A regulatory RNA required for antitermination of biofilm and capsular polysaccharide operons in Bacillales

Abstract

Formation of a Bacillus subtilis biofilm community requires an abundant matrix protein, TasA and an exopolysaccharide. The transcriptional regulatory pathways that control synthesis of these structural features are complex and responsive to multiple physiological and population signals. We report herein that an additional layer of co-transcriptional regulation is required for exopolysaccharide (eps) expression. This mechanism is mediated by a novel cis-acting RNA element, coined 'EAR', located between the second and third gene of the eps operon. The presence of the EAR element within the eps operon is required for readthrough of distally located termination signals. We also find that the EAR element promotes readthrough of heterologous termination sites. Based upon these observations, we hypothesize that the EAR element associates with RNA polymerase to promote processive antitermination, a process wherein the transcription elongation complex is altered by accessory factors to become resistant to pausing and termination signals. It is likely that this mechanism is required for eps expression to ensure full synthesis of the unusually long transcript (16 kb). We also identify the EAR element in other species within the order Bacillales, suggesting that a similar mechanism is required for synthesis of biofilm and capsular polysaccharide operons in other microorganisms.