Abstract
This study explores the diversity and structure of prokaryotic communities (Archaea and Bacteria) of 2 tropical volcanic lakes (Nyos and Monoun) in Cameroon, using 16SrRNA sequences. Metagenomics analysis of sequences showed that most OTUs (Operational Taxonomic Units) were associated with 26 phyla (23 for Bacteria and 3 for Archaea) in Nyos and 36 phyla (33 for Bacteria and 3 for Archaea) in Monoun. In both lakes, Proteobacteria for Bacteria and Crenarchaea for Archaea were predominant and present at all depths but in different proportions. Bacterial community compositions were generally dominated by members of Proteobacteria, Firmicutes, Actinobacteria, Chloroflexi and Bacteroidetes covering about 98% of the sequences. Crenarchaea, Thaumarchaea and Euryarchaea were the three main phyla of Archaea common to both lakes. The amount of virus and total bacteria was determined by flow cytometry technic and the evaluated ratio ranged from 0.2 to 1.2 at Nyos and from 0.6 to 2.6 at Monoun. For both lakes, the correlation was very significant between viruses and total bacteria. The depth-dependent variability is discussed with chemical and physical environmental parameters. These could significantly influence virus-mediated bacterial lysis and abundance and vertical stratification of the prokaryotic community.
Highlights
Crater lakes are strongly influenced by volcanic or post-volcanic activities due to their position, act as chemical traps for magmatic volatiles
Bacterial community compositions were generally dominated by members of Proteobacteria, Firmicutes, Actinobacteria, Chloroflexi and Bacteroidetes covering about 98% of the sequences
The remaining rRNA 16S sequences were clustered into “molecular species” (OTU) at a 97% similarity threshold according to Kim et al [37] with vsearch and OTUs representing less than 0.005% of the total sequences were removed
Summary
Crater lakes are strongly influenced by volcanic or post-volcanic activities due to their position, act as chemical traps for magmatic volatiles. Catastrophic CO2 outgassing occurred on 15th August 1984 at Lake Monoun and on 21st August 1986 at Lake Nyos, killing 37 and 1746 people, respectively [2] [3] [4] [5]. These authors highlighted the vertical distribution of bacterial communities and Archaea in Lakes Nyos and Monoun. Viruses are considered to constitute an important component of aquatic microbial communities They have been shown to be the most abundant biological entities in the plankton, where they play a crucial role in bacterial mortality and diversity [21] [22] [23]. We sampled the water column of Lake Nyos and Monoun and analysed viral communities with their potential prokaryotic hosts. We had four objectives: 1) analyze the diversity of prokaryotes (Bacteria and Archaea) by high throughput sequencing; 2) evaluate and compare the total abundances of pro-
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