Catabolite repression of the Bacillus subtilis FadR regulon, which is involved in fatty acid catabolism

Analysis of heterologous expression of phaCBA promotes the acetoin stress response mechanism in Bacillus subtilis using transcriptomics and metabolomics approaches

Acetoin, a versatile platform chemical and popular food additive, poses a challenge to the biosafety strain Bacillus subtilis when produced in high concentrations due to its intrinsic toxicity. Incorporating the PHB synthesis pathway into Bacillus subtilis 168 has been shown to significantly enhance the strain's acetoin tolerance. This study aims to elucidate the molecular mechanisms underlying the response of B. subtilis 168-phaCBA to acetoin stress, employing transcriptomic and metabolomic analyses. Acetoin stress induces fatty acid degradation and disrupts amino acid synthesis. In response, B. subtilis 168-phaCBA down-regulates genes associated with flagellum assembly and bacterial chemotaxis, while up-regulating genes related to the ABC transport system encoding amino acid transport proteins. Notably, genes coding for cysteine and D-methionine transport proteins (tcyB, tcyC and metQ) and the biotin transporter protein bioY, are up-regulated, enhancing cellular tolerance. Our findings highlight that the expression of phaCBA significantly increases the ratio of long-chain unsaturated fatty acids and modulates intracellular concentrations of amino acids, including L-tryptophan, L-tyrosine, L-leucine, L-threonine, L-methionine, L-glutamic acid, L-proline, D-phenylalanine, L-arginine, and membrane fatty acids, thereby imparting acetoin tolerance. Furthermore, the supplementation with specific exogenous amino acids (L-alanine, L-proline, L-cysteine, L-arginine, L-glutamic acid, and L-isoleucine) alleviates acetoin's detrimental effects on the bacterium. Simultaneously, the introduction of phaCBA into the acetoin-producing strain BS03 addressed the issue of insufficient intracellular cofactors in the fermentation strain, resulting in the successful production of 70.14 g/L of acetoin through fed-batch fermentation. This study enhances our understanding of Bacillus's cellular response to acetoin-induced stress and provides valuable insights for the development of acetoin-resistant Bacillus strains.

The fadXDEBA locus of Staphylococcus aureus is required for metabolism of exogenous palmitic acid and in vivo growth

In Staphylococcus aureus, genes that should confer the capacity to metabolize fatty acids by β-oxidation occur in the fadXDEBA locus, but their function has not been elucidated. Previously, incorporation into phospholipid through the fatty acid kinase FakA pathway was thought to be the only option available for S. aureus to metabolize exogenous saturated fatty acids. We now find that in S. aureus USA300, a fadX::lux reporter was repressed by glucose and induced by palmitic acid but not stearic acid, while in USA300ΔfakA basal expression was significantly elevated, and enhanced in response to both fatty acids. When cultures were supplemented with palmitic acid, palmitoyl-CoA representing the first metabolite in the β-oxidation pathway was detected in USA300, but not in a fadXDEBA deletion mutant USA300Δfad, which relative to USA300 exhibited increased incorporation of palmitic acid into phospholipid accompanied by a rapid loss of viability. USA300Δfad also exhibited significantly reduced viability in a murine tissue abscess infection model. Our data are consistent with FakA-mediated incorporation of fatty acids into phospholipid as a preferred pathway for metabolism of exogenous fatty acids, while the fad locus is critical for metabolism of palmitic acid, which is the most abundant free fatty acid in human plasma.

Transcriptome analysis and prediction of the metabolic state of stress-induced viable but non-culturable Bacillus subtilis cells

Many bacteria adapt their physiology and enter the viable but non-culturable state to survive prolonged exposure to adverse environmental conditions. The VBNC cells maintain active metabolism, membrane integrity and gene transcription. However, they lose the ability to form colonies on a conventional culture media. Thus, standard colony counting methods cannot detect these alive but dormant cells. The Gram-positive bacterium Bacillus subtilis was found to enter the VBNC state when pre-exposed to osmotic stress and treated with a lethal dose of kanamycin. These cells reduced their metabolic activity, ceased growth and division and became kanamycin-tolerant. Interestingly, despite active metabolism, the majority of the kanamycin tolerant cells could not be revived on LB agar. In this study, we use a robust RNA-Seq technique to elucidate the differences in transcriptional profiles of B. subtilis VBNC cells. A comparative analysis of differently expressed genes and operons performed in this study indicates high similarities in transcriptional responses of VBNC and kanamycin-sensitive cells to antibiotic treatment. Moreover, this work reveals that VBNC cells strongly upregulate genes involved in proline uptake and catabolism, suggesting a putative role of proline as nutrient in VBNC cells.

RhgKL and CcpA directly regulate the rhiLFGN-rhgR-yesTUV operon involved in the metabolism of rhamnogalacturonan type I in Bacillus subtilis

The Bacillus subtilis rhiLFGN-rhgR-yesTUVWXYZ (formerly yesOPQRSTUVWXYZ) gene cluster includes genes for metabolizing rhamnogalacturonan type I (RG-I), a major pectin constituent, and the rhgR gene encoding an AraC/XylS transcriptional activator. The yesL-rhgKL (formerly yesLMN) operon, adjacent to the rhiL gene, includes the rhgKL genes encoding a two-component regulatory system. The reporter analyses showed that three promoters immediately upstream of the rhiL, yesW, and yesL genes were induced by RG-I and repressed by glucose in the medium. The reporter analyses also showed that RhgL and RhgR contribute to the RG-I-dependent induction of the rhiL promoter and that CcpA mediates the catabolite repression of the rhiL and yesL promoters. The in vitro experiments demonstrated that the RhgL response regulator and the CcpA complex bind to each site in the rhiL promoter region. The RT-PCR analysis and the different properties of the rhiL and yesW promoters suggested the rhiLFGN-rhgR-yesTUV genes as an operon.

Transcriptome Analysis Reveals Catabolite Control Protein A Regulatory Mechanisms Underlying Glucose-Excess or -Limited Conditions in a Ruminal Bacterium, Streptococcus bovis

Ruminants may suffer from rumen acidosis when fed with high-concentrate diets due to the higher proliferation and overproduction of lactate by Streptococcus bovis. The catabolite control protein A (CcpA) regulates the transcription of lactate dehydrogenase (ldh) and pyruvate formate-lyase (pfl) in S. bovis, but its role in response to different carbon concentrations remains unclear. To characterize the regulatory mechanisms of CcpA in S. bovis S1 at different levels of carbon, herein, we analyzed the transcriptomic and physiological characteristics of S. bovis S1 and its ccpA mutant strain grown in glucose-excess and glucose-limited conditions. A reduced growth rate and a shift in fermentation pattern from homofermentation to heterofermentation were observed under glucose-limited condition as compared to glucose-excess condition, in S. bovis S1. Additionally, the inactivation of ccpA significantly affected the growth and end metabolites in both conditions. For the glycolytic intermediate, fructose 1,6-bisphosphate (FBP), the concentration significantly reduced at lower glucose conditions; its concentration decreased significantly in the ccpA mutant strain. Transcriptomic results showed that about 46% of the total genes were differentially transcribed between the wild-type strain and ccpA mutant strain grown in glucose-excess conditions; while only 12% genes were differentially transcribed in glucose-limited conditions. Different glucose concentrations led to the differential expression of 38% genes in the wild-type strain, while only half of these were differentially expressed in the ccpA-knockout strain. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that the substrate glucose concentration significantly affected the gene expression in histidine metabolism, nitrogen metabolism, and some carbohydrate metabolism pathways. The deletion of ccpA affected several genes involved in carbohydrate metabolism, such as glycolysis, pyruvate metabolism, fructose and mannose metabolism, as well as in fatty acid biosynthesis pathways in bacteria grown in glucose-excess conditions; this effect was attenuated under glucose-limited conditions. Overall, these findings provide new information on gene transcription and metabolic mechanisms associated with substrate glucose concentration and validate the important role of CcpA in the regulation of carbon metabolism in S. bovis S1 at differential glucose availability.

Machine learning uncovers independently regulated modules in the Bacillus subtilis transcriptome

The transcriptional regulatory network (TRN) of Bacillus subtilis coordinates cellular functions of fundamental interest, including metabolism, biofilm formation, and sporulation. Here, we use unsupervised machine learning to modularize the transcriptome and quantitatively describe regulatory activity under diverse conditions, creating an unbiased summary of gene expression. We obtain 83 independently modulated gene sets that explain most of the variance in expression and demonstrate that 76% of them represent the effects of known regulators. The TRN structure and its condition-dependent activity uncover putative or recently discovered roles for at least five regulons, such as a relationship between histidine utilization and quorum sensing. The TRN also facilitates quantification of population-level sporulation states. As this TRN covers the majority of the transcriptome and concisely characterizes the global expression state, it could inform research on nearly every aspect of transcriptional regulation in B. subtilis.

The systems-level regulatory structure underlying gene expression in bacteria can be inferred using machine learning algorithms. Here we show this structure for Bacillus subtilis, present five hypotheses gleaned from it, and analyse the process of sporulation from its perspective.

TnFLX: a Third-Generation mariner-Based Transposon System for Bacillus subtilis

Random transposon mutagenesis is a powerful and unbiased genetic approach to answer fundamental biological questions. Here, we introduce an improved mariner-based transposon system with enhanced stability during propagation and versatile applications in mutagenesis. We used a low-copy-number plasmid as a transposon delivery vehicle, which affords a lower frequency of unintended recombination during vector construction and propagation in Escherichia coli We generated a variety of transposons allowing for gene disruption or artificial overexpression, each in combination with one of four different antibiotic resistance markers. In addition, we provide transposons that will report gene/protein expression due to transcriptional or translational coupling. We believe that the TnFLX system will help enhance the flexibility of future transposon modification and application in Bacillus and other organisms.IMPORTANCE The stability of transposase-encoding vectors during cloning and propagation is crucial for the reliable application of transposons. Here, we increased the stability of the mariner delivery vehicle in E. coli Moreover, the TnFLX transposon system will improve the application of forward genetic methods with an increased number of antibiotic resistance markers and the ability to generate unbiased green fluorescent protein (GFP) fusions to report on protein translation and subcellular localization.

Sequential evolution of virulence and resistance during clonal spread of community-acquired methicillin-resistant Staphylococcus aureus

The past two decades have witnessed an alarming expansion of staphylococcal disease caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). The factors underlying the epidemic expansion of CA-MRSA lineages such as USA300, the predominant CA-MRSA clone in the United States, are largely unknown. Previously described virulence and antimicrobial resistance genes that promote the dissemination of CA-MRSA are carried by mobile genetic elements, including phages and plasmids. Here, we used high-resolution genomics and experimental infections to characterize the evolution of a USA300 variant plaguing a patient population at increased risk of infection to understand the mechanisms underlying the emergence of genetic elements that facilitate clonal spread of the pathogen. Genetic analyses provided conclusive evidence that fitness (manifest as emergence of a dominant clone) changed coincidently with the stepwise emergence of (i) a unique prophage and mutation of the regulator of the pyrimidine nucleotide biosynthetic operon that promoted abscess formation and colonization, respectively, thereby priming the clone for success; and (ii) a unique plasmid that conferred resistance to two topical microbiocides, mupirocin and chlorhexidine, frequently used for decolonization and infection prevention. The resistance plasmid evolved through successive incorporation of DNA elements from non-S. aureus spp. into an indigenous cryptic plasmid, suggesting a mechanism for interspecies genetic exchange that promotes antimicrobial resistance. Collectively, the data suggest that clonal spread in a vulnerable population resulted from extensive clinical intervention and intense selection pressure toward a pathogen lifestyle that involved the evolution of consequential mutations and mobile genetic elements.

Functional analysis of the role of CcpA in Lactobacillus plantarum grown on fructooligosaccharides or glucose: a transcriptomic perspective

Background

The catabolite control protein A (CcpA) is a master regulator of many important cellular processes in Gram-positive bacteria. In Lactobacillus plantarum, CcpA directly or indirectly controls the transcription of a large number of genes that are involved in carbohydrate metabolism, aerobic and anaerobic growth, stress response and metabolite production, but its role in response to different carbon sources remains unclear.

Results

Here a combined transcriptomic and physiological approach was used to survey the global alterations that occurred during the logarithmic growth phase of wild-type and ccpA mutant strains of L. plantarum ST-III using fructooligosaccharides (FOS) or glucose as the sole carbon source. The inactivation of ccpA significantly affected the growth and production of metabolites under both carbon sources. About 15% of the total genes were significantly altered between wild-type and ccpA strains grown on glucose and the value is deceased to 12% when these two strains were compared on FOS, while only 7% were obviously changed due to the loss of CcpA when comparing strains grown on glucose and FOS. Although most of the differentially expressed genes mediated by CcpA are glucose dependent, FOS can also induce carbon catabolite repression (CCR) through the CcpA pathway. Moreover, the inactivation of ccpA led to a transformation from homolactic fermentation to mixed fermentation under aerobic conditions. CcpA can control genes directly by binding in the regulatory region of the target genes (mixed fermentation), indirectly through local regulators (fatty acid biosynthesis), or have a double effect via direct and indirect regulation (FOS metabolism).

Conclusion

Overall, our results show that CcpA plays a central role in response to carbon source and availability of L. plantarum and provide new insights into the complex and extended regulatory network of lactic acid bacteria.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-1050-4) contains supplementary material, which is available to authorized users.

Bacillus subtilis highly efficient protein expression systems that are chromosomally integrated and controllable by glucose and rhamnose

To achieve rhamnose-inducible efficient protein expression in Bacillus subtilis, we assembled the strong promoters of B. subtilis cdd and ylbP genes and the regulatory region (PrhaEW) of B. subtilis rhaEWRBMA operon, whose transcription is induced by rhamnose and repressed by glucose, to produce various hybrid constructs. These constructs were evaluated using B. subtilis strains carrying a fusion of each construct to the gene encoding a mutated green fluorescent protein in the chromosome. When these strains were cultivated in the presence of glucose or rhamnose, the strain carrying a fusion of a partial PrhaEW region, lacking the intrinsic Shine-Dalgarno (SD) sequence, and the ylbP SD sequence most strictly controlled the promoter activity depending on sugar species. Moreover, the strain carrying a fusion of the cdd core promoter and the ylbP SD sequence showed the highest promoter activity when it was cultivated in the presence of glucose until the late stationary phase. Abbreviations: RNAP: RNA polymerase; cre: catabolite-responsive element; SD: Shine-Dalgarno; PAGE: polyacrylamide gel electrophoresis; GFP: green fluorescent protein; OD₆₀₀: optical density at 600 nm; LB: Luria-Bertani; a.u.: arbitrary unit; SDS: sodium dodecyl sulfate.

Regulation of the rhaEWRBMA Operon Involved in l-Rhamnose Catabolism through Two Transcriptional Factors, RhaR and CcpA, in Bacillus subtilis

The Bacillus subtilis rhaEWRBMA (formerly yuxG-yulBCDE) operon consists of four genes encoding enzymes for l-rhamnose catabolism and the rhaR gene encoding a DeoR-type transcriptional regulator. DNase I footprinting analysis showed that the RhaR protein specifically binds to the regulatory region upstream of the rhaEW gene, in which two imperfect direct repeats are included. Gel retardation analysis revealed that the direct repeat farther upstream is essential for the high-affinity binding of RhaR and that the DNA binding of RhaR was effectively inhibited by L-rhamnulose-1-phosphate, an intermediate of L-rhamnose catabolism. Moreover, it was demonstrated that the CcpA/P-Ser-HPr complex, primarily governing the carbon catabolite control in B. subtilis, binds to the catabolite-responsive element, which overlaps the RhaR binding site. In vivo analysis of the rhaEW promoter-lacZ fusion in the background of ccpA deletion showed that the L-rhamnose-responsive induction of the rhaEW promoter was negated by the disruption of rhaA or rhaB but not rhaEW or rhaM, whereas rhaR disruption resulted in constitutive rhaEW promoter activity. These in vitro and in vivo results clearly indicate that RhaR represses the operon by binding to the operator site, which is detached by L-rhamnulose-1-phosphate formed from L-rhamnose through a sequence of isomerization by RhaA and phosphorylation by RhaB, leading to the derepression of the operon. In addition, the lacZ reporter analysis using the strains with or without the ccpA deletion under the background of rhaR disruption supported the involvement of CcpA in the carbon catabolite repression of the operon.

IMPORTANCE

Since L-rhamnose is a component of various plant-derived compounds, it is a potential carbon source for plant-associating bacteria. Moreover, it is suggested that L-rhamnose catabolism plays a significant role in some bacteria-plant interactions, e.g., invasion of plant pathogens and nodulation of rhizobia. Despite the physiological importance of L-rhamnose catabolism for various bacterial species, the transcriptional regulation of the relevant genes has been poorly understood, except for the regulatory system of Escherichia coli. In this study, we show that, in Bacillus subtilis, one of the plant growth-promoting rhizobacteria, the rhaEWRBMA operon for L-rhamnose catabolism is controlled by RhaR and CcpA. This regulatory system can be another standard model for better understanding the regulatory mechanisms of L-rhamnose catabolism in other bacterial species.

Transcriptional Profile of Bacillus subtilis sigF-Mutant during Vegetative Growth

Sigma factor F is the first forespore specific transcription factor in Bacillus subtilis and controls genes required for the early stages of prespore development. The role of sigF is well studied under conditions that induce sporulation. Here, the impact of sigF disruption on the transcriptome of exponentially growing cultures is studied by micro-array analysis. Under these conditions that typically don’t induce sporulation, the transcriptome showed minor signs of sporulation initiation. The number of genes differentially expressed and the magnitude of expression were, as expected, quite small in comparison with sporulation conditions. The genes mildly down-regulated were mostly involved in anabolism and the genes mildly up-regulated, in particular fatty acid degradation genes, were mostly involved in catabolism. This is probably related to the arrest at sporulation stage II occurring in the sigF mutant, because continuation of growth from the formed disporic sporangia may require additional energy. The obtained knowledge is relevant for various experiments, such as industrial fermentation, prolonged experimental evolution or zero-growth studies, where sporulation is an undesirable trait that should be avoided, e.g by a sigF mutation.

Role of fatty acids in Bacillus environmental adaptation

The large bacterial genus Bacillus is widely distributed in the environment and is able to colonize highly diverse niches. Some Bacillus species harbor pathogenic characteristics. The fatty acid (FA) composition is among the essential criteria used to define Bacillus species. Some elements of the FA pattern composition are common to Bacillus species, whereas others are specific and can be categorized in relation to the ecological niches of the species. Bacillus species are able to modify their FA patterns to adapt to a wide range of environmental changes, including changes in the growth medium, temperature, food processing conditions, and pH. Like many other Gram-positive bacteria, Bacillus strains display a well-defined FA synthesis II system that is equilibrated with a FA degradation pathway and regulated to efficiently respond to the needs of the cell. Like endogenous FAs, exogenous FAs may positively or negatively affect the survival of Bacillus vegetative cells and the spore germination ability in a given environment. Some of these exogenous FAs may provide a powerful strategy for preserving food against contamination by the Bacillus pathogenic strains responsible for foodborne illness.

Physiological and cell morphology adaptation of Bacillus subtilis at near-zero specific growth rates: a transcriptome analysis

Nutrient scarcity is a common condition in nature, but the resulting extremely low growth rates (below 0.025 h(-1) ) are an unexplored research area in Bacillus subtilis. To understand microbial life in natural environments, studying the adaptation of B. subtilis to near-zero growth conditions is relevant. To this end, a chemostat modified for culturing an asporogenous B. subtilis sigF mutant strain at extremely low growth rates (also named a retentostat) was set up, and biomass accumulation, culture viability, metabolite production and cell morphology were analysed. During retentostat culturing, the specific growth rate decreased to a minimum of 0.00006 h(-1) , corresponding to a doubling time of 470 days. The energy distribution between growth and maintenance-related processes showed that a state of near-zero growth was reached. Remarkably, a filamentous cell morphology emerged, suggesting that cell separation is impaired under near-zero growth conditions. To evaluate the corresponding molecular adaptations to extremely low specific growth, transcriptome changes were analysed. These revealed that cellular responses to near-zero growth conditions share several similarities with those of cells during the stationary phase of batch growth. However, fundamental differences between these two non-growing states are apparent by their high viability and absence of stationary phase mutagenesis under near-zero growth conditions.

Effect of bodily fluids from honey bee (Apis mellifera) larvae on growth and genome-wide transcriptional response of the causal agent of American Foulbrood disease (Paenibacillus larvae)

Paenibacillus larvae, the causal agent of American Foulbrood disease (AFB), affects honey bee health worldwide. The present study investigates the effect of bodily fluids from honey bee larvae on growth velocity and transcription for this Gram-positive, endospore-forming bacterium. It was observed that larval fluids accelerate the growth and lead to higher bacterial densities during stationary phase. The genome-wide transcriptional response of in vitro cultures of P. larvae to larval fluids was studied by microarray technology. Early responses of P. larvae to larval fluids are characterized by a general down-regulation of oligopeptide and sugar transporter genes, as well as by amino acid and carbohydrate metabolic genes, among others. Late responses are dominated by general down-regulation of sporulation genes and up-regulation of phage-related genes. A theoretical mechanism of carbon catabolite repression is discussed.

DarR, a TetR-like transcriptional factor, is a cyclic di-AMP-responsive repressor in Mycobacterium smegmatis

Cyclic dinucleotides, including cyclic di-AMP (c-di-AMP), are known to be ubiquitous second messengers involved in bacterial signal transduction. However, no transcriptional regulator has been characterized as a c-di-AMP receptor/effector to date. In the present study, using a c-di-AMP/transcription factor binding screen, we identified Ms5346, a TetR family regulator in Mycobacterium smegmatis, as a c-di-AMP receptor in bacteria. Ms5346 could specifically bind c-di-AMP with K(d) of 2.3 ± 0.5 μM. Using EMSA and DNase I footprinting assays, c-di-AMP was found to stimulate the DNA binding activity of Ms5346 and to enhance its ability to protect its target DNA sequence. A conserved 14-bp palindromic motif was identified as the DNA-binding site for Ms5346. Further, Ms5346 was found to negatively regulate expression of three target genes including Ms5347 (encoding a major facilitator family transporter), Ms5348 (encoding a medium chain fatty acyl-CoA ligase), and Ms5696 (encoding a cold shock protein, CspA). Ms5346 is the first cyclic di-AMP receptor regulator to be identified in bacteria, and we have designated it as DarR. Our findings enhance our understanding of the function and regulatory mechanism of the second messenger c-di-AMP in bacteria.

Equilibrium binding and kinetic characterization of putative tetracycline repressor family transcription regulator Fad35R from Mycobacterium tuberculosis

Fatty acids play critical role in the survival and virulence of Mycobacterium tuberculosis (Mtb). Activation of fatty acids by acyl-CoA synthetases (Fad) into fatty acyl-CoA is the first and one of the crucial steps in fatty acid metabolism. Mtb possesses 36 fatty acyl-CoA synthetases, unlike Escherichia coli, which has single enzyme. However, the mechanisms by which the expression of these multiple Fad genes is regulated remain uncharacterized. We characterized the DNA- and ligand-binding properties of a putative tetracycline repressor family regulator, named Fad35R, located upstream of the Fad35 gene and ScoA-citE operon. We identified a palindromic regulatory motif upstream of Fad35 and characterized the binding of Fad35R to this motif. Equilibrium binding studies show that Fad35R binds to this motif with high affinity (K(d) ∼ 0.033 μm) and the specificity of binding was confirmed by an electromobility gel shift assay. Kinetic studies indicate that faster association (k(a,avg) ∼ 5.4 × 10(4) m(-1) · s(-1)) and slower dissociation rates (k(d,avg) ∼ 5.84 × 10(-4) s(-1)) confer higher affinity. The affinity for the promoter is maximum at 300 mm NaCl but decreases rapidly beyond this range. Ligand-binding studies indicate that Fad35R binds specifically to tetracycline and also binds to fatty acid derivatives. The promoter-binding affinity is decreased significantly in the presence of palmityl-CoA, suggesting that Fad35R can sense the levels of activated fatty acids and alter its DNA-binding activity. Our results suggest that Fad35R may be the functional homologue of FadR and controls the expression of genes in a metabolite-dependent manner.

A copper-responsive global repressor regulates expression of diverse membrane-associated transporters and bacterial drug resistance in mycobacteria

Sequencing of entire bacterial genomes has led to the identification of many membrane-associated transporters, including several multidrug resistance transport proteins, in recent years. However, the regulators and signaling pathways involved in the expression of these genes remain largely unknown. In this study, we have identified Ms2173, a GntR/FadR family transcription factor, as a novel global regulator in Mycobacterium smegmatis. Ms2173 was found to specifically recognize a 15-bp palindromic motif and to broadly regulate expression of 292 genes, including 37 genes that encode membrane-associated transport proteins. Copper ions induced Ms2173 to form inactive proteins lacking DNA-binding activity. Ms2173 was shown to function as a repressor of its target genes. Interestingly, we found that the function of Ms2173 was linked to mycobacterial drug resistance. Compared with the substantially enhanced drug resistance in the Ms2173-deleted mutant strain, the strains overexpressing Ms2173 were more sensitive to anti-tuberculosis drugs than the wild-type strain. Additionally, copper ions could partially counteract the in vivo function of Ms2173. We have thus characterized the first mycobacterial GntR/Fad-like transcription factor that functions as a copper ion-responsive global repressor that we have renamed GfcR. These findings further enhance our understanding of membrane-associated transporter regulation and drug resistance in mycobacteria.