Assessment of salinity-related mortality of freshwater bacteria in the saint lawrence estuary

Painchaud, Jean; Therriault, Jean‐Claude; Legendre, Louis

doi:10.1128/aem.61.1.205-208.1995

Cited by 41 publications

(25 citation statements)

References 27 publications

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“…Our data also suggest that there may be an actual succession of physiological states along the salinity gradient, where cells undergo different levels of stress along the passage from fresh-to saltwater (Painchaud et al 1995). The greatest shifts in all indices occurred within the transition zone, but not all the indices showed equally large shifts, and, in addition, the peaks or troughs were often spatially displaced.…”

Section: The Ecological Significance Of Single-cell Measurements-mentioning

confidence: 53%

Linking the physiologic and phylogenetic successions in free‐living bacterial communities along an estuarine salinity gradient

Giorgio

Bouvier

2002

Limnology & Oceanography

158

125

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In this paper we assess whether the bacterial compositional succession that occurs along an estuarine salinity gradient is accompanied by changes in both community and single-cell metabolic activity in the free-living bacterioplankton. In addition, we explore whether up-and downstream estuarine communities, which are dominated by different phylogenetic groups, show distinct patterns in single-cell activity and characteristics. We have characterized the physiological succession of the bacterioplankton along the salinity gradient in the Choptank River Estuary (Maryland), using a combination of indices of single-cell activity, which include respiratory activity, membrane polarization and integrity, and DNA and RNA contents, combined with flow cytometry. We have also measured bacterioplankton community production, respiration, and growth efficiency along the estuary. Our data suggest that the sharp phylogenetic succession that occurs within the fresh to saltwater transition region is accompanied by profound metabolic changes both at the single-cell and community levels and that the phylogenetic succession occurs together with measurable physiological stress. The different indices of single-cell characteristics that we have used converge to suggest that within the fresh to saltwater transition zone, there is generalized decline in growth and possibly a loss of activity and even significant cell mortality. At the community level, these changes in singlecell physiology at the site of the phylogenetic succession appear to translate into a generalized decline in bacterial growth efficiency with a decrease in bacterial growth and production but an actual increase in bacterial carbon consumption. Our data also suggest that different phylogenetic groups may have intrinsically different levels of single-cell activity or at least respond differently to the activity assays that we currently use.There are now a relatively large number of published studies that have described the bacterial composition in a range of aquatic ecosystems by use of a variety of molecular techniques. Overall, these studies have shown, for example, that bacterial communities in fresh-and saltwater systems are often dominated by very different taxonomic groups, even at the broadest phylogenetic levels (Glöckner et al. 1999;Giovanonni and Rappé 2000). The bacterial phylogenetic succession that occurs along environmental gradients, such as salinity gradients, has received considerably less attention than the description of the phylogenetic composition in individual systems. There are at least two fundamental aspects of the phylogenetic succession in bacterioplankton assemblages along environmental gradients that remain to be explored. First, it is still unclear whether the succession proceeds mostly as a physical replacement of major phylogenetic groups or whether the succession proceeds through activation/inactivation of the various groups that are already present in the assemblage. Second, it is still unclear whether 1 Present address: Dépt des ...

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Section: The Ecological Significance Of Single-cell Measurements-mentioning

confidence: 53%

Linking the physiologic and phylogenetic successions in free‐living bacterial communities along an estuarine salinity gradient

Giorgio

Bouvier

2002

Limnology & Oceanography

158

125

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“…These limits varied over seasons but in each case corresponded well with the salinity range of the transition (4 to 10), suggesting that salinity may play a significant role in the transition between ␣ and ␤proteobacteria. However, previous studies have also shown that osmotic changes of 10 typically result in only modest declines in bacterial growth rate (Painchaud et al 1995). It is thus not clear whether the range in salinity alone observed along the Choptank and Pocomoke River estuaries was enough to drive the bacterial community succession.…”

Section: Discussionmentioning

confidence: 93%

Compositional changes in free‐living bacterial communities along a salinity gradient in two temperate estuaries

Bouvier

Giorgio

2002

Limnology & Oceanography

344

232

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There is now clear evidence for major differences in heterotrophic bacterial composition between freshwater and marine ecosystems. A fundamental question that remains unresolved is whether the compositional succession occurs by a gradual replacement of the major phylotypes, or whether there are drastic compositional shifts in discrete areas along the gradient from one system to another. The aim of this study is to examine the change in the phylogenetic composition of the free-living bacterioplankton across the salinity gradient in both the Choptank and the Pocomoke Rivers, both subestuaries of the Chesapeake Bay, using fluorescence in situ hybridization (FISH). The proportion of free-living cells that could be detected using FISH varied widely (3 to 80%), and the majority of cells detected belonged to bacteria, whereas archaea represented less than 3%. The distribution of the different members of bacteria exhibited a clear pattern along the salinity gradient, with the dominance of ␣-proteobacteria in the lower, saltwater regions and of ␤-proteobacteria in the upper freshwater regions. The cytophaga-flavobacterium cluster prevailed in the turbidity maximum located in the middle estuary, and the ␥-proteobacteria showed sporadic peaks along the transect that may have been related to local events. The replacement of ␣-for ␤-proteobacteria along the salinity gradient was not gradual but rather occurred rapidly within the turbidity maximum region of the estuaries where the fresh and salt waters mix. The pattern of phylogenetic succession was linked to the development of the turbidity maximum, which is related to rainfall and the ensuing hydrological conditions. There is indication that the phylogenetic succession is accompanied by strong physiological changes in the bacterial assemblage, expressed as a decline in bacterial growth efficiency and community production. The transition appears not to be simply the result of conservative mixing of riverine and estuarine bacterial assemblages, but rather appears to involve cell inactivation and/or death. Different molecular approaches are converging to show that there are major differences in the phylogenetic composition of bacterial assemblages between terrestrial and aquatic systems, and also among different aquatic ecosystems (Amann et al. 1995; Glöckner et al. 1999;Rappé et al. 2000). For example, studies using fluorescence in situ hybridization (FISH; e.g., Glöckner et al. 1999) have shown that lakes and rivers are generally dominated by the beta-subclass proteobacteria (␤-proteobacteria), whereas the alpha-subclass proteobacteria (␣-proteobacteria) and the cytophaga-flavobacterium cluster (CF) are more prevalent in marine areas. González and Moran (1997) and Crump et al. (1999) have used PCR to show strong compositional changes in the bacterioplankton between freshwater and saltwater portions of the estuaries. Similarly, Murray et al. (1996) suggest a replacement of the phylotypes along the environmental gradient in Tomales Bay and San Francisco Bay. The fact...

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“…Salinity in this freshwater-saltwater transition zone ranges from 0.2 to 10 and turbidity reaches several hundred NTU. There is a shift in the bacterial community across the ETZ, from free-living to attached cells (Painchaud et al 1995), and the food web structure changes substantially. Amphipods (Gammarus spp.)…”

Section: Methodsmentioning

confidence: 99%

Trophic position of zebra mussel veligers and their use of dissolved organic carbon

et al. 2006

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We evaluated by stable isotope analysis the trophic structure of an estuarine transition zone (ETZ) food web and the role of an invasive species, the veliger stage of the zebra mussel Dreissena polymorpha. In the St. Lawrence ETZ, where zebra mussel veligers are now the dominant zooplankton in summer, d 13 C ranged from 231.2% (seston) to 216.1% (adult fish) and d 15 N ranged from 2.6% to 17.4%. Isotopic analysis of samples indicated that the overall food web was largely supported by autochthonous phytoplankton rather than by allochthonous terrestrial carbon. Large differences among the isotopic signals of veligers, cladocerans, and copepods suggested the use of different proportions of food items, and the isotopic values of fish larvae indicated no significant assimilation of veligers. The d 13 C signature of the veligers was in a range consistent with feeding on free-living bacteria and dissolved organic carbon (DOC) or both, and freshwater algae incubated in situ. To investigate the possibility of DOC uptake by the veligers, we incubated veligers on 14 C-labelled algal lysates. There was rapid uptake of DOC and incorporation into biomass, equivalent to 6% of the soft tissue dry weight per hour. Zebra mussel veligers are likely using autochthonous DOC as an alternate food source, and they occupy an exotic trophic position in which there is little direct interaction with other major components of the ETZ food web.

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Assessment of salinity-related mortality of freshwater bacteria in the saint lawrence estuary

Cited by 41 publications

References 27 publications

Linking the physiologic and phylogenetic successions in free‐living bacterial communities along an estuarine salinity gradient

Linking the physiologic and phylogenetic successions in free‐living bacterial communities along an estuarine salinity gradient

Compositional changes in free‐living bacterial communities along a salinity gradient in two temperate estuaries

Trophic position of zebra mussel veligers and their use of dissolved organic carbon

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