De novo designed self-assembling helicomimetic lipooligoureas with antibacterial activity.

The overuse of antibiotics has led to a rise in infections caused by multidrug-resistant bacteria, resulting in a need for new antibacterial compounds with different modes of action. In this paper, we describe a new class of compounds called lipooligoureas, which are foldamer-based mimetics of antimicrobial lipopeptides. The lipooligoureas consist of an acyl chain connected to the N-terminus of an oligourea head group that exhibits a well-defined 2.5-helix secondary structure, which is further stabilized by the attachment of the lipophilic chain to the oligourea moiety. These compounds meet the established criteria for membranolytic compounds by possessing an amphiphilic structure that promotes the internalization and partitioning of the molecules into the lipid membrane. The presence of positively charged urea residues promotes electrostatic interactions with the negatively charged bacterial membrane. The subtle structural differences in oligourea head group influence the compounds' aggregation behavior, with the number and position of positively charged urea residues correlating with their aggregation ability. The biological activity of these compounds in inhibiting bacterial growth is correlated with their ability to aggregate, with stronger antibacterial properties exhibited by those that aggregate more easily. However, the concentration inhibiting bacterial growth is significantly lower than the critical aggregation concentration values, suggesting that the mechanism of action involves the monomeric forms of lipooligoureas. Nonetheless, a mechanism based on membrane-induced aggregation cannot be ruled out. The lipooligoureas exhibit higher activity towards Gram-positive bacteria than against Gram-negative bacteria, which is indicative of certain selectivity of these compounds. It is also demonstrated that lipooligoureas exhibit increased stability against proteolytic degradation in human blood serum.

A Plasmid-Borne Gene Cluster Flanked by Two Restriction-Modification Systems Enables an Arctic Strain of Psychrobacter sp. to Decompose SDS.

The cold-adapted Psychrobacter sp. strain DAB_AL62B, isolated from ornithogenic deposits on the Arctic island of Spitsbergen, harbors a 34.5 kb plasmid, pP62BP1, which carries a genetic SLF module predicted to enable the host bacterium to metabolize alkyl sulfates including sodium dodecyl sulfate (SDS), a common anionic surfactant. In this work, we experimentally confirmed that the pP62BP1-harboring strain is capable of SDS degradation. The slfCHSL genes were shown to form an operon whose main promoter, PslfC, is negatively regulated by the product of the slfR gene in the absence of potential substrates. We showed that lauryl aldehyde acts as an inducer of the operon. The analysis of the draft genome sequence of the DAB_AL62B strain revealed that the crucial enzyme of the SDS degradation pathway-an alkyl sulfatase-is encoded only within the plasmid. The SLF module is flanked by two restriction-modification systems, which were shown to exhibit the same sequence specificity. We hypothesize that the maintenance of pP62BP1 may be dependent on this unique genetic organization.

Plasmidome of Listeria spp.-The repA-Family Business.

Bacteria of the genus Listeria (phylum Firmicutes) include both human and animal pathogens, as well as saprophytic strains. A common component of Listeria spp. genomes are plasmids, i.e., extrachromosomal replicons that contribute to gene flux in bacteria. This study provides an in-depth insight into the structure, diversity and evolution of plasmids occurring in Listeria strains inhabiting various environments under different anthropogenic pressures. Apart from the components of the conserved plasmid backbone (providing replication, stable maintenance and conjugational transfer functions), these replicons contain numerous adaptive genes possibly involved in: (i) resistance to antibiotics, heavy metals, metalloids and sanitizers, and (ii) responses to heat, oxidative, acid and high salinity stressors. Their genomes are also enriched by numerous transposable elements, which have influenced the plasmid architecture. The plasmidome of Listeria is dominated by a group of related replicons encoding the RepA replication initiation protein. Detailed comparative analyses provide valuable data on the level of conservation of these replicons and their role in shaping the structure of the Listeria pangenome, as well as their relationship to plasmids of other genera of Firmicutes, which demonstrates the range and direction of flow of genetic information in this important group of bacteria.

Interactions of Linear Analogues of Battacin with Negatively Charged Lipid Membranes.

The increasing resistance of bacteria to available antibiotics has stimulated the search for new antimicrobial compounds with less specific mechanisms of action. These include the ability to disrupt the structure of the cell membrane, which in turn leads to its damage. In this context, amphiphilic lipopeptides belong to the class of the compounds which may fulfill this requirement. In this paper, we describe two linear analogues of battacin with modified acyl chains to tune the balance between the hydrophilic and hydrophobic portion of lipopeptides. We demonstrate that both compounds display antimicrobial activity with the lowest values of minimum inhibitory concentrations found for Gram-positive pathogens. Therefore, their mechanism of action was evaluated on a molecular level using model lipid films mimicking the membrane of Gram-positive bacteria. The surface pressure measurements revealed that both lipopeptides show ability to bind and incorporate into the lipid monolayers, resulting in decreased ordering of lipids and membrane fluidization. Atomic force microscopy (AFM) imaging demonstrated that the exposure of the model bilayers to lipopeptides leads to a transition from the ordered gel phase to disordered liquid crystalline phase. This observation was confirmed by attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) results, which revealed that lipopeptide action causes a substantial increase in the average tilt angle of lipid acyl chains with respect to the surface normal to compensate for lipopeptide insertion into the membrane. Moreover, the peptide moieties in both molecules do not adopt any well-defined secondary structure upon binding with the lipid membrane. It was also observed that a small difference in the structure of a lipophilic chain, altering the balance between hydrophobic and hydrophilic portion of the molecules, results in different insertion depth of the active compounds.

Physicochemical and Biological Characterization of Novel Membrane-Active Cationic Lipopeptides with Antimicrobial Properties.

We have designed and synthesized new short lipopeptides composed of tetrapeptide conjugated to fatty acids with different chain lengths. The amino acid sequence of the peptide moiety included d-phenylalanine, two residues of l-2,4-diaminobutyric acid and l-leucine. To explore the possible mechanism of lipopeptide action, we have provided a physicochemical characterization of their interactions with artificial lipid membranes. For this purpose, we have used monolayers and bilayers composed of lipids representative of Gram-negative and Gram-positive bacterial membranes. Using surface pressure measurements and atomic force microscopy, we were able to monitor the changes occurring within the films upon exposure to lipopeptides. Our experiments revealed that all lipopeptides can penetrate the lipid membranes and affect their molecular ordering. The latter results in membrane thinning and fluidization. However, the effect is stronger in the lipid films mimicking Gram-positive bacterial membranes. The results of the physicochemical characterization were compared with the biological activity of lipopeptides. The effect of lipopeptides on bacterial growth was tested on several strains of bacteria. It was revealed that lipopeptides show stronger antimicrobial activity against Gram-positive bacteria. At the same time, all tested compounds display relatively low hemolytic activity.

Targeting Type II Toxin-Antitoxin Systems as Antibacterial Strategies.

The identification of novel targets for antimicrobial agents is crucial for combating infectious diseases caused by evolving bacterial pathogens. Components of bacterial toxin-antitoxin (TA) systems have been recognized as promising therapeutic targets. These widespread genetic modules are usually composed of two genes that encode a toxic protein targeting an essential cellular process and an antitoxin that counteracts the activity of the toxin. Uncontrolled toxin expression may elicit a bactericidal effect, so they may be considered "intracellular molecular bombs" that can lead to elimination of their host cells. Based on the molecular nature of antitoxins and their mode of interaction with toxins, TA systems have been classified into six groups. The most prevalent are type II TA systems. Due to their ubiquity among clinical isolates of pathogenic bacteria and the essential processes targeted, they are promising candidates for the development of novel antimicrobial strategies. In this review, we describe the distribution of type II TA systems in clinically relevant human pathogens, examine how these systems could be developed as the targets for novel antibacterials, and discuss possible undesirable effects of such therapeutic intervention, such as the induction of persister cells, biofilm formation and toxicity to eukaryotic cells.

In vivo creation of plasmid pCRT01 and its use for the construction of carotenoid-producing Paracoccus spp. strains that grow efficiently on industrial wastes.

BACKGROUND: Carotenoids are natural tetraterpene pigments widely utilized in the food, pharmaceutical and cosmetic industries. Currently, chemical synthesis of these compounds outperforms their production in Escherichia coli or yeast due to the limited efficiency of the latter. The use of natural microbial carotenoid producers, such as bacteria of the genus Paracoccus (Alphaproteobacteria), may help to optimize this process. In order to couple the ability to synthesize these pigments with the metabolic versatility of this genus, we explored the possibility of introducing carotenoid synthesis genes into strains capable of efficient growth on simple low-cost media. RESULTS: We constructed two carotenoid-producing strains of Paracoccus carrying a new plasmid, pCRT01, which contains the carotenoid synthesis gene locus crt from Paracoccus marcusii OS22. The plasmid was created in vivo via illegitimate recombination between crt-carrying vector pABW1 and a natural "paracoccal" plasmid pAMI2. Consequently, the obtained fusion replicon is stably maintained in the bacterial population without the need for antibiotic selection. The introduction of pCRT01 into fast-growing "colorless" strains of Paracoccus aminophilus and Paracoccus kondratievae converted them into efficient producers of a range of both carotenes and xanthophylls. The exact profile of the produced pigments was dependent on the strain genetic background. To reduce the cost of carotenoid production in this system, we tested the growth and pigment synthesis efficiency of the two strains on various simple media, including raw industrial effluent (coal-fired power plant flue gas desulfurization wastewater) supplemented with molasses, an industrial by-product rich in sucrose. CONCLUSIONS: We demonstrated a new approach for the construction of carotenoid-producing bacterial strains which relies on a single plasmid-mediated transfer of a pigment synthesis gene locus between Paracoccus strains. This strategy facilitates screening for producer strains in terms of synthesis efficiency, pigment profile and ability to grow on low-cost industrial waste-based media, which should increase the cost-effectiveness of microbial production of carotenoids.

Inactivation of Genes Encoding MutL and MutS Proteins Influences Adhesion and Biofilm Formation by Neisseria gonorrhoeae.

Neisseria gonorrhoeae is an etiological agent of gonorrhea, which remains a global health problem. This bacterium possesses MutL and MutS DNA repair proteins encoded by mutL and mutS genes, whose inactivation causes a mutator phenotype. We have demonstrated the differential gene expression in N. gonorrhoeae mutL and mutS mutants using DNA microarrays. A subset of differentially expressed genes encodes proteins that can influence adhesion and biofilm formation. Compared to the wild-type strain, N. gonorrhoeae mutL and mutS mutants formed denser biofilms with increased biofilm-associated biomass on the abiotic surface. The N. gonorrhoeae mutS::km, but not the mutL mutant, was also more adherent and invasive to human epithelial cells. Further, during infection of epithelial cells with N. gonorrhoeae mutS::km, the expression of some bacterial genes encoding proteins that can influence gonococcal adhesion was changed compared with their expression in cells infected with the wild-type gonococcus, as well as of human genes' encoding receptors utilized by N. gonorrhoeae (CD46, CEACAM 1, HSPG 2). Thus, deficiency in the mutS gene resulting in increased mutation frequency in singular organisms can be beneficial in populations because these mutants can be a source of features linked to microbial fitness.

Genome Structure of the Opportunistic Pathogen Paracoccus yeei (Alphaproteobacteria) and Identification of Putative Virulence Factors.

Bacteria of the genus Paracoccus are common components of the microbiomes of many naturally- and anthropogenically shaped environments. One species, Paracoccus yeei, is unique within the genus because it is associated with opportunistic human infections. Therefore, strains of P. yeei may serve as an interesting model to study the transition from a saprophytic to a pathogenic lifestyle in environmental bacteria. Unfortunately, knowledge concerning the biology, genetics and genomic content of P. yeei is fragmentary; also the mechanisms of pathogenicity of this bacterium remain unclear. In this study we provide the first insight into the genome composition and metabolic potential of a clinical isolate, P. yeei CCUG 32053. This strain has a multipartite genome (4,632,079 bp) composed of a circular chromosome plus eight extrachromosomal replicons pYEE1-8: 3 chromids and 5 plasmids, with a total size of 1,247,173 bp. The genome has been significantly shaped by the acquisition of genomic islands, prophages (Myoviridae and Siphoviridae phage families) and numerous insertion sequences (ISs) representing seven IS families. Detailed comparative analysis with other complete genomic sequences of Paracoccus spp. (including P. yeei FDAARGOS_252 and TT13, as well as non-pathogenic strains of other species in this genus) enabled us to identify P. yeei species-specific genes and to predict putative determinants of virulence. This is the first attempt to identify pathoadaptive genetic information of P. yeei and to estimate the role of the mobilome in the evolution of pathogenicity in this species.

Genome content, metabolic pathways and biotechnological potential of the psychrophilic Arctic bacterium Psychrobacter sp. DAB_AL43B, a source and a host of novel Psychrobacter-specific vectors.

Psychrobacter sp. DAB_AL43B, isolated from ornithogenic soil collected on the Arctic island of Spitsbergen, is a newly sequenced psychrophilic strain susceptible to conjugation and electrotransformation. Its genome consists of a circular chromosome (3.3 Mb) and four plasmids (4.4-6.4kb). In silico genome mining and microarray-based phenotypic analysis were performed to describe the metabolic potential of this strain and identify possible biotechnological applications. Metabolic reconstruction indicated that DAB_AL43B prefers low-molecular-weight carboxylates and amino acids as carbon and energy sources. Genetic determinants of heavy-metal resistance, anthracene degradation and possible aerobic denitrification were also identified. Comparative analyses revealed a relatively close relationship between DAB_AL43B and other sequenced Psychrobacter species. In addition, the plasmids of this strain were used as the basis for the construction of Escherichia coli-Psychrobacter spp. shuttle vectors. Taken together, the results of this work suggest that DAB_AL43B is a promising candidate as a new model strain for studies on Psychrobacter spp.

Plasmid pP62BP1 isolated from an Arctic Psychrobacter sp. strain carries two highly homologous type II restriction-modification systems and a putative organic sulfate metabolism operon.

The complete nucleotide sequence of plasmid pP62BP1 (34,467 bp), isolated from Arctic Psychrobacter sp. DAB_AL62B, was determined and annotated. The conserved plasmid backbone is composed of several genetic modules, including a replication system (REP) with similarities to the REP region of the iteron-containing plasmid pPS10 of Pseudomonas syringae. The additional genetic load of pP62BP1 includes two highly related type II restriction-modification systems and a set of genes (slfRCHSL) encoding enzymes engaged in the metabolism of organic sulfates, plus a putative transcriptional regulator (SlfR) of the AraC family. The pP62BP1 slf locus has a compact and unique structure. It is predicted that the enzymes SlfC, SlfH, SlfS and SlfL carry out a chain of reactions leading to the transformation of alkyl sulfates into acyl-CoA, with dodecyl sulfate (SDS) as a possible starting substrate. Comparative analysis of the nucleotide sequences of pP62BP1 and other Psychrobacter spp. plasmids revealed their structural diversity. However, the presence of a few highly conserved DNA segments in pP62BP1, plasmid 1 of P. cryohalolentis K5 and pRWF-101 of Psychrobacter sp. PRwf-1 is indicative of recombinational shuffling of genetic information, and is evidence of lateral gene transfer in the Arctic environment.