The biosynthesis and regulation of bacterial prodiginines

Prodigiosin is not a determinant factor in lysis of Leishmania (Viannia) braziliensis after interaction with Serratia marcescens D-mannose sensitive fimbriae

In this paper, the lytic activity of two variants of Serratia marcescens against promastigotes of Leishmania braziliensis was studied. In vitro assays showed that S. marcescens variant SM365 lyses L. braziliensis promastigotes, while the variant DB11 did not. Scanning electron microscopy (SEM) revealed that S. marcescens SM365 adheres to all cellular body and flagellum of the parasite. Several filamentous structures were formed and identified as biofilms. After 120min incubation, they connect the protozoan to the developing bacterial clusters. SEM also demonstrated that bacteria, adhered onto L. braziliensis promastigote surface, formed small filamentous structures which apparently penetrates into the parasite membrane. d-mannose protects L. braziliensis against the S. marcescens SM365 lytic effect in a dose dependent manner. SM365 variant pre cultivated at 37 degrees C did not synthesize prodigiosin although the adherence and lysis of L. braziliensis were similar to the effect observed with bacteria cultivated at 28 degrees C, which produce high concentrations of prodigiosin. Thus, we suggest that prodigiosin is not involved in the lysis of promastigotes and that adherence promoted by bacterial mannose-sensitive (MS) fimbriae is a determinant factor in the lysis of L. braziliensis by S. marcescens SM365.

Characterization of rrdA, a TetR family protein gene involved in the regulation of secondary metabolism in Streptomyces coelicolor

Streptomyces not only exhibits complex morphological differentiation but also produces a plethora of secondary metabolites, particularly antibiotics. To improve our general understanding of the complex network of undecylprodigiosin (Red) biosynthesis regulation, we used an in vivo transposition system to identify novel regulators that influence Red production in Streptomyces coelicolor M145. Using this screening system, we obtained 25 Red-deficient mutants. Twenty-four of these mutants had a transposon inserted in the previously described Red biosynthetic gene cluster and produced different amounts of another secondary metabolite, actinorhodin (Act). One mutant was shown to have an insertion in a different region of the chromosome upstream of the previously uncharacterized gene rrdA (regulator of redD, sco1104), which encodes a putative TetR family transcription factor. Compared with wild-type strain M145, the rrdA null mutant exhibited increased Red production and decreased Act production. A high level of rrdA expression resulted in a severe reduction in Red production and Act overproduction. Reverse transcription-PCR analysis showed that RrdA negatively regulated Red production by controlling redD mRNA abundance, while no change was observed at the transcript level of the Act-specific activator gene, actII-orf4. The effects on Act biosynthesis might arise from competition for precursors that are common to both pathways.

Prodigiosin down-regulates survivin to facilitate paclitaxel sensitization in human breast carcinoma cell lines

Prodigiosin is a bacterial metabolite with potent anticancer activity, which is attributed to its proapoptotic effect selectively active in malignant cells. Still, the molecular mechanisms whereby prodigiosin induces apoptosis remain largely unknown. In particular, the role of survivin, a vital inhibitor of apoptosis, in prodigiosin-induced apoptosis has never been addressed before and hence was the primary goal of this study. Our results showed that prodigiosin dose-dependently induced down-regulation of survivin in multiple breast carcinoma cell lines, including MCF-7, T-47D and MDA-MB-231. This down-regulation is mainly regulated at the level of transcription, as prodigiosin reduced the levels of both survivin mRNA and survivin promoter activity but failed to rescue survivin expression when proteasome-mediated degradation is abolished. Importantly, overexpression of survivin rendered cells more resistant to prodigiosin, indicating an essential role of survivin down-regulation in prodigiosin-induced apoptosis. In addition, we found that prodigiosin synergistically enhanced cell death induced by paclitaxel, a chemotherapy drug known to up-regulate survivin that in turn confers its own resistance. This paclitaxel sensitization effect of prodigiosin is ascribed to the lowering of survivin expression, because prodigiosin was shown to counteract survivin induction by paclitaxel and, notably, the sensitization effect was severely abrogated in cells that overexpress survivin. Taken together, our results argue that down-regulation of survivin is an integral component mediating prodigiosin-induced apoptosis in human breast cancer cells, and further suggest the potential of prodigiosin to sensitize anticancer drugs, including paclitaxel, in the treatment of breast cancer.

Effects of extracellular ATP on the physiology of Streptomyces coelicolor A3(2)

Because ATP is an extracellular effector in animal and plant systems and derivatives of ATP, such as S-adenosylmethionine and cAMP, can control antibiotic production and morphological differentiation in Streptomyces, we hypothesized that extracellular ATP (exATP) can also affect physiologies of Streptomyces. We found that the addition of 10 microM exATP to Streptomyces coelicolor A3(2) cultures resulted in enhanced actinorhodin and undecylprodigiosin production and morphological differentiation on solid medium. However, these phenotypes were reduced by the addition of a 10-fold higher concentration of exATP (100 microM). Intracellular ATP concentrations were also modulated in response to changes in exATP. ATP analogs, added at a 100-fold lower concentration, affected Streptomyces similarly to that seen for 10 microM exATP. The enhanced promoter activity of actII-orf4 indicated that 10 microM exATP affect the transcriptional level for actinorhodin production. Results from this study suggest that exATP is an effector for the physiology of S. coelicolor and careful manipulation of exATP may significantly enhance the high-yield production of antibiotics by S. coelicolor.

A 2-substituted prodiginine, 2-(p-hydroxybenzyl)prodigiosin, from Pseudoalteromonas rubra

In the course of work aimed at the discovery of new pharmaceutical lead compounds from marine bacteria, a lipophilic extract of the bacterium Pseudoalteromonas rubra displayed significant cytotoxicity against SKOV-3, a human ovarian adenocarcinoma cell line. Bioassay-directed fractionation of this extract resulted in the isolation of a series of known and new prodiginine-type azafulvenes. The structure of the major metabolite was elucidated by interpretation of spectroscopic data as a 2-substituted prodigiosin, which we named 2-(p-hydroxybenzyl)prodigiosin (HBPG).

Antimicrobial property of a herbal preparation containing Dalbergia sissoo and Datura tramonium with cow urine against pathogenic bacteria

In this study, a herbal preparation containing Dalbergia sissoo and Datura stramoium with cow urine (DSDS), was evaluated for its antibacterial potential against pathogenic strains of gram-positive (Staphylococcus aureus and Streptococcus pneumoniae) and gram-negative (Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae) bacteria. Antibacterial activity was compared to standard antibiotic drugs i.e. Chloramphenicol (30 mcg), Ampicillin (10 mcg), Nalidixic acid (10 mcg) and Rifampicin (30 mcg). Cow urine extract was found to be most active against both gram-positive as well as gram-negative bacteria. Clinical isolate of S. aureus showed higher sensitivity towards cow urine extract of DSDS than standard strains, and inhibited growth on most regulatory levels such as inhibition of protein, DNA, RNA and peptidoglycan synthesis. The results of the present study shows that the cow urine extract of DSDS may be used as a potent antiseptic preparation for prevention and treatment of chronic bacterial infections.

Analysis of the Pseudoalteromonas tunicata genome reveals properties of a surface-associated life style in the marine environment

BACKGROUND

Colonisation of sessile eukaryotic host surfaces (e.g. invertebrates and seaweeds) by bacteria is common in the marine environment and is expected to create significant inter-species competition and other interactions. The bacterium Pseudoalteromonas tunicata is a successful competitor on marine surfaces owing primarily to its ability to produce a number of inhibitory molecules. As such P. tunicata has become a model organism for the studies into processes of surface colonisation and eukaryotic host-bacteria interactions.

METHODOLOGY/PRINCIPAL FINDINGS

To gain a broader understanding into the adaptation to a surface-associated life-style, we have sequenced and analysed the genome of P. tunicata and compared it to the genomes of closely related strains. We found that the P. tunicata genome contains several genes and gene clusters that are involved in the production of inhibitory compounds against surface competitors and secondary colonisers. Features of P. tunicata's oxidative stress response, iron scavenging and nutrient acquisition show that the organism is well adapted to high-density communities on surfaces. Variation of the P. tunicata genome is suggested by several landmarks of genetic rearrangements and mobile genetic elements (e.g. transposons, CRISPRs, phage). Surface attachment is likely to be mediated by curli, novel pili, a number of extracellular polymers and potentially other unexpected cell surface proteins. The P. tunicata genome also shows a utilisation pattern of extracellular polymers that would avoid a degradation of its recognised hosts, while potentially causing detrimental effects on other host types. In addition, the prevalence of recognised virulence genes suggests that P. tunicata has the potential for pathogenic interactions.

CONCLUSIONS/SIGNIFICANCE

The genome analysis has revealed several physiological features that would provide P. tunciata with competitive advantage against other members of the surface-associated community. We have also identified properties that could mediate interactions with surfaces other than its currently recognised hosts. This together with the detection of known virulence genes leads to the hypothesis that P. tunicata maintains a carefully regulated balance between beneficial and detrimental interactions with a range of host surfaces.

Kinetic analysis of growth rate, ATP, and pigmentation suggests an energy-spilling function for the pigment prodigiosin of Serratia marcescens

Serratia marcescens is a gram-negative environmental bacterium and opportunistic pathogen. S. marcescens expresses prodigiosin, a bright red and cell-associated pigment which has no known biological function for producing cells. We present here a kinetic model relating cell, ATP, and prodigiosin concentration changes for S. marcescens during cultivation in batch culture. Cells were grown in a variety of complex broth media at temperatures which either promoted or essentially prevented pigmentation. High growth rates were accompanied by large decreases in cellular prodigiosin concentration; low growth rates were associated with rapid pigmentation. Prodigiosin was induced most strongly during limited growth as the population transitioned to stationary phase, suggesting a negative effect of this pigment on biomass production. Mathematically, the combined rate of formation of biomass and bioenergy (as ATP) was shown to be equivalent to the rate of prodigiosin production. Studies with cyanide inhibition of both oxidative phosphorylation and pigment production indicated that rates of biomass and net ATP synthesis were actually higher in the presence of cyanide, further suggesting a negative regulatory role for prodigiosin in cell and energy production under aerobic growth conditions. Considered in the context of the literature, these results suggest that prodigiosin reduces ATP production by a process termed energy spilling. This process may protect the cell by limiting production of reactive oxygen compounds. Other possible functions for prodigiosin as a mediator of cell death at population stationary phase are discussed.

PigZ, a TetR/AcrR family repressor, modulates secondary metabolism via the expression of a putative four-component resistance-nodulation-cell-division efflux pump, ZrpADBC, in Serratia sp. ATCC 39006

The Gram-negative enterobacterium, Serratia sp. ATCC 39006 synthesizes several secondary metabolites, including prodigiosin (Pig) and a carbapenem antibiotic (Car). A complex hierarchical network of regulatory proteins control Pig and Car production. In this study we characterize a TetR family regulator, PigZ, which represses transcription of a divergently transcribed putative resistance-nodulation-cell-division (RND) efflux pump, encoded by zrp (PigZ repressed pump) ADBC, via direct binding to the zrpA-pigZ intergenic region. Unusually, this putative RND pump contains two predicted membrane fusion proteins (MFPs), ZrpA and ZrpD. A mutation in pigZ resulted in multiple phenotypic changes, including exoenzyme production, motility and differential regulation of Pig and Car production. A polar suppressor mutation, within zrpA, restored all tested phenotypes to parental strain levels, indicating that the changes observed are due to the increase in expression of ZrpADBC in the absence of the repressor, PigZ. Genomic deletions of zrpA and zrpD indicate that the MFP ZrpD, but not ZrpA, is essential for activity of the putative pump. Bioinformatic analysis revealed that putative RND efflux pumps encoding two MFP components are not uncommon, particularly among plant-associated, Gram-negative bacteria. In addition, based on phylogenetic analysis, we propose that these pairs of MFPs consist of two distinct subtypes.

Cycloprodigiosin hydrochloride activates the Ras-PI3K-Akt pathway and suppresses protein synthesis inhibition-induced apoptosis in PC12 cells

Cycloprodigiosin hydrochloride (cPrG-HCl), a member of the prodigiosin family of compounds, has been reported to act as an H(+)/Cl(-) symporter. This compound induces apoptosis in several cancer cells and acts as an antitumor drug in animal models. In this study, we found a novel function of cPrG-HCl; to suppress cell death in PC12 cells, which is caused by protein synthesis inhibitors cycloheximide and actinomycin D. cPrG-HCl activated Akt and suppressed apoptosis, and this was accompanied by inhibition of caspase-3 activity and DNA fragmentation independently of its H(+)/Cl(-) symporter activity. Wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, and dominant-negative Ras attenuated the anti-apoptotic activity of cPrG-HCl, which indicates that cPrG-HCl activated the Ras-PI3K-Akt pathway suppressing apoptosis. On the other hand, serum-deprivation-induced apoptosis was not suppressed by cPrG-HCl.

Natural products to drugs: natural product-derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or are in registration (as at 31st December 2007) have been reviewed, as well as natural product-derived compounds for which clinical trials have been halted or discontinued since 2005. Also discussed are natural product-derived drugs launched since 2005, new natural product templates and late-stage development candidates.

Chemoenzymatic synthesis of prodigiosin analogues--exploring the substrate specificity of PigC

Analogues of prodigiosin, a tripyrrolic pigment produced by Serratia species with potent immunosuppressive and anticancer activities, have been produced by feeding synthetic analogues of the normal precursor MBC to mutants of Serratia sp. ATCC 39006 or to engineered strains of Escherichia coli; in this way it has been shown that the prodigiosin synthesising enzyme, PigC, has a relaxed substrate-specificity.

Anticancer and immunosuppressive properties of bacterial prodiginines

Bacterial prodiginines are a family of red-pigmented, tripyrrolic compounds that display numerous biological activities, including antibacterial, antifungal, antiprotozoal, antimalarial, immunosuppressive and anticancer properties. Recently, significant progress has been made in understanding the biosynthesis and regulation of bacterial prodiginines. An understanding of the biosynthesis of prodiginines will allow engineering of bacterial strains capable of synthesizing novel prodiginines through rational design and mutasynthesis experiments. Bacterial prodiginines and synthetic derivatives are effective proapoptotic agents with multiple cellular targets, and they are active against numerous cancer cell lines, including multidrug-resistant cells, with little or no toxicity towards normal cell lines. A synthetic derivative, GX15-070 (Obatoclax), developed through structure-activity relationship studies of the pyrrolic ring A of GX15, is in multiple Phase I and II clinical trials in both single and dual-agent studies to treat different types of cancer. Therefore, prodiginines have real therapeutic potential in the clinic.

The anticancer agent prodigiosin induces p21WAF1/CIP1 expression via transforming growth factor-beta receptor pathway

The anticancer agent prodigiosin has been shown to act as an efficient immunosuppressant, eliciting cell cycle arrest at non-cytotoxic concentrations, and potent proapoptotic and antimetastatic effects at higher concentrations. Gene expression profiling of MCF-7 cells after treatment with a non-cytotoxic concentration of prodigiosin showed that expression of the p21WAF1/CIP1 gene, a negative cell cycle regulator was induced. In this study, we show that prodigiosin induces p21 expression leading to cell cycle blockade. Subsequently, we attempted to elucidate the molecular mechanisms involved in prodigiosin-mediated p21 gene expression. We demonstrate that prodigiosin induces p21 in a p53-independent manner as prodigiosin induced p21 in cells with both mutated and dominant negative p53. Conversely, the transforming growth factor-beta (TGF-beta) pathway has been found to be necessary for p21 induction. Prodigiosin-mediated p21 expression was blocked by SB431542, a TGF-beta receptor inhibitor. Nevertheless, this pathway alone is not enough to induce p21 expression. The TGF-beta family member (nonsteroidal anti-inflammatory drug)-activated gene 1/growth differentiation factor 15 (NAG-1) may activate this pathway, as it has previously been suggested to signal through the TGF-beta pathway and is overexpressed in response to prodigiosin treatment. We show that NAG-1 colocalizes with TGF-beta receptor type I, suggesting a possible interaction between them. Taken together, these results suggest the TGF-beta pathway is required for induction of p21 expression after prodigiosin treatment of MCF-7 cells.

Virulence and prodigiosin antibiotic biosynthesis in Serratia are regulated pleiotropically by the GGDEF/EAL domain protein, PigX

Gram-negative bacteria of the genus Serratia are opportunistic human, plant, and insect pathogens. Serratia sp. strain ATCC 39006 secretes pectinases and cellulases and produces the secondary metabolites carbapenem and prodigiosin. Mutation of a gene (pigX) resulted in an extremely pleiotropic phenotype: prodigiosin antibiotic biosynthesis, plant virulence, and pectinase production were all elevated. PigX controlled secondary metabolism by repressing the transcription of the target prodigiosin biosynthetic operon (pigA-pigO). The transcriptional start site of pigX was determined, and pigX expression occurred in parallel with Pig production. Detailed quantitative intracellular proteome analyses enabled the identification of numerous downstream targets of PigX, including OpgG, mutation of which reduced the production of the plant cell wall-degrading enzymes and virulence. The highly pleiotropic PigX regulator contains GGDEF and EAL domains with noncanonical motifs and is predicted to be membrane associated. Genetic evidence suggests that PigX might function as a cyclic dimeric GMP phosphodiesterase. This is the first characterization of a GGDEF and EAL domain protein in Serratia and the first example of the regulation of antibiotic production by a GGDEF/EAL domain protein.

Mechanisms of prodigiosin cytotoxicity in human neuroblastoma cell lines

Prodigiosin is a bacterial red pigment with cytotoxic properties and potential antitumor activity that has been tested against different cancerous cells. In this study we report the effect and mechanisms of action of prodigiosin against different human neuroblastoma cell lines: SH-SY5Y, LAN-1, IMR-32 (N-type) and SK-N-AS (S-type). We compare the anticancerous effect of prodigiosin with that of cisplatin at different concentrations during 24 h of exposure. Prodigiosin is more potent, with IC50 values lower than 1.5 microM in N-type neuroblastoma cells and around 7 microM in the S-type neuroblastoma cell line. We describe prodigiosin as a proton sequestering agent that destroys the intracellular pH gradient, and propose that its main cytotoxic effect could be related to its action on mitochondria, where it exerts an uncoupling effect on the electronic chain transport of protons to mitochondrial ATP synthase. As a result of this action, ATP production is reduced but without decreasing in oxygen consumption. This mechanism of action differs from those induced by conventional chemotherapeutic drugs, suggesting a possible role for prodigiosin to enhance the effect of antitumor agents in the treatment of neuroblastoma.

Quorum sensing in Serratia

Many bacteria use cell-cell communication to monitor their population density, synchronize their behaviour and socially interact. This communication results in a coordinated gene regulation and is generally called quorum sensing. In gram-negative bacteria, the most common quorum signal molecules are acylated homoserine lactones (AHLs), although other low-molecular-mass signalling molecules have been described such as Autoinducer-2 (AI-2). The phenotypes that are regulated in Serratia species by means of AHLs are remarkably diverse and of profound biological and ecological significance, and often interconnected with other global regulators. Furthermore, AHL- and AI-2-mediated systems (less profoundly studied) are continuously being discovered and explored in Serratia spp., many having interesting twists on the basic theme. Therefore, this review will highlight the current known quorum sensing systems in Serratia spp., including the important nosocomial pathogen Serratia marcescens.

Suppression of AP-1 Activity by Cycloprodigiosin Hydrochloride

Cycloprodigiosin hydrochloride (cPrG.HCl), a compound isolated from a marine bacterium, acts as an immunosuppressant and an anti-cancer drug. We have previously reported that cPrG.HCl suppressed the transcriptional activation of nuclear factor (NF)-kappaB. Here we studied the effect of cPrG.HCl on activation of another transcription factor, activator protein 1 (AP-1). cPrG.HCl potently suppressed AP-1 activity induced by tumor necrosis factor (TNF) alpha and phorbol myristate acetate (PMA). cPrG.HCl did not inhibit any of the mitogen-activated protein kinase (MAPK) families, whereas it did suppress transcriptional activation of AP-1 induced by constitutively activated mutants of MEKK1 or Ras. cPrG.HCl inhibited neither TNFalpha- or PMA-induced DNA-binding of AP-1 nor co-activator p300-induced activation of AP-1. Taken together, cPrG.HCl suppresses AP-1-dependent gene expression downstream of MAPK group through the inhibition of the transcription activation step of the AP-1 promoter complex.