Cyclic AMP in prokaryotes

The biosynthesis and regulation of bacterial prodiginines

The red-pigmented prodiginines are bioactive secondary metabolites produced by both Gram-negative and Gram-positive bacteria. Recently, these tripyrrole molecules have received renewed attention owing to reported immunosuppressive and anticancer properties. The enzymes involved in the biosynthetic pathways for the production of two of these molecules, prodigiosin and undecylprodigiosin, are now known. However, the biochemistry of some of the reactions is still poorly understood. The physiology and regulation of prodiginine production in Serratia and Streptomyces are now well understood, although the biological role of these pigments in the producer organisms remains unclear. However, research into the biology of pigment production will stimulate interest in the bioengineering of strains to synthesize useful prodiginine derivatives.

Removal of antibiotic resistance of live vaccine strain Escherichia coli MM-3 and evaluation of the immunogenicity of the new strain

MM-3 was a live vaccine strain candidate for protecting neonatal piglets from diarrhea. Designed in the 1980s, a high degree of protection from colibacillosis was afforded to piglets in a challenge study and field trials. However MM-3 had a drawback of carrying the antibiotic resistance gene (chloramphenicol acetyltransferase gene, cat). The introduction of a host-plasmid balanced lethal system into the vaccine was a good idea to solve the problem. The lambda-Red recombination system was adopted in this study to realize the replacement of cat by aspartate-semialdehyde dehydrogenase gene (asd) in the plasmid pMM085. The new plasmid named pMMASD was introduced into an Escherichia coli strain chi6097 and Salmonella typhimurium chi4072 where the asd gene had been knocked out in their chromosomes. Cultured in an Erlenmeyer flask, expression levels of two antigens K88ac fimbriae and heat-labile enterotoxin B subunit (LTB) in cell lysate were similar among MM-3, chi4072(pMMASD) and chi6097(pMMASD). However, chi4072(pMMASD) possessed the more effective secretion mechanism to transport LTB enterotoxin into culture liquid. The relatively higher stability of pMMASD in Salmonella typhimurium chi4072 than that of pMM085 in MM-3 was determined both in vitro in the absence of selective pressure, and in vivo following oral inoculation. Oral immunization of BALB/c mice with chi4072(pMMASD) or chi6097(pMMASD) was sufficient to elicit IgA responses in mucosal tissues as well as systemic IgG antibody responses to the K88 fimbriae, while MM-3 failed to elicit specific antibody responses to K88 fimbriae in mucosal tissues. Among three live strains, only chi4072(pMMASD) could develop strong humoral responses against LTB enterotoxin. The results suggest that chi4072(pMMASD) is expected to be a promising live vaccine strain.

Regulation of the expression of whiB1 in Mycobacterium tuberculosis: role of cAMP receptor protein

The wbl (whiB-like) genes encode putative transcription factors unique to actinomycetes. This study characterized the promoter element of one of the seven wbl genes of Mycobacterium tuberculosis, whiB1 (Rv3219c). The results reveal that whiB1 is transcribed by a class I-type cAMP receptor protein (CRP)-dependent promoter, harbouring a CRP-binding site positioned at -58.5 with respect to its transcription start point. In vivo promoter activity analysis and electrophoretic mobility shift assays suggest that the expression of whiB1 is indeed regulated by cAMP-dependent binding of CRP(M) (encoded by the M. tuberculosis gene Rv3676) to the whiB1 5' untranslated region (5'UTR). beta-Galactosidase gene fusion analysis revealed induction of the whiB1 promoter in M. tuberculosis on addition of exogenous dibutyric cAMP (a diffusible cAMP analogue) only when an intact CRP-binding site was present. These results indicate that M. tuberculosis whiB1 transcription is regulated in part by cAMP levels via direct binding of cAMP-activated CRP(M) to a consensus CRP-binding site in the whiB1 5'UTR.

New messages from old messengers: cAMP and mycobacteria

Cyclic nucleotides are ancient second messengers, and the enzymes that synthesize cAMP and cGMP [cyclic nucleotide monophosphates (cNMPs)] are encoded in the genomes of several bacteria. We focus here on recent biochemical and structural information on the proteins that make and break cyclic nucleotides in mycobacteria, namely the nucleotide cyclases and phosphodiesterases, respectively. The presence of these enzymes along with putative cNMP-binding proteins suggests an intricate regulation of cAMP metabolism and utilization by these organisms. It is anticipated that future research will be directed towards identifying cellular processes that are regulated by cAMP in mycobacteria and deciphering the cross-talk between mycobacterial pathogens and their eukaryotic host.

Structural and biochemical analysis of the Rv0805 cyclic nucleotide phosphodiesterase from Mycobacterium tuberculosis

Cyclic nucleotide monophosphate (cNMP) hydrolysis in bacteria and eukaryotes is brought about by distinct cNMP phosphodiesterases (PDEs). Since these enzymes differ in amino acid sequence and properties, they have evolved by convergent evolution. Cyclic NMP PDEs cleave cNMPs to NMPs, and the Rv0805 gene product is, to date, the only identifiable cNMP PDE in the genome of Mycobacterium tuberculosis. We have shown that Rv0805 is a cAMP/cGMP dual specificity PDE, and is unrelated in amino acid sequence to the mammalian cNMP PDEs. Rv0805 is a dimeric, Fe(3+)-Mn(2+) binuclear PDE, and mutational analysis demonstrated that the active site metals are co-ordinated by conserved aspartate, histidine and asparagine residues. We report here the structure of the catalytic core of Rv0805, which is distantly related to the calcineurin-like phosphatases. The crystal structure of the Rv0805 dimer shows that the active site metals contribute to dimerization and thus play an additional structural role apart from their involvement in catalysis. We also present the crystal structures of the Asn97Ala mutant protein that lacks one of the Mn(2+) co-ordinating residues as well as the Asp66Ala mutant that has a compromised cAMP hydrolytic activity, providing a structural basis for the catalytic properties of these mutant proteins. A molecule of phosphate is bound in a bidentate manner at the active site of the Rv0805 wild-type protein, and cacodylate occupies a similar position in the crystal structure of the Asp66Ala mutant protein. A unique substrate binding pocket in Rv0805 was identified by computational docking studies, and the role of the His140 residue in interacting with cAMP was validated through mutational analysis. This report on the first structure of a bacterial cNMP PDE thus significantly extends our molecular understanding of cAMP hydrolysis in class III PDEs.

Mutation in cyaA in Enterobacter cloacae decreases cucumber root colonization

Strains of Enterobacter cloacae show promise as biological control agents for Pythium ultimum-induced damping-off on cucumber and other crops. Enterobacter cloacae M59 is a mini-Tn5 Km transposon mutant of strain 501R3. Populations of M59 were significantly lower on cucumber roots and decreased much more rapidly than those of strain 501R3 with increasing distance from the soil line. Strain M59 was decreased or deficient in growth and chemotaxis on most individual compounds detected in cucumber root exudate and on a synthetic cucumber root exudate medium. Strain M59 was also slightly less acid resistant than strain 501R3. Molecular characterization of strain M59 demonstrated that mini-Tn5 Km was inserted in cyaA, which encodes adenylate cyclase. Adenylate cyclase catalyzes the formation of cAMP and cAMP levels in cell lysates from strain M59 were approximately 2% those of strain 501R3. Addition of exogenous, nonphysiological concentrations of cAMP to strain M59 restored growth (1 mM) and chemotaxis (5 mM) on synthetic cucumber root exudate and increased cucumber seedling colonization (5 mM) by this strain without serving as a source of reduced carbon, nitrogen, or phosphorous. These results demonstrate a role for cyaA in colonization of cucumber roots by Enterobacter cloacae.

Fatty acid regulation of adenylyl cyclase Rv2212 from Mycobacterium tuberculosis H37Rv

Adenylyl cyclase Rv2212 from Mycobacterium tuberculosis has a domain composition identical to the pH-sensing isoform Rv1264, an N-terminal regulatory domain and a C-terminal catalytic domain. The maximal velocity of Rv2212 was the highest of all 10 mycobacterial cyclases investigated to date (3.9 micromol cAMP.mg(-1).min(-1)), whereas ATP substrate affinity was low (SC(50) = 2.1 mm ATP). Guanylyl cyclase side activity was absent. The activities and kinetics of the holoenzyme and of the catalytic domain alone were similar, i.e. in distinct contrast to the Rv1264 adenylyl cyclase, in which the N-terminal domain is autoinhibitory. Unsaturated fatty acids strongly stimulated Rv2212 activity by increasing substrate affinity. In addition, fatty acids greatly enhanced the pH sensitivity of the holoenzyme, thus converting Rv2212 to a pH sensor adenylyl cyclase. Fatty acid binding to Rv2212 was modelled by homology to a recent structure of the N-terminal domain of Rv1264, in which a fatty acid-binding pocket is defined. Rv2212 appears to integrate three cellular parameters: ATP concentration, presence of unsaturated fatty acids, and pH. These regulatory properties open the possibility that novel modes of cAMP-mediated signal transduction exist in the pathogen.

Coactivation of Vibrio vulnificus putAP operon by cAMP receptor protein and PutR through cooperative binding to overlapping sites

The cAMP receptor protein (CRP) positively regulates the expression of Vibrio vulnificus putAP genes encoding a proline dehydrogenase and a proline permease. In the present study, an open reading frame encoding PutR was identified downstream of the putAP genes and a mutational analysis revealed that the PutR protein was also involved in regulating the putAP transcription by activating Pput promoter. Although CRP acts as a primary activator and the influence of PutR on Pput is mediated by CRP, the level of Pput activity observed when PutR and CRP functioned together was greater than the sum of Pput activities achieved by each activator alone. Western blot analyses demonstrated that the cellular levels of PutR and CRP were not significantly affected by each other, indicating that PutR and CRP coactivate Pput rather than function sequentially in a regulatory cascade. Two adjacent binding sites for PutR mapped by in vitro DNase I protection assays were found to overlap the CRP binding sites and were centred -91.5 (PCBI) and -133.5 bp (PCBII) upstream of the transcription start site of Pput respectively. PutR and CRP bind to the sites cooperatively and a dissection of the role of the binding sites revealed that CRP at PCBI plays the most crucial role in the activation of Pput. Accordingly, the present results revealed that PutR and CRP coactivate the expression of Pput and exert their effect by cooperatively binding to the promoter.

Proceedings of the SMBE Tri-National Young Investigators' Workshop 2005. Positional conservation of clusters of overlapping promoter-like sequences in enterobacterial genomes

The selective mechanisms operating in regulatory regions of bacterial genomes are poorly understood. We have previously shown that, in most bacterial genomes, regulatory regions contain high densities of sigma70 promoter-like signals that are significantly above the densities detected in nonregulatory genomic regions. In order to investigate the molecular evolutionary forces that operate in bacterial regulatory regions and how they affect the observed redundancy of promoter-like signals, we have undertaken a comparative analysis across the completely sequenced genomes of enteric gamma-proteobacteria. This analysis detects significant positional conservation of promoter-like signal clusters across enterics, some times in spite of strong primary sequence divergence. This suggests that the conservation of the nature and exact position of specific nucleotides is not necessarily the priority of selection for maintaining the transcriptional function in these bacteria. We have further characterized the structural conservation of the regulatory regions of dnaQ and crp across all enterics. These two regions differ in essentiality and mode of regulation, the regulation of crp being more complex and involving interactions with several transcription factors. This results in substantially different modes of evolution, with the dnaQ region appearing to evolve under stronger purifying selection and the crp region showing the likely effects of stabilizing selection for a complex pattern of gene expression. The higher flexibility of the crp region is consistent with the observed less conservation of global regulators in evolution. Patterns of regulatory evolution are also found to be markedly different in endosymbiotic bacteria, in a manner consistent with regulatory regions suffering some level of degradation, as has been observed for many other characters in these genomes. Therefore, the mode of evolution of bacterial regulatory regions appears to be highly dependent on both the lifestyle of the bacterium and the specific regulatory requirements of different genes. In fact, in many bacteria, the mode of evolution of genes requiring significant physiological adaptability in expression levels may follow patterns similar to those operating in the more complex regulatory regions of eukaryotic genomes.

dps expression in Escherichia coli O157:H7 requires an extended -10 region and is affected by the cAMP receptor protein

The DNA binding protein from starved cells (Dps) is a general stress protein that provides Escherichia coli protection from osmotic, oxidative, and acid stresses. While Dps production and accumulation is primarily associated with stationary phase, during log phase, this protein protects against oxidative stress in an OxyR-dependent manner. In this study, evidence is provided that expands the role of Dps in acid tolerance to both log- and stationary-phase E. coli O157:H7. The transcription of dps occurred in log-phase cells without OxyR or stress and was upregulated during entry into stationary phase. The expression in log and stationary phase involved sigma70 and sigmas, respectively, with both sigma factors recognizing the same promoter region. Site-directed mutagenesis identified an extended -10 region that was essential to both sigma70 and sigmas transcription of dps. cAMP receptor protein (CRP) was found to repress dps expression as a crp mutant had a significant increase in the dps mRNA level. However, a CRP binding site was not found in the dps promoter and upregulation of dps in the crp mutant was absent in a crp rpoS double mutant. The findings from this study demonstrated that dps was expressed at a basal level during growth, both sigma70- and sigmas-driven transcription required an extended -10, and CRP repression is mediated through the alternative sigma factor sigmas (rpoS).

NaCl enhances cellular cAMP and upregulates genes related to heterocyst development in the cyanobacterium, Anabaena sp. strain PCC 7120

Cellular cAMP was rapidly increased in the nitrogen-fixing cyanobacterium, Anabaena sp. PCC 7120, by the addition of 200 mM NaCl to the culture medium. Other alkaline-metal chlorides such as KCl or LiCl caused a lesser increase. The increase in cellular cAMP was transient and diminished when an adenylate cyclase, CyaC, which contains the conserved domains of the bacterial two-component regulatory system, was disrupted. DNA microarray analysis showed that expression of a gene cluster containing all5347 and alr5351 (hglE) was upregulated by NaCl in the wild-type strain but not in the cyaC mutant. Primer extension analysis indicated that transcription levels of all5347 and hglE were rapidly increased in response to the NaCl addition, and that these genes have NaCl-dependent transcription start sites. It was concluded that NaCl induced expression of genes related to heterocyst envelope formation in this cyanobacterium, possibly via a CyaC-cAMP signal transduction system.

Salmonella enterica serovar Choleraesuis infection of the porcine jejunal Peyer's patch rapidly induces IL-1beta and IL-8 expression

Salmonella enterica serovar Choleraesuis is an enteric pathogen of swine, producing septicemia, enterocolitis, pneumonia, and hepatitis. The initial molecular events at the site of Salmonella infection are hypothesized to be critical in the initiation of innate and adaptive immune responses; however, the acute immune response elicited by porcine intestinal tissues is not well understood. To address this need, we employed explants of jejunal Peyer's patch (JPP) mucosa from pigs to examine Salmonella-induced immune responses under controlled conditions as well as to overcome limitations of whole animal approaches. JPP explants mounted in Ussing chambers maintained normal histological structure for 2 h and stable short-circuit current and electrical conductance for 2.5 h. After ex vivo luminal exposure to Salmonella serovar Choleraesuis, JPP responded with an increase in mRNA expression of IL-1beta and IL-8, but not TNFalpha. Increased IL-1beta and IL-8 expression were dependent on efficient Salmonella adhesion and internalization, whereas mutant Salmonella did not induce inflammatory cytokine expression. Commensal enteric bacteria, present in some experiments, also did not induce inflammatory cytokine expression. These findings indicate that Salmonella uptake by Peyer's patch is important in the induction of an innate response involving expression of IL-1beta and IL-8, and that ex vivo intestinal immune tissue explants provide an intact tissue model that will facilitate investigation of mucosal immunity in swine.

Essential role of an adenylate cyclase in regulating Vibrio vulnificus virulence

Vibrio vulnificus, a halophilic estuarine bacterium, causes a fatal septicemia and necrotizing wound infection. To investigate the role of cAMP in V. vulnificus virulence regulation, an in-frame deletion mutant of the cya gene encoding adenylate cyclase was constructed. The cya null mutation resulted in a pleiotropic change of virulence phenotypes. The production of hemolysin and protease, the motility, and the cytotoxicity were decreased by the cya mutation. The defects in the cya mutant were functionally complemented in trans by a plasmid carrying the wild type cya allele. The V. vulnificus cya mutant exhibited a 100-fold increase in LD50 to mice. The result indicates that cAMP plays an essential role in the global regulation of V. vulnificus virulence.

Point mutations in the DNA- and cNMP-binding domains of the homologue of the cAMP receptor protein (CRP) in Mycobacterium bovis BCG: implications for the inactivation of a global regulator and strain attenuation

The genome of Mycobacterium tuberculosis H37Rv includes a homologue of the CRP/FNR (cAMP receptor protein/fumarate and nitrate reduction regulator) family of transcription regulators encoded by Rv3676. Sequencing of the orthologous gene from attenuated Mycobacterium bovis Bacille Calmette-Guérin (BCG) strains revealed point mutations that affect the putative DNA-binding and cNMP-binding domains of the encoded protein. These mutations are not present in the published sequences of the Rv3676 orthologues in M. bovis, M. tuberculosis or Mycobacterium leprae. An Escherichia coli lacZ reporter system was used to show that the M. tuberculosis Rv3676 protein binds to DNA sites for CRP, but this DNA binding was decreased or abolished with the Rv3676 protein counterparts from BCG strains. The DNA-binding ability of the M. tuberculosis Rv3676 protein was decreased by the introduction of base changes corresponding to the BCG point mutations. Conversely, the DNA binding of the BCG Rv3676 proteins from BCG strains was restored by removing the mutations. These data show that in this reporter system the point mutations present in the Rv3676 orthologue in BCG strains render its function defective (early strains) or abolished (late strains) and suggest that this protein might be naturally defective in M. bovis BCG strains. This raises the possibility that a contributing factor to the attenuation of BCG strains may be an inability of this global regulator to control the expression of genes required for in vivo survival and persistence.

A Myxococcus xanthus CbpB containing two cAMP-binding domains is involved in temperature and osmotic tolerances

Our previous data indicated that a Myxococcus xanthus sensor-type adenylyl cyclase (CyaA) functions in signal transduction during osmotic stress. However, the cAMP-mediated signal transduction pathway in this bacterium was unknown. Here, we isolated a clone from a M. xanthus genomic DNA library using oligonucleotide probes designed based on the conserved cAMP-binding domains of the cAMP-dependent protein kinase (PKA) regulatory subunits. The clone contained two open-reading frames (ORFs), cbpA and cbpB, encoding hydrophilic proteins with one and two cAMP-binding domains, respectively. The CbpB exhibited partial primary structural similarity to PKA regulatory subunits. cbpA and cbpB mutants, generated by gene disruption, showed normal growth, development and spore germination. However, the cbpB mutant cultured under high- or low-temperature conditions exhibited a marked reduction in growth. cbpB mutant cells were also more sensitive to osmotic stress than wild-type cells. The cbpA mutant possessed normal resistance to such stress. The phenotype of cbpB mutant was similar to those of PKA regulatory subunit mutants of some eukaryotic microorganisms.

Modeling and experimental validation of the signal transduction via the Escherichia coli sucrose phospho transferase system

Bacterial signal processing was investigated concerning the sucrose phosphotransferase system (sucrose PTS) in the bacterium Escherichia coli as an example. The about 20 different phosphotransferase systems (PTSs) of the cell fulfill besides the transport of various carbohydrates, also the function of one signal processing system. Extra- and intracellular signals are converted within the PTS protein chain to important regulatory signals affecting, e.g. carbon metabolism and chemotaxis. A detailed dynamical model of the sucrose PTS was developed describing transport and signal processing function. It was formulated using a detailed description of complex formation and phosphate transfer between the chain proteins. Model parameters were taken from literature or were identified with own experiments. Simulation studies together with experimental hints showed that the dynamic behavior of phosphate transfer in the PTS runs within 1 s. Therefore a description of steady state characteristics is sufficient for describing the signaling properties of the sucrose PTS. A steady state characteristic field describes the degree of phosphorylation of the PTS protein EIIACrr as a function of the input variables extracellular sucrose concentration and intracellular phosphoenolpyruvate (PEP):pyruvate ratio. The model has been validated with different experiments performed in a CSTR using a sucrose positive E. coli W3110 derivative. A method for determining intracellular metabolite concentrations has been developed. A sample preparation technique using a boiling ethanol buffer solution was successfully applied. The PTS output signal degree of phosphorylation of EIIACrr was also measured. Steady state conditions with varying dilution rate and dissolved oxygen concentration and dynamical variations applying different stimuli to the culture were considered. Pulse, and stop feeding experiments with limiting sucrose concentrations were performed. Simulation and experimental results matched well. The same holds for the expanded sucrose PTS and glycolysis model.

Two cAMP receptor proteins with different biochemical properties in the filamentous cyanobacterium Anabaena sp. PCC 7120

Two open reading frames (ORFs), alr0295 and alr2325, are found to encode putative cAMP receptor proteins (CRPs) in the genome of the filamentous cyanobacterium Anabaena sp. PCC 7120. These ORFs were named cAMP receptor protein-like gene A in Anabaena sp. PCC 7120 (ancrpA) and cAMP receptor protein-like gene B in Anabaena sp. PCC 7120 (ancrpB), respectively, and those translated products were investigated. The equilibrium dialysis measurements revealed that AnCrpA bound with cAMP specifically, while AnCrpB bound with both cAMP and cGMP, though the affinity for cGMP was weak. The binding affinity for cAMP of AnCrpA showed the lowest dissociation constant, approximately 0.8 microM, among bacterial CRPs. A gel mobility shift assay elucidated that AnCrpA and AnCrpB formed a complex with the consensus DNA sequence in the presence of cAMP, although AnCrpB did not have ordinary DNA-binding motifs.

Comparison of Different Attenuation Strategies in Development of a Salmonella hadar Vaccine

The purpose of this work was to develop a live, attenuated vaccine strain to protect chickens against colonization by group C Salmonella. We constructed two candidate vaccines: a deltacya deltacrp derivative and a deltaphoP derivative of Salmonella hadar. White Leghorn chickens were vaccinated at day of age and at 2 wk with one of the two strains. A nonvaccinated group served as a control. At 4 wk of age, all birds were challenged with wild-type S. hadar and necropsied 6 days later. Numbers of S. hadar in the ceca were determined. Enzyme-linked immunosorbent assay-derived serum immunoglobulin G responses against S. hadar lipopolysaccharide indicated that both strains induced a serum antibody response. The average optical density450 for birds vaccinated with the deltaphoP or deltacya deltacrp derivatives was 0.456 and 0.881, respectively. Although the deltacya deltacrp derivative induced higher levels of serum antibody, it did not provide an immune response protective against colonization by S. hadar. Conversely, birds vaccinated with the deltaphoP strain showed significant protection against S. hadar challenge. Seventy percent of the nonvaccinates, 60% of the deltacya deltacrp vaccinates, and 15% of deltaphoP vaccinates were positive for S. hadar in tissues. In a second experiment, birds were vaccinated with either the deltaphoP strain or buffer and challenged with a 10-fold higher dose than in the first experiment. After challenge, all of the birds in both groups were colonized. The geometric mean number of cecal S. hadar isolated from the control group was 1.0 x 10(6) colony-forming units (CFU)/g, and from the vaccinated group, this value was 32 CFU/g, indicating a four to five log reduction in colonization by the challenge strain.

Identification of an extracellular matrix protein adhesin, EmaA, which mediates the adhesion of Actinobacillus actinomycetemcomitans to collagen

Actinobacillus actinomycetemcomitansis an aetiologic agent in the development of periodontal and some systemic diseases in humans. This pathogen localizes to the underlying connective tissue of the oral cavity in individuals with periodontal disease. The adhesion ofA. actinomycetemcomitansto extracellular matrix components of the connective tissue prompted this study to identify gene products mediating the interaction ofA. actinomycetemcomitansto these molecules. A transposon mutagenesis system was optimized for use inA. actinomycetemcomitansand used to generate an insertional mutant library. A total of 2300 individual insertion transposon mutants were screened for changes in the adhesion to collagen and fibronectin. Mutants were identified which exhibited the following phenotypes: a decrease in collagen binding; a decrease in fibronectin binding; a decrease in binding to both proteins; and an increase in binding to both collagen and fibronectin. The identification of mutants defective in adhesion to the individual proteins indicates that distinct adhesins are expressed by this organism. Molecular analysis of these mutants implicated 11 independent loci in protein adhesion. One gene,emaA, is likely to encode a direct mediator of collagen adhesion, based on predicted protein features homologous to the collagen-binding protein YadA ofYersinia enterocolitica. EmaA was localized to the outer membrane, as expected for an adhesin. Reduction in fibronectin adhesion appeared to be influenced by abrogation of proteins involved in molybdenum-cofactor biosynthesis. Several other loci identified as reducing or increasing adhesion to both collagen and fibronectin are suggested to be involved in regulatory cascades that promote or repress expression of collagen and fibronectin adhesins. Collectively, the results support the hypothesis thatA. actinomycetemcomitanshost colonization involves afimbrial adhesins for extracellular matrix proteins, and that the expression of adhesion is modulated by global regulatory mechanisms.

Transcription profiling of cyclic AMP signaling in Candida albicans

We used transcription profiling in Candida albicans to investigate cellular regulation involving cAMP. We found that many genes require the adenylyl cyclase Cdc35p for proper expression. These include genes encoding ribosomal subunit proteins and RNA polymerase subunit proteins, suggesting that growth could be controlled in part by cAMP-mediated modulation of gene expression. Other genes influenced by loss of adenylyl cyclase are involved in metabolism, the cell wall, and stress response and include a group of genes of unknown function that are unique to C. albicans. The profiles generated by loss of the adenylyl cyclase regulator Ras1p and a downstream effector Efg1p were also examined. The loss of Ras1p function disturbs the expression of a subset of the genes regulated by adenylyl cyclase, suggesting both that the primary role of Ras1p in transcriptional regulation involves its influence on the function of Cdc35p and that there are Ras1p independent roles for Cdc35p. The transcription factor Efg1p is also needed for the expression of many genes; however, these genes are distinct from those modulated by Cdc35p with the exception of a class of hyphal-specific genes. Therefore transcription profiling establishes that cAMP plays a key role in the overall regulation of gene expression in C. albicans, and enhances our detailed understanding of the circuitry controlling this regulation.

TbPDE1, a novel class I phosphodiesterase of Trypanosoma brucei

Cyclic nucleotide specific phosphodiesterases (PDEs) are important components of all cAMP signalling networks. In humans, 11 different PDE families have been identified to date, all of which belong to the class I PDEs. Pharmacologically, they have become of great interest as targets for the development of drugs for a large variety of clinical conditions. PDEs in parasitic protozoa have not yet been extensively investigated, despite their potential as antiparasitic drug targets. The current study presents the identification and characterization of a novel class I PDE from the parasitic protozoon Trypanosoma brucei, the causative agent of human sleeping sickness. This enzyme, TbPDE1, is encoded by a single-copy gene located on chromosome 10, and it functionally complements PDE-deficient strains of Saccharomyces cerevisiae. Its C-terminal catalytic domain shares about 30% amino acid identity, including all functionally important residues, with the catalytic domains of human PDEs. A fragment of TbPDE1 containing the catalytic domain could be expressed in active form in Escherichia coli. The recombinant enzyme is specific for cAMP, but exhibits a remarkably high Km of > 600 microm for this substrate.

Systematic single base-pair substitution analysis of DNA binding by the cAMP receptor protein in cyanobacteriumSynechocystissp. PCC 6803

The cAMP receptor protein SYCRP1 in cyanobacterium Synechocystis sp. PCC 6803 is a regulatory protein that binds to the consensus DNA sequence (5'-AAATGTGATCTAGATCACATTT-3') for the cAMP receptor protein CRP in Escherichia coli. Here we examined the effects of systematic single base-pair substitutions at positions 4-8 (TGTGA) of the consensus sequence on the specific binding of SYCRP1. The consensus sequence exhibited the highest affinity, and the effects of base-pair substitutions at positions 5 and 7 were the most deleterious. The result is similar to that previously reported for CRP, whereas there were differences between SYCRP1 and CRP in the rank order of affinity for each substitution.

Metabolic switching in the sugar phosphotransferase system of Escherichia coli

Bacteria grown in a mixture of multiple sugars will first metabolize a preferred sugar until it is nearly depleted, only then turning to other carbon sources in the medium. This sharp switching of metabolic preference is characteristic of systems that optimize fitness. Here we consider the mechanism by which switching can occur in the Escherichia coli phosphotransferase system (PTS), which regulates the uptake and metabolism of several sugars. Using a model combining the description of fast biochemical processes and slower genetic regulation, we derive metabolic phase diagrams for the uptake of two PTS sugars, indicating regions of distinct sugar preference as a function of external sugar concentrations. We then propose a classification of bacterial phenotypes based on the topology of the metabolic phase diagram, and enumerate the possible topologically distinct phenotypes that can be achieved through mutations of the PTS. This procedure reveals that there is only one nontrivial switching phenotype that is insensitive to large changes in biochemical parameters. This phenotype exhibits diauxic growth, a manifestation of the winner-take-all dynamics enforced by PTS architecture. Winner-take-all behavior is implemented by the induction of sugar-specific operons, combined with competition between sugars for limited phosphoryl flux. We propose that flux-limited competition could be a common mechanism for introducing repressive interactions in cellular networks, and we argue that switching behavior similar to that described here should occur generically in systems that implement such a mechanism.

Why the phosphotransferase system of Escherichia coli escapes diffusion limitation

We calculated the implications of diffusion for the phosphoenolpyruvate:glucose phosphotransferase system (glucose-PTS) of Escherichia coli in silicon cells of various magnitudes. For a cell of bacterial size, diffusion limitation of glucose influx was negligible. Nevertheless, a significant concentration gradient for one of the enzyme species, nonphosphorylated IIA(Glc), was found. This should have consequences because the phosphorylation state of IIA(Glc) is an important intracellular signal. For mammalian cell sizes we found significant diffusion limitation, as well as strong concentration gradients in many PTS components, and strong effects on glucose and energy signaling. We calculated that the PTS may sense both extracellular glucose and the intracellular free-energy state. We discuss i), that the effects of diffusion on cell function should prevent this highly effective bacterial system from functioning in eukaryotic cells, ii), that in the larger eukaryotic cell any similar chain of mobile group-transfer proteins can neither sustain the same volumetric flux as in bacteria nor transmit a signal far into the cell, and iii), that systems such as these may exhibit spatial differentiation in their sensitivity to different signals.

Proteomic studies of diauxic lag in the differentiating prokaryote Streptomyces coelicolor reveal a regulatory network of stress-induced proteins and central metabolic enzymes

Bacteria typically undergo intermittent periods of starvation and adaptation, emulated as diauxic growth in the laboratory. In association with growth arrest elicited by metabolic stress, the differentiating eubacterium Streptomyces coelicolor not only adapts its primary metabolism, but can also activate developmental programmes leading to morphogenesis and antibiotic biosynthesis. Here, we report combined proteomic and metabolomic data of S. coelicolor used to analyse global changes in gene expression during diauxic growth in a defined liquid medium. Cultures initially grew on glutamate, providing the nitrogen source and feeding carbon (as 2-oxoglutarate) into the TCA cycle, followed by a diauxic delay allowing reorientation of metabolism and a second round of growth supported by NH4+, formed during prediauxic phase, and maltose, a glycolytic substrate. Cultures finally entered stationary phase as a result of nitrogen starvation. These four physiological states had previously been defined statistically by their distinct patterns of protein synthesis and heat shock responses. Together, these data demonstrated that the rates of synthesis of heat shock proteins are determined not only by temperature increase but also by the patterns and rates of metabolic flux in certain pathways. Synthesis profiles for metabolic- and stress-induced proteins can now be interpreted by the identification of 204 spots (SWICZ database presented at http://proteom.biomed.cas.cz). Cluster analysis showed that the activity of central metabolic enzymes involved in glycolysis, the TCA cycle, starvation or proteolysis each displayed identifiable patterns of synthesis that logically underlie the metabolic state of the culture. Diauxic lag was accompanied by a structured regulatory programme involving the sequential activation of heat-, salt-, cold- and bacteriostatic antibiotic (pristinamycin I, PI)-induced stimulons. Although stress stimulons presumably provide protection during environmental- or starvation-induced stress, their identities did not reveal any coherent adaptive or developmental functions. These studies revealed interactive regulation of metabolic and stress response systems including some proteins known to support developmental programmes in S. coelicolor.

Genomic analysis of protein kinases, protein phosphatases and two-component regulatory systems of the cyanobacterium Anabaena sp. strain PCC 7120

Anabaena sp. PCC 7120 is a cyanobacterium capable of performing several important biological functions: photosynthesis, nitrogen fixation, cell differentiation, cell-cell communication, etc. These activities require an extensive signaling capability in order to respond to the changing environment. Based on the genomic data, we have retrieved several gene families encoding signaling components. It is estimated that 211 genes encode two-component signaling elements, and 66 genes encode Ser/Thr kinases and phosphatases. These genes together represent 4.2% of the coding capacity of the whole genome, making Anabaena PCC 7120 a leading member among prokaryotes in terms of its signaling potential. It is known that two-component systems are composed of a few basic modules that can arrange into different structures best adapted for each signaling system. Many proteins in Anabaena PCC 7120 have incorporated both modules of two-component systems and catalytic domains of either Ser/Thr kinases or phosphatases. A family of 13 genes encode proteins with both a Ser/Thr kinase domain and a His kinase domain, and another four genes were also found whose products have both a response regulator domain and a Ser/Thr phosphatase domain. Of all the signaling proteins in Anabaena PCC 7120, about one third (35%) are conserved in the genome of the unicellular cyanobacterium strain Synechocystis sp. PCC 6803. Interestingly, one subfamily of His kinases and two subfamilies of response regulators are found in Anabaena PCC 7120 but are absent in Synechocystis PCC 6803. This study constitutes a basis for analyses of signal transduction in Anabaena PCC 7120 using functional genomic approaches.

Evidence for cAMP-dependent protein kinase in the dinoflagellate, Amphidinium operculatum

A cAMP dependent protein kinase (PKA) was identified in the dinoflagellate Amphidinium operculum. In vitro kinase activity towards kemptide, a PKA-specific substrate, was not detectable in crude lysates. However, fractionation of dinoflagellate extracts by gel filtration chromatography showed PKA-like activity toward kemptide at approximately 66 kDa. These findings suggest that possible low molecular mass inhibitors in crude lysates were removed by the gel filtration chromatography. Pre-incubation of extracts with cAMP prior to chromatography resulted in an apparent molecular mass shift in the in vitro kinase assay to 40 kDa. An in-gel kinase assay reflected activity of the free catalytic subunit at approximately 40 kDa. Furthermore, western blotting with an antibody to the human PKA catalytic subunit confirmed a catalytic subunit with a mass of approximately 40 kDa. Results from this study indicate that the PKA in A. operculatum has a catalytic subunit of similar size to that in higher eukaryotes, but with a holoenzyme of a size suggesting a dimeric, rather than tetrameric structure.

Antibacterial activity of surfactants against Escherichia coli cells is influenced by carbon source and anaerobiosis

AIMS

In order to clarify the involvement of an energy-yielding system in the antibacterial action of surfactants, the effects of carbon source and anaerobiosis during the growth period on the surfactant sensitivity of Escherichia coli cells were investigated.

METHODS AND RESULTS

Cetyltrimethylammonium bromide (CTAB) and N-dodecyl-N,N-dimethylglycine, at relatively low concentrations, caused a delay in growth of E. coli cells. Cells grown in M9 medium supplemented with glycerol, succinate or acetate as a carbon source were more sensitive to surfactants and had a higher respiratory activity than those grown with glucose. Cultivation under anaerobiosis made cells resistant to CTAB.

CONCLUSIONS

Bacterial sensitivity to surfactants was affected by carbon source and anaerobiosis.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained should be helpful in determining suitable conditions of treatment in the practical use of surfactants for bacterial decontamination.

Binding modes of cyclic AMP and environments of tryptophan residues in 1:1 and 1:2 complexes of cyclic AMP receptor protein and cyclic AMP

Cyclic AMP (cAMP) receptor protein (CRP) forms 1:1 and 1:2 complexes with cAMP, and the former complex is considered to be the most active form of CRP in binding to specific DNA sequences and in modulating gene transcription by RNA polymerases. We examine the cAMP binding modes and structural changes of CRP upon cAMP binding by UV resonance Raman spectroscopy. The Raman spectra of CRP-(cAMP)(1) and CRP-(cAMP)(2) extracted from those of CRP-cAMP mixtures at varied mixing ratios clearly show that the hydrogen bonding state and the conformation of cAMP in both complexes in solution are very similar to those found in the X-ray crystal structure of CRP-(cAMP)(2), which is evidence that the cAMP binding mode does not differ between the two complexes. The environmental hydrophobicity of Trp85 monitored by UV resonance Raman intensity shows a significant decrease upon binding of the first cAMP molecule, whereas no further change occurs in the second cAMP binding step. The environmental change of Trp85 suggests an opening of the cleft between the N-terminal cAMP and C-terminal DNA binding domains in the process of CRP activation by binding of a single cAMP molecule.

Effect of vfr mutation on global gene expression and catabolite repression control of Pseudomonas aeruginosa

Vfr of Pseudomonas aeruginosa is 91% similar to the cAMP receptor protein (CRP) of Escherichia coli. Based on the high degree of sequence homology between the two proteins, the question arose whether Vfr had a global regulatory effect on gene expression for P. aeruginosa as CRP did for E. coli. This report provides two-dimensional polyacrylamide gel electrophoretic evidence that Vfr is a global regulator of gene expression in P. aeruginosa. In a vfr101::aacC1 null mutant, at least 43 protein spots were absent or decreased when compared to the proteome pattern of the parent strain. In contrast, 17 protein spots were absent or decreased in the parent strain when compared to the vfr101::aacC1 mutant. Thus, a mutation in vfr affected production of at least 60 proteins in P. aeruginosa. In addition, the question whether Vfr and CRP shared similar mechanistic characteristics was addressed. To ascertain whether Vfr, like CRP, can bind cAMP, Vfr and CRP were purified to homogeneity and their apparent dissociation constants (K(d)) for binding to cAMP were determined. The K(d) values were 1.6 microM for Vfr and 0.4 microM for CRP, suggesting that these proteins have a similar affinity for cAMP. Previously the authors had demonstrated that Vfr could complement a crp mutation and modulate catabolite repression in E. coli. This study presents evidence that Vfr binds to the E. coli lac promoter and that this binding requires the presence of cAMP. Finally, the possible involvement of Vfr in catabolite repression control in P. aeruginosa was investigated. It was found that succinate repressed production of mannitol dehydrogenase, glucose-6-phosphate dehydrogenase, amidase and urocanase both in the parent and in two vfr null mutants. This implied that catabolite repression control was not affected by the vfr null mutation. In support of this, the cloned vfr gene failed to complement a mutation in the P. aeruginosa crc gene. Thus, although Vfr is structurally similar to CRP, and is a global regulator of gene expression in P. aeruginosa, Vfr is not required for catabolite repression control in this bacterium.

A cAMP receptor protein, SYCRP1, is responsible for the cell motility of Synechocystis sp. PCC 6803

Disruption of the sycrp1 gene encoding a cyanobacterial cAMP receptor protein makes cells of Synechocystis sp. PCC 6803 non-motile. Electron microscopy showed that the sycrp1-deficient strain had a reduced number of thick pili on the cell surface compared with the wild-type strain. It is suggested that cAMP-SYCRP1 complex controls the biogenesis of pili.

Plasmid effects on Escherichia coli metabolism

The idea that plasmids replicate within hosts at the expense of cell metabolic energy and preformed cellular blocks depicts plasmids as a kind of molecular parasites that, even when they may eventually provide plasmid-carrying strains with growth advantages over plasmid-free strains, doom hosts to bear an unavoidable metabolic burden. Due to the consistency with experimental data, this idea was rapidly adopted and used as a basis of different hypotheses to explain plasmid-host interactions. In this article we critically discuss current ideas about plasmid effects on host metabolism, and present evidence suggesting that the complex interaction between plasmids and hosts is related to the alteration of the cellular regulatory status.

Genomic survey of cAMP and cGMP signalling components in the cyanobacterium Synechocystis PCC 6803

Cyanobacteria modulate intracellular levels of cAMP and cGMP in response to environmental conditions (light, nutrients and pH). In an attempt to identify components of the cAMP and cGMP signalling pathways in Synechocystis PCC 6803, the authors screened its complete genome sequence by using bioinformatic tools and data from sequence-function studies performed on both eukaryotic and prokaryotic cAMP/cGMP-dependent proteins. Sll1624 and Slr2100 were tentatively assigned as being two putative cyclic nucleotide phosphodiesterases. Five proteins were identified as having all the determinants required to be cyclic nucleotide receptors, two of them being probably more specific for cGMP (an element of two-component regulatory systems - Slr2104 - and a putative cyclic-nucleotide-gated cation channel - Slr1575), the three others being probably more specific for cAMP: (i) a protein of unidentified function (Slr0842); (ii) a putative cyclic-nucleotide-modulated permease (Slr0593), previously annotated as a kinase A regulatory subunit; and (iii) a putative transcription factor (CRP-SYN: =Sll1371), which possesses cAMP- and DNA-binding determinants homologous to those of the cAMP receptor protein of Escherichia coli (CRP-EC:). This homology, together with the presence in Synechocystis of CRP-EC:-like binding sites upstream of crp, cya1, slr1575, and several genes encoding enzymes involved in transport and metabolism, strongly suggests that CRP-SYN: is a global regulator.

Mechanism of catabolite repression in the bgl operon of Escherichia coli: involvement of the anti-terminator BglG, CRP-cAMP and EIIAGlc in mediating glucose effect downstream of transcription initiation

BACKGROUND

Expression of the bgl operon of Escherichia coli, involved in the regulated uptake and utilization of aromatic beta-glucosides, is extremely sensitive to the presence of glucose in the growth medium. We have analysed the mechanism by which glucose exerts its inhibitory effect on bgl expression.

RESULTS

Our studies show that initiation of transcription from the bgl promoter is only marginally sensitive to glucose. Instead, glucose exerts a more significant inhibition on the elongation of transcription beyond the rho-independent terminator present within the leader sequence. Transcriptional analyses using plasmids that carry mutations in bglG or within the terminator, suggest that the target for glucose-mediated repression is the anti-terminator protein, BglG. Introduction of multiple copies of bglG or the presence of mutations that inhibit its phosphorylation by Enzyme IIBgl (BglF), result in loss of glucose repression. Studies using crp, cya and crr strains show that both CRP-cAMP and the Enzyme IIAGlc (EIIAGlc) are involved in the regulation. Although transcription initiation is normal in a crp, cya double mutant, no detectable transcription is seen downstream of the terminator, which is restored by a mutation within the terminator. Transcription past the terminator is also partly restored by the addition of exogenous cAMP to glucose-grown cultures of a crp+ strain. Glucose repression is lost in the crr mutant strain.

CONCLUSIONS

The results summarized above indicate that glucose repression in the bgl operon is mediated at the level of transcription anti-termination, and glucose affects the activity of BglG by altering its phosphorylation by BglF. The CRP-cAMP complex is also involved in this regulation. The results using the crr mutant suggest a negative role for EIIAGlc in the catabolite repression of the bgl genes.

Bacterial viability and culturability

Renewed interest in the relationships between viability and culturability in bacteria stems from three sources: (1) the recognition that there are many bacteria in the biosphere that have never been propagated or characterized in laboratory culture; (2) the proposal that some readily culturable bacteria may respond to certain stimuli by entering a temporarily non-culturable state termed 'viable but non-culturable' (VBNC) by some authors; and (3) the development of new techniques that facilitate demonstration of activity, integrity and composition of non-culturable bacterial cells. We review the background to these areas of interest emphasizing the view that, in an operational context, the term VBNC is self-contradictory (Kell et al., 1998) and the likely distinctions between temporarily non-culturable bacteria and those that have never been cultured. We consider developments in our knowledge of physiological processes in bacteria that may influence the outcome of a culturability test (injury and recovery, ageing, adaptation and differentiation, substrate-accelerated death and other forms of metabolic self-destruction, prophages, toxin-antitoxin systems and cell-to-cell communication). Finally, we discuss whether it is appropriate to consider the viability of individual bacteria or whether, in some circumstances, it may be more appropriate to consider viability as a property of a community of bacteria.

Autoregulation of lactose uptake through the LacY permease by enzyme IIAGlc of the PTS in Escherichia coli K-12

Bacterial growth on one or more carbon sources requires careful control of the uptake and metabolism of these carbon sources. In Escherichia coli, the phosphorylation state of enzyme IIAGlc of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) is involved in this control in two ways. The unphosphorylated form of IIAGlc causes 'inducer exclusion', the inhibition of uptake of a number of non-PTS carbon sources, including lactose uptake by the lactose permease. The phosphorylated form of enzyme IIAGlc probably activates adenylate cyclase. In cells growing on lactose, enzyme IIAGlc was approximately 50% dephosphorylated, suggesting that lactose could inhibit its own uptake. This inhibition could be demonstrated by comparing lactose uptake rates in the wild-type strain and in a mutant in which the lactose carrier was insensitive to inducer exclusion. In this deregulated mutant strain, lactose was consumed much faster, and large amounts of glucose were excreted. It was shown that enzyme IIAGlc was dephosphorylated more strongly and that the cAMP level was lower in the mutant, most probably causing the observed decrease in lac expression level. When the lac expression level in the mutant strain was increased to that of the parent strain by adding exogenous cAMP, growth on lactose was slower, suggesting that enzyme IIAGlc-mediated inhibition of lactose uptake and downregulation of the lac expression level protected the cells against excessive lactose influx. An even stronger increase in the lac expression level in a mutant lacking enzyme IIAGlc caused complete growth arrest. We conclude that the autoregulatory mechanism that controls lactose uptake is an important mechanism for the cells in adjusting the uptake rate to their metabolic capacity.

Identification of a novel adenylate cyclase in the ruminal anaerobe, Prevotella ruminicola D31d

Our previous evaluation of ruminal and other anaerobic bacteria showed only Prevotella ruminicola D31d produced detectable concentrations of cyclic AMP. In order to investigate the synthesis of this important metabolic regulator, the gene for adenylate cyclase (cya), which produces cyclic AMP, was cloned and expressed in a cyaA mutant of Escherichia coli. The cloned P. ruminicola D31d gene was able to complement the cyaA mutation and permitted fermentation of lactose on MacConkey Lactose agar plates. Analysis of the DNA sequence of the 2.5-kilobase pair insert revealed an open reading frame encoding for a 67-kDa protein. This protein was novel in that no amino acid similarity was observed with other procaryotic or eucaryotic adenylate cyclases in the GenBank database. Production of cyclic AMP in the E. coli clone was confirmed with a radioimmunoassay technique. This is the first example of an adenylate cyclase gene identified from an anaerobic bacterium.

Simulations of CRP:(cAMP)2 in noncrystalline environments show a subunit transition from the open to the closed conformation

The CRP:cAMP complex functions as a transcription factor that facilitates RNA polymerase recognition of several bacterial promoters. Detailed crystal structure information is available for CRP:(cAMP)2 and for CRP:(cAMP)2 complexed with DNA. In the crystalline environment, CRP:(cAMP)2 subunits are asymmetrically related; one subunit has a closed conformation and the other has an open conformation. The CRP:(cAMP)2 complexed with DNA shows both subunits in a closed conformation. We have studied the molecular dynamics of CRP:(cAMP)2 in noncrystalline environments. CRP:(cAMP)2 was simulated for 625 ps in vacuo and for 140 ps in solution. The crystal structure of CRP:(cAMP)2 in the absence of DNA was used as the initial conformation. Molecule optimal dynamic coordinates (MODCs) (García A, 1992, Phys Rev Lett 68:2696) were used to analyze protein conformations sampled during the course of the simulations. Two MODCs define a transition of the open subunit to a closed subunit conformation during the first 125 ps of simulation in vacuo; the resulting subunit conformation is similar to that observed in CRP:(cAMP)2:DNA crystals. Simulation of CRP:(cAMP)2 in solution showed that a transition from the open to the closed state also occurs when water is explicitly included in the calculations. These calculations suggest that the asymmetric conformation of CRP:(cAMP)2 is stabilized by crystal lattice interactions. The predicted solution conformation is more symmetric, with both subunits in a closed conformation.

Role of cyclic adenosine monophosphate in phospholipid synthesis in Mycobacterium smegmatis ATCC 607

The present study was undertaken to examine the influence of intracellular levels of cyclic AMP on phospholipid synthesis in Mycobacterium smegmatis ATCC 607. The cyclic AMP levels were modulated by growing cells in the presence of activator (forskolin) and inhibitor (atropine) of adenylate cyclase, the synthesizing enzyme of cyclic AMP. Forskolin-grown cells exhibited a 1.4-fold increase in the level of cAMP while a similar decrease (1.8-fold) was seen with atropine-grown cells. These altered levels of cAMP in turn affected the total content, composition and synthesis of phospholipids. Total phospholipid content increased and decreased in cells grown in the presence of forskolin and atropine, respectively. These observations were further supported by alterations in [14C]acetate incorporation as well as in activities of glycerol kinase and glycerol-3-phosphate acyltransferase, the key enzymes of phospholipid synthesis. Protein phosphorylation mechanism seems to be involved in phospholipid metabolism as the activities of protein kinase increased and decreased in cells grown in forskolin or atropine cells. Our results demonstrate a correlation between phospholipid synthesis and intracellular levels of cAMP in M. smegmatis.