Molecular analysis of the diversity of genus Psychrobacter present within a temperate estuary.

Many members of the genus Psychrobacter are endemic in extremely cold and saline environments and the genus has been described as only marginally successful in warmer habitats. In a previous study the Psychrobacter genus was, unexpectedly, the most frequently isolated bacterial genus from the sea-surface microlayer (SML) and the underlying water (UW) of a temperate estuary (Ria de Aveiro, Portugal). Here we analysed the diversity in Psychrobacter populations inhabiting this estuary. Samples were collected at three dates and three locations from sea-SML and UW. Isolated Psychrobacter strains were well-adapted to temperatures and salt concentrations above the ones described as optimal for most members of this genus. Hydrocarbon-degrading potential was not confirmed for these strains. We developed and optimized a reliable and specific denaturing gradient gel electrophoresis (DGGE)-based method for the analysis of Psychrobacter populations in aquatic systems. DGGE profiles inferred that Psychrobacter populations were very stable in the estuary, a strong indication for the presence of well-adapted phylotypes. The analysis of genus-specific clone libraries revealed a surprisingly high diversity among Psychrobacter in Ria de Aveiro. Results indicated that novel species were probably cultivated. Significant differences between sea-SML and UW Psychrobacter communities were revealed. Observed diversity trends may be related to environmental factors such as salinity and/or anthropogenic pressures such as contamination with hydrocarbons.