Tangential flow diafiltration: an improved technique for estimation of virioplankton production

Accurate estimates of viral production in natural environments are critical for assessing the impacts of viral lysis on bacterial mortality and dissolved organic matter release. Here, viral production was estimated using a tangential flow diafiltration (TFD) dilution method, which reduced viral abundance to about 25% of ambient while maintaining near ambient levels of bacterial abundance. In subsequent incubations, the rate of virus-like particle increase was measured and used to calculate viral production. TFD viral production estimates were compared to those from simultaneous incubations using a vacuum diafiltration procedure. At 4 stations in the Chesapeake and Delaware Bays, viral production averaged 4.8 +/- 1.7 x 10(10) and 5.9 +/- 4.4 x 10(10) viruses l(-1) d(-1) as assessed by the TFD and vacuum methods, respectively. The TFD procedure improved upon the vacuum-based method by recovering significantly more of the bacterial community and requiring less sample processing time. Optimization tests of the TFD procedure found that a 0.22 mu m pore size filter with a flushing rate of 40 ml min(-1), and a flushing volume 4-fold the initial sample volume gave the best combination of bacterial recovery, viral dilution, and processing time. Based on TFD viral production estimates, viral lysis was responsible for the loss of 14 to 93% of the bacterial standing stock and the release of 22 to 47 mu g C l(-1) d(-1) in the Chesapeake and Delaware Bays. These results indicate that viral lysis is a significant factor for microbial mortality and dissolved organic matter cycling within these estuaries.