Non-Coding RNAs are Differentially Expressed by Nocardia brasiliensis in Vitro and in Experimental Actinomycetoma

Nocardia spp. are common soil-inhabiting bacteria that frequently infect humans through traumatic injuries or inhalation routes and cause infections, such as actinomycetoma and nocardiosis, respectively. Nocardia brasiliensis is the main aetiological agent of actinomycetoma in various countries. Many bacterial non-coding RNAs are regulators of genes associated with virulence factors.

The aim of this work was to identify non-coding RNAs (ncRNAs) expressed during infection conditions and in free-living form (in vitro) in Nocardia brasiliensis.

The N. brasiliensis transcriptome (predominately < 200 nucleotides) was determined by RNA next-generation sequencing in both conditions. A total of seventy ncRNAs were identified in both conditions. Among these ncRNAs, 18 were differentially expressed, 12 were located within intergenic regions, and 2 were encoded as antisense of 2 different genes. Finally, 10 of these ncRNAs were studied by rapid amplification of cDNA ends and/or quantitative reverse transcription polymerase chain reaction. Interestingly, 3 transcripts corresponded to tRNA-derived fragments (tRNAs^{Cys, Met, Thr}), and one transcript was overlapped between an intergenic region and the 5´end of the 23S rRNA. Expression of these last four transcripts was increased during N. brasiliensis infection compared with the in vitro conditions.

The results of this work suggest a possible role for these transcripts in the regulation of virulence genes in actinomycetoma pathogenesis.