Bacillus subtilis 6S-1 RNA regulates transcription of genes related to surfactin biosynthesis

The biosurfactant surfactin is a cyclic lipopeptide produced by different representatives of the genus Bacillus. It has a large surface activity and is considered as a prospective biodegradable detergent. In the present study, we investigated the impact of non-coding 6S-1 RNA - a global transcription regulator in bacteria - on surfactin biosynthesis in the undomesticated B. subtilis strain NCIB 3610. It was found by RT-qPCR that a 6S-1 RNA knockout (KO) (ΔbsrA, ΔA) leads to increase of mRNA levels of several genes positively affecting surfactin biosynthesis, in particular the surfactin synthetase operon srfA. However, the lack of 6S-1 RNA did not result in an increase of surfactin amounts secreted by NCIB 3610 cells, as was shown by colorimetric and HPLC methods. Likewise, expression analysis of a GFP reporter construct provided no evidence that elevated transcript levels derived from the srfA promoter are paralleled by higher levels of translation products in the ΔA strain. We further identified a number of key factors also dysregulated in the ΔA strain, including a 20-fold increased level of rocG mRNA encoding glutamate dehydrogenase, an enzyme that may deplete the building block L-glutamate required for surfactin synthesis. Here we present the first study that evaluates the role of 6S-1 RNA in surfactin biosynthesis. We demonstrated that the absence of the riboregulator 6S-1 RNA profoundly destabilizes mRNA levels of genes, related to surfactin biosynthesis, in the undomesticated B. subtilis NCIB 3610.