Diversity and Structure of the Prokaryotic Communities Indigenous to Two Volcanic Lakes: Nyos and Monoun in Cameroon

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.

Metabolic activities of marine ammonia-oxidizing archaea orchestrated by quorum sensing

Ammonia-oxidizing archaea(AOA)play crucial roles in marine carbon and nitrogen cycles by fixing inorganic carbon and performing the initial step of nitrification.Evaluation of carbon and nitrogen metabolism popularly relies on functional genes such as amoA and accA.Increasing studies suggest that quorum sensing(QS)mainly studied in biofilms for bacteria may serve as a universal communication and regulatory mechanism among prokaryotes;however,this has yet to be demonstrated in marine planktonic archaea.To bridge this knowledge gap,we employed a combination of metabolic activity markers(amoA,accA,and grs)to elucidate the regulation of AOA-mediated nitrogen,carbon processes,and their interactions with the sur-rounding heterotrophic population.Through co-transcription investigations linking metabolic markers to potential key QS genes,we discovered that QS molecules could regulate AOA's carbon,nitrogen,and lipid metabolisms under different conditions.Interestingly,specific AOA ecotypes showed a preference for employing distinct QS systems and a distinct QS circuit involving a typical population.Overall,our data demonstrate that Qs orchestrates nitrogen and carbon metabolism,including the exchange of organic metabolites between AOA and surrounding heterotrophic bacteria,which has been pre-viously overlooked in marine AOA research.