Analysis of double-stranded RNA from microbial communities identifies double-stranded RNA virus-like elements.

Double-stranded RNA (dsRNA) can function as genetic information and may have served as genomic material before the existence of DNA-based life. By developing a method to purify dsRNA, we have investigated the diversity of dsRNA in microbial populations. We detect large dsRNAs in multiple microbial populations. Analysis of an aquatic microbial population reveals that some dsRNA sequences match metagenomic DNA, suggesting that microbes contain pools of sense-antisense transcripts. In addition, ∼30% of the dsRNA sequences are not present in the corresponding DNA pool and are strongly biased toward encoding novel proteins. Of these "dsRNA unique" sequences, only a small percentage share similarity to known viruses, a large fraction assemble into RNA virus-like contigs, and the remaining fraction has an unexplained origin. These results have uncovered dsRNA virus-like elements and underscore that dsRNA potentially represents an additional reservoir of genetic information in microbial populations.