Characterization of 3-Oxacyl-Acyl Carrier Protein Reductase Homolog Genes in Pseudomonas aeruginosa PAO1

An atypical 3-ketoacyl ACP synthase III required for acyl homoserine lactone synthesis in Pseudomonas syringae pv. syringae B728a

The last step of the initiation phase of fatty acid biosynthesis in most bacteria is catalyzed by the 3-ketoacyl-acyl carrier protein (ACP) synthase III (FabH). Pseudomonas syringae pv. syringae strain B728a encodes two FabH homologs, Psyr_3467 and Psyr_3830, which we designated PssFabH1 and PssFabH2, respectively. Here, we explored the roles of these two 3-ketoacyl-ACP synthase (KAS) III proteins. We found that PssFabH1 is similar to the Escherichia coli FabH in using acetyl-acetyl-coenzyme A (CoA ) as a substrate in vitro, whereas PssFabH2 uses acyl-CoAs (C4-C10) or acyl-ACPs (C6-C10). Mutant analysis showed that neither KAS III protein is essential for the de novo fatty acid synthesis and cell growth. Loss of PssFabH1 reduced the production of an acyl homoserine lactone (AHL) quorum-sensing signal, and this production was partially restored by overexpressing FabH homologs from other bacteria. AHL production was also restored by inhibiting fatty acid elongation and providing exogenous butyric acid. Deletion of PssFabH1 supports the redirection of acyl-ACP toward biosurfactant synthesis, which in turn enhances swarming motility. Our study revealed that PssFabH1 is an atypical KAS III protein that represents a new KAS III clade that functions in providing a critical fatty acid precursor, butyryl-ACP, for AHL synthesis.IMPORTANCEAcyl homoserine lactones (AHLs) are important quorum-sensing compounds in Gram-negative bacteria. Although their formation requires acylated acyl carrier proteins (ACPs), how the acylated intermediate is shunted from cellular fatty acid synthesis to AHL synthesis is not known. Here, we provide in vivo evidence that Pseudomonas syringae strain B728a uses the enzyme PssFabH1 to provide the critical fatty acid precursor butyryl-ACP for AHL synthesis. Loss of PssFabH1 reduces the diversion of butyryl-ACP to AHL, enabling the accumulation of acyl-ACP for synthesis of biosurfactants that contribute to bacterial swarming motility. We report that PssFabH1 and PssFabH2 each encode a 3-ketoacyl-acyl carrier protein synthase (KAS) III in P. syringae B728a. Whereas PssFabH2 is able to function in redirecting intermediates from β-oxidation to fatty acid synthesis, PssFabH1 is an atypical KAS III protein that represents a new KAS III clade based on its sequence, non-involvement in cell growth, and novel role in AHL synthesis.

Diversity in fatty acid elongation enzymes: The FabB long-chain β-ketoacyl-ACP synthase I initiates fatty acid synthesis in Pseudomonas putida F1

The condensation of acetyl-CoA with malonyl-acyl carrier protein (ACP) by β-ketoacyl-ACP synthase III (KAS III, FabH) and decarboxylation of malonyl-ACP by malonyl-ACP decarboxylase are the two pathways that initiate bacterial fatty acid synthesis (FAS) in Escherichia coli. In addition to these two routes, we report that Pseudomonas putida F1 β-ketoacyl-ACP synthase I (FabB), in addition to playing a key role in fatty acid elongation, also initiates FAS in vivo. We report that although two P. putida F1 fabH genes (PpfabH1 and PpfabH2) both encode functional KAS III enzymes, neither is essential for growth. PpFabH1 is a canonical KAS III similar to E. coli FabH whereas PpFabH2 catalyzes condensation of malonyl-ACP with short- and medium-chain length acyl-CoAs. Since these two KAS III enzymes are not essential for FAS in P. putida F1, we sought the P. putida initiation enzyme and unexpectedly found that it was FabB, the elongation enzyme of the oxygen-independent unsaturated fatty acid pathway. P. putida FabB decarboxylates malonyl-ACP and condenses the acetyl-ACP product with malonyl-ACP for initiation of FAS. These data show that P. putida FabB, unlike the paradigm E. coli FabB, can catalyze the initiation reaction in FAS.

Potential functions of the shared bacterial taxa in the citrus leaf midribs determine the symptoms of Huanglongbing

Instruction

Citrus is a globally important fruit tree whose microbiome plays a vital role in its growth, adaptability, and resistance to stress.

Methods

With the high throughput sequencing of 16S rRNA genes, this study focused on analyzing the bacterial community, especially in the leaf midribs, of healthy and Huanglongbing (HLB)-infected plants.

Results

We firstly identified the shared bacterial taxa in the midribs of both healthy and HLB-infected plants, and then analyzed their functions. Results showed that the shared bacterial taxa in midribs belonged to 62 genera, with approximately 1/3 of which modified in the infected samples. Furthermore, 366 metabolic pathways, 5851 proteins, and 1833 enzymes in the shared taxa were predicted. Among these, three metabolic pathways and one protein showed significant importance in HLB infection. With the random forest method, six genera were identified to be significantly important for HLB infection. Notably, four of these genera were also among the significantly different shared taxa. Further functional characterization of these four genera revealed that Pseudomonas and Erwinia likely contributed to plant defense against HLB, while Streptomyces might have implications for plant defense against HLB or the pathogenicity of Candidatus Liberibacter asiaticus (CLas).

Disccusion

Overall, our study highlights that the functions of the shared taxa in leaf midribs are distinguished between healthy and HLB-infected plants, and these microbiome-based findings can contribute to the management and protection of citrus crops against CLas.

A Novel XRE-Type Regulator Mediates Phage Lytic Development and Multiple Host Metabolic Processes in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen, the leading cause of acute and chronic infections in immunocompromised patients, frequently with high morbidity and mortality rates. The xenobiotic response element (XRE) family proteins are the second most common transcriptional regulators (TRs) in P. aeruginosa. However, only a few XRE-like TRs have been reported to regulate multiple bacterial cellular processes, encompassing virulence, metabolism, antibiotic synthesis or resistance, stress responses, and phage infection, etc. Our understanding of what roles these XRE-like small regulatory proteins play in P. aeruginosa remains limited. Here, we aimed to decipher the role of a putative XRE-type transcriptional regulator (designated LfsT) from a prophage region on the chromosome of a clinical P. aeruginosa isolate, P8W. Southern blot and reverse transcription quantitative PCR (RT-qPCR) assays demonstrated that LfsT controlled host sensitivity to the phage PP9W2 and was essential for efficient phage replication. In addition, electrophoretic mobility shift assays (EMSAs) and transcriptional lacZ fusion analyses indicated that LfsT repressed the lysogenic development and promoted the lytic cycle of phage PP9W2 by binding to the promoter regions of the gp71 gene (encoding a CI-like repressor) and several vital phage genes. Combined with RNA-seq and a series of phenotypic validation tests, our results showed that LfsT bound to the flexible palindromic sites within the promoters upstream of several genes in the bacterial genome, regulating fatty acid (FA) metabolism, spermidine (SPD) transport, as well as the type III secretion system (T3SS). Overall, this study reveals novel regulatory roles of LfsT in P. aeruginosa, improving our understanding of the molecular mechanisms behind bacterium-phage interactions. IMPORTANCE This work elucidates the novel roles of a putative XRE family TR, LfsT, in the intricate regulatory systems of P. aeruginosa. We found that LfsT bound directly to the core promoter regions upstream of the start codons of numerous genes involved in various processes, including phage infection, FA metabolism, SPD transport, and the T3SS, regulating as the repressor or activator. The identified partial palindromic motif NAACN(5,8)GTTN recognized by LfsT suggests extensive effects of LfsT on gene expression by maintaining preferential binding to nucleotide sites under evolutionary pressure. In summary, these findings indicate that LfsT enhances metabolic activity in P. aeruginosa, while it reduces host resistance to the phage. This study helps us better understand the coevolution of bacteria and phages (e.g., survival comes at a cost) and provides clues for designing novel antimicrobials against P. aeruginosa infections.

MsmR1, a global transcription factor, regulates polymyxin synthesis and carbohydrate metabolism in Paenibacillus polymyxa SC2

The multiple-sugar metabolism regulator (MsmR), a transcription factor belonging to the AraC/XylS family, participates in polysaccharide metabolism and virulence. However, the transcriptional regulatory mechanisms of MsmR1 in Paenibacillus polymyxa remain unclear. In this study, knocking out msmR1 was found to reduce polymyxin synthesis by the SC2-M1 strain. Chromatin immunoprecipitation assay with sequencing (ChIP-seq) revealed that most enriched pathway was that of carbohydrate metabolism. Additionally, electromobility shift assays (EMSA) confirmed the direct interaction between MsmR1 and the promoter regions of oppC3, sucA, sdr3, pepF, yycN, PPSC2_23180, pppL, and ydfp. MsmR1 stimulates polymyxin biosynthesis by directly binding to the promoter regions of oppC3 and sdr3, while also directly regulating sucA and influencing the citrate cycle (TCA cycle). In addition, MsmR1 directly activates pepF and was beneficial for spore and biofilm formation. These results indicated that MsmR1 could regulate carbohydrate and amino acid metabolism, and indirectly affect biological processes such as polymyxin synthesis, biofilm formation, and motility. Moreover, MsmR1 could be autoregulated. Hence, this study expand the current knowledge of MsmR1 and will be beneficial for the application of P. polymyxa SC2 in the biological control against the certain pathogens in pepper.

Microbial Metagenomics of the Extubated Lacrimal Stents Following Dacryocystorhinostomy: The Lacriome Paper 4

PURPOSE

To study the metagenome of the microbes present on the extubated lacrimal stents following a dacryocystorhinostomy.

METHODS

A prospective study was performed on 10 consecutive extubated lacrimal stents obtained for the metagenomic analysis from the patients following an endoscopic dacryocystorhinostomy. The stents were extubated at 4 weeks postoperatively under endoscopic guidance and immediately transported on ice to the laboratory. Following DNA extraction and library preparation, a whole shotgun metagenome sequencing was performed on the Illumina platform. The downstream processing and bioinformatics of the samples were performed using multiple software packaged in SqueezeMeta pipeline or MG-RAST pipeline.

RESULTS

The taxonomic hit distribution across the stent samples showed that bacteria were the most common isolates (mean, 69.70%), followed by viruses (mean, 0.02%) and archaea (0.003%). The 3 major phyla identified were Firmicutes, Actinobacteria, and Proteobacteria. The prevalent organisms include Pseudomonas aeruginosa, Staphylococcus aureus, Corynebacterium accolens, Dolosigranulum pigrum, Citrobacter koserii, Staphylococcus epidermidis, E. coli, and Hemophilus influenza . The functional subsystem profiling demonstrated microbial genes associated with metabolism, cellular, and information processing. The functional subsystem categories were metabolism involving carbohydrates, amino acids, DNA and RNA, cell wall or cell capsule biogenesis, membrane transport, virulence, and defense mechanisms.

CONCLUSIONS

The present study is the first whole metagenome sequencing of the microbes isolated from the extubated lacrimal stents. The stents harbor diverse microbial communities with distinct ecosystem dynamics. Further studies on microbes-host interactions in the early postoperative period would provide valuable insights.

Bacillus licheniformis MCC 2514 genome sequencing and functional annotation for providing genetic evidence for probiotic gut adhesion properties and its applicability as a bio-preservative agent

Bacillus licheniformis is a well-known probiotic that can be found in a variety of foods. The strain Bacillus licheniformis MCC 2514 was previously characterized by our group for its bio-physiological capabilities establishing it as a promising probiotic, but information on the genetic evidence for its attributes was lacking. In the current study, whole genome analysis identified the underlying molecular determinants responsible for its probiotic potential. The circular genome of MCC 2514 was 4,230,480 bp with 46.2% GC content, 24 rRNA, and 83 tRNA genes. The pangenome analysis between B. licheniformis MCC 2514 and 12 other B. licheniformis strains revealed a pangenome of 6008 genes and core genome of 3775 genes. Genome mining revealed NRPS and bacteriocins producing gene clusters indicating its biocontrol properties. Several genes encoding carbohydrate degrading enzymes, which aid in proper food degradation in the intestine, were also observed. Stress tolerance, vitamin, and essential amino acids biosynthesis related genes were found, which are important characteristics of a probiotic strain. Additionally, vital genes responsible for gut adhesion and biofilm formation were observed in its genome. The bacterium has been shown to improve the shelf life of idli batter by preventing whey separation, CO_2, and odour production while maintaining the pH of 3.96-4.29, especially at cold temperatures. It has significantly reduced coliform contamination at both room and low temperatures, demonstrating its bio-preservative ability, which is also corroborated by the presence of the NRPS and bacteriocin gene clusters in its genome. The present study helped to understand both, the ability of B. licheniformis MCC 2514 to adapt the intestinal gut environment and its probiotic functionality for food preservation.

Effects of the Sex Steroid Hormone Estradiol on Biofilm Growth of Cystic Fibrosis Pseudomonas aeruginosa Isolates

Women with cystic fibrosis (CF) have a significantly lower life expectancy compared to men, which is indicated by an earlier impairment of lung function due to chronic colonization with biofilm formed by Pseudomonas aeruginosa. There is growing evidence that blood serum concentrations of the steroid sex hormone estradiol (E₂) correlate with the occurrence of pulmonary exacerbations in CF but also play a role in the mucoid switch of P. aeruginosa. This study aims to shed light on possible microbiological reasons for sexual dimorphism in CF by investigating the influence of E₂ on biofilm formation of P. aeruginosa CF isolates. For this purpose, 10 CF isolates of the respiratory tract derived from different CF patients have been treated with E₂ in a microtiter plate biofilm model. Biofilms have been examined by crystal violet assays, field emission scanning electron microscopy (FE-SEM), 3D laser scanning microscopy (LSM), and quorum sensing (QS) reporter assays of the supernatants taken from biofilms. This allowed us to simultaneously investigate the effects of E₂ on attached biofilm mass, biofilm ultrastructure, and QS activity. Upon E₂ treatment, six out of 10 investigated CF isolates showed an increase of attached biofilm mass, whereas biofilms from two tested non-CF laboratory strains (PAO1 and ATCC19660) did not. Moreover, FE-SEM and 3D LSM analyses of the E₂ responsive CF biofilms revealed ultrastructural remodeling of biofilm structure at different scales with increased formation of prominent biofilm spots, enhanced coverage with extracellular polymeric substance (EPS), and extended average surface roughness. QS activity measurements performed in biofilm supernatants via luminescence acyl homoserine lactone (AHL) reporter assays further showed that E₂ treatment may also modulate QS signaling, as shown in an E₂ sensitive CF isolate. Together, our results suggest the biofilm modulating effects of E₂ on various clinical CF isolates that are documented by both biomass and ultrastructural changes of biofilms. The gained new insight into the influence of steroid hormones on P. aeruginosa biofilm phenotypes might pave the way for novel future approaches in personalized medicine based on the patients’ sex and hormonal status.

Genome sequencing of turmeric provides evolutionary insights into its medicinal properties

Curcuma longa, or turmeric, is traditionally known for its immense medicinal properties and has diverse therapeutic applications. However, the absence of a reference genome sequence is a limiting factor in understanding the genomic basis of the origin of its medicinal properties. In this study, we present the draft genome sequence of C. longa, belonging to Zingiberaceae plant family, constructed using 10x Genomics linked reads and Oxford Nanopore long reads. For comprehensive gene set prediction and for insights into its gene expression, transcriptome sequencing of leaf tissue was also performed. The draft genome assembly had a size of 1.02 Gbp with ~70% repetitive sequences, and contained 50,401 coding gene sequences. The phylogenetic position of C. longa was resolved through a comprehensive genome-wide analysis including 16 other plant species. Using 5,388 orthogroups, the comparative evolutionary analysis performed across 17 species including C. longa revealed evolution in genes associated with secondary metabolism, plant phytohormones signaling, and various biotic and abiotic stress tolerance responses. These mechanisms are crucial for perennial and rhizomatous plants such as C. longa for defense and environmental stress tolerance via production of secondary metabolites, which are associated with the wide range of medicinal properties in C. longa.

Insights into Acinetobacter baumannii fatty acid synthesis 3-oxoacyl-ACP reductases

Treatments for 'superbug' infections are the focus for innovative research, as drug resistance threatens human health and medical practices globally. In particular, Acinetobacter baumannii (Ab) infections are repeatedly reported as difficult to treat due to increasing antibiotic resistance. Therefore, there is increasing need to identify novel targets in the development of different antimicrobials. Of particular interest is fatty acid synthesis, vital for the formation of phospholipids, lipopolysaccharides/lipooligosaccharides, and lipoproteins of Gram-negative envelopes. The bacterial type II fatty acid synthesis (FASII) pathway is an attractive target for the development of inhibitors and is particularly favourable due to the differences from mammalian type I fatty acid synthesis. Discrete enzymes in this pathway include two reductase enzymes: 3-oxoacyl-acyl carrier protein (ACP) reductase (FabG) and enoyl-ACP reductase (FabI). Here, we investigate annotated FabG homologs, finding a low-molecular weight 3-oxoacyl-ACP reductase, as the most likely FASII FabG candidate, and high-molecular weight 3-oxoacyl-ACP reductase (HMwFabG), showing differences in structure and coenzyme preference. To date, this is the second bacterial high-molecular weight FabG structurally characterized, following FabG4 from Mycobacterium. We show that ΔAbHMwfabG is impaired for growth in nutrient rich media and pellicle formation. We also modelled a third 3-oxoacyl-ACP reductase, which we annotated as AbSDR. Despite containing residues for catalysis and the ACP coordinating motif, biochemical analyses showed limited activity against an acetoacetyl-CoA substrate in vitro. Inhibitors designed to target FabG proteins and thus prevent fatty acid synthesis may provide a platform for use against multidrug-resistant pathogens including A. baumannii.

Computational Systems Biology of Alfalfa - Bacterial Blight Host-Pathogen Interactions: Uncovering the Complex Molecular Networks for Developing Durable Disease Resistant Crop

Medicago sativa (also known as alfalfa), a forage legume, is widely cultivated due to its high yield and high-value hay crop production. Infectious diseases are a major threat to the crops, owing to huge economic losses to the agriculture industry, worldwide. The protein-protein interactions (PPIs) between the pathogens and their hosts play a critical role in understanding the molecular basis of pathogenesis. Pseudomonas syringae pv. syringae ALF3 suppresses the plant's innate immune response by secreting type III effector proteins into the host cell, causing bacterial stem blight in alfalfa. The alfalfa-P. syringae system has little information available for PPIs. Thus, to understand the infection mechanism, we elucidated the genome-scale host-pathogen interactions (HPIs) between alfalfa and P. syringae using two computational approaches: interolog-based and domain-based method. A total of ∼14 M putative PPIs were predicted between 50,629 alfalfa proteins and 2,932 P. syringae proteins by combining these approaches. Additionally, ∼0.7 M consensus PPIs were also predicted. The functional analysis revealed that P. syringae proteins are highly involved in nucleotide binding activity (GO:0000166), intracellular organelle (GO:0043229), and translation (GO:0006412) while alfalfa proteins are involved in cellular response to chemical stimulus (GO:0070887), oxidoreductase activity (GO:0016614), and Golgi apparatus (GO:0005794). According to subcellular localization predictions, most of the pathogen proteins targeted host proteins within the cytoplasm and nucleus. In addition, we discovered a slew of new virulence effectors in the predicted HPIs. The current research describes an integrated approach for deciphering genome-scale host-pathogen PPIs between alfalfa and P. syringae, allowing the researchers to better understand the pathogen's infection mechanism and develop pathogen-resistant lines.

Pseudomonas aeruginosa core metabolism exerts a widespread growth-independent control on virulence

To assess the role of core metabolism genes in bacterial virulence - independently of their effect on growth - we correlated the genome, the transcriptome and the pathogenicity in flies and mice of 30 fully sequenced Pseudomonas strains. Gene presence correlates robustly with pathogenicity differences among all Pseudomonas species, but not among the P. aeruginosa strains. However, gene expression differences are evident between highly and lowly pathogenic P. aeruginosa strains in multiple virulence factors and a few metabolism genes. Moreover, 16.5%, a noticeable fraction of the core metabolism genes of P. aeruginosa strain PA14 (compared to 8.5% of the non-metabolic genes tested), appear necessary for full virulence when mutated. Most of these virulence-defective core metabolism mutants are compromised in at least one key virulence mechanism independently of auxotrophy. A pathway level analysis of PA14 core metabolism, uncovers beta-oxidation and the biosynthesis of amino-acids, succinate, citramalate, and chorismate to be important for full virulence. Strikingly, the relative expression among P. aeruginosa strains of genes belonging in these metabolic pathways is indicative of their pathogenicity. Thus, P. aeruginosa strain-to-strain virulence variation, remains largely obscure at the genome level, but can be dissected at the pathway level via functional transcriptomics of core metabolism.