Genome-wide transcription start site mapping in the facultative intracellular pathogen Brucella melitensis by Capping-seq

Brucella melitensis (B. melitensis) is an important facultative intracellular bacterium that causes global zoonotic diseases. Continuous intracellular survival and replication are the main obstruction responsible for the accessibility of prevention and treatment of brucellosis. Bacteria respond to complex environment by regulating gene expression. Many regulatory factors function at loci where RNA polymerase initiates messenger RNA synthesis. However, limited gene annotation is a current obstacle for the research on expression regulation in bacteria. To improve annotation and explore potential functional sites, we proposed a novel genome-wide method called Capping-seq for transcription start site (TSS) mapping in B. melitensis. This technique combines capture of capped primary transcripts with Single Molecule Real-Time (SMRT) sequencing technology. We identified 2,369 TSSs at single nucleotide resolution by Capping-seq. TSSs analysis of Brucella transcripts showed a preference of purine on the TSS positions. Our results revealed that -35 and -10 elements of promoter contained consensus sequences of TTGNNN and TATNNN, respectively. The 5' ends analysis showed that 57% genes are associated with more than one TSS and 47% genes contain long leader regions, suggested potential complex regulation at the 5' ends of genes in B. melitensis. Moreover, we identified 52 leaderless genes that are mainly involved in the metabolic processes. Overall, Capping-seq technology provides a unique solution for TSS determination in prokaryotes. Our findings develop a systematic insight into the primary transcriptome characterization of B. melitensis. This study represents a critical basis for investigating gene regulation and pathogenesis of Brucella.