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Junier, Pilar

Nom
Junier, Pilar
Affiliation principale
Fonction
Professeure assistante
Email
pilar.junier@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/362

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  • Publication
    Accès libre
    Habitat partitioning of denitrifying bacterial communities carrying nirS or nirK genes in the stratified water column of Lake Kinneret, Israel
    Junier, Pilar 
    ;
    Kim, Ok-Sun
    ;
    Witzel, Karl-Paul
    ;
    Imhoff, Johannes F
    ;
    Hadas, Ora
    The community composition of denitrifying bacteria was studied in the stratified water column of Lake Kinneret. The nitrite reductase genes nirS and nirK were amplified by PCR from water samples taken at 1, 14, 19 and 22 m depth, which represent the epi-, meta- and hypolimnion of the lake. The PCR products were analyzed with terminal restriction fragment length polymorphism (T-RFLP) and clone libraries. The highest diversity of nirS denitrifying communities was observed at 1 m depth. According to the T-RFLP profiles and clone libraries of nirS products, 2 groups of denitrifiers were common to and dominant in all depths. Deduced protein sequences from one of these groups displayed low identity (77%) with other nirS sequences reported in GenBank. Denitrifying bacterial communities with nirK were most diverse at 22 m and showed highest similarity to those at 19 m depth. Sequences unrelated to nirK dominated the clone libraries from 1 m depth, suggesting that denitrifying bacteria with copper-containing nitrite reductase were less frequent at this depth. The results suggest that microorganisms with nirK and those with nirS respond differently to the environmental conditions in the stratified water column of Lake Kinneret.
  • Publication
    Accès libre
    Distribution of denitrifying bacterial communities in the stratified water column and sediment–water interface in two freshwater lakes and the Baltic Sea
    Kim, Ok-Sun
    ;
    Imhoff, Johannes F
    ;
    Witzel, Karl-Paul
    ;
    Junier, Pilar 
    We have studied the distribution and community composition of denitrifying bacteria in the stratified water column and at the sediment–water interface in lakes Plußsee and Schöhsee, and a near-shore site in the Baltic Sea in Germany. Although environmental changes induced by the stratification of the water column in marine environments are known to affect specific populations of denitrifying bacteria, little information is available for stratified freshwater lakes and brackish water. The aim of the present study was to fill this gap and to demonstrate specific distribution patterns of denitrifying bacteria in specific aquatic habitats using two functional markers for the nitrite reductase (nirK and nirS genes) as a proxy for the communities. The leading question to be answered was whether communities containing the genes nirK and nirS have similar, identical, or different distribution patterns, and occupy the same or different ecological niches. The genes nirK and nirS were analyzed by PCR amplification with specific primers followed by terminal restriction fragment length polymorphism (T-RFLP) and by cloning and sequence analysis. Overall, nirS-denitrifiers were more diverse than nirK-denitrifiers. Denitrifying communities in sediments were clearly different from those in the water column in all aquatic systems, regardless of the gene analyzed. A differential distribution of denitrifying assemblages was observed for each particular site. In the Baltic Sea and Lake Plußsee, nirK-denitrifiers were more diverse throughout the water column, while nirS-denitrifiers were more diverse in the sediment. In Lake Schöhsee, nirS-denitrifiers showed high diversity across the whole water body. Habitat-specific clusters of nirS sequences were observed for the freshwater lakes, while nirK sequences from both freshwater lakes and the Baltic Sea were found in common phylogenetic clusters. These results demonstrated differences in the distribution of bacteria containing nirS and those containing nirK indicating that both types of denitrifiers apparently occupy different ecological niches.