Olney, S. G. | Search bioRxiv

bioRxiv2025

Spx inhibits expression of the SwrA*DegU master flagellar activator in Bacillus subtilis.

Flagella are trans-envelope nanomachines expressed from genes organized in a complex regulatory hierarchy governed at the highest level by transcription factors called master activators. The master activator of flagellar biosynthesis in Bacillus subtilis is a hybrid of SwrA*DegU that is required to increase flagellar density to swarm over solid surfaces. Here we show that the ClpX unfoldase subunit of the ClpP protease is required for swarming motility, and that cells mutated for ClpX fail to swarm due to restricted levels of both SwrA and DegU. Suppressor mutations were found that increased expression of the fla/che operon under SwrA*DegU control, and mutation of the LonA protease elevates the levels of SwrA protein while mutation of the global transcriptional regulator Spx increases transcription of both the degU and swrA genes. We conclude that ClpX promotes swarming motility via degradation of Spx, which represses motility gene transcription including the Pfla/che, PdegU, and PswrA promoters each activated by DegU. The ClpX-dependent regulatory proteolysis of Spx is relieved upon stress conditions, and we infer that Spx may dampen DegU-mediated positive feedback to limit cell envelope stress caused by excessive flagellar biosynthesis.

microbiology↗

bioRxiv2017

Promoter boundaries for the luxCDABE and betIBA-proXWV operons in Vibrio harveyi defined by the method RAIL: Rapid Arbitrary PCR Insertion Libraries

Experimental studies of transcriptional regulation in bacteria require the ability to precisely measure changes in gene expression, often accomplished through the use of reporter genes. However, the boundaries of promoter sequences required for transcription are often unknown, thus complicating construction of reporters and genetic analysis of transcriptional regulation. Here, we analyze reporter libraries to define the promoter boundaries of the luxCDABE bioluminescence operon and the betIBA-proXWV osmotic stress operon in Vibrio harveyi. We describe a new method called RAIL (Rapid Arbitrary PCR Insertion Libraries) that combines the power of arbitrary PCR and isothermal DNA assembly to rapidly clone promoter fragments of various lengths upstream of reporter genes to generate large libraries. To demonstrate the versatility and efficiency of RAIL, we analyzed the promoters driving expression of the luxCDABE and betIBA-proXWV operons and created libraries of DNA fragments from these loci fused to fluorescent reporters. Using flow cytometry sorting and deep sequencing, we identified the DNA regions necessary and sufficient for maximum gene expression for each promoter. These analyses uncovered previously unknown regulatory sequences and validated known transcription factor binding sites. We applied this high-throughput method to gfp, mCherry, and lacZ reporters and multiple promoters in V. harveyi. We anticipate that the RAIL method will be easily applicable to other model systems for genetic, molecular, and cell biological applications.\n\nImportanceGene reporter constructs have long been essential tools for studying gene regulation in bacteria, particularly following the recent advent of fluorescent gene reporters. We developed a new method that enables efficient construction of promoter fusions to reporter genes to study gene regulation. We demonstrate the versatility of this technique in the model bacterium Vibrio harveyi by constructing promoter libraries for three bacterial promoters using three reporter genes. These libraries can be used to determine the DNA sequences required for gene expression, revealing regulatory elements in promoters. This method is applicable to various model systems and reporter genes for assaying gene expression.

molecular biology↗