The release of extracellular DNA molecules (eDNA) contributes to various biological processes, such as biofilm formation, virulence, and stress tolerance. The quantity of eDNA released by bacteria is usually regulated by extracellular nucleases that are secreted by different systems. In this study, we show that high concentrations of eDNA inhibit the growth of two strains of Deinococcaceae, Deinococcus radiodurans, and Deinococcus radiopugnans, but have no effect on other selected organisms, such as Escherichia coli. In D. radiodurans, an extracellular nuclease was shown to be secreted through the Sec pathway. Disruption of one member of this pathway, SecD/F, inhibited cell growth, suggesting that the Sec pathway plays an important role in growth rate. However, the Sec pathway mutant exhibited a greater deficiency in growth rate compared with the extracellular nuclease mutant, indicating that the pathway not only secretes the extracellular nuclease, but has other unknown functions as well.