title: Application of a rapid direct viable count method to deep-sea sediment bacteria.
abstract: For the first time, a Live/Dead (L/D) Bacterial Viability Kit (BacLight ) protocol was adapted to marine sediments and applied to deep-sea sediment samples to assess the viability (based on membrane integrity) of benthic bacterial communities. Following a transect of nine stations in the Fram Strait (Arctic Ocean), we observed a decrease of both bacterial viability and abundance with increasing water (1250-5600 m) and sediment depth (0-5 cm). Percentage of viable (and thus potentially active) cells ranged between 20-60% within the first and 10-40% within the fifth centimetre of sediment throughout the transect, esterase activity estimations (FDA) similarly varied from highest (13.3+/-5.4 nmol cm(-3) h(-1)) to lowest values below detection limit down the sediment column. Allowing for different bottom depths and vertical sediment sections, bacterial viability was significantly correlated with FDA estimations (p<0.001), indicating that viability assessed by BacLight staining is a good indicator for bacterial activity in deep-sea sediments. Comparisons between total L/D and DAPI counts not only indicated a complete bacterial cell coverage, but a better ability of BacLight staining to detect cells under low activity conditions. Time course experiments confirmed the need of a rapid method for viability measurements of deep-sea sediment bacteria, since changes in pressure and temperature conditions caused a decrease in bacterial viability of up to 50% within the first 48 h after sample retrieval. The Bacterial Viability Kit proved to be easy to handle and to provide rapid and reliable information. It's application to deep-sea samples in absence of pressure-retaining gears is very promising, as short staining exposure time is assumed to lessen profound adverse effects on bacterial metabolism due to decompression.
authors.affiliation: Alfred-Wegener-Institute for Polar and Marine Research, Columbusstrasse, 27568 Bremerhaven, Germany. nqueric@awi-bremerhaven.de
authors.forename: Nadia-Valérie
authors.initials: NV
authors.lastname: Quéric
authors.forename: Thomas
authors.initials: T
authors.lastname: Soltwedel
authors.forename: Wolf E
authors.initials: WE
authors.lastname: Arntz
mesh_terms: D001110:Arctic Regions; D001419:Bacteria / Q000201:enzymology / Q000254:growth & development*; D001431:Bacteriological Techniques / Q000379:methods*; D017753:Ecosystem; D004950:Esterases / Q000378:metabolism; D005456:Fluorescent Dyes / Q000737:chemistry; D019015:Geologic Sediments / Q000382:microbiology*; D008856:Microscopy, Fluorescence / Q000379:methods; D009792:Oceans and Seas
chemical_list: D005456:Fluorescent Dyes; D004950:Esterases