Diversity and metabolism of marine bacteria cultivated on dissolved DNA

Dissolved DNA (dDNA) is a potentially important source of energy and nutrients in aquatic ecosystems. However, little is known about the identity, metabolism, and interactions of the microorganisms capable of consuming dDNA. Bacteria from Eel Pond (Woods Hole, MA) were cultivated on low-molecular-weight (LMW) or high-molecular-weight (HMW) dDNA, which served as the primary source of carbon, nitrogen, and phosphorus. Cloning and sequencing of 16S rRNA genes revealed that distinct bacterial assemblages with comparable levels of taxon richness developed on LMW and HMW dDNA. Since the LMW and HMW dDNA used in this study were stoichiometrically identical, the results confirm that the size alone of dissolved organic matter can influence bacterial community composition. Variation in the growth and metabolism of isolates provided insight into mechanisms that may have generated differences in bacterial community composition. For example, bacteria from LMW dDNA enrichments generally grew better on LMW dDNA than on HMW dDNA. In contrast, bacteria isolated from HMW dDNA enrichments were more effective at degrading HMW dDNA than bacteria isolated from LMW dDNA enrichments. Thus, marine bacteria may experience a trade-off between their ability to compete for LMW dDNA and their ability to access HMW dDNA via extracellular nuclease production. Together, the results of this study suggest that dDNA turnover in marine ecosystems may involve a succession of microbial assemblages with specialized ecological strategies.