High niche specificity and host genetic diversity of groundwater viruses

Viruses are key members of microbial communities that exert control over host abundance and metabolism, thereby influencing ecosystem processes and biogeochemical cycles. Aquifers are known to host taxonomically diverse microbial life, yet little is known about viruses infecting groundwater microbial communities. Here, we analysed 16 metagenomes from a broad range of groundwater physicochemistries. We recovered 1571 viral genomes that clustered into 468 high-quality viral operational taxonomic units. At least 15% were observed to be transcriptionally active, although lysis was likely constrained by the resource-limited groundwater environment. Most were unclassified (95%), and the remaining 5% were Caudoviricetes. Comparisons with viruses inhabiting other aquifers revealed no shared species, indicating substantial unexplored viral diversity. In silico predictions linked 22.4% of the viruses to microbial host populations, including to ultra-small prokaryotes, such as Patescibacteria and Nanoarchaeota. Many predicted hosts were associated with the biogeochemical cycling of carbon, nitrogen, and sulfur. Metabolic predictions revealed the presence of 205 putative auxiliary metabolic genes, involved in diverse processes associated with the utilization of the host's intracellular resources for biosynthesis and transformation reactions, including those involved in nucleotide sugar, glycan, cofactor, and vitamin metabolism. Viruses, prokaryotes overall, and predicted prokaryotic hosts exhibited narrow spatial distributions, and relative abundance correlations with the same groundwater parameters (e.g. dissolved oxygen, nitrate, and iron), consistent with host control over viral distributions. Results provide insights into underexplored groundwater viruses, and indicate the large extent to which viruses may manipulate microbial communities and biogeochemistry in the terrestrial subsurface.

Quantification of the Regional Properties of Gastric Motility Using Dynamic Magnetic Resonance Images

Goal: To quantify the regional properties of gastric motility from free-breathing dynamic MRI data. Methods: Free-breathing MRI scans were performed on 10 healthy human subjects. Motion correction was applied to reduce the respiratory effect. A stomach centerline was automatically generated and used as a reference axis. Contractions were quantified and visualized as spatio-temporal contraction maps. Gastric motility properties were reported separately for the lesser and greater curvatures in the proximal and distal regions of the stomach. Results: Motility properties varied in different regions of the stomach. The mean contraction frequencies for the lesser and greater curvatures were both 3.1±0.4 cycles per minute. The contraction speed was significantly higher on the greater curvature than the lesser curvature (3.5±0.7 vs 2.5±0.4 mm/s, p<0.001) while contraction size on both curvatures was comparable (4.9±1.2 vs 5.7±2.4 mm, p = 0.326). The mean gastric motility index was significantly higher in the distal greater curvature (28.13±18.89 mm²/s) compared to the other regions of the stomach (11.16-14.12 mm²/s). Conclusions: The results showed the effectiveness of the proposed method for visualization and quantification of motility patterns from MRI data.