substrate amount and incubation time as well as on the comparison of various viable bacteria count procedures related to trophic situation of seawater samples.