Bacterial uptake and utilization of dissolved DNA

Abstract

Concentrations and bacterial uptake of extracellular dissolved DNA (D-DNA) were followed d u n n g a 2 wk period in 5300 1 mesocosms under natural and enriched nutrient conditions in an estuary. The nutnent addition (21 mg C I-', 6 m g N I-' and 2.3 m g P 1.') caused a 10-to 15-fold increase of the natural bacterial populations, followed by a rapid decline. D-DNA in the mesocosms varied from 2 to 11 pg I-' Maximum concentrations and uptake rates of D-DNA, determined from the uptake of [3H]labelled h H ~n d DNA, coincided with the highest bacterial growth rates. Bacterial uptake of D-DNA ranged from 0.04 to 0.9 pg I-' h-' Before the nutrient additions, D-DNA was estimated to account for up to 6. 8 and 46% of the bacterial C, N and P requirements, respectively. Addition of the nutrients reduced these values to 0.8, 2 and g % , respectively Test of uptake preference by the bacterioplankton for DNA at different sizes (100, 250 and 569 bp) demonstrated that the smallest DNA fragment was favoured over the larger fragments Most of the assimilated DNA was incorporated into cell constituents and could not be extracted after treatment xvith tnchloroacetic acid. Our experiments suggest that D-DNA nlay be an important source of nutrients, especially phosphorus, to bacterioplankton.