SUN, Y. | Search bioRxiv

bioRxiv2022

Genome Enrichment of Rare, Unknown Species from Complicated Microbiome by Nanopore Selective Sequencing

Rare species are vital members of a microbial community, but retrieving their genomes is difficult due to their low abundance. The ReadUntil (RU) approach allows nanopore devices to sequence specific DNA molecules selectively in real-time, which provides an opportunity for enriching rare species. However, there is still a gap in RU-based enriching of rare and unknown species in environmental samples whose community composition is unclear, and many species lack corresponding reference in public databases. Here we present metaRUpore to overcome this challenge. We applied metaRUpore to a thermophilic anaerobic digester (TAD) community, it successfully redirected the sequencing throughput from high-abundance populations to rare species while facilitating the recovery of 41 high-quality metagenome-assembled genomes (MAGs) at low sequencing effort. The simplicity and robustness of the approach make it accessible for labs with moderate computational resources and hold the potential to become the standard practice in future metagenomic sequencing of complicated microbiomes.

bioinformatics↗

bioRxiv2020

Snowball Earths, population bottlenecks, and the evolution of marine photosynthetic bacteria

Prochlorococcus are the most abundant photosynthetic organisms in the modern ocean. A massive DNA loss event occurred in their early evolutionary history, leading to highly reduced genomes in nearly all lineages, as well as enhanced efficiency in both nutrient uptake and light absorption. The environmental landscape that shaped this ancient genome reduction, however, remained unknown. Through careful molecular clock analyses, we established that this Prochlorococcus genome reduction occurred during the Neoproterozoic Snowball Earth climate catastrophe. The lethally low temperature and exceedingly dim light during the Snowball Earth event would have inhibited Prochlorococcus growth and proliferation and caused severe population bottlenecks. These bottlenecks are recorded as an excess of deleterious mutations that accumulated across genomic regions in the descendant lineages. Prochlorococcus adaptation to extreme environmental conditions during Snowball Earth intervals can be inferred by tracing the evolutionary paths of genes that encode key metabolic potential. This metabolic potential includes modified lipopolysaccharide structure, strengthened peptidoglycan biosynthesis, the replacement of a sophisticated circadian clock with an hourglass-like mechanism that resets daily for dim light adaption, and the adoption of ammonia diffusion as an efficient membrane transporter-independent mode of nitrogen acquisition. In this way, the Neoproterozoic Snowball Earth event altered the physiological characters of Prochlorococcus, shaping their ecologically vital role as the most abundant primary producers in the modern oceans.

microbiology↗