Negative regulation of Bacillus anthracis sporulation by the Spo0E family of phosphatases

A conserved switch controls virulence, sporulation, and motility in C. difficile

Spore formation is required for environmental survival and transmission of the human enteropathogenic Clostridioides difficile. In all bacterial spore formers, sporulation is regulated through activation of the master response regulator, Spo0A. However, the factors and mechanisms that directly regulate C. difficile Spo0A activity are not defined. In the well-studied Bacillus species, Spo0A is directly inactivated by Spo0E, a small phosphatase. To understand Spo0E function in C. difficile, we created a null mutation of the spo0E ortholog and assessed sporulation and physiology. The spo0E mutant produced significantly more spores, demonstrating Spo0E represses C. difficile sporulation. Unexpectedly, the spo0E mutant also exhibited increased motility and toxin production, and enhanced virulence in animal infections. We uncovered that Spo0E interacts with both Spo0A and the toxin and motility regulator, RstA. Direct interactions between Spo0A, Spo0E, and RstA constitute a previously unknown molecular switch that coordinates sporulation with motility and toxin production. Reinvestigation of Spo0E function in B. subtilis revealed that Spo0E induced motility, demonstrating Spo0E regulation of motility and sporulation among divergent species. Further, 3D structural analyses of Spo0E revealed specific and exclusive interactions between Spo0E and binding partners in C. difficile and B. subtilis that provide insight into the conservation of this regulatory mechanism among different species.

Identification of potential RapJ hits as sporulation pathway inducer candidates in Bacillus coagulans via structure-based virtual screening and molecular dynamics simulation studies

BACKGROUND

The bacterium Bacillus coagulans has attracted interest because of its ability to produce spores and advantageous probiotic traits, such as facilitating food digestion in the intestine, managing some disorders, and controlling the symbiotic microbiota. Spore-forming probiotic bacteria are especially important in the probiotic industry compared to non-spore-forming bacteria due to their stability during production and high resistance to adverse factors such as stomach acid. When spore-forming bacteria are exposed to environmental stresses, they enter the sporulation pathway to survive. This pathway is activated by the final phosphorylation of the master regulator of spore response, Spo0A, and upon achieving the phosphorylation threshold. Spo0A is indirectly inhibited by some enzymes of the aspartate response regulator phosphatase (Rap) family, such as RapJ. RapJ is one of the most important Rap enzymes in the sporogenesis pathway, which is naturally inhibited by the pentapeptides.

METHODS

This study used structure-based virtual screening and molecular dynamics (MD) simulation studies to find potential RapJ hits that could induce the sporulation pathway. The crystal structures of RapJ complexed with pentapeptide clearly elucidated their interactions with the enzyme active site.

RESULTS

Based on the binding compartment, through molecular docking, MD simulation, hydrogen bonds, and binding-free energy calculations, a series of novel hits against RapJ named tandutinib, infigratinib, sitravatinib, linifanib, epertinib, surufatinib, and acarbose were identified. Among these compounds, acarbose obtained the highest score, especially in terms of the number of hydrogen bonds, which plays a major role in stabilizing RapJ-ligand complexes, and also according to the occupancy percentages of hydrogen bonds, its hydrogen bonds were more stable during the simulation time. Consequently, acarbose is probably the most suitable hit for RapJ enzyme. Notably, experimental validation is crucial to confirm the effectiveness of the selected ligands.

A Conserved Switch Controls Virulence, Sporulation, and Motility in C. difficile

Spore formation is required for environmental survival and transmission of the human enteropathogenic Clostridioides difficile . In all bacterial spore formers, sporulation is regulated through activation of the master response regulator, Spo0A. However, the factors and mechanisms that directly regulate C. difficile Spo0A activity are not defined. In the well-studied Bacillus species, Spo0A is directly inactivated by Spo0E, a small phosphatase. To understand Spo0E function in C. difficile , we created a null mutation of the spo0E ortholog and assessed sporulation and physiology. The spo0E mutant produced significantly more spores, demonstrating Spo0E represses C. difficile sporulation. Unexpectedly, the spo0E mutant also exhibited increased motility and toxin production, and enhanced virulence in animal infections. We uncovered that Spo0E interacts with both Spo0A and the toxin and motility regulator, RstA. Direct interactions between Spo0A, Spo0E, and RstA constitute a previously unknown molecular switch that coordinates sporulation with motility and toxin production. Reinvestigation of Spo0E function in B. subtilis revealed that Spo0E induced motility, demonstrating Spo0E regulation of motility and sporulation among divergent species. Further, we found that Spo0E orthologs are widespread among prokaryotes, suggesting that Spo0E performs conserved regulatory functions in diverse bacteria.

The influence of extrachromosomal elements in the anthrax "cross-over" strain Bacillus cereus G9241

Bacillus cereus G9241 was isolated from a welder who survived a pulmonary anthrax-like disease. Strain G9241 carries two virulence plasmids, pBCX01 and pBC210, as well as an extrachromosomal prophage, pBFH_1. pBCX01 has 99.6% sequence identity to pXO1 carried by Bacillus anthracis and encodes the tripartite anthrax toxin genes and atxA, a mammalian virulence transcriptional regulator. This work looks at how the presence of pBCX01 and temperature may affect the lifestyle of B. cereus G9241 using a transcriptomic analysis and by studying spore formation, an important part of the B. anthracis lifecycle. Here we report that pBCX01 has a stronger effect on gene transcription at the mammalian infection relevant temperature of 37°C in comparison to 25°C. At 37°C, the presence of pBCX01 appears to have a negative effect on genes involved in cell metabolism, including biosynthesis of amino acids, whilst positively affecting the transcription of many transmembrane proteins. The study of spore formation showed B. cereus G9241 sporulated rapidly in comparison to the B. cereus sensu stricto type strain ATCC 14579, particularly at 37°C. The carriage of pBCX01 did not affect this phenotype suggesting that other genetic elements were driving rapid sporulation. An unexpected finding of this study was that pBFH_1 is highly expressed at 37°C in comparison to 25°C and pBFH_1 expression leads to the production of Siphoviridae-like phage particles in the supernatant of B. cereus G9241. This study provides an insight on how the extrachromosomal genetic elements in B. cereus G9241 has an influence in bacterial phenotypes.

The wilt pathogen induces different variations of root-associated microbiomes of plant

Root-associated compartments, including the rhizosphere, rhizoplane, and endosphere, live with diverse microbial communities which profoundly affect plant growth and health. However, a systematic understanding of the microbiome assembly across the rhizosphere, rhizoplane, and endosphere under pathogen invasion remains elusive. Using 16S high-throughput sequencing, we studied how bacterial wilt disease affected the variation and assembly of the three continuous root-associated microbiomes of tobacco. The results indicated that microorganisms were gradually filtered from the rhizosphere to the endosphere. With the pathogen invasion, the rhizosphere, rhizoplane and endosphere microbiomes selected and recruited different beneficial bacterial taxa. Some recruited bacteria were also identified as keystone members in networks (i.e., Bosea in the endosphere). The microbiomes of endosphere and rhizoplane were more sensitive to plant disease than the rhizosphere microbiome. Still, response strategies of the rhizoplane and endosphere to disease were obviously different. Microbial networks of the rhizoplane became complex in diseased samples and genes involved in sporulation formation and cell cycle were enriched. However, microbial networks of the diseased endosphere were disrupted, and functional genes related to nitrogen utilization and chemotaxis were significantly increased, indicating the importance of nitrogen resources supply of plants for the endosphere microbiome under pathogen invasion. Our results provide novel insights for understanding the different responses of the root-associated microbiomes to plant disease.

Folding cooperativity and allosteric function in the tandem-repeat protein class

The term allostery was originally developed to describe structural changes in one binding site induced by the interaction of a partner molecule with a distant binding site, and it has been studied in depth in the field of enzymology. Here, we discuss the concept of action at a distance in relation to the folding and function of the solenoid class of tandem-repeat proteins such as tetratricopeptide repeats (TPRs) and ankyrin repeats. Distantly located repeats fold cooperatively, even though only nearest-neighbour interactions exist in these proteins. A number of repeat-protein scaffolds have been reported to display allosteric effects, transferred through the repeat array, that enable them to direct the activity of the multi-subunit enzymes within which they reside. We also highlight a recently identified group of tandem-repeat proteins, the RRPNN subclass of TPRs, recent crystal structures of which indicate that they function as allosteric switches to modulate multiple bacterial quorum-sensing mechanisms. We believe that the folding cooperativity of tandem-repeat proteins and the biophysical mechanisms that transform them into allosteric switches are intimately intertwined. This opinion piece aims to combine our understanding of the two areas and develop ideas on their common underlying principles.This article is part of a discussion meeting issue 'Allostery and molecular machines'.

A Dual Role for the Bacillus anthracis Master Virulence Regulator AtxA: Control of Sporulation and Anthrax Toxin Production

Bacillus anthracis is an endemic soil bacterium that exhibits two different lifestyles. In the soil environment, B. anthracis undergoes a cycle of saprophytic growth, sporulation, and germination. In mammalian hosts, the pathogenic lifestyle of B. anthracis is spore germination followed by vegetative cell replication, but cells do not sporulate. During infection, and in specific culture conditions, transcription of the structural genes for the anthrax toxin proteins and the biosynthetic operon for capsule synthesis is positively controlled by the regulatory protein AtxA. A critical role for the atxA gene in B. anthracis virulence has been established. Here we report an inverse relationship between toxin production and sporulation that is linked to AtxA levels. During culture in conditions favoring sporulation, B. anthracis produces little to no AtxA. When B. anthracis is cultured in conditions favoring toxin gene expression, AtxA is expressed at relatively high levels and sporulation rate and efficiency are reduced. We found that a mutation within the atxA promoter region resulting in AtxA over-expression leads to a marked sporulation defect. The sporulation phenotype of the mutant is dependent upon pXO2-0075, an atxA-regulated open reading frame located on virulence plasmid pXO2. The predicted amino acid sequence of the pXO2-0075 protein has similarity to the sensor domain of sporulation sensor histidine kinases. It was shown previously that pXO2-0075 overexpression suppresses sporulation. We have designated pXO2-0075 “skiA” for “sporulation kinase inhibitor.” Our results indicate that in addition to serving as a positive regulator of virulence gene expression, AtxA modulates B. anthracis development.

Loss of σI affects heat-shock response and virulence gene expression in Bacillus anthracis

The pathogenesis of Bacillus anthracis depends on several virulence factors, including the anthrax toxin. Loss of the alternative sigma factor σI results in a coordinate decrease in expression of all three toxin subunits. Our observations suggest that loss of σI alters the activity of the master virulence regulator AtxA, but atxA transcription is unaffected by loss of σI. σI-containing RNA polymerase does not appear to directly transcribe either atxA or the toxin gene pagA. As in Bacillus subtilis, loss of σI in B. anthracis results in increased sensitivity to heat shock and transcription of sigI, encoding σI, is induced by elevated temperature. Encoded immediately downstream of and part of a bicistronic message with sigI is an anti-sigma factor, RsgI, which controls σI activity. Loss of RsgI has no direct effect on virulence gene expression. sigI appears to be expressed from both the σI and σA promoters, and transcription from the σA promoter is likely more significant to virulence regulation. We propose a model in which σI can be induced in response to heat shock, whilst, independently, σI is produced under non-heat-shock, toxin-inducing conditions to indirectly regulate virulence gene expression.

Loss of Homogentisate 1,2-Dioxygenase Activity in Bacillus anthracis Results in Accumulation of Protective Pigment

Melanin production is important to the pathogenicity and survival of some bacterial pathogens. In Bacillus anthracis, loss of hmgA, encoding homogentisate 1,2-dioxygenase, results in accumulation of a melanin-like pigment called pyomelanin. Pyomelanin is produced in the mutant as a byproduct of disrupted catabolism of L-tyrosine and L-phenylalanine. Accumulation of pyomelanin protects B. anthracis cells from UV damage but not from oxidative damage. Neither loss of hmgA nor accumulation of pyomelanin alter virulence gene expression, sporulation or germination. This is the first investigation of homogentisate 1,2-dioxygenase activity in the Gram-positive bacteria, and these results provide insight into a conserved aspect of bacterial physiology.

Cytochrome c551 and the cytochrome c maturation pathway affect virulence gene expression in Bacillus cereus ATCC 14579

Loss of the cytochrome c maturation system in Bacillus cereus results in increased transcription of the major enterotoxin genes nhe, hbl, and cytK and the virulence regulator plcR. Increased virulence factor production occurs at 37°C under aerobic conditions, similar to previous findings in Bacillus anthracis. Unlike B. anthracis, much of the increased virulence gene expression can be attributed to loss of only c551, one of the two small c-type cytochromes. Additional virulence factor expression occurs with loss of resBC, encoding cytochrome c maturation proteins, independently of the presence of the c-type cytochrome genes. Hemolytic activity of strains missing either cccB or resBC is increased relative to that in the parental strain, while sporulation efficiency is unaffected in the mutants. Increased virulence gene expression in the ΔcccB and ΔresBC mutants occurs only in the presence of an intact plcR gene, indicating that this process is PlcR dependent. These findings suggest a new mode of regulation of B. cereus virulence and reveal intriguing similarities and differences in virulence regulation between B. cereus and B. anthracis.

The two CcdA proteins of Bacillus anthracis differentially affect virulence gene expression and sporulation

The cytochrome c maturation system influences the expression of virulence factors in Bacillus anthracis. B. anthracis carries two copies of the ccdA gene, encoding predicted thiol-disulfide oxidoreductases that contribute to cytochrome c maturation, while the closely related organism Bacillus subtilis carries only one copy of ccdA. To investigate the roles of the two ccdA gene copies in B. anthracis, strains were constructed without each ccdA gene, and one strain was constructed without both copies simultaneously. Loss of both ccdA genes results in a reduction of cytochrome c production, an increase in virulence factor expression, and a reduction in sporulation efficiency. Complementation and expression analyses indicate that ccdA2 encodes the primary CcdA in B. anthracis, active in all three pathways. While CcdA1 retains activity in cytochrome c maturation and virulence control, it has completely lost its activity in the sporulation pathway. In support of this finding, expression of ccdA1 is strongly reduced when cells are grown under sporulation-inducing conditions. When the activities of CcdA1 and CcdA2 were analyzed in B. subtilis, neither protein retained activity in cytochrome c maturation, but CcdA2 could still function in sporulation. These observations reveal the complexities of thiol-disulfide oxidoreductase function in pathways relevant to virulence and physiology.

Suitability of Commercial Transport Media for Biological Pathogens under Nonideal Conditions

There is extensive data to support the use of commercial transport media as a stabilizer for known clinical samples; however, there is little information to support their use outside of controlled conditions specified by the manufacturer. Furthermore, there is no data to determine the suitability of said media for biological pathogens, specifically those of interest to the US military. This study evaluates commercial off-the-shelf (COTS) transport media based on sample recovery, viability, and quality of nucleic acids and peptides for nonpathogenic strains of Bacillus anthracis, Yersinia pestis, and Venezuelan equine encephalitis virus, in addition to ricin toxin. Samples were stored in COTS, PBST, or no media at various temperatures over an extended test period. The results demonstrate that COTS media, although sufficient for the preservation of nucleic acid and proteinaceous material, are not capable of maintaining an accurate representation of biothreat agents at the time of collection.

Structural insights into inhibition of Bacillus anthracis sporulation by a novel class of non-heme globin sensor domains

Pathogenesis by Bacillus anthracis requires coordination between two distinct activities: plasmid-encoded virulence factor expression (which protects vegetative cells from immune surveillance during outgrowth and replication) and chromosomally encoded sporulation (required only during the final stages of infection). Sporulation is regulated by at least five sensor histidine kinases that are activated in response to various environmental cues. One of these kinases, BA2291, harbors a sensor domain that has ∼35% sequence identity with two plasmid proteins, pXO1-118 and pXO2-61. Because overexpression of pXO2-61 (or pXO1-118) inhibits sporulation of B. anthracis in a BA2291-dependent manner, and pXO2-61 expression is strongly up-regulated by the major virulence gene regulator, AtxA, it was suggested that their function is to titrate out an environmental signal that would otherwise promote untimely sporulation. To explore this hypothesis, we determined crystal structures of both plasmid-encoded proteins. We found that they adopt a dimeric globin fold but, most unusually, do not bind heme. Instead, they house a hydrophobic tunnel and hydrophilic chamber that are occupied by fatty acid, which engages a conserved arginine and chloride ion via its carboxyl head group. In vivo, these domains may therefore recognize changes in fatty acid synthesis, chloride ion concentration, and/or pH. Structure-based comparisons with BA2291 suggest that it binds ligand and dimerizes in an analogous fashion, consistent with the titration hypothesis. Analysis of newly sequenced bacterial genomes points to the existence of a much broader family of non-heme, globin-based sensor domains, with related but distinct functionalities, that may have evolved from an ancestral heme-linked globin.

Glucose-dependent activation of Bacillus anthracis toxin gene expression and virulence requires the carbon catabolite protein CcpA

Sensing environmental conditions is an essential aspect of bacterial physiology and virulence. In Bacillus anthracis, the causative agent of anthrax, transcription of the two major virulence factors, toxin and capsule, is triggered by bicarbonate, a major compound in the mammalian body. Here it is shown that glucose is an additional signaling molecule recognized by B. anthracis for toxin synthesis. The presence of glucose increased the expression of the protective antigen toxin component-encoding gene (pagA) by stimulating induction of transcription of the AtxA virulence transcription factor. Induction of atxA transcription by glucose required the carbon catabolite protein CcpA via an indirect mechanism. CcpA did not bind specifically to any region of the extended atxA promoter. The virulence of a B. anthracis strain from which the ccpA gene was deleted was significantly attenuated in a mouse model of infection. The data demonstrated that glucose is an important host environment-derived signaling molecule and that CcpA is a molecular link between environmental sensing and B. anthracis pathogenesis.

Bacillus anthracis physiology and genetics

Bacillus anthracis is a member of the Bacillus cereus group species (also known as the "group 1 bacilli"), a collection of Gram-positive spore-forming soil bacteria that are non-fastidious facultative anaerobes with very similar growth characteristics and natural genetic exchange systems. Despite their close physiology and genetics, the B. cereus group species exhibit certain species-specific phenotypes, some of which are related to pathogenicity. B. anthracis is the etiologic agent of anthrax. Vegetative cells of B. anthracis produce anthrax toxin proteins and a poly-d-glutamic acid capsule during infection of mammalian hosts and when cultured in conditions considered to mimic the host environment. The genes associated with toxin and capsule synthesis are located on the B. anthracis plasmids, pXO1 and pXO2, respectively. Although plasmid content is considered a defining feature of the species, pXO1- and pXO2-like plasmids have been identified in strains that more closely resemble other members of the B. cereus group. The developmental nature of B. anthracis and its pathogenic (mammalian host) and environmental (soil) lifestyles of make it an interesting model for study of niche-specific bacterial gene expression and physiology.

Two small c-type cytochromes affect virulence gene expression in Bacillus anthracis

Regulated expression of the genes for anthrax toxin proteins is essential for the virulence of the pathogenic bacterium Bacillus anthracis. Induction of toxin gene expression depends on several factors, including temperature, bicarbonate levels, and metabolic state of the cell. To identify factors that regulate toxin expression, transposon mutagenesis was performed under non-inducing conditions and mutants were isolated that untimely expressed high levels of toxin. A number of these mutations clustered in the haem biosynthetic and cytochrome c maturation pathways. Genetic analysis revealed that two haem-dependent, small c-type cytochromes, CccA and CccB, located on the extracellular surface of the cytoplasmic membrane, regulate toxin gene expression by affecting the expression of the master virulence regulator AtxA. Deregulated AtxA expression in early exponential phase resulted in increased expression of toxin genes in response to loss of the CccA-CccB signalling pathway. This is the first function identified for these two small c-type cytochromes of Bacillus species. Extension of the transposon screen identified a previously uncharacterized protein, BAS3568, highly conserved across many bacterial and archeal species, as involved in cytochrome c activity and virulence regulation. These findings are significant not only to virulence regulation in B. anthracis, but also to analysis of virulence regulation in many pathogenic bacteria and to the study of cytochrome c activity in Gram-positive bacteria.

The bicarbonate transporter is essential for Bacillus anthracis lethality

In the pathogenic bacterium Bacillus anthracis, virulence requires induced expression of the anthrax toxin and capsule genes. Elevated CO2/bicarbonate levels, an indicator of the host environment, provide a signal ex vivo to increase expression of virulence factors, but the mechanism underlying induction and its relevance in vivo are unknown. We identified a previously uncharacterized ABC transporter (BAS2714-12) similar to bicarbonate transporters in photosynthetic cyanobacteria, which is essential to the bicarbonate induction of virulence gene expression. Deletion of the genes for the transporter abolished induction of toxin gene expression and strongly decreased the rate of bicarbonate uptake ex vivo, demonstrating that the BAS2714-12 locus encodes a bicarbonate ABC transporter. The bicarbonate transporter deletion strain was avirulent in the A/J mouse model of infection. Carbonic anhydrase inhibitors, which prevent the interconversion of CO2 and bicarbonate, significantly affected toxin expression only in the absence of bicarbonate or the bicarbonate transporter, suggesting that carbonic anhydrase activity is not essential to virulence factor induction and that bicarbonate, and not CO2, is the signal essential for virulence induction. The identification of this novel bicarbonate transporter essential to virulence of B. anthracis may be of relevance to other pathogens, such as Streptococcus pyogenes, Escherichia coli, Borrelia burgdorferi, and Vibrio cholera that regulate virulence factor expression in response to CO2/bicarbonate, and suggests it may be a target for antibacterial intervention.

A unique GTP-dependent sporulation sensor histidine kinase in Bacillus anthracis

The Bacillus anthracis BA2291 gene codes for a sensor histidine kinase involved in the induction of sporulation. Genes for orthologs of the sensor domain of the BA2291 kinase exist in virulence plasmids in this organism, and these proteins, when expressed, inhibit sporulation by converting BA2291 to an apparent phosphatase of the sporulation phosphorelay. Evidence suggests that the sensor domains inhibit BA2291 by titrating its activating signal ligand. Studies with purified BA2291 revealed that this kinase is uniquely specific for GTP in the forward reaction and GDP in the reverse reaction. The G1 motif of BA2291 is highly modified from ATP-specific histidine kinases, and modeling this motif in the structure of the kinase catalytic domain suggested how guanine binds to the region. A mutation in the putative coiled-coil linker between the sensor domain and the catalytic domains was found to decrease the rate of the forward autophosphorylation reaction and not affect the reverse reaction from phosphorylated Spo0F. The results suggest that the activating ligand for BA2291 is a critical signal for sporulation and in a limited concentration in the cell. Decreasing the response to it either by slowing the forward reaction through mutation or by titration of the ligand by expressing the plasmid-encoded sensor domains switches BA2291 from an inducer to an inhibitor of the phosphorelay and sporulation.

Dual promoters control expression of the Bacillus anthracis virulence factor AtxA

The AtxA virulence regulator of Bacillus anthracis is required for toxin and capsule gene expression. AtxA is a phosphotransferase system regulatory domain-containing protein whose activity is regulated by phosphorylation/dephosphorylation of conserved histidine residues. Here we report that transcription of the atxA gene occurs from two independent promoters, P1 (previously described by Dai et al. [Z. Dai, J. C. Sirard, M. Mock, and T. M. Koehler, Mol. Microbiol. 16:1171-1181, 1995]) and P2, whose transcription start sites are separated by 650 bp. Both promoters have -10 and -35 consensus sequences compatible with recognition by sigma(A)-containing RNA polymerase, and neither promoter depends on the sporulation sigma factor SigH. The dual promoter activity and the extended untranslated mRNA suggest that as-yet-unknown regulatory mechanisms may act on this region to influence the level of AtxA in the cell.

Virulence gene expression is independent of ResDE-regulated respiration control in Bacillus anthracis

The ResDE two-component system regulates the synthesis of several components of the aerobic and anaerobic respiratory pathways in bacilli. The ResD response regulator transcription factor has been implicated in the regulation of virulence factors in a number of gram-positive species, including Bacillus anthracis. The precise deletions of resD and resE in B. anthracis that retained the classical respiratory phenotypes did not affect the expression of the gene for the protective antigen of the anthrax toxin, pagA, or that of the toxin regulator, atxA. The results indicate that the loss of ResDE-controlled respiratory capacity does not affect the synthesis of anthrax toxin.

Commingling regulatory systems following acquisition of virulence plasmids by Bacillus anthracis

The conversion of a bacterium from a non-pathogenic to a pathogenic existence is usually associated with the acquisition of virulence factors, the genes of which gain entry through bacteriophage infection, transposable elements or plasmid transfer. Pathogenesis research is mostly focused on how these factors enable the bacterium to infect the host or evade the repertoire of host defenses. Less effort is expended on understanding how the invading genes are affected by the complex regulatory circuits of the bacterium and how virulence is the result of converting these regulatory circuits to make them complicit with pathogenesis. An example of such a conversion is seen in Bacillus anthracis, and how acquired plasmid regulatory functions affect the activity of the regulatory processes of the bacterium, and vice versa, is now being revealed.