Anaerobic Microbial Communities in Lake Pavin, a Unique Meromictic Lake in France

Abstract

The Bacteria and Archaea from the meromictic Lake Pavin were analyzed in samples collected along a vertical profile in the anoxic monimolimnion and were compared to those in samples from the oxic mixolimnion. Nine targeted 16S rRNA oligonucleotide probes were used to assess the distribution of Bacteria and Archaea and to investigate the in situ occurrence of sulfate-reducing bacteria and methane-producing Archaea involved in the terminal steps of the anaerobic degradation of organic material. The diversity of the complex microbial communities was assessed from the 16S rRNA polymorphisms present in terminal restriction fragment (TRF) depth patterns. The densities of the microbial community increased in the anoxic layer, and Archaea detected with probe ARCH915 represented the largest microbial group in the water column, with a mean Archaea/ Eubacteria ratio of 1.5. Terminal restriction fragment length polymorphism (TRFLP) analysis revealed an elevated archaeal and bacterial phylotype richness in anoxic bottom-water samples. The structure of the Archaea community remained rather homogeneous, while TRFLP patterns for the eubacterial community revealed a heterogeneous distribution of eubacterial TRFs.Permanent anoxic basins are of great interest to microbial ecologists, and during the last decade several papers have been published on microbial assemblages from different marine anoxic basins (e.g., see references 42 and 36). Among permanent anoxic aquatic systems, meromictic lakes are unusual and provide a special opportunity for research in aquatic biology for several reasons, e.g., the high physical stability of the water masses, clearly separated compartments, a relatively constant vertical stratification of bacterial populations, a compact and stable transition zone between the oxic mixolimnion and the anoxic monimolimnion, and in many cases the presence of a dense microbial community at the redox transition zone (6). These small and well-defined ecosystems can be useful for studying anaerobic microbial community structure and diversity and providing information on global carbon cycling and biogeochemical processes. Although molecular characterizations of microbial communities from Lake Saelenvannet (31, 41), Lake Cadagno (6), Mono Lake (18), and Mariager Fjord (34, 40) have been reported, the microbial populations and communities living in anaerobic zones of meromictic lakes remain largely unexplored.This paper focuses on the in situ distribution, abundance, and diversity of the Bacteria and Archaea communities in the anoxic zone of Lake Pavin, which has the advantage of being in a steady state (28). We have conducted culture-independent studies of the anoxic water column of Lake Pavin and of samples collected from the oxic zone to provide comparative information. Terminal restriction fragment length polymorphism (TRFLP) and fluorescent in situ hybridization analyses were performed on samples from between 50-and 90-m depths to characterize the microbial assemblages using 16S rRNA genes. Because previous geochemic...

Vertical Distribution of Functional Potential and Active Microbial Communities in Meromictic Lake Kivu

“…Besides, the anoxic water compartment of Lake Kivu was also more diverse in types as pointed out by the richness estimations (p<0.02). It was previously suggested that anoxic environments maintain a higher diversity of energetic pathways and that this complexity permits the retention of higher metabolic and thus ecological diversity [3,84].…”

“…It has a surface area of 2370 km 2 , a total volume of 580 km 3 , and a maximum depth of 485 m. Surface waters are considered to be oligotrophic with moderate primary production compared to other African lakes [22,23]. Further details on the hydrology, physicochemistry, and biology of the lake are published elsewhere [22][23][24][25].…”

“…Meromictic lakes are good model systems for microbial ecology research due to the high vertical stability of the water masses and physicochemical gradients (in particular oxygen) that lead to relatively constant stratification of microbial populations [1][2][3]. Since microbes are key players in biogeochemical cycles, investigations on microbial diversity and community composition are important to understand the ecological functioning of lakes.…”

Relationships between physico-chemical and microbiological parameters in the monimolimnion of a forest meromictic lake

“…In our study, we observed a decrease of DGGE bacterial OTUs number with depth. Øvreås et al (1997) and Lehours et al (2005Lehours et al ( , 2007 also found that the structures of both the bacterial and archaeal communities in the anoxic zone of a meromictic lake changed with depth and the number of Bacterial OTUs bands decreased with depth. On the other hand, the numbers of Archaeal populations usually increased with depth (Øvreås et al 1997(Øvreås et al , Lehours et al 2005.…”

16S rRNA Gene Microarray Analysis of Microbial Communities in Ethanol-Stimulated Subsurface Sediment

“…The 16S microarray approach is also subject to such bias, since the DNA analyzed on the array was generated by PCR. Both the 27F-927R (used for the clone libraries) and 27F-1492R primers (used for the 16S microarray) target all known bacteria and have been widely used in previous microbial ecological studies (5,14,18,20,27,30). Discrepancy in the assessment of bacterial diversity due to differences in the primer sets used was thus probably insignificant, especially given that all of the sequences identified in the clone libraries were detected by the array.…”