Isolation and distribution of oligotrophic marine bacteria

Abstract

A useful plate culture method for isolating oligotrophic bacteria found in the low-nutrient environment of the open sea was developed. The method uses a glass-fiber filter substitute for agar. Nutritional requirements of oligotrophic bacteria consisted of a dilute nutrient solution containing 16.8 mg C/l total organic C aseptically added to the sterilized filter. Distribution of bacteria in oceanic and neritic seawater was determined using the membrane filter method. In the case of seawater containing less that 0.5 mg/l dissolved carbohydrates, plate counts of oligotrophic bacteria were several- to 100-fold greater than the heterotrophic bacterial counts enumerated by standard methods routinely used for enumeration. In seawater containing approximately over 0.5 mg/l dissolved carbohydrates, heterotrophic bacterial counts were 10-fold greater than oligotrophic bacterial counts.