Bacterial adaptation to low-nutrient conditions as studied with algal extracellular products

Kinetic analyses indicate that members of natural bacterial populations from 2 marine environments near Woods Hole, MA, possess enzyme-mediated transport systems which permit utilization of(14)C-labeled extracellular organic C ((14)C-EOC) prepared from the algae,Skeletonema costatum, Thalassiosira pseudonana, andDunaliella tertiolecta, and supplied over a concentration range of 15-150μC·liter(-1). It is shown that previous exposure of the bacteria to the EOC from these algae cannot explain the linear kinetic patterns obtained. Therefore, the ability to utilize algal EOC at low concentrations is a general feature of metabolically active bacterial populations. Further, as the native bacteria do not restrict this ability to a specific EOC pool, the results are consistent with the hypothesis that bacteria adapted to low nutrient environments possess uptake systems of high substrate affinity and low substrate specificity. Elevation of substrate levels with as little as 10 mg·1(-1) peptone is shown to favor development of a bacterial population that lacks these adaptations. Standard enrichment techniques typically result in the isolation of bacteria that are poor models for evaluating the ecology of native microbiota.