Sulfane sulfur post-translationally modifies the global regulator AdpA to influence actinorhodin production and morphological differentiation of Streptomyces coelicolor

The transcription factor AdpA is a key regulator controlling both secondary metabolism and morphological differentiation in Streptomyces. Due to its critical functions, its expression undergoes multi-level regulations at transcriptional, post-transcriptional, and translational levels, yet no post-translational regulation has been reported. Sulfane sulfur, such as organic polysulfide (RSnH, n³2), is common inside microorganisms, but its physiological functions are largely unknown. Herein, we discovered that sulfane sulfur post-translationally modifies AdpA in S. coelicolor via specifically reacting with Cys62 of AdpA to form a persulfide (Cys62-SSH). This modification decreases the affinity of AdpA to its self-promoter PadpA, allowing increased expression of adpA, further promoting the expression of its target genes actII-4 and wblA. ActII-4 activates actinorhodin biosynthesis and WblA regulates morphological development. Bioinformatics analyses indicated that AdpA-Cys62 is highly conserved in Streptomyces, suggesting the prevalence of such modification in this genus. Thus, our study unveils a new type of regulation on the AdpA activity and sheds a light on how sulfane sulfur stimulates the production of antibiotics in Streptomyces.

Investigating the role of the carbon storage regulator A (CsrA) in Leptospira spp.

Carbon Storage Regulator A (CsrA) is a well-characterized post-transcriptional global regulator that plays a critical role in response to environmental changes in many bacteria. CsrA has been reported to regulate several metabolic pathways, motility, biofilm formation, and virulence-associated genes. The role of csrA in Leptospira spp., which are able to survive in different environmental niches and infect a wide variety of reservoir hosts, has not been characterized. To investigate the role of csrA as a gene regulator in Leptospira, we generated a L. biflexa csrA deletion mutant (ΔcsrA) and csrA overexpressing Leptospira strains. The ΔcsrA L. biflexa displayed poor growth under starvation conditions. RNA sequencing revealed that in rich medium only a few genes, including the gene encoding the flagellar filament protein FlaB3, were differentially expressed in the ΔcsrA mutant. In contrast, 575 transcripts were differentially expressed when csrA was overexpressed in L. biflexa. Electrophoretic mobility shift assay (EMSA) confirmed the RNA-seq data in the ΔcsrA mutant, showing direct binding of recombinant CsrA to flaB3 mRNA. In the pathogen L. interrogans, we were not able to generate a csrA mutant. We therefore decided to overexpress csrA in L. interrogans. In contrast to the overexpressing strain of L. biflexa, the overexpressing L. interrogans strain had poor motility on soft agar. The overexpressing strain of L. interrogans also showed significant upregulation of the flagellin flaB1, flaB2, and flaB4. The interaction of L. interrogans rCsrA and flaB4 was confirmed by EMSA. Our results demonstrated that CsrA may function as a global regulator in Leptospira spp. under certain conditions that cause csrA overexpression. Interestingly, the mechanisms of action and gene targets of CsrA may be different between non-pathogenic and pathogenic Leptospira strains.

RNA-seq analysis identified glucose-responsive genes and YqfO as a global regulator in Bacillus subtilis

Objective We observed that the addition of glucose enhanced the expression of sigX and sigM, encoding extra-cytoplasmic function sigma factors in Bacillus subtilis. Several regulatory factors were identified for this phenomenon, including YqfO, CshA (RNA helicase), and YlxR (nucleoid-associated protein). Subsequently, the relationships among these regulators were analyzed. Among them, YqfO is conserved in many bacterial genomes and may function as a metal ion insertase or metal chaperone, but has been poorly characterized. Thus, to further characterize YqfO, we performed RNA sequencing (RNA-seq) analysis of YqfO in addition to CshA and YlxR. Results We first performed comparative RNA-seq to detect the glucose-responsive genes. Next, to determine the regulatory effects of YqfO in addition to CshA and YlxR, three pairs of comparative RNA-seq analyses were performed (yqfO/wt, cshA/wt, and ylxR/wt). We observed relatively large regulons (approximately 420, 780, and 180 for YqfO, CshA, and YlxR, respectively) and significant overlaps, indicating close relationships among the three regulators. This study is the first to reveal that YqfO functions as a global regulator in B. subtilis.

Deleting qseC downregulates virulence and promotes cross-protection in Pasteurella multocida

QseC, a histidine sensor kinase of the QseBC two-component system, acts as a global regulator of bacterial stress resistance, biofilm formation, and virulence. The function of QseC in some bacteria is well understood, but not in Pasteurella multocida. We found that deleting qseC in P. multocida serotype A:L3 significantly down-regulated bacterial virulence. The mutant had significantly reduced capsule production but increased resistance to oxidative stress and osmotic pressure. Deleting qseC led to a significant increase in qseB expression. Transcriptome sequencing analysis showed that 1245 genes were regulated by qseC, primarily those genes involved in capsule and LPS biosynthesis and export, biofilm formation, and iron uptake/utilization, as well as several immuno-protection related genes including ompA, ptfA, plpB, vacJ, and sodA. In addition to presenting strong immune protection against P. multocida serotypes A:L1 and A:L3 infection, live ΔqseC also exhibited protection against P. multocida serotype B:L2 and serotype F:L3 infection in a mouse model. The results indicate that QseC regulates capsular production and virulence in P. multocida. Furthermore, the qseC mutant can be used as an attenuated vaccine against P. multocida strains of multiple serotypes.

LuxT is a Global Regulator of Low-Cell Density Behaviors Including Type III Secretion, Siderophore Production, and Aerolysin Secretion in Vibrio harveyi

Quorum sensing (QS) is a chemical communication process in which bacteria produce, release, and detect extracellular signaling molecules called autoinducers. Via combined transcriptional and post-transcriptional regulatory mechanisms, QS allows bacteria to collectively alter gene expression on a population-wide scale. Recently, the LuxT transcription factor was shown to control V. harveyiqrr1, encoding the Qrr1 small RNA that functions at the core of the QS regulatory cascade. Here, we use RNA-Sequencing to reveal that, beyond control of qrr1, LuxT is a global regulator of 414 V. harveyi genes including those involved in type III secretion, siderophore production, and aerolysin toxin biosynthesis. Importantly, LuxT directly represses swrZ, encoding a transcription factor, and LuxT control of type III secretion, siderophore, and aerolysin genes occurs by two mechanisms, one that is SwrZ-dependent and one that is SwrZ-independent. All of these target genes specify QS-controlled behaviors that are enacted when V. harveyi is at low cell density. Thus, LuxT and SwrZ function in parallel with QS to drive particular low cell density behaviors. Phylogenetic analyses reveal that luxT is highly conserved among Vibrionaceae, but swrZ is less well conserved. In a test case to examine the relationship between LuxT and SwrZ, we find that in Aliivibrio fischeri, LuxT also functions as a swrZ repressor, and LuxT activates A. fischeri siderophore production via swrZ repression. Our results indicate that LuxT is a major regulator among Vibrionaceae, and, in the species that also possess swrZ, LuxT functions with SwrZ to control gene expression.

The cvn8 Conservon System Is a Global Regulator of Specialized Metabolism in Streptomyces coelicolor during Interspecies Interactions

Interactions between different species of actinomycete bacteria often trigger one of the strains to produce specialized metabolites, such as antibiotics. However, how this induction occurs at the genetic level is poorly understood.