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

Abstract

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.