Maciej Maselko

Genetics of germination-arrest factor (GAF) production by Pseudomonas fluorescens WH6: identification of a gene cluster essential for GAF biosynthesis

The genetic basis of the biosynthesis of the germination-arrest factor (GAF) produced by Pseudomonas fluorescens WH6, and previously identified as 4-formylaminooxyvinylglycine, has been investigated here. In addition to inhibiting the germination of a wide range of grassy weeds, GAF exhibits a selective antimicrobial activity against the bacterial plant pathogen Erwinia amylovora. We utilized the in vitro response of E. amylovora to GAF as a rapid screen for loss-of-function GAF phenotypes generated by transposon mutagenesis. A Tn5 mutant library consisting of 6364 WH6 transformants was screened in this Erwinia assay, resulting in the identification of 18 non-redundant transposon insertion sites that led to loss of GAF production in WH6, as confirmed by TLC analysis. These insertions mapped to five different genes and four intergenic regions. Three of these genes, including two putative regulatory genes (gntR and iopB homologues), were clustered in a 13 kb chromosomal region containing 13 putative ORFs. A GAF mutation identified previously as affecting an aminotransferase also maps to this region. We suggest that three of the genes in this region (a carbamoyltransferase, an aminotransferase and a formyltransferase) encode the enzymes necessary to synthesize dihydroGAF, the putative immediate precursor of GAF in a proposed GAF biosynthetic pathway. RT-qPCR analyses demonstrated that mutations in the gntR and iopB regulatory genes, as well as in a prtR homologue identified earlier as controlling GAF formation, suppressed transcription of at least two of the putative GAF biosynthetic genes (encoding the aminotransferase and formyltransferase) located in this 13 kb region.

A RhoA-Derived Peptide Inhibits Human Immunodeficiency Virus-1 Entry In Vitro

RhoA-derived peptides have been shown to have antiviral activity against both human respiratory syncytial virus and human parainfluenza virus-3. The present study investigates the toxicity, anti-HIV-1 activity and mechanism of action of a RhoA-derived peptide (RhoA 77-95). The efficacy of this peptide was compared to a scrambled peptide of the same amino acid composition and Enfuvirtide, a HIV entry inhibitor. Our data show that this RhoA-derived peptide is a non-toxic and effective inhibitor of a CXCR4 tropic strain of HIV-1. We also demonstrate that the mechanism of entry inhibition is likely mediated by polyanionic properties and is dependent on the dimerization of peptides.

Negative regulation of germination-arrest factor production in Pseudomonas fluorescens WH6 by a putative extracytoplasmic function sigma factor.

Pseudomonas fluorescens WH6 secretes a germination-arrest factor (GAF) that we have identified previously as 4-formylaminooxyvinylglycine. GAF irreversibly inhibits germination of the seeds of numerous grassy weeds and selectively inhibits growth of the bacterial plant pathogen Erwinia amylovora. WH6-3, a mutant that has lost the ability to produce GAF, contains a Tn5 insertion in prtR, a gene that has been described previously in some strains of P. fluorescens as encoding a transmembrane regulator. As in these other pseudomonads, in WH6, prtR occurs immediately downstream of prtI, which encodes a protein homologous to extracytoplasmic function (ECF) sigma factors. These two genes have been proposed to function as a dicistronic operon. In this study, we demonstrated that deletion of prtI in WT WH6 had no effect on GAF production. However, deletion of prtI in the WH6-3 mutant overcame the effects of the Tn5 insertion in prtR and restored GAF production in the resulting double mutant. Complementation of the double prtIR mutant with prtI suppressed GAF production. This overall pattern of prtIR regulation was also observed for the activity of an AprX protease. Furthermore, reverse transcription quantitative real-time PCR analysis demonstrated that alterations in GAF production were mirrored by changes in the transcription of two putative GAF biosynthetic genes. Thus, we concluded that PrtI exerted a negative regulatory effect on GAF production, although the mechanism has not yet been determined. In addition, evidence was obtained that the transcription of prtI and prtR in WH6 may be more complex than predicted by existing models.

Functional analysis of a biosynthetic cluster essential for production of 4-formylaminooxyvinylglycine, a germination-arrest factor from Pseudomonas fluorescens WH6.

Rhizosphere-associated Pseudomonas fluorescens WH6 produces the germination-arrest factor 4-formylaminooxyvinylglycine (FVG). FVG has previously been shown to both arrest the germination of weedy grasses and inhibit the growth of the bacterial plant pathogen Erwinia amylovora. Very little is known about the mechanism by which FVG is produced. Although a previous study identified a region of the genome that may be involved in FVG biosynthesis, it has not yet been determined which genes within that region are sufficient and necessary for FVG production. In the current study, we explored the role of each of the putative genes encoded in that region by constructing deletion mutations. Mutant strains were assayed for their ability to produce FVG with a combination of biological assays and TLC analyses. This work defined the core FVG biosynthetic gene cluster and revealed several interesting characteristics of FVG production. We determined that FVG biosynthesis requires two small ORFs of less than 150 nucleotides and that multiple transporters have overlapping but distinct functionality. In addition, two genes in the centre of the biosynthetic gene cluster are not required for FVG production, suggesting that additional products may be produced from the cluster. Transcriptional analysis indicated that at least three active promoters play a role in the expression of genes within this cluster. The results of this study enrich our knowledge regarding the diversity of mechanisms by which bacteria produce non-proteinogenic amino acids like vinylglycines.Rhizosphere-associated Pseudomonas fluorescens WH6 produces the germination-arrest factor, 4-formylaminooxyvinylglycine (FVG). FVG has previously been shown to both arrest the germination of weedy grasses and to inhibit the growth of the bacterial plant pathogen Erwinia amylovora. Very little is known about the mechanism by which FVG is produced. Although a previous study identified a region of the genome that may be involved in FVG biosynthesis, it has not yet been determined which genes within that region are sufficient and necessary for FVG production. In the current study, we explored the role of each of the putative genes encoded in that region by constructing deletion mutations. Mutant strains were assayed for their ability to produce FVG with a combination of biological assays and thin-layer chromatographic analyses. This work defined the core FVG biosynthetic gene cluster and revealed several interesting characteristics of FVG production. We determined that FVG biosynthesis requires two small open reading frames of less than 150 nucleotides and that multiple transporters have overlapping but distinct functionality. In addition, two genes in the center of the biosynthetic gene cluster are not required for FVG production, suggesting that additional products may be produced from the cluster. Transcriptional analysis indicated that at least three active promoters play a role in the expression of genes within this cluster. The results of this study enrich our knowledge regarding the diversity of mechanisms by which bacteria produce non-proteinogenic amino acids like vinylglycines.

Engineering species-like barriers to sexual reproduction

Controlling the exchange of genetic information between sexually reproducing populations has applications in agriculture, eradication of disease vectors, control of invasive species, and the safe study of emerging biotechnology applications. Here we introduce an approach to engineer a genetic barrier to sexual reproduction between otherwise compatible populations. Programmable transcription factors drive lethal gene expression in hybrid offspring following undesired mating events. As a proof of concept, we target the ACT1 promoter of the model organism Saccharomyces cerevisiae using a dCas9-based transcriptional activator. Lethal overexpression of actin results from mating this engineered strain with a strain containing the wild-type ACT1 promoter.Genetic isolation of a genetically modified organism represents a useful strategy for biocontainment. Here the authors use dCas9-VP64-driven gene expression to construct a ‘species-like’ barrier to reproduction between two otherwise compatible populations.

Basant, a Polyherbal Topical Microbicide Candidate Inhibits different Clades of Both CCR5 and CXCR4 Tropic, Lab-Adapted and Primary Isolates of Human Immunodeficiency Virus-1 in Vitro Infection

Topical microbicides applied to the vaginal mucosa as pre-exposure prophylactic measures for controlling sexually transmitted diseases have great potential to combat theHIV-1 pandemic in the developing world. Basant is a polyherbal topical microbicide candidate with demonstrated activity against CXCR4 co-receptor tropic HIV-1 as well as fungal and bacterial sexually transmitted infections. The current study demonstrates that Basant is effective against both CCR5 and CXCR4 tropic HIV-1 lab-adapted strains and primary isolates from different clades. We also investigate the kinetics of Basant inhibition as compared to the fusion inhibitor Enfuvirtide and report that Basant inhibits HIV-1 at an early stage of infection. We conclude that Basant may be considered as a potential candidate for use as an effective vaginal microbicide in preventing HIV-1 transmission

Variability, Seasonality, and Persistence of Fecal Coliform Bacteria in a Cold-Region, Urban Stream

Fecal coliform FC analyses were conducted on weekly water samples collected from a single watershed over a 2-year period in Anchorage, Alaska. Although peak FC concentrations 100 FC/100 mL were observed primarily during the warmer months, lower FC levels 20 FC/100 mL could be observed throughout the year in the urbanized portion of the watershed. Me- dian annual FC counts ranged from 3 FC/100 mL at an undeveloped site to 49 FC/100 mL at one of the urbanized sites. Median FC concentrations were found to be significantly higher in the summer compared to the winter at two locations directly downstream from a lake p=0.011 and 0.029, but not at the sites up- stream or distant from the lake. FC-discharge relationships indicated a significant negative correlation between FC concentration and discharge at two sites p =0.030 and 0.035 and no significant correlation at the remaining three sites. In total, the results indicated that the water quality was impacted not only by peak

Interaction of the Human Respiratory Syncytial Virus matrix protein with cellular adaptor protein complex 3 plays a critical role in trafficking

Human Respiratory Syncytial Virus (HRSV) is a leading cause of bronchopneumonia in infants and the elderly. To date, knowledge of viral and host protein interactions within HRSV is limited and are critical areas of research. Here, we show that HRSV Matrix (M) protein interacts with the cellular adaptor protein complex 3 specifically via its medium subunit (AP-3Mu3A). This novel protein-protein interaction was first detected via yeast-two hybrid screen and was further confirmed in a mammalian system by immunofluorescence colocalization and co-immunoprecipitation. This novel interaction is further substantiated by the presence of a known tyrosine-based adaptor protein MU subunit sorting signal sequence, YXXФ: where Ф is a bulky hydrophobic residue, which is conserved across the related RSV M proteins. Analysis of point-mutated HRSV M derivatives indicated that AP-3Mu3A- mediated trafficking is contingent on the presence of the tyrosine residue within the YXXL sorting sequence at amino acids 197–200 of the M protein. AP-3Mu3A is up regulated at 24 hours post-infection in infected cells versus mock-infected HEp2 cells. Together, our data suggests that the AP-3 complex plays a critical role in the trafficking of HRSV proteins specifically matrix in epithelial cells. The results of this study add new insights and targets that may lead to the development of potential antivirals and attenuating mutations suitable for candidate vaccines in the future.

Pathway control in the self-construction of complex precipitation forms in a Cu(II)-oxalate system

Text AbstractBackgroundMany biological systems contain complex precipitation patterns. These structures are considered to be the result of finely tuned and genetically encoded developmental pathways. The amount of encoded information needed to generate and manipulate these structures is poorly understood. Investigating the dynamics of spontaneous pattern formation in non-biological systems provides insights to the physio-chemical phenomena that biological systems must have harnessed for living systems and that modern scientists need to understand for complex nano-technological applications.ResultsHere we show that highly complex, precipitation patterns similar to those found in biological systems can be formed in simple Cu(II)-oxalate systems. In these Cu(II)-oxalate systems, structures are constructed by a hierarchy of multiple processes that are precisely self-organized in space and time to form interconnected causal networks that generate complex and diverse structures dependent on construction trajectories that can be controlled by minor variations of initial conditions.ConclusionsHighly complex precipitation patterns similar to those found in biological systems can be generated without a correspondingly complex set of instructions. Our result has implications for understanding early biotic systems that existed prior to the evolution of sophisticated genetic machinery. From an applications perspective, processes and structures that occur spontaneously are the building blocks for novel system chemistry based technologies where products are self-constructed. We also provide a simple model of chemical system that generates biomimetic structures for the study of fundamental processes involved in chemical self-construction.

Increased Survivorship and Altered Cytokine Profile from Treatment of Influenza A H1N1-Infected Mice with Ekybion: A Drug Complex of Natural Extracts and Inorganic Compounds

Ekybion is a drug complex of 16 natural extracts and inorganic compounds designed to treat a variety of respiratory pathogens of bacterial and viral origin. It is licensed throughout Europe for the treatment of respiratory tract infections from equine parainfluenza type 3 and equine herpes virus type 1 in equine stables. The purpose of this paper was to test the efficacy of Ekybion on a well-developed animal model of influenza A infection and determine a mode of action. Experiments were performed with Balb/c mice infected with a lethal dose of influenza A/PR/8/34 H1N1 virus and treated with nebulized Ekybion every 8 h in a time-dependant or dose-dependant fashion. These experiments showed that mice treated prior to infection with Ekybion had a higher survival rates (~46%) compared with untreated animals (~0%). Paradoxically, these mice showed no significant difference in lung virus titer or weight loss. There was, however, a decrease in the level of GM-CSF, IL-6, and G-CSF cytokines in the lungs of Ekybion-treated, infected mice. It is possible that decreases in proinflammatory cytokines may have contributed to increased survivorship in Ekybion-treated influenza-infected mice.