Oxylipins produced by Pseudomonas aeruginosa promote biofilm formation and virulence

The Oxylipin Dependent Quorum Sensing System enhances Pseudomonas aeruginosa dissemination during burn-associated infection

Following severe burn injury, Pseudomonas aeruginosa is the leading cause of life-threatening infection. Herein, we unveil how P. aeruginosa strategically employs host-derived oleic acid, released as consequence of burn-injury, to induce a hypervirulent phenotype via its Oxylipin Dependent Quorum Sensing system (ODS). ODS activation enhanced P. aeruginosa invasion of burned skin and promoted its dissemination to distant organs in vivo. ODS regulation of P. aeruginosa virulence involved the control of nitic oxide levels, a key signaling molecule in bacteria, through upregulation of the nitric oxide reductases NorCB. Immunization with OdsA, one of the enzymes involved in oxylipin generation, or treatment with a pharmacological inhibitor of OdsA, protected mice against lethal P. aeruginosa infection following burn-injury. Our findings reveal a new mechanism underlying P. aeruginosa hypervirulence in burn wounds and identifies OdsA as a promising target for preventing disseminated infections following burns.

Clinical Evaluation of Microbial Communities and Associated Biofilms with Breast Augmentation Failure

The incidence of breast implant illness (BII) and BII-related explant procedures has not decreased with current surgical and treatment techniques. It is speculated the main underlying cause of BII complications is the result of chronic, sub-clinical infections residing on and around the implant. The infection, and subsequent biofilm, produce antagonistic compounds that drive chronic inflammation and immune responses. In this study, the microbial communities in over 600 consecutive samples of infected explant capsules and tissues were identified via next-generation sequencing to identify any commonality between samples. The majority of the bacteria identified were Gram-positive, with Cutibacterium acnes and Staphylococcus epidermidis being the dominant organisms. No correlation between sample richness and implant filling was found. However, there was a significant correlation between sample richness and patient age. Due to the complex nature, breast augmentation failures may be better addressed from a holistic approach than one of limited scope.

Natural and synthetic molecules with potential to enhance biofilm formation and virulence properties in Pseudomonas aeruginosa

Pseudomonas aeruginosa can efficiently adapt to changing environmental conditions due to its ubiquitous nature, intrinsic/acquired/adaptive resistance mechanisms, high metabolic versatility, and the production of numerous virulence factors. As a result, P. aeruginosa becomes an opportunistic pathogen, causing chronic infection in the lungs and several organs of patients suffering from cystic fibrosis. Biofilm established by P. aeruginosa in host tissues and medical device surfaces has been identified as a major obstruction to antimicrobial therapy. P. aeruginosa is very likely to be closely associated with the various microorganisms in the host tissues or organs in a pathogenic or nonpathogenic behavior. Aside from host-derived molecules, other beneficial and pathogenic microorganisms produce a diverse range of secondary metabolites that either directly or indirectly favor the persistence of P. aeruginosa. Thus, it is critical to understand how P. aeruginosa interacts with different molecules and ions in the host and abiotic environment to produce extracellular polymeric substances and virulence factors. Thus, the current review discusses how various natural and synthetic molecules in the environment induce biofilm formation and the production of multiple virulence factors.

Assessment of Fatty Acid and Oxylipin Profile of Resprouting Olive Trees Positive to Xylella fastidiosa subsp. pauca in Salento (Apulia, Italy)

Xylella fastidiosa subsp. pauca ST53 (XFP), the causal agent of olive quick decline syndrome (OQDS), was thoroughly investigated after a 2013 outbreak in the Salento region of Southern Italy. Some trees from Ogliarola Salentina and Cellina di Nardò, susceptible cultivars in the Gallipoli area, the first XFP infection hotspot in Italy, have resprouted crowns and are starting to flower and yield fruits. Satellite imagery and Normalized Difference Vegetation Index analyses revealed a significant improvement in vegetation health and productivity from 2018 to 2022 of these trees. Lipid molecules have long been recognized as plant defense modulators, and recently, we investigated their role in XFP-positive hosts and in XFP-resistant as well as in XFP-susceptible cultivars of olive trees. Here, we present a case study regarding 36 olive trees (12 XFP-positive resprouting, 12 XFP-positive OQDS-symptomatic, and 12 XFP-negative trees) harvested in 2022 within the area where XFP struck first, killing millions of trees in a decade. These trees were analyzed for some free fatty acid, oxylipin, and plant hormones, in particular jasmonic and salicylic acid, by targeted LC-MS/MS. Multivariate analysis revealed that lipid markers of resistance (e.g., 13-HpOTrE), along with jasmonic and salicylic acid, were accumulated differently in the XFP-positive resprouting trees from both cultivars with respect to XFP-positive OQDS symptomatic and XFP-negative trees, suggesting a correlation of lipid metabolism with the resprouting, which can be an indication of the resiliency of these trees to OQDS. This is the first report concerning the resprouting of OQDS-infected olive trees in the Salento area.

Oral microbiota dysbiosis alters chronic restraint stress-induced depression-like behaviors by modulating host metabolism

Studies have shown that the microbiota-gut-brain axis is highly correlated with the pathogenesis of depression in humans. However, whether independent oral microbiome that do not depend on gut microbes could affect the progression of depression in human beings remains unclear, neither does the presence and underlying mechanisms of the microbiota-oral-brain axis in the development of the condition. Hence this study that encompasses clinical and animal experiments aims at investigating the correlation between oral microbiota and the onset of depression via mediating the microbiota-oral-brain axis. We compared the oral microbial compositions and metabolomes of 87 patients with depressive symptoms versus 70 healthy controls. We found that the oral microbial and metabolic signatures were significantly different between the two groups. Significantly, germ-free (GF) mice transplanted with saliva from mice exposing to chronic restraint stress (CRS) displayed depression-like behavior and oral microbial dysbiosis. This was characterized by a significant differential abundance of bacterial species, including the enrichment of Pseudomonas, Pasteurellaceae, and Muribacter, as well as the depletion of Streptococcus. Metabolomic analysis showed the alternation of metabolites in the plasma of CRS-exposed GF mice, especially Eicosapentaenoic Acid. Furthermore, oral and gut barrier dysfunction caused by CRS-induced oral microbiota dysbiosis may be associated with increased blood-brain barrier permeability. Pseudomonas aeruginosa supplementation exacerbated depression-like behavior, while Eicosapentaenoic Acid treatment conferred protection against depression-like states in mice. These results suggest that oral microbiome and metabolic function dysbiosis may be relevant to the pathogenesis and pathophysiology of depression. The proposed microbiota-oral-brain axis provides a new way and targets for us to study the pathogenesis of depression.

Modified oxylipins as inhibitors of biofilm formation in Staphylococcus epidermidis

New approaches to combating microbial drug resistance are being sought, with the discovery of biofilm inhibitors considered as alternative arsenal for treating infections. Natural products have been at the forefront of antimicrobial discovery and serve as inspiration for the design of new antibiotics. We probed the potency, selectivity, and mechanism of anti-biofilm activity of modified oxylipins inspired by the marine natural product turneroic acid. Structure-activity relationship (SAR) evaluation revealed the importance of the trans-epoxide moiety, regardless of the position, for inhibiting biofilm formation. trans-12,13-epoxyoctadecanoic acid (1) and trans-9,10 epoxyoctadecanoic acid (4) selectively target the early stage of biofilm formation, with no effect on planktonic cells. These compounds interrupt the formation of a protective polysaccharide barrier by significantly upregulating the ica operon's transcriptional repressor. This was corroborated by docking experiment with SarA and scanning electron micrographs showing reduced biofilm aggregates and the absence of thread-like structures of extrapolymeric substances. In silico evaluation revealed that 1 and 4 can interfere with the AgrA-mediated communication language in Staphylococci, typical to the diffusible signal factor (DSF) capacity of lipophilic chains.

Volatile methyl jasmonate from roots triggers host-beneficial soil microbiome biofilms

The rhizosphere is a niche surrounding plant roots, where soluble and volatile molecules mediate signaling between plants and the associated microbiota. The preferred lifestyle of soil microorganisms is in the form of biofilms. However, less is known about whether root volatile organic compounds (rVOCs) can influence soil biofilms beyond the 2-10 mm rhizosphere zone influenced by root exudates. We report that rVOCs shift the microbiome composition and growth dynamics of complex soil biofilms. This signaling is evolutionarily conserved from ferns to higher plants. Methyl jasmonate (MeJA) is a bioactive signal of rVOCs that rapidly triggers both biofilm and microbiome changes. In contrast to the planktonic community, the resulting biofilm community provides ecological benefits to the host from a distance via growth enhancement. Thus, a volatile host defense signal, MeJA, is co-opted for assembling host-beneficial biofilms in the soil microbiota and extending the sphere of host influence in the rhizosphere.

Biofilm-derived oxylipin 10-HOME mediated immune response in women with breast implants

Breast implant illness (BII) is a poorly understood disease in which patients develop symptoms typical of autoimmune conditions following breast implantation. There is no known underlying cause, and patients often resort to breast implant removal and capsulectomy to alleviate symptoms. In this issue of the JCI, Khan and colleagues examined 86 breast explants from patients that reported BII symptoms and 55 control explants. The BII group showed a disproportionally high degree of biofilm, which was associated with oxylipin (10-HOME) on the implant surfaces. Injections of 10-HOME in the mammary fat pad of a murine model recapitulated BII symptoms and increased Th1 cell populations. Notably, macrophages in the periprosthetic tissue from BII patients were more likely to exhibit a proinflammatory phenotype, and naive T cells exposed to 10-HOME caused naive macrophages to differentiate to a proinflammatory phenotype. This work provides a pathophysiologic mechanism for a currently understudied and poorly characterized disease.

Whole-Cell Biosensors for Qualitative and Quantitative Analysis of Quorum Sensing Signal Molecules and the Investigation of Quorum Quenching Agents

In Pseudomonas aeruginosa relevant features including virulence and biofilm formation are controlled by quorum sensing (QS), a cell density-dependent intercellular communication system based on the production and response to signal molecules. P. aeruginosa has evolved chemically distinct compounds employed as QS signal molecules (QSSMs) that can be detected and quantified through rapid, sensitive, and low-cost methods based on whole-cell biosensors. Here, we present a series of protocols based on whole-cell biosensors for qualitative and quantitative analysis of QSSMs produced by P. aeruginosa. These protocols can be used to investigate the impact of environmental conditions, genetic modifications, or quorum quenching agents on the production of QSSMs in P. aeruginosa.

Biofilm-derived oxylipin 10-HOME-mediated immune response in women with breast implants

This study investigates a mechanistic link of bacterial biofilm-mediated host-pathogen interaction leading to immunological complications associated with breast implant illness (BII). Over 10 million women worldwide have breast implants. In recent years, women have described a constellation of immunological symptoms believed to be related to their breast implants. We report that periprosthetic breast tissue of participants with symptoms associated with BII had increased abundance of biofilm and biofilm-derived oxylipin 10-HOME compared with participants with implants who are without symptoms (non-BII) and participants without implants. S. epidermidis biofilm was observed to be higher in the BII group compared with the non-BII group and the normal tissue group. Oxylipin 10-HOME was found to be immunogenically capable of polarizing naive CD4+ T cells with a resulting Th1 subtype in vitro and in vivo. Consistently, an abundance of CD4+Th1 subtype was observed in the periprosthetic breast tissue and blood of people in the BII group. Mice injected with 10-HOME also had increased Th1 subtype in their blood, akin to patients with BII, and demonstrated fatigue-like symptoms. The identification of an oxylipin-mediated mechanism of immune activation induced by local bacterial biofilm provides insight into the possible pathogenesis of the implant-associated immune symptoms of BII.

Drosophila melanogaster as an organism model for studying cystic fibrosis and its major associated microbial infections

Cystic fibrosis (CF) is a human genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator gene that encodes a chloride channel. The most severe clinical manifestation is associated with chronic pulmonary infections by pathogenic and opportunistic microbes. Drosophila melanogaster has become the invertebrate model of choice for modeling microbial infections and studying the induced innate immune response. Here, we review its contribution to the understanding of infections with six major pathogens associated with CF (Staphylococcus aureus, Pseudomonas aeruginosa, Burkholderia cepacia, Mycobacterium abscessus, Streptococcus pneumoniae, and Aspergillus fumigatus) together with the perspectives opened by the recent availability of two CF models in this model organism.

Microbiota of long-term indwelling hemodialysis catheters during renal transplantation perioperative period: a cross-sectional metagenomic microbial community analysis

Background: Catheter-related infection (CRI) is a major complication in patients undergoing hemodialysis. The lack of high-throughput research on catheter-related microbiota makes it difficult to predict the occurrence of CRI. Thus, this study aimed to delineate the microbial structure and diversity landscape of hemodialysis catheter tips among patients during the perioperative period of kidney transplantation (KTx) and provide insights into predicting the occurrence of CRI.Methods: Forty patients at the Department of Transplantation undergoing hemodialysis catheter removal were prospectively included. Samples, including catheter tip, catheter outlet skin swab, catheter blood, peripheral blood, oropharynx swab, and midstream urine, from the separate pre- and post-KTx groups were collected and analyzed using metagenomic next-generation sequencing (mNGS). All the catheter tips and blood samples were cultured conventionally.Results: The positive detection rates for bacteria using mNGS and traditional culture were 97.09% (200/206) and 2.65% (3/113), respectively. Low antibiotic-sensitivity biofilms with colonized bacteria were detected at the catheter tip. In asymptomatic patients, no statistically significant difference was observed in the catheter tip microbial composition and diversity between the pre- and post-KTx group. The catheter tip microbial composition and diversity were associated with fasting blood glucose levels. Microorganisms at the catheter tip most likely originated from catheter outlet skin and peripheral blood.Conclusions: The long-term colonization microbiota at the catheter tip is in a relatively stable state and is not readily influenced by KTx. It does not act as the source of infection in all CRIs, but could reflect hematogenous infection to some extent.

Fungal and bacterial oxylipins are signals for intra- and inter-cellular communication within plant disease

Lipids are central at various stages of host-pathogen interactions in determining virulence and modulating plant defense. Free fatty acids may act as substrates for oxidizing enzymes [e.g., lipoxygenases (LOXs) and dioxygenases (DOXs)] that synthesize oxylipins. Fatty acids and oxylipins function as modulators of several pathways in cell-to-cell communication; their structural similarity among plant, fungal, and bacterial taxa suggests potential in cross-kingdom communication. We provide a prospect of the known role of fatty acids and oxylipins in fungi and bacteria during plant-pathogen interactions. In the pathogens, oxylipin-mediated signaling pathways are crucial both in development and host infection. Here, we report on case studies suggesting that oxylipins derived from oleic, linoleic, and linolenic acids are crucial in modulating the pathogenic lifestyle in the host plant. Intriguingly, overlapping (fungi-plant/bacteria-plant) results suggest that different inter-kingdom pathosystems use similar lipid signals to reshape the lifestyle of the contenders and occasionally determine the outcome of the challenge.

Pseudomonas aeruginosa Secretes the Oxylipin Autoinducer Synthases OdsA and OdsB via the Xcp Type 2 Secretion System

The oxylipin-dependent quorum-sensing system (ODS) of Pseudomonas aeruginosa relies on the production and sensing of two extracellular oxylipins, 10S-hydroxy-(8E)-octadecenoic acid (10-HOME) and 7S,10S-dihydroxy-(8E)-octadecenoic acid (7,10-DiHOME). Here, we implemented a genetic screen of P. aeruginosa strain PAO1 aimed to identify genes required for 10-HOME and 7,10-DiHOME production. Among the 14 genes identified, four encoded previously known components of the ODS and 10 encoded parts of the Xcp type II secretion system (T2SS). We subsequently created a clean xcpQ deletion mutant, which encodes the necessary outer membrane component of Xcp, and found it recapitulated the impaired functionality of the T2SS transposon mutants. Further studies showed that the ΔxcpQ mutant was unable to secrete the oxylipin synthase enzymes across the outer membrane. Specifically, immunoblotting for OdsA, which is responsible for the generation of 10-HOME from oleic acid, detected the enzyme in supernatants from wild-type PAO1 but not ΔxcpQ cultures. Likewise, chromatography of supernatants found that 10-HOME was not in supernatants collected from the ΔxcpQ mutant. Accordingly, diol synthase activity was increased in the periplasm of ΔxcpQ mutant consistent with a stoppage in its transport. Importantly, after exposure of the ΔxcpQ mutant to exogenous 10-HOME and 7,10-DiHOME, the ODS effector genes become active; thus, the sensing component of the ODS does not involve the T2SS. Finally, we observed that Xcp contributed to robust in vitro and in vivo biofilm formation in oleic acid availability- and ODS-dependent manner. Thus, T2SS-mediated transport of the oxylipin synthase enzymes to outside the bacterial cell is required for ODS functionality. IMPORTANCE We previously showed that the ODS of P. aeruginosa produces and responds to oxylipins derived from host oleic acid by enhancing biofilm formation and virulence. Here, we developed a genetic screen strategy to explore the molecular basis for oxylipins synthesis and detection. Unexpectedly, we found that the ODS autoinducer synthases cross the outer membrane using the Xcp type 2 secretion system (T2SS) of P. aeruginosa, and so the biosynthesis of oxylipins occurs extracellularly. T2SS promoted biofilm formation in the presence of oleic acid as a result of ODS activation. Our results identify two new T2SS secreted proteins in P. aeruginosa and reveal a new way by which this important opportunistic pathogen interacts with the host environment.

Integrated omics approach to unveil antifungal bacterial polyynes as acetyl-CoA acetyltransferase inhibitors

Bacterial polyynes are highly active natural products with a broad spectrum of antimicrobial activities. However, their detailed mechanism of action remains unclear. By integrating comparative genomics, transcriptomics, functional genetics, and metabolomics analysis, we identified a unique polyyne resistance gene, masL (encoding acetyl-CoA acetyltransferase), in the biosynthesis gene cluster of antifungal polyynes (massilin A 1, massilin B 2, collimonin C 3, and collimonin D 4) of Massilia sp. YMA4. Crystallographic analysis indicated that bacterial polyynes serve as covalent inhibitors of acetyl-CoA acetyltransferase. Moreover, we confirmed that the bacterial polyynes disrupted cell membrane integrity and inhibited the cell viability of Candida albicans by targeting ERG10, the homolog of MasL. Thus, this study demonstrated that acetyl-CoA acetyltransferase is a potential target for developing antifungal agents.

In a multi-omics analysis, bacterial polyynes are found to act as antifungal agents by inhibiting the Candida albicans polyyne resistance gene ERG10, the homolog of MasL encoding acetyl-CoA acetyltransferase.

Mass Spectrometry-Based Targeted Lipidomics and Supervised Machine Learning Algorithms in Detecting Disease, Cultivar, and Treatment Biomarkers in Xylella fastidiosa subsp. pauca-Infected Olive Trees

In 2013, Xylella fastidiosa (Xf) was detected for the first time in Apulia and, subsequently, recognized as the causal agent of the olive quick decline syndrome (OQDS). To contain the disease, the olive germplasm was evaluated for resistance to Xf, identifying cultivars with different susceptibility to the pathogen. Regarding this, the resistant cultivar Leccino has generally a lower bacterial titer compared with the susceptible cultivar Ogliarola salentina. Among biomolecules, lipids could have a pivotal role in the interaction of Xf with its host. In the grapevine Pierce's disease, fatty acid molecules, the diffusible signaling factors (DSFs), act as regulators of Xf lifestyle and are crucial for its virulence. Other lipid compounds derived from fatty acid oxidation, namely, oxylipins, can affect, in vitro, biofilm formation in Xf subsp. pauca (Xfp) strain De Donno, that is, the strain causing OQDS. In this study, we combined high-performance liquid chromatography-mass spectrometry-MS-based targeted lipidomics with supervised learning algorithms (random forest, support vector machine, and neural networks) to classify olive tree samples from Salento. The dataset included samples from either OQDS-positive or OQDS-negative olive trees belonging either to cultivar Ogliarola salentina or Leccino treated or not with the zinc-copper-citric acid biocomplex Dentamet^®. We built classifiers using the relative differences in lipid species able to discriminate olive tree samples, namely, (1) infected and non-infected, (2) belonging to different cultivars, and (3) treated or untreated with Dentamet^®. Lipid entities emerging as predictors of the thesis are free fatty acids (C16:1, C18:1, C18:2, C18:3); the LOX-derived oxylipins 9- and 13-HPOD/TrE; the DOX-derived oxylipin 10-HPOME; and diacylglyceride DAG36:4(18:1/18:3).

A Cross-Kingdom View on the Immunomodulatory Role of MIF/D-DT Proteins in Mammalian and Plant Pseudomonas Infections

Gram-negative Pseudomonas bacteria are largely harmless saprotrophs, but some species can be potent pathogens of both plants and mammals. Macrophage migration inhibitory factor (MIF) and its homolog D-dopachrome tautomerase (D-DT, also referred to as MIF-2) are multifunctional proteins that in addition to their intracellular functions also serve as extracellular signaling molecules (cytokines) in orchestrating mammalian immune responses. It recently emerged that plants also possess MIF-like proteins, termed MIF/D-DT-like (MDL) proteins. We here provide a comparative cross-kingdom view on the immunomodulatory role of MIF and MDL proteins during Pseudomonas infections in mammals and plants. Although in both kingdoms the lack of MIF/MDL proteins is associated with a reduction in bacterial load and disease symptoms, the underlying molecular principles seem to be different. We provide a perspective for future research activities to unravel additional commonalities and differences in the MIF/MDL-mediated adjustment of antibacterial immune activities.

Silencing of a Pseudo-nitzschia arenysensis lipoxygenase transcript leads to reduced oxylipin production and impaired growth

Because of their importance as chemical mediators, the presence of a rich and varied family of lipoxygenase (LOX) products, collectively named oxylipins, has been investigated thoroughly in diatoms, and the involvement of these products in important processes such as bloom regulation has been postulated. Nevertheless, little information is available on the enzymes and pathways operating in these protists. Exploiting transcriptome data, we identified and characterized a LOX gene, PaLOX, in Pseudo-nitzschia arenysensis, a marine diatom known to produce different species of oxylipins by stereo- and regio-selective oxidation of eicosapentaenoic acid (EPA) at C12 and C15. PaLOX RNA interference correlated with a decrease of the lipid-peroxidizing activity and oxylipin synthesis, as well as with a reduction of growth of P. arenysensis. In addition, sequence analysis and structure models of the C-terminal part of the predicted protein closely fitted with the data for established LOXs from other organisms. The presence in the genome of a single LOX gene, whose downregulation impairs both 12- and 15-oxylipins synthesis, together with the in silico 3D protein modelling suggest that PaLOX encodes for a 12/15S-LOX with a dual specificity, and provides additional support to the correlation between cell growth and oxylipin biosynthesis in diatoms.

Oxylipins From Different Pathways Trigger Mitochondrial Stress Signaling Through Respiratory Complex III

Plant oxylipins are signaling molecules produced from fatty acids by oxidative pathways, mainly initiated by 9- and 13-lipoxygenases (9-LOX and 13-LOX), alpha-dioxygenases or non-enzymatic oxidation. Oxylipins from the 9-LOX pathway induce oxidative stress and control root development and plant defense. These activities have been associated with mitochondrial processes, but precise cellular targets and pathways remain unknown. In order to study oxylipin signaling, we previously generated a collection of Arabidopsis thaliana mutants that were insensitive to the 9-LOX products 9(S)-hydroxy-10,12, 15-octadecatrienoic acid (9-HOT) and its ketone derivative 9-KOT (noxy mutants). Here, we describe noxy1, noxy3, noxy5, noxy23, and noxy54 mutants, all affected in nucleus-encoded mitochondrial proteins, and use them to study the role of mitochondria in oxylipin signaling. Functional and phenotypic analyses showed that noxy plants displayed mitochondrial aggregation, reduced respiration rates and resistance to the complex III inhibitor Antimycin A (AA), thus indicating a close similarity of the oxylipin signaling and mitochondrial stress. Application of 9-HOT and 9-KOT protected plants against subsequent mitochondrial stress, whereas they boosted root growth reduction when applied in combination with complex III inhibitors but did not with inhibitors of other respiratory complexes. A similar effect was caused by linear-chain oxylipins from 13-LOX or non-enzymatic pathways having α,β-unsaturated hydroxyl or keto groups in their structure. Studies to investigate 9-HOT and 9-KOT activity indicated that they do not reduce respiration rates, but their action is primarily associated with enhanced ROS responses. This was supported by the results showing that 9-HOT or 9-KOT combined with AA amplified the expression of oxylipin- and ROS-responding genes but not of the AA marker AOX1a, thus implying the activation of a specific mitochondria retrograde signaling pathway. Our results implicate mitochondrial complex III as a hub in the signaling activity of multiple oxylipin pathways and point at downstream ROS responses as components of oxylipin function.

Oxygen Self-Supplying Nanotherapeutic for Mitigation of Tissue Hypoxia and Enhanced Photodynamic Therapy of Bacterial Keratitis

Hypoxia, a common characteristic of bacterial infections, is known to be closely associated with the emergence of multidrug-resistant bacteria, which hastens the need to develop advanced microbicides and antibacterial techniques. Photodynamic therapy is a promising strategy to reduce bacterial antibiotic resistance and employs photosensitizers, excitation light sources, and sufficient oxygen to generate toxic reactive oxygen species (ROS). The inherent limitation of PDT is that the generation of ROS is restricted by the hypoxic microenvironment in infection sites. Here, an oxygen self-supplying nanotherapeutic is developed to enhance antibacterial activity against multidrug-resistant bacteria on the basis of fluorinated boron dipyrromethene (BODIPY)-based glycomimetics. The nanotherapeutic not only could capture the bacteria efficiently but also was able to act as an oxygen carrier to relieve the hypoxic microenvironment of bacterial infections, thus achieving enhanced PDT efficacy. In a Pseudomonas aeruginosa infection of a rat cornea, typical administration of the nanotherapeutic decreased the infiltrate and showed a faster healing capacity in comparison with BODIPY-based glycomimetics. Self-supplying oxygen nanotherapeutics that relieve the hypoxic microenvironment and interfere with bacterial colonization have been shown to be a promising candidate for the management of drug-resistant microbial keratitis.

Speaking the language of lipids: the cross-talk between plants and pathogens in defence and disease

Lipids and fatty acids play crucial roles in plant immunity, which have been highlighted over the past few decades. An increasing number of studies have shown that these molecules are pivotal in the interactions between plants and their diverse pathogens. The roles played by plant lipids fit in a wide spectrum ranging from the first physical barrier encountered by the pathogens, the cuticle, to the signalling pathways that trigger different immune responses and expression of defence-related genes, mediated by several lipid molecules. Moreover, lipids have been arising as candidate biomarkers of resistance or susceptibility to different pathogens. Studies on the apoplast and extracellular vesicles have been highlighting the possible role of lipids in the intercellular communication and the establishment of systemic acquired resistance during plant-pathogen interactions. From the pathogen perspective, lipid metabolism and specific lipid molecules play pivotal roles in the pathogen's life cycle completion, being crucial during recognition by the plant and evasion from the host immune system, therefore potentiating infection. Studies conducted in the last years have contributed to a better understanding of the language of lipids during the cross-talk between plants and pathogens. However, it is essential to continue exploring the knowledge brought up to light by transcriptomics and proteomics studies towards the elucidation of lipid signalling processes during defence and disease. In this review, we present an updated overview on lipids associated to plant-pathogen interactions, exploiting their roles from the two sides of this battle.

Potential of N2 Gas Flushing to Hinder Dairy-Associated Biofilm Formation and Extension

Worldwide, the dairy sector remains of vital importance for food production despite severe environmental constraints. The production and handling conditions of milk, a rich medium, promote inevitably the entrance of microbial contaminants, with notable impact on the quality and safety of raw milk and dairy products. Moreover, the persistence of high concentrations of microorganisms (especially bacteria and bacterial spores) in biofilms (BFs) present on dairy equipment or environments constitutes an additional major source of milk contamination from pre- to post-processing stages: in dairies, BFs represent a major concern regarding the risks of disease outbreaks and are often associated with significant economic losses. One consumption trend toward "raw or low-processed foods" combined with current trends in food production systems, which tend to have more automation and longer processing runs with simultaneously more stringent microbiological requirements, necessitate the implementation of new and obligatory sustainable strategies to respond to new challenges regarding food safety. Here, in light of studies, performed mainly with raw milk, that considered dominant "planktonic" conditions, we reexamine the changes triggered by cold storage alone or combined with nitrogen gas (N2) flushing on bacterial populations and discuss how the observed benefits of the treatment could also contribute to limiting BF formation in dairies.

Drosophila as a Model Organism in Host-Pathogen Interaction Studies

Owing to the genetic similarities and conserved pathways between a fruit fly and mammals, the use of the Drosophila model as a platform to unveil novel mechanisms of infection and disease progression has been justified and widely instigated. Gaining proper insight into host-pathogen interactions and identifying chief factors involved in host defense and pathogen virulence in Drosophila serves as a foundation to establish novel strategies for infectious disease prevention and control in higher organisms, including humans.

Xylella fastidiosa subsp. pauca and olive produced lipids moderate the switch adhesive versus non-adhesive state and viceversa

Global trade and climate change are re-shaping the distribution map of pandemic pathogens. One major emerging concern is Xylella fastidiosa, a tropical bacterium recently introduced into Europe from America. In last decades, X. fastidiosa was detected in several European countries. X. fastidiosa is an insect vector-transmitted bacterial plant pathogen associated with severe diseases in a wide range of hosts. X. fastidiosa through a tight coordination of the adherent biofilm and the planktonic states, invades the host systemically. The planktonic phase is correlated to low cell density and vessel colonization. Increase in cell density triggers a quorum sensing system based on mixture of cis 2-enoic fatty acids-diffusible signalling factors (DSF) that promote stickiness and biofilm. The lipidome profile of Olea europaea L. (cv. Ogliarola salentina) samples, collected in groves located in infected zones and uninfected zones was performed. The untargeted analysis of the lipid profiles of Olive Quick Decline Syndrome (OQDS) positive (+) and negative (-) plants showed a clustering of OQDS+ plants apart from OQDS-. The targeted lipids profile of plants OQDS+ and OQDS- identified a shortlist of 10 lipids that increase their amount in OQDS+ and X. fastidiosa positive olive trees. These lipid entities, provided to X. fastidiosa subsp. pauca pure culture, impact on the dual phase, e.g. planktonic ↔ biofilm. This study provides novel insights on OQDS lipid hallmarks and on molecules that might modulate biofilm phase in X. fastidiosa subsp. pauca.

Beyond Antagonism: The Interaction Between Candida Species and Pseudomonas aeruginosa

There are many examples of the interaction between prokaryotes and eukaryotes. One such example is the polymicrobial colonization/infection by the various opportunistic pathogenic yeasts belonging to the genus Candida and the ubiquitous bacterium, Pseudomonas aeruginosa. Although this interaction has simplistically been characterized as antagonistic to the yeast, this review highlights the complexity of the interaction with various factors influencing both microbes. The first section deals with the interactions in vitro, looking specifically at the role of cell wall components, quorum sensing molecules, phenazines, fatty acid metabolites and competition for iron in the interaction. The second part of this review places all these interactions in the context of various infection or colonization sites, i.e., lungs, wounds, and the gastrointestinal tract. Here we see that the role of the host, as well as the methodology used to establish co-infection, are important factors, influencing the outcome of the disease. Suggested future perspectives for the study of this interaction include determining the influence of newly identified participants of the QS network of P. aeruginosa, oxylipin production by both species, as well as the genetic and phenotypic plasticity of these microbes, on the interaction and outcome of co-infection.

Pseudomonas aeruginosa esterase PA2949, a bacterial homolog of the human membrane esterase ABHD6: expression, purification and crystallization

The human membrane-bound α/β-hydrolase domain 6 (ABHD6) protein modulates endocannabinoid signaling, which controls appetite, pain and learning, as well as being linked to Alzheimer's and Parkinson's diseases, through the degradation of the key lipid messenger 2-arachidonylglycerol (2-AG). This makes ABHD6 an attractive therapeutic target that lacks structural information. In order to better understand the molecular mechanism of 2-AG-hydrolyzing enzymes, the PA2949 protein from Pseudomonas aeruginosa, which has 49% sequence similarity to the ABHD6 protein, was cloned, overexpressed, purified and crystallized. Overexpression of PA2949 in the homologous host yielded the membrane-bound enzyme, which was purified in milligram amounts. Besides their sequence similarity, the enzymes both show specificity for the hydrolysis of 2-AG and esters of medium-length fatty acids. PA2949 in the presence of n-octyl β-D-glucoside showed a higher activity and stability at room temperature than those previously reported for PA2949 overexpressed and purified from Escherichia coli. A suitable expression host and stabilizing detergent were crucial for obtaining crystals, which belonged to the tetragonal space group I4122 and diffracted to a resolution of 2.54 Å. This study provides hints on the functional similarity of ABHD6-like proteins in prokaryotes and eukaryotes, and might guide the structural study of these difficult-to-crystallize proteins.

Oxylipins mediate cell-to-cell communication in Pseudomonas aeruginosa

Oxygenated unsaturated fatty acids, known as oxylipins, are signaling molecules commonly used for cell-to-cell communication in eukaryotes. However, a role for oxylipins in mediating communication in prokaryotes has not previously been described. Bacteria mainly communicate via quorum sensing, which involves the production and detection of diverse small molecules termed autoinducers. Here we show that oleic acid-derived oxylipins produced by Pseudomonas aeruginosa function as autoinducers of a novel quorum sensing system. We found that this system controls the cell density-dependent expression of a gene subset independently of the quorum sensing systems thus far described in this bacterium. We identified a LysR-type transcriptional regulator as the primary receptor of the oxylipin signal. The discovery of this oxylipin-dependent quorum sensing system reveals that prokaryote-derived oxylipins also mediate cell-to-cell communication in bacteria.

Eriel Martínez et al. report that the bacterial pathogen Pseudomonas aeruginosa can convert oleic acids into oxylipins for use in cell-cell communication. This quorum sensing system is regulated by the bacterial protein called oxylipin-dependent diol synthase regulator OdsR.

Manipulation of the silkworm immune system by a metalloprotease from the pathogenic bacterium Pseudomonas aeruginosa

Antimicrobial peptide (AMP) production and melanization are two key humoral immune responses in insects. Induced synthesis of AMPs results from Toll and IMD signal transduction whereas melanization depends on prophenoloxidase (PPO) activation system. During invasion, pathogens produce toxins and other virulent factors to counteract host immune responses. Here we show that the pathways leading to PPO activation and AMP synthesis in the silkworm Bombyx mori are affected by a metalloprotease, named elastase B, secreted by Pseudomonas aeruginosa (PAO1). The metalloprotease gene (lasB) was expressed shortly after PAO1 cells had been injected into the larval silkworm hemocoel, leading to an increase of elastase activity. Injection of the purified PAO1 elastase B into silkworm hemolymph compromised PPO activation. In contrast, the protease caused a level increase of gloverin, an AMP in the hemolymph. To verify our results obtained using the purified elastase B, we infected B. mori with PAO1 ΔlasB mutant and found that PO activity in hemolymph of the PAO1 ΔlasB-infected larvae was significantly higher than that in the wild type-infected. The mutant-inhabited hemolymph had lower levels of gloverin and antimicrobial activity. PAO1 ΔlasB showed a decreased viability in the silkworm hemolymph whereas the host had a lower mortality. In addition, the effects caused by the ΔlasB mutant were restored by a complementary strain. These data collectively indicated that the elastase B produced by PAO1 is an important virulent factor that manipulates the silkworm immune system during infection.

Molecular characterization of Penicillium oxalicum 6R,8R-linoleate diol synthase with new regiospecificity

Diol synthase-derived metabolites are involved in the sexual and asexual life cycles of fungi. A putative diol synthase from Penicillium oxalicum was found to convert palmitoleic acid (16:1n-7), oleic acid (18:1n-9), linoleic acid (18:2n-6), and α-linolenic acid (18:3n-3) to 6S,8R-dihydroxy-9(Z)-hexadecenoic acid, 6R,8R-dihydroxy-9(Z)-octadecenoic acid, 6R,8R-dihydroxy-9,12(Z,Z)-octadecadienoic acid, and 6S,8R-dihydroxy-9,12,15(Z,Z,Z)-octadecatrienoic acid, respectively, which were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR) spectroscopy analyses. The specific activity and catalytic efficiency of P. oxalicum 6,8-diol synthase were the highest for 18:2n-6, indicating that the enzyme is a 6R,8R-linoleate diol synthase (6R,8R-LDS) with new regiospecificity. This is the first report of a 6R,8R-LDS. LDS is a fusion protein consisting of a dioxygenase domain at the N-terminus and a cytochrome P450/hydroperoxide isomerase (P450/HPI) domain at the C-terminus. The putative active-site residues in the C-terminal domain of P. oxalicum 6R,8R-LDS were proposed based on a substrate-docking homology model. The results of the site-directed mutagenesis within C-terminal P450 domain suggested that Asn⁸⁸⁶, Arg⁷⁰⁷, and Arg⁹³⁴, are catalytic importance and belong to the catalytic groove. Phe⁷⁹⁴ and Gln⁸⁸⁹ were found to be involved in the regiospecific rearrangement of hydroperoxide, while the F794E and Q889A variants of P. oxalicum 6,8-LDS acted as 7,8- and 8,11-LDSs, respectively. All these mutations critically affected the HPI activity of P. oxalicum 6R,8R-LDS.

Lipid Profile of Xylella fastidiosa Subsp. pauca Associated With the Olive Quick Decline Syndrome

Lipids, components of the plasma and intracellular membranes as well as of droplets, provide different biological functions related to energy, carbon storage, and stress responses. Bacterial species display diverse membrane composition that changes in response to the different environmental conditions. During plant-pathogen interactions, lipids might have roles in several aspects such as recognition, signal transduction, and downstream responses. Among lipid entities, free fatty acids (FFAs) and their oxidized form, the oxylipins, represent an important class of signaling molecules in host-pathogen perception, especially related to virulence and defense. In bacteria, FFAs (e.g., diffusible signaling factors) and oxylipins have a crucial role in modulating motility, biofilm formation, and virulence. In this study, we explore by LC-TOF and LC-MS/MS the lipid composition of Xylella fastidiosa subsp. pauca strain De Donno in pure culture; some specific lipids (e.g., ornithine lipids and the oxylipin 7,10-diHOME), characteristic of other pathogenic bacteria, were revealed. Nicotiana tabacum was used for testing the ability of this pathogen in producing such lipids in the host. Different lipid compounds present a clear distribution pattern within the infected plant tissues compared to the uninfected ones.

Lipoxygenases and Lipoxygenase Products in Marine Diatoms

Marine diatoms negatively affect reproduction and later larval development of dominant zooplankton grazers such as copepods, thereby lowering the recruitment of the next generations of these small crustaceans that are a major food source for larval fish species. The phenomenon has been explained in terms of chemical defense due to grazer-induced synthesis of oxylipins, lipoxygenase-derived oxygenated fatty acid derivatives. Since this first report, studies about diatom oxylipins have multiplied and broadened toward other aspects concerning bloom dynamics, cell growth, and cell differentiation. Diatom oxylipins embrace a number of diverse structures that are recognized as chemical signals in ecological and physiological processes in many other organisms. In diatoms, the most studied examples include polyunsaturated aldehydes (PUAs) and nonvolatile oxylipins (NVOs). The purpose of this chapter is to provide the analytical tools to deal with identification, analysis and biosynthesis of these compounds. Emphasis is given to identification of the enzymatic steps and characterization of the species-specific lipoxygenases even in absence of the availability of molecular information.

Recent perspectives on the molecular basis of biofilm formation by Pseudomonas aeruginosa and approaches for treatment and biofilm dispersal

Pseudomonas aeruginosa, a Gram-negative, rod-shaped bacterium causes widespread diseases in humans. This bacterium is frequently related to nosocomial infections such as pneumonia, urinary tract infections (UTIs) and bacteriaemia especially in immunocompromised patients. The current review focuses on the recent perspectives on biofilms formation by these bacteria. Biofilms are communities of microorganisms in which cells stick to each other and often adhere to a surface. These adherent cells are usually embedded within a self-produced matrix of extracellular polymeric substance (EPS). Pel, psl and alg operons present in P. aeruginosa are responsible for the biosynthesis of extracellular polysaccharide which plays an important role in cell surface interactions during biofilm formation. Recent studies suggested that cAMP signalling pathway, quorum-sensing pathway, Gac/Rsm pathway and c-di-GMP signalling pathway are the main mechanism that leads to the biofilm formation. Understanding the bacterial virulence depends on a number of cell-associated and extracellular factors and is very essential for the development of potential drug targets. Thus, the review focuses on the major genes involved in the biofilm formation, the state of art update on the biofilm treatment and the dispersal approaches such as targeting adhesion and maturation, targeting virulence factors and other strategies such as small molecule-based inhibitors, phytochemicals, bacteriophage therapy, photodynamic therapy, antimicrobial peptides and natural therapies and vaccines to curtail the biofilm formation by P. aeruginosa.

Microbes and associated soluble and volatile chemicals on periodically wet household surfaces

BACKGROUND

Microorganisms influence the chemical milieu of their environment, and chemical metabolites can affect ecological processes. In built environments, where people spend the majority of their time, very little is known about how surface-borne microorganisms influence the chemistry of the indoor spaces. Here, we applied multidisciplinary approaches to investigate aspects of chemical microbiology in a house.

METHODS

We characterized the microbial and chemical composition of two common and frequently wet surfaces in a residential setting: kitchen sink and bathroom shower. Microbial communities were studied using culture-dependent and independent techniques, including targeting RNA for amplicon sequencing. Volatile and soluble chemicals from paired samples were analyzed using state-of-the-art techniques to explore the links between the observed microbiota and chemical exudates.

RESULTS

Microbial analysis revealed a rich biological presence on the surfaces exposed in kitchen sinks and bathroom shower stalls. Microbial composition, matched for DNA and RNA targets, varied by surface type and sampling period. Bacteria were found to have an average of 25× more gene copies than fungi. Biomass estimates based on qPCR were well correlated with measured total volatile organic compound (VOC) emissions. Abundant VOCs included products associated with fatty acid production. Molecular networking revealed a diversity of surface-borne compounds that likely originate from microbes and from household products.

CONCLUSIONS

Microbes played a role in structuring the chemical profiles on and emitted from kitchen sinks and shower stalls. Microbial VOCs (mVOCs) were predominately associated with the processing of fatty acids. The mVOC composition may be more stable than that of microbial communities, which can show temporal and spatial variation in their responses to changing environmental conditions. The mVOC output from microbial metabolism on kitchen sinks and bathroom showers should be apparent through careful measurement, even against a broader background of VOCs in homes, some of which may originate from microbes in other locations within the home. A deeper understanding of the chemical interactions between microbes on household surfaces will require experimentation under relevant environmental conditions, with a finer temporal resolution, to build on the observational study results presented here.