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PubMed2006

Transcriptomic assessment of isozymes in the biphenyl pathway of Rhodococcus sp. strain RHA1.

Rhodococcus sp. RHA1 grows on a broad range of aromatic compounds and vigorously degrades polychlorinated biphenyls (PCBs). Previous work identified RHA1 genes encoding multiple isozymes for most of the seven steps of the biphenyl (BPH) pathway, provided evidence for coexpression of some of these isozymes, and indicated the involvement of some of these enzymes in the degradation of BPH, ethylbenzene (ETB), and PCBs. To investigate the expression of these isozymes and better understand how they contribute to the robust degradative capacity of RHA1, we comprehensively analyzed the 9.7-Mb genome of RHA1 for BPH pathway genes and characterized the transcriptome of RHA1 growing on benzoate (BEN), BPH, and ETB. Sequence analyses revealed 54 potential BPH pathway genes, including 28 not previously reported. Transcriptomic analysis with a DNA microarray containing 70-mer probes for 8,213 RHA1 genes revealed a suite of 320 genes of diverse functions that were upregulated during growth both on BPH and on ETB, relative to growth on the control substrate, pyruvate. By contrast, only 65 genes were upregulated during growth on BEN. Quantitative PCR assays confirmed microarray results for selected genes and indicated that some of the catabolic genes were upregulated over 10,000-fold. Our analysis suggests that up to 22 enzymes, including 8 newly identified ones, may function in the BPH pathway of RHA1. The relative expression levels of catabolic genes did not differ for BPH and ETB, suggesting a common regulatory mechanism. This study delineated a suite of catabolic enzymes for biphenyl and alkyl-benzenes in RHA1, which is larger than previously recognized and which may serve as a model for catabolism in other environmentally important bacteria having large genomes.

Base Sequence↗
PubMed2004

Prolonged maltose-limited cultivation of Saccharomyces cerevisiae selects for cells with improved maltose affinity and hypersensitivity.

Prolonged cultivation (>25 generations) of Saccharomyces cerevisiae in aerobic, maltose-limited chemostat cultures led to profound physiological changes. Maltose hypersensitivity was observed when cells from prolonged cultivations were suddenly exposed to excess maltose. This substrate hypersensitivity was evident from massive cell lysis and loss of viability. During prolonged cultivation at a fixed specific growth rate, the affinity for the growth-limiting nutrient (i.e., maltose) increased, as evident from a decreasing residual maltose concentration. Furthermore, the capacity of maltose-dependent proton uptake increased up to 2.5-fold during prolonged cultivation. Genome-wide transcriptome analysis showed that the increased maltose transport capacity was not primarily due to increased transcript levels of maltose-permease genes upon prolonged cultivation. We propose that selection for improved substrate affinity (ratio of maximum substrate consumption rate and substrate saturation constant) in maltose-limited cultures leads to selection for cells with an increased capacity for maltose uptake. At the same time, the accumulative nature of maltose-proton symport in S. cerevisiae leads to unrestricted uptake when maltose-adapted cells are exposed to a substrate excess. These changes were retained after isolation of individual cell lines from the chemostat cultures and nonselective cultivation, indicating that mutations were involved. The observed trade-off between substrate affinity and substrate tolerance may be relevant for metabolic engineering and strain selection for utilization of substrates that are taken up by proton symport.

Biological Transport, Active↗
PubMed2005

Differential gene expression profiling of Staphylococcus aureus cultivated under biofilm and planktonic conditions.

It is well known that biofilm formation by pathogenic staphylococci on implanted medical devices leads to "chronic polymer-associated infections." Bacteria in these biofilms are more resistant to antibiotics and the immune defense system than their planktonic counterparts, which suggests that the cells in a biofilm have altered metabolic activity. To determine which genes are up-regulated in Staphylococcus aureus biofilm cells, we carried out a comparative transcriptome analysis. Biofilm growth was simulated on dialysis membranes laid on agar plates. Staphylococci were cultivated planktonically in Erlenmeyer flasks with shaking. mRNA was isolated at five time points from cells grown under both conditions and used for hybridization with DNA microarrays. The gene expression patterns of several gene groups differed under the two growth conditions. In biofilm cells, the cell envelope appeared to be a very active compartment since genes encoding binding proteins, proteins involved in the synthesis of murein and glucosaminoglycan polysaccharide intercellular adhesin, and other enzymes involved in cell envelope synthesis and function were significantly up-regulated. In addition, evidence was obtained that formate fermentation, urease activity, the response to oxidative stress, and, as a consequence thereof, acid and ammonium production are up-regulated in a biofilm. These factors might contribute to survival, persistence, and growth in a biofilm environment. Interestingly, toxins and proteases were up-regulated under planktonic growth conditions. Physiological and biochemical tests for the up-regulation of urease, formate dehydrogenase, proteases, and the synthesis of staphyloxanthin confirmed the microarray data.

Ammonia↗
PubMed2006

Butyrate specifically down-regulates salmonella pathogenicity island 1 gene expression.

Invasion of intestinal epithelial cells by Salmonella enterica is decreased after exposure to butyric acid. To understand the molecular mechanisms of this phenomenon, a comparative transcriptomic analysis of Salmonella enterica serovar Enteritidis and Salmonella enterica serovar Typhimurium grown in medium supplemented with butyrate was performed. We found that butyrate down-regulated the expression of 19 genes common to both serovars by a factor of twofold or more, and 17 of these genes localized to the Salmonella pathogenicity island 1 (SPI1). These included the SPI1 regulatory genes hilD and invF. Of the remaining two genes, ampH has 91% homology to an Escherichia coli penicillin-binding protein and sopE2 encodes a type III-secreted effector protein associated with invasion but located at a separate site on the chromosome from SPI1.

Animals↗
PubMed2006

In vitro generation of human high-density-lipoprotein-resistant Trypanosoma brucei brucei.

The host range of African trypanosomes is influenced by innate protective molecules in the blood of primates. A subfraction of human high-density lipoprotein (HDL) containing apolipoprotein A-I, apolipoprotein L-I, and haptoglobin-related protein is toxic to Trypanosoma brucei brucei but not the human sleeping sickness parasite Trypanosoma brucei rhodesiense. It is thought that T. b. rhodesiense evolved from a T. b. brucei-like ancestor and expresses a defense protein that ablates the antitrypanosomal activity of human HDL. To directly investigate this possibility, we developed an in vitro selection to generate human HDL-resistant T. b. brucei. Here we show that conversion of T. b. brucei from human HDL sensitive to resistant correlates with changes in the expression of the variant surface glycoprotein (VSG) and abolished uptake of the cytotoxic human HDLs. Complete transcriptome analysis of the HDL-susceptible and -resistant trypanosomes confirmed that VSG switching had occurred but failed to reveal the expression of other genes specifically associated with human HDL resistance, including the serum resistance-associated gene (SRA) of T. b. rhodesiense. In addition, we found that while the original active expression site was still utilized, expression of three expression site-associated genes (ESAG) was altered in the HDL-resistant trypanosomes. These findings demonstrate that resistance to human HDLs can be acquired by T. b. brucei.

Amino Acid Sequence↗
PubMed2006

Response of Staphylococcus aureus to salicylate challenge.

Growth of Staphylococcus aureus with the nonsteroidal anti-inflammatory salicylate reduces susceptibility of the organism to multiple antimicrobials. Transcriptome analysis revealed that growth of S. aureus with salicylate leads to the induction of genes involved with gluconate and formate metabolism and represses genes required for gluconeogenesis and glycolysis. In addition, salicylate induction upregulates two antibiotic target genes and downregulates a multidrug efflux pump gene repressor (mgrA) and sarR, which represses a gene (sarA) important for intrinsic antimicrobial resistance. We hypothesize that these salicylate-induced alterations jointly represent a unique mechanism that allows S. aureus to resist antimicrobial stress and toxicity.

Anti-Infective Agents↗
PubMed2007

An unusual response regulator influences sporulation at early and late stages in Streptomyces coelicolor.

WhiI, a regulator required for efficient sporulation septation in the aerial mycelium of Streptomyces coelicolor, resembles response regulators of bacterial two-component systems but lacks some conserved features of typical phosphorylation pockets. Four amino acids of the abnormal "phosphorylation pocket" were changed by site-directed mutagenesis. Unlike whiI null mutations, these point mutations did not interfere with sporulation septation but had various effects on spore maturation. Transcriptome analysis was used to compare gene expression in the wild-type strain, a D27A mutant (pale gray spores), a D69E mutant (wild-type spores), and a null mutant (white aerial mycelium, no spores) (a new variant of PCR targeting was used to introduce the point mutations into the chromosomal copy of whiI). The results revealed 45 genes that were affected by the deletion of whiI. Many of these showed increased expression in the wild type at the time when aerial growth and development were taking place. About half of them showed reduced expression in the null mutant, and about half showed increased expression. Some, but not all, of these 45 genes were also affected by the D27A mutation, and a few were affected by the D69E mutation. The results were consistent with a model in which WhiI acts differently at sequential stages of development. Consideration of the functions of whiI-influenced genes provides some insights into the physiology of aerial hyphae. Mutation of seven whiI-influenced genes revealed that three of them play roles in spore maturation.

Amino Acid Substitution↗
PubMed2003

XopC and XopJ, two novel type III effector proteins from Xanthomonas campestris pv. vesicatoria.

Pathogenicity of the gram-negative plant pathogen Xanthomonas campestris pv. vesicatoria depends on a type III secretion (TTS) system which translocates bacterial effector proteins into the plant cell. Previous transcriptome analysis identified a genome-wide regulon of putative virulence genes that are coexpressed with the TTS system. In this study, we characterized two of these genes, xopC and xopJ. Both genes encode Xanthomonas outer proteins (Xops) that were shown to be secreted by the TTS system. In addition, type III-dependent translocation of both proteins into the plant cell was demonstrated using the AvrBs3 effector domain as a reporter. XopJ belongs to the AvrRxv/YopJ family of effector proteins from plant and animal pathogenic bacteria. By contrast, XopC does not share significant homology to proteins in the database. Sequence analysis revealed that the xopC locus contains several features that are reminiscent of pathogenicity islands. Interestingly, the xopC region is flanked by 62-bp inverted repeats that are also associated with members of the Xanthomonas avrBs3 effector family. Besides xopC, a second gene of the locus, designated hpaJ, was shown to be coexpressed with the TTS system. hpaJ encodes a protein with similarity to transglycosylases and to the Pseudomonas syringae pv. maculicola protein HopPmaG. HpaJ secretion and translocation by the X. campestris pv. vesicatoria TTS system was not detectable, which is consistent with its predicted Sec signal and a putative function as transglycosylase in the bacterial periplasm.

Bacterial Proteins↗
PubMed2005

Screening for quorum-sensing inhibitors (QSI) by use of a novel genetic system, the QSI selector.

With the widespread appearance of antibiotic-resistant bacteria, there is an increasing demand for novel strategies to control infectious diseases. Furthermore, it has become apparent that the bacterial life style also contributes significantly to this problem. Bacteria living in the biofilm mode of growth tolerate conventional antimicrobial treatments. The discovery that many bacteria use quorum-sensing (QS) systems to coordinate virulence and biofilm development has pointed out a new, promising target for antimicrobial drugs. We constructed a collection of screening systems, QS inhibitor (QSI) selectors, which enabled us to identify a number of novel QSIs among natural and synthetic compound libraries. The two most active were garlic extract and 4-nitro-pyridine-N-oxide (4-NPO). GeneChip-based transcriptome analysis revealed that garlic extract and 4-NPO had specificity for QS-controlled virulence genes in Pseudomonas aeruginosa. These two QSIs also significantly reduced P. aeruginosa biofilm tolerance to tobramycin treatment as well as virulence in a Caenorhabditis elegans pathogenesis model.

4-Butyrolactone↗
PubMed2006

Autoinducer 2 controls biofilm formation in Escherichia coli through a novel motility quorum-sensing regulator (MqsR, B3022).

The cross-species bacterial communication signal autoinducer 2 (AI-2), produced by the purified enzymes Pfs (nucleosidase) and LuxS (terminal synthase) from S-adenosylhomocysteine, directly increased Escherichia coli biofilm mass 30-fold. Continuous-flow cells coupled with confocal microscopy corroborated these results by showing the addition of AI-2 significantly increased both biofilm mass and thickness and reduced the interstitial space between microcolonies. As expected, the addition of AI-2 to cells which lack the ability to transport AI-2 (lsr null mutant) failed to stimulate biofilm formation. Since the addition of AI-2 increased cell motility through enhanced transcription of five motility genes, we propose that AI-2 stimulates biofilm formation and alters its architecture by stimulating flagellar motion and motility. It was also found that the uncharacterized protein B3022 regulates this AI-2-mediated motility and biofilm phenotype through the two-component motility regulatory system QseBC. Deletion of b3022 abolished motility, which was restored by expressing b3022 in trans. Deletion of b3022 also decreased biofilm formation significantly, relative to the wild-type strain in three media (46 to 74%) in 96-well plates, as well as decreased biomass (8-fold) and substratum coverage (19-fold) in continuous-flow cells with minimal medium (growth rate not altered and biofilm restored by expressing b3022 in trans). Deleting b3022 changed the wild-type biofilm architecture from a thick (54-mum) complex structure to one that contained only a few microcolonies. B3022 positively regulates expression of qseBC, flhD, fliA, and motA, since deleting b3022 decreased their transcription by 61-, 25-, 2.4-, and 18-fold, respectively. Transcriptome analysis also revealed that B3022 induces crl (26-fold) and flhCD (8- to 27-fold). Adding AI-2 (6.4 muM) increased biofilm formation of wild-type K-12 MG1655 but not that of the isogenic b3022, qseBC, fliA, and motA mutants. Adding AI-2 also increased motA transcription for the wild-type strain but did not stimulate motA transcription for the b3022 and qseB mutants. Together, these results indicate AI-2 induces biofilm formation in E. coli through B3022, which then regulates QseBC and motility; hence, b3022 has been renamed the motility quorum-sensing regulator gene (the mqsR gene).

Biofilms↗
PubMed2006

The Fnr regulon of Bacillus subtilis.

The Bacillus subtilis transcriptional regulator Fnr is an integral part of the regulatory cascade required for the adaptation of the bacterium to low oxygen tension. The B. subtilis Fnr regulon was defined via transcriptomic analysis in combination with bioinformatic-based binding site prediction. Four distinct groups of Fnr-dependent genes were observed. Group 1 genes (narKfnr, narGHJI, and arfM) are generally induced by Fnr under anaerobic conditions. All corresponding promoters contain an essential Fnr-binding site centered -41.5/-40.5 bp upstream of the transcriptional start point, suggesting their induction by direct Fnr interaction. Group 2 genes (alsSD, ldh lctP, ywcJ, and cydABCD) are characterized by anaerobic repression in the presence of nitrate. Mutational analysis of the Fnr-binding sites found in three of the corresponding promoters excluded their function in Fnr-mediated repression. Genetic evidence showing that group 2 genes are anaerobically repressed by nitrate reductase formation was accumulated. A possible role of the redox regulator YdiH in the regulation of group 2 genes was initially investigated. Group 3 genes are characterized by their Fnr-dependent activation in the presence of nitrate and the lack of an Fnr-binding site in their promoters. The analysis of Group 3 gene transcription (ykuNOP and ydbN) indicated that Fnr induces nitrate reductase production, which leads to the formation of the regulatory compound nitrite from nitrate. Finally, the group 4 operon acoABCL, lacking an Fnr-binding site, requires Fnr-dependent nitrate reductase formation for its general anaerobic induction. A regulatory model for the observed complex Fnr-mediated gene expression was deduced.

Bacillus subtilis↗
PubMed2006

The transcriptional antiterminator RfaH represses biofilm formation in Escherichia coli.

We investigated the influence of regulatory and pathogenicity island-associated factors (Hha, RpoS, LuxS, EvgA, RfaH, and tRNA5Leu) on biofilm formation by uropathogenic Escherichia coli (UPEC) strain 536. Only inactivation of rfaH, which encodes a transcriptional antiterminator, resulted in increased initial adhesion and biofilm formation by E. coli 536. rfaH inactivation in nonpathogenic E. coli K-12 isolate MG1655 resulted in the same phenotype. Transcriptome analysis of wild-type strain 536 and an rfaH mutant of this strain revealed that deletion of rfaH correlated with increased expression of flu orthologs. flu encodes antigen 43 (Ag43), which mediates autoaggregation and biofilm formation. We confirmed that deletion of rfaH leads to increased levels of flu and flu-like transcripts in E. coli K-12 and UPEC. Supporting the hypothesis that RfaH represses biofilm formation through reduction of the Ag43 level, the increased-biofilm phenotype of E. coli MG1655rfaH was reversed upon inactivation of flu. Deletion of the two flu orthologs, however, did not modify the behavior of mutant 536rfaH. Our results demonstrate that the strong initial adhesion and biofilm formation capacities of strain MG1655rfaH are mediated by both increased steady-state production of Ag43 and likely increased Ag43 presentation due to null rfaH-dependent lipopolysaccharide depletion. Although the roles of rfaH in the biofilm phenotype are different in UPEC strain 536 and K-12 strain MG1655, this study shows that RfaH, in addition to affecting the expression of bacterial virulence factors, also negatively controls expression and surface presentation of Ag43 and possibly another Ag43-independent factor(s) that mediates cell-cell interactions and biofilm formation.

Adhesins, Bacterial↗
PubMed2006

A caulobacter crescentus extracytoplasmic function sigma factor mediating the response to oxidative stress in stationary phase.

Alternative sigma factors of the extracytoplasmic function (ECF) subfamily are important regulators of stress responses in bacteria and have been implicated in the control of homeostasis of the extracytoplasmic compartment of the cell. This work describes the characterization of sigF, encoding 1 of the 13 members of this subfamily identified in Caulobacter crescentus. A sigF-null strain was obtained and shown to be severely impaired in resistance to oxidative stress, caused by hydrogen peroxide treatment, exclusively during the stationary phase. Although sigF mRNA levels decrease in stationary-phase cells, the amount of sigma(F) protein is greatly increased at this stage, indicating a posttranscriptional control. Data obtained indicate that the FtsH protease is either directly or indirectly involved in the control of sigma(F) levels, as cells lacking this enzyme present larger amounts of the sigma factor. Increased stability of sigma(F) protein in stationary-phase cells of the parental strain and in exponential-phase cells of the ftsH-null strain is also demonstrated. Transcriptome analysis of the sigF-null strain led to the identification of eight genes regulated by sigma(F) during the stationary phase, including sodA and msrA, which are known to be involved in oxidative stress response.

Bacterial Proteins↗
PubMed2006

Global control of cysteine metabolism by CymR in Bacillus subtilis.

YrzC has previously been identified as a repressor controlling ytmI expression via its regulation of YtlI activator synthesis in Bacillus subtilis. We identified YrzC as a master regulator of sulfur metabolism. Gene expression profiles of B. subtilis delta yrzC mutant and wild-type strains grown in minimal medium with sulfate as the sole sulfur source were compared. In the mutant, increased expression was observed for 24 genes previously identified as repressed in the presence of sulfate. Since several genes involved in the pathways leading to cysteine formation were found, we propose to rename YrzC CymR, for "cysteine metabolism repressor." A CymR-dependent binding to the promoter region of the ytlI, ssuB, tcyP, yrrT, yxeK, cysK, or ydbM gene was demonstrated using gel shift experiments. A potential CymR target site, TAAWNCN2ANTWNAN3ATMGGAATTW, was found in the promoter region of these genes. In a DNase footprint experiment, the protected region in the ytlI promoter region contained this consensus sequence. Partial deletion or introduction of point mutations in this sequence confirmed its involvement in ytlI, yrrT, and yxeK regulation. The addition of O-acetylserine in gel shift experiments prevented CymR-dependent binding to DNA for all of the targets characterized. Transcriptome analysis of a delta cymR mutant and the wild-type strain also brought out significant changes in the expression level of a large set of genes related to stress response or to transition toward anaerobiosis.

Bacillus subtilis↗
PubMed2006

Effect of Neisseria meningitidis fur mutations on global control of gene transcription.

The ferric uptake regulator Fur is a well-known iron-responsive repressor of gene transcription, which is used by many bacteria to respond to the low-iron environment that pathogens encounter during infection. In this study we used comparative transcriptome analysis to define the role of the Fur protein in the global control of gene transcription and iron regulation in Neisseria meningitidis. By using the Fur-null mutant and its complemented derivative, we identified 83 genes whose transcription is controlled by Fur. We report that Fur may control differential expression of these genes by binding directly to their promoters or through indirect mechanisms. In addition, mutation of the fur gene resulted in the induction of the heat shock response, and transcription of these genes does not respond to iron limitation. Furthermore, analysis of the iron starvation stimulon in the Fur-null mutant provided evidences of iron-responsive regulation that is independent of Fur. We began to dissect the regulatory networks of Fur and the heat shock (stress) response in N. meningitidis, and the observed interlink between the two circuits is discussed.

Bacterial Outer Membrane Proteins↗
PubMed2026

A conserved partner-switching system controls terminal differentiation in multicellular cyanobacteria.

UNLABELLED: Canonical partner-switching systems (PSSs) regulate sigma factor activity through reversible phosphorylation, but their established roles have been largely limited to stress responses and sporulation in Firmicutes. Whether this regulatory mechanism also controls developmental cell fate decisions in other bacterial phyla has remained unknown. Here, we identify a canonical PSS that governs heterocyst differentiation in the multicellular cyanobacterium Anabaena sp. PCC 7120. This system comprises the anti-sigma factor All2284 (NfsS) and the anti-anti-sigma factor All2283 (NfsR). Structural predictions and biochemical assays showed that NfsS phosphorylates NfsR on a conserved serine residue, whereas bacterial two-hybrid and co-purification assays demonstrated that NfsS binds the developmental sigma factors SigC and SigE. Deletion of nfsR abolished heterocyst formation and diazotrophic growth, and transcriptomic analysis revealed broad failure to induce late heterocyst genes, including nitrogen fixation functions such as nifHDK and fdxH. Phylum-wide comparative genomics further showed that PSS genes and putative functional clusters are strongly enriched in filamentous and heterocyst-forming taxa, indicating an association between the expansion of these signaling modules and the emergence of multicellularity and developmental specialization. Together, these findings establish a PSS as a direct regulator of terminal cell differentiation in a gram-negative bacterium and reveal partner switching as a conserved regulatory principle linking environmental signaling to developmental fate in a major bacterial phylum. IMPORTANCE: While partner-switching systems are classically associated with stress responses and sporulation control in Firmicutes, whether this regulatory logic governs developmental decisions in other bacterial phyla has remained unknown. Here, we establish that a related partner-switching mechanism operates in a distinct bacterial lineage, the cyanobacteria, where it controls a major developmental transition involving terminal cell differentiation. Specifically, we show that a phosphorylation-dependent checkpoint involving the anti-sigma factor NfsS and the anti-anti-sigma factor NfsR directly regulates heterocyst formation. Disruption of this switch abolishes cell differentiation and diazotrophic growth, revealing that this system is an obligate gatekeeper for terminal differentiation. Conceptually, these findings substantially extend the known functional repertoire of partner-switching circuits: rather than controlling stress adaptation or spore dormancy, this module has been co-opted to govern a complex, multicellular developmental program in an organism that underpins global carbon and nitrogen cycles. This work, therefore, establishes a new paradigm for phosphorylation-based control of developmental sigma factors and provides a tractable model for dissecting how conserved signaling modules are rewired to drive lineage-specific innovations across the bacterial domain.

cell differentiation↗
PubMed2003

GATA-1-mediated proliferation arrest during erythroid maturation.

Transcription factor GATA-1 is essential for erythroid and megakaryocytic maturation. GATA-1 mutations are associated with hematopoietic precursor proliferation and leukemogenesis, suggesting a role in cell cycle control. While numerous GATA-1 target genes specifying mature hematopoietic phenotypes have been identified, how GATA-1 regulates proliferation remains unknown. We used a complementation assay based on synchronous inducible rescue of GATA-1(-) erythroblasts to show that GATA-1 promotes both erythroid maturation and G(1) cell cycle arrest. Molecular studies combined with microarray transcriptome analysis revealed an extensive GATA-1-regulated program of cell cycle control in which numerous growth inhibitors were upregulated and mitogenic genes were repressed. GATA-1 inhibited expression of cyclin-dependent kinase (Cdk) 6 and cyclin D2 and induced the Cdk inhibitors p18(INK4C) and p27(Kip1) with associated inactivation of all G(1) Cdks. These effects were dependent on GATA-1-mediated repression of the c-myc (Myc) proto-oncogene. GATA-1 inhibited Myc expression within 3 h, and chromatin immunoprecipitation studies indicated that GATA-1 occupies the Myc promoter in vivo, suggesting a direct mechanism for gene repression. Surprisingly, enforced expression of Myc prevented GATA-1-induced cell cycle arrest but had minimal effects on erythroid maturation. Our results illustrate how GATA-1, a lineage-determining transcription factor, coordinates proliferation arrest with cellular maturation through distinct, interrelated genetic programs.

Cell Cycle↗
PubMed2024

Adaptation for Staphylococcus aureus to hosts via insertion mutation in the accessory gene regulator agrC gene: decreased virulence and enhanced persistence capacity.

UNLABELLED: Staphylococcus aureus is an important human pathogen due to its vast array of virulence factors regulated by multiple regulatory mechanisms, including the accessory gene regulator. In this study, two S. aureus strains were simultaneously isolated from the blood of a febrile patient, belonging to the same clone, designated as 23H with a complete hemolytic phenotype, and 23B, exhibiting an incomplete hemolytic phenotype. The genomic comparison between strains 23B and 23H revealed that 23B had a single adenine base insertion at position 923 in the agrC gene, leading to a functional loss of the encoded AgrC. Experimental findings showed that strain 23B had decreased hemolytic activity, lower cytotoxicity against human alveolar epithelial A549 cells and in the Galleria mellonella model, and a reduced ability to survive intracellularly after infecting macrophages, in comparison to 23H. Conversely, 23B exhibited enhanced biofilm formation, greater adherence to A549 cells, and increased persistence in the face of vancomycin and daptomycin treatment. Transcriptomic analysis revealed that 23B upregulated surface protein-encoding genes while simultaneously reducing the expression levels of virulence factors, highlighting the intricate regulatory adjustments facilitating its persistence and reducing pathogenic potential. ATP assay results indicated that 23B maintained elevated ATP levels during the exponential phase yet exhibited reduced levels in the stationary phase when compared with 23H. Our findings suggested that the mutation in the agrC gene of S. aureus results in diminished virulence but markedly enhances persistence. This mutated strain warrants clinical attention because it may lead to treatment failures and persist in patients. IMPORTANCE: In clinical antimicrobial therapy, bacterial strains often develop resistance to antimicrobial agents. Additionally, mutations in their gene regulatory networks can increase their persistence, especially in immunocompromised patients. This study identified an insertion mutation in the accessory gene regulator, agrC gene, carried by a Staphylococcus aureus strain isolated from the blood of a febrile patient, leading to the functional loss of AgrC. Further research revealed that despite the reduced virulence of the mutated strain, it significantly bolstered the capacity to adapt and endure within the host during prolonged infections. This was evidenced by increased adhesion and biofilm formation capabilities, development of antimicrobial tolerance, and decreased ATP levels linked to persistence. Therefore, monitoring these mutations in S. aureus is crucial clinically, as they can complicate treatment strategies.

Staphylococcus aureus↗