Early diagenesis and trophic role of extracellular DNA in different benthic ecosystems

To provide new insights into the early diagenesis of extracellular deoxyribonucleic acid ( DNA) and its relevance in trophodynamic processes, we collected sediment samples from a variety of coastal and deep-sea sites. Turnover times of extracellular DNA were approximately threefold shorter in coastal benthic systems than in deep-sea sediments (0.35 yr and 1.2 yr, respectively). This was due to the higher concentrations of bioavailable extracellular DNA in deep-sea over coastal sediments (19.8 +/- 0.6 and 9.8 +/- 2.6 mg DNA g(-1), respectively), since deoxyribonuclease (DNase) activities did not show significant differences between sampling sites (135.8 +/- 72.7 and 62.8 +/- 19.0 ng DNA g(-1) d(-1), in coastal and deep-sea sediments, respectively). The coastal benthic systems were characterized by DNase activities per prokaryotic cell significantly lower than those of their deep-sea counterparts (0.12 +/- 0.05 and 0.27 +/- 0.06 fg DNA degraded cell(-1) d(-1), respectively), although carbon production per cell was not significantly different (6.9 +/- 4.4 and 2.6 +/- 0.9 fg C cell(-1) d(-1), respectively). These results suggest that DNase activity per cell may be more dependent on the amount of bioavailable substrate rather than on prokaryotic metabolism. Extracellular DNA may supply 20% and 47% of the daily prokaryote anabolic requirements for organic phosphorous in both coastal and deep-sea sediments, respectively. Overall, our data suggest that bioavailable extracellular DNA might represent an important nutrient source for benthic heterotrophic metabolism and open new perspectives for a better understanding of the factors that influence the functioning of benthic systems.