Vertical structure of small eukaryotes in three lakes that differ by their trophic status: a quantitative approach

Abstract

In lakes, the diversity of eukaryotic picoplankton has been recently studied by the analysis of 18S ribosomal RNA gene sequences; however, quantitative data are rare. In this study, the vertical structure and abundance of the small eukaryotic size fraction (0.2-5 lm) were investigated in three lakes by tyramide signal amplification-fluorescent in situ hybridization targeting six phylogenetic groups: Chlorophyta, Haptophyta, Cercozoa, LKM11, Perkinsozoa and fungi. The groups targeted in this study are found in all lakes; however, both the abundance and structure of small eukaryotes are dependent on the system's productivity and depth. These data highlighted the presence of Chlorophyta contributing on an average to 19.3%, 14.7% and 41.2% of total small eukaryotes in lakes Bourget, Aydat and Pavin, respectively. This study also revealed the unexpected importance of Haptophyta, reaching 62.8% of eukaryotes in the euphotic zone of Lake Bourget. The high proportions of these pigmented cells highlight the underestimation of these groups by PCR-based methods. The presence of pigmented Chlorophyta in the deepest zones of the lakes suggests a mixotrophic behaviour of these taxa. We also confirmed the presence of putative parasites such as Perkinsozoa (5.1% of small eukaryotes in Lake Pavin and Bourget) and, with lower abundances, fungi (targeted by the MY1574 probe). Cells targeted by LKM11 probes represented the second group of abundance within heterotrophs. Open questions regarding the functional roles of the targeted groups arise from this study, especially regarding parasitism and mixotrophy, which are interactions poorly taken into account in planktonic food web models.

Contrasting taxonomic stratification of microbial communities in two hypersaline meromictic lakes

“…The depth profiles of ammonium concentration were comparable for both Ursu and Fara Fund lakes, and similar to the ones described in other stratified lakes (Auguet et al, 2012;La Cono et al, 2013;Yau et al, 2013). The vertical profiles of nutrients (sulfate, sulfide, nitrite, nitrate and phosphate) were found to be a result of sedimentation, biogeochemical cycling or conservative mixing (Pasche et al, 2009), and were also comparable with those found in other studied lakes (Lepère et al, 2010;La Cono et al, 2013;Marteinsson et al, 2013).…”

Evaluation of DNA extraction methods for freshwater eukaryotic microalgae

“…In contrast, the study of microalgae within natural and engineered freshwater systems using molecular biology techniques is in its infancy. A few studies have been carried out on photoautotrophic picoplankton communities from lakes using fluorescence in situ hybridisation (FISH) (Lepere et al, 2010) and clone libraries, based on the 18S rRNA gene (See et al, 2005;Lefranc et al, 2005), though the majority of freshwater studies focus on cyanobacteria (Zwart et al, 2005;Ye et al, 2011). Very few studies have used molecular approaches to study microalgal communities in wastewater treatment.…”

High habitat-specificity in fungal communities in oligo-mesotrophic, temperate Lake Stechlin (North-East Germany)

“…The few studies that have investigated lake or pond sediments reported Chytridiomycota and Rozellomycota (at that time referred to as LKM11 & LKM15) to be the dominant fungal phyla (Luo et al 2005;Slapeta et al 2005). Rozellomycota species appear to occur in the hypolimnion of lakes (Lepère et al 2010) and also in anoxic habitats (Jones et al 2011), but their ecological function remains unclear . Similarly enigmatic was the appearance of Zygomycota (Mortierella) at the sediment surface in our study.…”

“…Zhao et al 2011;Lefèvre et al 2012;Taib et al 2013). Several studies have found evidence for vertical and horizontal structuring of fungal communities in the water column (Lefèvre et al 2007;Chen et al 2008; Lepère et al 2010), suggesting that there is an important spatial component of diversity. A recent meta-analysis of global diversity found that aquatic fungi clustered in habitat-specific biomes, with freshwater biomes having the highest diversity at the phylum level (Panzer et al 2015).…”