Diversity of active viral infections within the Sphagnum microbiome

Abstract

Sphagnum-dominated peatlands play an important role in global carbon storage and represent significant sources of economic and ecological value. While recent efforts to describe microbial diversity and metabolic potential of the Sphagnum microbiome have demonstrated the importance of its microbial community, little is known about the viral constituents. We used metatranscriptomics to describe the diversity and activity of viruses infecting microbes within the Sphagnum peat bog. The vegetative portions of 6 Sphagnum plants were obtained from a peatland in northern Minnesota and total RNA extracted and sequenced. Metatranscriptomes were assembled and contigs screened for the presence of conserved virus marker genes. Using bacteriophage capsid protein, gp23, as a marker for phage diversity, we identified 33 contigs representing undocumented phage s that were active in the community at the time of sampling. Similarly, RNA-dependent RNA polymerase and the Nucleo-Cytoplasmic Large DNA Virus (NCLDV) major capsid protein were used as markers for ssRNA viruses and NCLDV, respectively. In total 114 contigs were identified as originating from undescribed ssRNA viruses, 22 of which represent near-complete genomes. An additional 64 contigs were identified as being from NCLDVs. Finally, 7 contigs were identified as putative virophage or polinto-like viruses. We developed co-occurrence networks with these markers in relation to the expression of potential-host housekeeping gene rpb1 to predict virus-host relationships, identifying 13 groups. Together, our approach offers new tools for the identification of virus diversity and interactions in understudied clades, and suggest viruses may play a considerable role in the ecology of the Sphagnum microbiome.\n\nSignificanceSphagnum-dominated peatlands play an important role in maintaining atmospheric carbon dioxide levels by modifying conditions in the surrounding soil to favor its own growth over other plant species. This slows rates of decomposition and facilitates the accumulation of fixed carbon in the form of partially decomposed biomass. The unique environment produced by Sphagnum enriches for the growth of a diverse microbial consortia that benefit from and support the mosss growth, while also maintaining the hostile soil conditions. While a growing body of research has begun to characterize the microbial groups that colonize Sphagnum, little is currently known about the ecological factors that constrain community structure and define ecosystem function. Top-down population control by viruses is almost completely undescribed. This study provides insight into the significant viral influence on the Sphagnum microbiome, and identifying new potential model systems to study virus-host interactions in the peatland ecosystem.