Bimodal distribution of seafloor microbiota diversity and function are associated with marine aquaculture.

The aim of the current work was to investigate the impact of marine aquaculture on seafloor biogeochemistry and diversity from pristine environments in the northern part of Norway. Our analytical approach included analyses of 182 samples from 16 aquaculture sites using 16S and 18S rRNA, shotgun analyses, visual examination of macro-organisms, in addition to chemical measurements. We observed a clear bimodal distribution of the prokaryote composition and richness, determined by analyses of 16S rRNA gene operational taxonomic units (OTUs). The high OTU richness cluster was associated with non-perturbed environments and farness from the aquaculture sites, while the low OTU richness cluster was associated with perturbed environments and proximity to the aquaculture sites. Similar patterns were also observed for eukaryotes using 18S rRNA gene analyses and visual examination, but without a bimodal distribution of OTU richness. Shotgun sequencing showed the archaeum Nitrosopumilus as dominant for the high OTU richness cluster, and the epsilon protobacterium Sulfurovum as dominant for the low OTU richness cluster. Metabolic reconstruction of Nitrosopumilus indicates nitrification as the main metabolic pathway. Sulfurovum, on the other hand, was associated with sulfur oxidation and denitrification. Changes in nitrogen and sulfur metabolism is proposed as a potential explanation for the difference between the high and low OTU richness clusters. In conclusion, these findings suggest that pollution from elevated loads of organic waste drives the microbiota towards a complete alteration of respiratory routes and species composition, in addition to a collapse in prokaryote OTU richness.

Association of gut microbiota with metabolism in juvenile Atlantic salmon.

The gut microbiome plays a key role in animal health and metabolism through the intricate functional interconnection between the feed, gut microbes, and the host. Unfortunately, in aquaculture, the links between gut microbes and fish genetics and production phenotypes are not well understood.In this study, we investigate the associations between gut microbial communities, fish feed conversion, and fish genetics in the domestic Atlantic salmon. Microbial community composition was determined for 230 juvenile fish from 23 full-sib families and was then regressed on growth, carbon and nitrogen metabolism, and feed efficiency. We only found weak associations between host genetics and microbial composition. However, we did identify significant (p < 0.05) associations between the abundance of three microbial operational taxonomical units (OTUs) and fish metabolism phenotypes. Two OTUs were associated with both carbon metabolism in adipose tissue and feed efficiency, while a third OTU was associated with weight gain.In conclusion, this study demonstrates an intriguing association between host lipid metabolism and the gut microbiota composition in Atlantic salmon. Video Abstract.

Prokaryote species richness is positively correlated with eukaryote abundance in wastewater treatment biofilms.

Biological treatment represents a key step in nutrient removal from wastewater. Until now these process has mainly been considered prokaryotic, with the interactions between prokaryotes and eukaryotes not being properly explored. We therefore investigated the co-occurrence of eukaryotes and prokaryotes in biological nitrogen removal biofilms. We found that biofilms in the nitrifying reactor contained the highest diversity and abundance of both prokaryotes and eukaryotes, with nearly three times higher prokaryote species richness than for the denitrifying reactor. The positive associations between eukaryote abundance and prokaryote diversity could potentially be explained by mutualism - and/or predator/prey interactions. Further mechanistic insight, however, is needed to determine the main diversifying mechanisms. In summary, eukaryote and prokaryote interactions seem to play a fundamental yet underexplored role in biological wastewater treatment. SIGNIFICANCE AND IMPACT OF THE STUDY: Eukaryote and prokaryote interactions may play an important role in wastewater treatment. This study found that prokaryote species richness was nearly three times higher in the aerobe nitrification than in an anaerobe denitrification reactor, coinciding with the highest level of eukaryotes. This knowledge can be important in process control, and potentially in the development of novel approaches based on nitrate accumulating denitrifying eukaryotes.