Pyrrolidinedione derivatives as antibacterial agents with a novel mode of action

A Review of Antibacterial Candidates with New Modes of Action

There is a lack of new antibiotics to combat drug-resistant bacterial infections that increasingly threaten global health. The current pipeline of clinical-stage antimicrobials is primarily populated by "new and improved" versions of existing antibiotic classes, supplemented by several novel chemical scaffolds that act on traditional targets. The lack of fresh chemotypes acting on previously unexploited targets (the "holy grail" for new antimicrobials due to their scarcity) is particularly unfortunate as these offer the greatest opportunity for innovative breakthroughs to overcome existing resistance. In recognition of their potential, this review focuses on this subset of high value antibiotics, providing chemical structures where available. This review focuses on candidates that have progressed to clinical trials, as well as selected examples of promising pioneering approaches in advanced stages of development, in order to stimulate additional research aimed at combating drug-resistant infections.

The expanding antimicrobial diversity of the genus Pantoea

With the rise of antimicrobial resistance, there is high demand for novel antimicrobials to combat multi-drug resistant pathogens. The bacterial genus Pantoea produces a diversity of antimicrobial natural products effective against a wide range of bacterial and fungal targets. These antimicrobials are synthesized by specialized biosynthetic gene clusters that have unique distributions across Pantoea as well as several other genera outside of the Erwiniaceae. Phylogenetic and genomic evidence shows that these clusters can mobilize within and between species and potentially between genera. Pantoea antimicrobials belong to unique structural classes with diverse mechanisms of action, but despite their potential in antagonizing a wide variety of plant, human, and animal pathogens, little is known about many of these metabolites and how they function. This review will explore the known antimicrobials produced by Pantoea: agglomerins, andrimid, D-alanylgriseoluteic acid, dapdiamide, herbicolins, pantocins, and the various Pantoea Natural Products (PNPs). It will include information on the structure of each compound, their genetic basis, biosynthesis, mechanism of action, spectrum of activity, and distribution, highlighting the significance of Pantoea antimicrobials as potential therapeutics and for applications in biocontrol.

Synthesis and biological evaluation of moiramide B derivatives

Moiramide B is a peptide-polyketide hybrid with a bacterial origin and interesting antibiotic activity. Besides its structurally conserved peptide part, it contains a highly variable fatty acid side chain. We modified this part of the molecule by introducing a terminal alkyne, and we then subjected it to click reactions and Sonogashira couplings. This provided a library of moiramide B derivatives with high and selective in vivo activities against S. aureus.

Synthesis and interest in medicinal chemistry of β-phenylalanine derivatives (β-PAD): an update (2010-2022)

β-Phenylalanine derivatives (β-PAD) represent a structural family of therapeutic interest, either as components of drugs or as starting materials for access to key compounds. As scaffolds for medicinal chemistry work, β-PAD offer the advantage of great diversity and modularity, a chiral pseudopeptidic character that opens up the capacity to be recognized by natural systems, and greater stability than natural α-amino acids. Nevertheless, their synthesis remains a challenge in drug discovery and numerous methods have been devoted to their preparation. This review is an update of the access routes to β-PAD and their various therapeutic applications.

Lipid-Centric Approaches in Combating Infectious Diseases: Antibacterials, Antifungals and Antivirals with Lipid-Associated Mechanisms of Action

One of the global challenges of the 21st century is the increase in mortality from infectious diseases against the backdrop of the spread of antibiotic-resistant pathogenic microorganisms. In this regard, it is worth targeting antibacterials towards the membranes of pathogens that are quite conservative and not amenable to elimination. This review is an attempt to critically analyze the possibilities of targeting antimicrobial agents towards enzymes involved in pathogen lipid biosynthesis or towards bacterial, fungal, and viral lipid membranes, to increase the permeability via pore formation and to modulate the membranes' properties in a manner that makes them incompatible with the pathogen's life cycle. This review discusses the advantages and disadvantages of each approach in the search for highly effective but nontoxic antimicrobial agents. Examples of compounds with a proven molecular mechanism of action are presented, and the types of the most promising pharmacophores for further research and the improvement of the characteristics of antibiotics are discussed. The strategies that pathogens use for survival in terms of modulating the lipid composition and physical properties of the membrane, achieving a balance between resistance to antibiotics and the ability to facilitate all necessary transport and signaling processes, are also considered.

Heterobivalent Inhibitors of Acetyl-CoA Carboxylase: Drug Target Residence Time and Time-Dependent Antibacterial Activity

The relationship between drug-target residence time and the post-antibiotic effect (PAE) provides insights into target vulnerability. To probe the vulnerability of bacterial acetyl-CoA carboxylase (ACC), a series of heterobivalent inhibitors were synthesized based on pyridopyrimidine 1 and moiramide B (3) which bind to the biotin carboxylase and carboxyltransferase ACC active sites, respectively. The heterobivalent compound 17, which has a linker of 50 Å, was a tight binding inhibitor of Escherichia coli ACC (Kiapp 0.2 nM) and could be displaced from ACC by a combination of both 1 and 3 but not just by 1. In agreement with the prolonged occupancy of ACC resulting from forced proximity binding, the heterobivalent inhibitors produced a PAE in E. coli of 1-4 h in contrast to 1 and 3 in combination or alone, indicating that ACC is a vulnerable target and highlighting the utility of kinetic, time-dependent effects in the drug mechanism of action.

Role of Cinchona Alkaloids in the Enantio- and Diastereoselective Synthesis of Axially Chiral Compounds

Asymmetric synthesis using organic catalysts has evolved since it was first realized and defined. Nowadays, it can be considered a valid alternative to transition metal catalysis for synthesizing chiral molecules. According to the literature, the number of asymmetric organocatalytic processes associated with atropisomer synthesis has rapidly increased over the past 10 years because organocatalysis addresses the challenges posed by the most widespread strategies used for preparing axially chiral molecules with satisfactory results.These strategies, useful to prepare a wide range of C-C, C-heteroatom, and N-N atropisomers, vary from kinetic resolution to direct arylation, desymmetrization, and central-to-axial chirality conversion. In this field, our contribution focuses on determining novel methods for synthesizing atropisomers, during which, in most cases, the construction of one or more stereogenic centers other than the stereogenic axis occurred. To efficiently address this challenge, we exploited the ability of catalysts based on a cinchona alkaloid scaffold to realize enantioselective organic transformations. Desymmetrization of N-(2-tert-butylphenyl) maleimides was one of the first strategies that we pursued for preparing C-N atropisomers. The main principle is based on the presence of a rotationally hindered C-N single bond owing to the presence of a large tert-butyl group. Following the peculiar reactivity of this type of substrate as a powerful electrophile and dienophile, we realized several transformations.First, we investigated the vinylogous Michael addition of 3-substituted cyclohexenones, where a stereogenic axis and two contiguous stereocenters were concomitantly and remotely formed and stereocontrolled using a primary amine catalyst. Subsequently, we realized desymmetrization via an organocatalytic Diels-Alder reaction of activated unsaturated ketones that enabled highly atropselective transformation with efficient diastereoselectivity, thereby simultaneously controlling four stereogenic elements. Employing chiral organic bases allowed us to realize efficient desymmetrizations using carbon nucleophiles, such as 1,3-dicarbonyl compounds, cyanoacetates, and oxindoles. These reactions, performed with different types of catalysts, highlighted the versatility of organocatalysis as a powerful strategy for atropselective desymmetrization of pro-axially chiral maleimides.Hereafter, we studied the Friedel-Crafts alkylation of naphthols with indenones, a powerful method for enantioselective synthesis of conformationally restricted diastereoisomeric indanones. We realized the first axially chiral selective Knoevenagel condensation using cinchona alkaloid primary amine as the catalyst. This reaction provided a powerful method to access enantioenriched olefins containing the oxindole core. Subsequently, we initiated an intense program for the computational investigation of the reaction mechanism of our atropselective processes. An understanding of the catalytic activity for vinylogous atropselective desymmetrization as well as of the role played by the acidic cocatalyst used for the experimental work was achieved.Recently, we have garnered interest in the novel frontiers of atropselective synthesis. As observed in recent publications, there is considerable interest in the development of methods for preparing N-N atropisomers, an emerging topic in the field of atropselective synthesis. We focused on the synthesis of hydrazide atropisomers by developing a one-pot sequential catalysis protocol based on two sequential organocatalytic reactions that provided high stereocontrol of two contiguous stereogenic elements.

Stereodivergent synthesis of chiral succinimides via Rh-catalyzed asymmetric transfer hydrogenation

Chiral succinimide moieties are ubiquitous in biologically active natural products and pharmaceuticals. Until today, despite the great interest, little success has been made for stereodivergent synthesis of chiral succinimides. Here, we report a general and efficient method for accessing 3,4-disubstituted succinimides through a dynamic kinetic resolution strategy based on asymmetric transfer hydrogenation. The Rh catalyst system exhibit high activities, enantioselectivities, and diastereoselectivities (up to 2000 TON, up to >99% ee, and up to >99:1 dr). Products with syn- and anti-configuration are obtained separately by control of the reaction conditions. For the N-unprotected substrates, both the enol and the imide group can be reduced by control of reaction time and catalyst loading. In addition, the detailed reaction pathway and origin of stereoselectivity are elucidated by control experiments and theoretical calculations. This study offers a straightforward and stereodivergent approach to the valuable enantioenriched succinimides (all 4 stereoisomers) from cheap chemical feedstocks in a single reaction step.

Asymmetric Synthesis of Both Enantiomers of Dimethyl 2-Methylsuccinate by the Ene-Reductase-Catalyzed Reduction at High Substrate Concentration

Chiral dimethyl 2-methylsuccinate (1) is a very important building block for the manufacturing of many active pharmaceutical ingredients and fine chemicals. The asymmetric reduction of C=C double bond of dimethyl citraconate (2), dimethyl mesaconate (3) or dimethyl itaconate (4) by ene-reductases (ERs) represents an attractive straightforward approach, but lack of high-performance ERs, especially (S)-selective ones, has limited implementing this method to prepare the optically pure dimethyl 2-methylsuccinate. Herein, three ERs (Bac-OYE1 from Bacillus sp., SeER from Saccharomyces eubayanus and AfER from Aspergillus flavus) with high substrate tolerance and stereoselectivity towards 2, 3 and 4 have been identified. Up to 500 mM of 3 was converted to (S)-dimethyl 2-methylsuccinate ((S)-1) by SeER in high yields (80%) and enantioselectivity (98% ee), and 700 mM of 2 and 400 mM of 4 were converted to (R)-1 by Bac-OYE1 and AfER, respectively, in high yields (86% and 77%) with excellent enantioselectivity (99% ee). The reductions of diethyl citraconate (5), diethyl mesaconate (6) and diethyl itaconate (7) were also tested with the three ERs. Although up to 500 mM of 5 was completely converted to (R)-diethyl 2-methylsuccinate ((R)-8) by Bac-OYE1 with excellent enantioselectivity (99% ee), the alcohol moiety of the esters had a great effect on the activity and enantioselectivity of ERs. This work provides an efficient methodology for the enantiocomplementary production of optically pure dimethyl 2-methylsuccinate from dimethyl itaconate and its isomers at high titer.

Metabolomics Approaches to Dereplicate Natural Products from Coral-Derived Bioactive Bacteria

Stony corals (Scleractinia) are invertebrates that form symbiotic relationships with eukaryotic algal endosymbionts and the prokaryotic microbiome. The microbiome has the potential to produce bioactive natural products providing defense and resilience to the coral host against pathogenic microorganisms, but this potential has not been extensively explored. Bacterial pathogens can pose a significant threat to corals, with some species implicated in primary and opportunistic infections of various corals. In response, probiotics have been proposed as a potential strategy to protect corals in the face of increased incidence of disease outbreaks. In this study, we screened bacterial isolates from healthy and diseased corals for antibacterial activity. The bioactive extracts were analyzed using untargeted metabolomics. Herein, an UpSet plot and hierarchical clustering analyses were performed to identify isolates with the largest number of unique metabolites. These isolates also displayed different antibacterial activities. Through application of in silico and experimental approaches coupled with genome analysis, we dereplicated natural products from these coral-derived bacteria from Florida's coral reef environments. The metabolomics approach highlighted in this study serves as a useful resource to select probiotic candidates and enables insights into natural product-mediated chemical ecology in holobiont symbiosis.

In Vitro and In Vivo Antibacterial Activity of Serratamid, a Novel Peptide-Polyketide Antibiotic Isolated from Serratia plymuthica C1, against Phytopathogenic Bacteria

A new hybrid non-ribosomal peptide-polyketide antibiotic (serratamid) for phytoprotection was isolated from the ethyl acetate layer of tryptic soy agar culture of the soil bacterium Serratia plymuthica C1 through bioassay-guided fractionation. Its chemical structure was elucidated using instrumental analyses, such as mass and nuclear magnetic resonance spectrometry. Serratamid showed antibacterial activity against 15 phytopathogenic bacteria, with minimum inhibitory concentration (MIC) values ranging from 0.244 to 31.25 μg/mL. In vitro, it displayed strong antibacterial activity against Ralstonia solanacearum and four Xanthomonas spp., with MIC values (0.244-0.488 μg/mL) superior to those of streptomycin sulfate, oxolinic acid, and oxytetracycline. Further, serratamid and the ethyl acetate layer of S. plymuthica C1 effectively reduced bacterial wilt caused by R. solanacearum on tomato seedlings and fire blight caused by Erwinia on apple fruits in a dose-dependent manner. These results suggest that serratamid is a promising candidate as a potent bactericide for controlling bacterial diseases.

Enantioselective [3 + 2] annulation of 3-hydroxymaleimides with quinone monoimines

Enantioselective [3 + 2] annulation of 3-hydroxymaleimides with quinone monoimines provided a large variety of succinimide fused indolines in moderate to good yields with moderate to good enantioselectivities.

Research progress in biological activities of succinimide derivatives

Succinimides are well recognized heterocyclic compounds in drug discovery which produce diverse therapeutically related applications in pharmacological practices. Researches in medicinal chemistry field have isolated and synthesized succinimide derivatives with multiple medicinal properties including anticonvulsant, anti-inflammatory, antitumor and antimicrobial agents, 5-HT receptor ligands and enzyme inhibitors. Simultaneously, SAR (Structure-Activity Relationship) analysis has been gradually possessed, along with a great deal of derivatives have been derived for potential targets. In this article, we comprehensively summarize the biological activities and SAR for succinimide derivatives, along with the featuring bioactive molecules reported in patents, wishing to provide an overall retrospect and prospect on the succinimide analogues.

N-Primary-amine tetrapeptide-catalyzed highly asymmetric Michael addition of aliphatic aldehydes to maleimides

The highly asymmetric Michael addition reaction between maleimides and aliphatic aldehydes catalyzed by low-loading β-turn tetrapeptides with excellent yields and enantioselectivities at room temperature was reported. α-Branched and α-unbranched aldehydes both are suitable nucleophiles. N-Aryl, alkyl and hydrogen maleimides all are well tolerated and led to high yields and enantioselectivities. The transformation can be enlarged to the gram scale without decrease in the yield and enantioselectivity. Furthermore, the succinimides were converted into γ-lactams and γ-lactones, showing good practicality of this work. Some reaction intermediates in the proposed reaction mechanism can be captured with the HR-MS method.

The Biological and Chemical Diversity of Tetramic Acid Compounds from Marine-Derived Microorganisms

Tetramic acid (pyrrolidine-2,4-dione) compounds, isolated from a variety of marine and terrestrial organisms, have attracted considerable attention for their diverse, challenging structural complexity and promising bioactivities. In the past decade, marine-derived microorganisms have become great repositories of novel tetramic acids. Here, we discuss the biological activities of 277 tetramic acids of eight classifications (simple 3-acyl tetramic acids, 3-oligoenoyltetramic acids, 3-decalinoyltetramic acid, 3-spirotetramic acids, macrocyclic tetramic acids, N-acylated tetramic acids, α-cyclopiazonic acid-type tetramic acids, and other tetramic acids) from marine-derived microbes, including fungi, actinobacteria, bacteria, and cyanobacteria, as reported in 195 research studies up to 2019.

Recent development in acetyl-CoA carboxylase inhibitors and their potential as novel drugs

Acetyl-CoA carboxylase (ACC), a critical enzyme in the regulation of fatty acid synthesis and metabolism, has emerged as an attractive target for a plethora of emerging diseases, such as diabetes mellitus, nonalcoholic fatty liver disease, cancer, bacterial infections and so on. With decades of efforts in medicinal chemistry, significant progress has been made toward the design and discovery of a considerable number of inhibitors of this enzyme. In this review, we not only clarify the role of ACC in emerging diseases, but also summarize recent developments of potent ACC inhibitors and discuss their molecular mechanisms of action and potentials as novel drugs as well as future perspectives toward the design and discovery of novel ACC inhibitors.

Cu-catalyzed oxygenation of alkene-tethered amides with O2 via unactivated C[double bond, length as m-dash]C bond cleavage: a direct approach to cyclic imides

An efficient aerobic unactivated C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bond cleavage process was achieved, in which the succinimide or glutarimide derivatives could be prepared directly from alkenyl amides.

The transformations of unactivated alkenes through C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bond double cleavage are always attractive but very challenging. We report herein a chemoselective approach to valuable cyclic imides by a novel Cu-catalyzed geminal amino-oxygenation of unactivated C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bonds. O₂ was successfully employed as the oxidant as well as the O-source and was incorporated into alkenyl amides via C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bond cleavage for the efficient preparation of succinimide or glutarimide derivatives. Moreover, the present strategy under simple conditions can be used in the late-stage modification of biologically active compounds and the synthesis of pharmaceuticals, which demonstrated the potential application.

Antibiotics from Gram-negative bacteria: a comprehensive overview and selected biosynthetic highlights

Covering: up to 2017The overwhelming majority of antibiotics in clinical use originate from Gram-positive Actinobacteria. In recent years, however, Gram-negative bacteria have become increasingly recognised as a rich yet underexplored source of novel antimicrobials, with the potential to combat the looming health threat posed by antibiotic resistance. In this article, we have compiled a comprehensive list of natural products with antimicrobial activity from Gram-negative bacteria, including information on their biosynthetic origin(s) and molecular target(s), where known. We also provide a detailed discussion of several unusual pathways for antibiotic biosynthesis in Gram-negative bacteria, serving to highlight the exceptional biocatalytic repertoire of this group of microorganisms.

Emerging biopharmaceuticals from bioactive peptides derived from marine organisms

Biologically active natural products are spontaneous medicinal entrants, which encourage synthetic access for enhancing and supporting drug discovery and development. Marine bioactive peptides are considered as a rich source of natural products that may provide long-term health, in addition to many prophylactic and curative medicinal drug treatments. The large literature concerning marine peptides has been collected, which shows high potential of nutraceutical and therapeutic efficacy encompassing wide spectra of bioactivities against a number of infection-causing agents. Their antimicrobial, antimalarial, antitumor, antiviral, and cardioprotective actions have achieved the attention of the pharmaceutical industry toward new design of drug formulations, for treatment and prevention of several infections. However, the mechanism of action of many peptide molecules has been still untapped. So in this regard, this paper reviews several peptide compounds by which they interfere with human pathogenesis. This knowledge is one of the key tools to be understood especially for the biotransformation of biomolecules into targeted medicines. The fact that different diseases have the capability to fight at different sites inside the body can lead to a new wave of increasing the chances to produce targeted medicines.

Bacterial fatty acid metabolism in modern antibiotic discovery

Bacterial fatty acid synthesis is essential for many pathogens and different from the mammalian counterpart. These features make bacterial fatty acid synthesis a desirable target for antibiotic discovery. The structural divergence of the conserved enzymes and the presence of different isozymes catalyzing the same reactions in the pathway make bacterial fatty acid synthesis a narrow spectrum target rather than the traditional broad spectrum target. Furthermore, bacterial fatty acid synthesis inhibitors are single-targeting, rather than multi-targeting like traditional monotherapeutic, broad-spectrum antibiotics. The single-targeting nature of bacterial fatty acid synthesis inhibitors makes overcoming fast-developing, target-based resistance a necessary consideration for antibiotic development. Target-based resistance can be overcome through multi-targeting inhibitors, a cocktail of single-targeting inhibitors, or by making the single targeting inhibitor sufficiently high affinity through a pathogen selective approach such that target-based mutants are still susceptible to therapeutic concentrations of drug. Many of the pathogens requiring new antibiotic treatment options encode for essential bacterial fatty acid synthesis enzymes. This review will evaluate the most promising targets in bacterial fatty acid metabolism for antibiotic therapeutics development and review the potential and challenges in advancing each of these targets to the clinic and circumventing target-based resistance. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.

Crystal Structure of Carboxyltransferase from Staphylococcus aureus Bound to the Antibacterial Agent Moiramide B

The dramatic increase in the prevalence of antibiotic-resistant bacteria has necessitated a search for new antibacterial agents against novel targets. Moiramide B is a natural product, broad-spectrum antibiotic that inhibits the carboxyltransferase component of acetyl-CoA carboxylase, which catalyzes the first committed step in fatty acid synthesis. Herein, we report the 2.6 Å resolution crystal structure of moiramide B bound to carboxyltransferase. An unanticipated but significant finding was that moiramide B bound as the enol/enolate. Crystallographic studies demonstrate that the (4S)-methyl succinimide moiety interacts with the oxyanion holes of the enzyme, supporting the notion that an anionic enolate is the active form of the antibacterial agent. Structure-activity studies demonstrate that the unsaturated fatty acid tail of moiramide B is needed only for entry into the bacterial cell. These results will allow the design of new antibacterial agents against the bacterial form of carboxyltransferase.

Toxicity of bioactive and probiotic marine bacteria and their secondary metabolites in Artemia sp. and Caenorhabditis elegans as eukaryotic model organisms

We have previously reported that some strains belonging to the marine Actinobacteria class, the Pseudoalteromonas genus, the Roseobacter clade, and the Photobacteriaceae and Vibrionaceae families produce both antibacterial and antivirulence compounds, and these organisms are interesting from an applied point of view as fish probiotics or as a source of pharmaceutical compounds. The application of either organisms or compounds requires that they do not cause any side effects, such as toxicity in eukaryotic organisms. The purpose of this study was to determine whether these bacteria or their compounds have any toxic side effects in the eukaryotic organisms Artemia sp. and Caenorhabditis elegans. Arthrobacter davidanieli WX-11, Pseudoalteromonas luteoviolacea S4060, P. piscicida S2049, P. rubra S2471, Photobacterium halotolerans S2753, and Vibrio coralliilyticus S2052 were lethal to either or both model eukaryotes. The toxicity of P. luteoviolacea S4060 could be related to the production of the antibacterial compound pentabromopseudilin, while the adverse effect observed in the presence of P. halotolerans S2753 and V. coralliilyticus S2052 could not be explained by the production of holomycin nor andrimid, the respective antibiotic compounds in these organisms. In contrast, the tropodithietic acid (TDA)-producing bacteria Phaeobacter inhibens DSM17395 and Ruegeria mobilis F1926 and TDA itself had no adverse effect on the target organisms. These results reaffirm TDA-producing Roseobacter bacteria as a promising group to be used as probiotics in aquaculture, whereas Actinobacteria, Pseudoalteromonas, Photobacteriaceae, and Vibrionaceae should be used with caution.

Antimicrobial peptides from marine proteobacteria

After years of inadequate use and the emergence of multidrug resistant (MDR) strains, the efficiency of "classical" antibiotics has decreased significantly. New drugs to fight MDR strains are urgently needed. Bacteria hold much promise as a source of unusual bioactive metabolites. However, the potential of marine bacteria, except for Actinomycetes and Cyanobacteria, has been largely underexplored. In the past two decades, the structures of several antimicrobial compounds have been elucidated in marine Proteobacteria. Of these compounds, polyketides (PKs), synthesised by condensation of malonyl-coenzyme A and/or acetyl-coenzyme A, and non-ribosomal peptides (NRPs), obtained through the linkage of (unusual) amino acids, have recently generated particular interest. NRPs are good examples of naturally modified peptides. Here, we review and compile the data on the antimicrobial peptides isolated from marine Proteobacteria, especially NRPs.

Inhibition of virulence gene expression in Staphylococcus aureus by novel depsipeptides from a marine photobacterium

During a global research expedition, more than five hundred marine bacterial strains capable of inhibiting the growth of pathogenic bacteria were collected. The purpose of the present study was to determine if these marine bacteria are also a source of compounds that interfere with the agr quorum sensing system that controls virulence gene expression in Staphylococcus aureus. Using a gene reporter fusion bioassay, we recorded agr interference as enhanced expression of spa, encoding Protein A, concomitantly with reduced expression of hla, encoding α-hemolysin, and rnaIII encoding RNAIII, the effector molecule of agr. A marine Photobacterium produced compounds interfering with agr in S. aureus strain 8325-4, and bioassay-guided fractionation of crude extracts led to the isolation of two novel cyclodepsipeptides, designated solonamide A and B. Northern blot analysis confirmed the agr interfering activity of pure solonamides in both S. aureus strain 8325-4 and the highly virulent, community-acquired strain USA300 (CA-MRSA). To our knowledge, this is the first report of inhibitors of the agr system by a marine bacterium.

Production of bioactive secondary metabolites by marine vibrionaceae

Bacteria belonging to the Vibrionaceae family are widespread in the marine environment. Today, 128 species of vibrios are known. Several of them are infamous for their pathogenicity or symbiotic relationships. Despite their ability to interact with eukaryotes, the vibrios are greatly underexplored for their ability to produce bioactive secondary metabolites and studies have been limited to only a few species. Most of the compounds isolated from vibrios so far are non-ribosomal peptides or hybrids thereof, with examples of N-containing compounds produced independent of nonribosomal peptide synthetases (NRPS). Though covering a limited chemical space, vibrios produce compounds with attractive biological activities, including antibacterial, anticancer, and antivirulence activities. This review highlights some of the most interesting structures from this group of bacteria. Many compounds found in vibrios have also been isolated from other distantly related bacteria. This cosmopolitan occurrence of metabolites indicates a high incidence of horizontal gene transfer, which raises interesting questions concerning the ecological function of some of these molecules. This account underlines the pending potential for exploring new bacterial sources of bioactive compounds and the challenges related to their investigation.

Is bacterial fatty acid synthesis a valid target for antibacterial drug discovery?

The emergence of resistance against most current drugs emphasizes the need to develop new approaches to control bacterial pathogens, particularly Staphylococcus aureus. Bacterial fatty acid synthesis is one such target that is being actively pursued by several research groups to develop anti-Staphylococcal agents. Recently, the wisdom of this approach has been challenged based on the ability of a Gram-positive bacterium to incorporate extracellular fatty acids and thus circumvent the inhibition of de novo fatty acid synthesis. The generality of this conclusion has been challenged, and there is enough diversity in the enzymes and regulation of fatty acid synthesis in bacteria to conclude that there is not a single organism that can be considered typical and representative of bacteria as a whole. We are left without a clear resolution to this ongoing debate and await new basic research to define the pathways for fatty acid uptake and that determine the biochemical and genetic mechanisms for the regulation of fatty acid synthesis in Gram-positive bacteria. These crucial experiments will determine whether diversity in the control of this important pathway accounts for the apparently different responses of Gram-positive bacteria to the inhibition of de novo fatty acid synthesis in presence of extracellular fatty acid supplements.