Competitive elimination of Enterobacteriaceae from seawater

Abstract

organisms of nonmarine origin in seawater is basically affected by the mere competition for growth-limiting nutrients, primarily carbon and energy sources (1). During recent studies on the growth kinetics of various marine isolates, data were obtained on the basis of which the role of growth competition, as compared to more specific inhibitory effects, could be evaluated and defined. A chemostat inoculated with a mixed population will select for that organism that exhibits the fastest growth rate under the specific conditions (composition of medium, temperature, etc.). These competitive processes were studied in detail (4) with sterile supplemented seawater as a medium and raw seawater as an inoculum. A number of bacterial strains belonging to different genera were enriched by varying the dilution rate or the concentration of the growth limiting substrate in the reservoir, or both. In these experiments, 0.1 to 10 mg/liter of lactate, glycerol, or glucose were added to filter-sterilized offshore seawater; ammonium and phosphate were added in sufficient concentrations to ascertain growth limitation by the carbon and energy source. Samples taken from the chemostat twice a retention time were streaked on agar that was prepared with the same medium but contained 100 mg/liter of the respective carbon source. Enrichments to at least 90% of