Molecular characterization of LhpR in control of hydroxyproline catabolism and transport in Pseudomonas aeruginosa PAO1

Characterization and Diversification of AraC/XylS Family Regulators Guided by Transposon Sequencing

In this study, we explored the development of engineered inducible systems. Publicly available data from previous transposon sequencing assays were used to identify regulators of metabolism in Pseudomonas putida KT2440. For AraC family regulators (AFRs) represented in these data, we posited AFR/promoter/inducer groupings. Twelve promoters were characterized for a response to their proposed inducers in P. putida, and the resultant data were used to create and test nine two-plasmid sensor systems in Escherichia coli. Several of these were further developed into a palette of single-plasmid inducible systems. From these experiments, we observed an unreported inducer response from a previously characterized AFR, demonstrated that the addition of a P. putida transporter improved the sensor dynamics of an AFR in E. coli, and identified an uncharacterized AFR with a novel potential inducer specificity. Finally, targeted mutations in an AFR, informed by structural predictions, enabled the further diversification of these inducible plasmids.

Anaerobic Hydroxyproline Degradation Involving C-N Cleavage by a Glycyl Radical Enzyme

Hydroxyprolines are highly abundant in nature as they are components of many structural proteins and osmolytes. Anaerobic degradation of trans-4-hydroxy-l-proline (t4L-HP) was previously found to involve the glycyl radical enzyme (GRE) t4L-HP dehydratase (HypD). Here, we report a pathway for anaerobic hydroxyproline degradation that involves a new GRE, trans-4-hydroxy-d-proline (t4D-HP) C-N-lyase (HplG). In this pathway, cis-4-hydroxy-l-proline (c4L-HP) is first isomerized to t4D-HP, followed by radical-mediated ring opening by HplG to give 2-amino-4-ketopentanoate (AKP), the first example of a ring opening reaction catalyzed by a GRE 1,2-eliminase. Subsequent cleavage by AKP thiolase (OrtAB) yields acetyl-CoA and d-alanine. We report a crystal structure of HplG in complex with t4D-HP at a resolution of 2.7 Å, providing insights into its catalytic mechanism. Different from HypD commonly identified in proline-reducing Clostridia, HplG is present in other types of fermenting bacteria, including propionate-producing bacteria, underscoring the diversity of enzymatic radical chemistry in the anaerobic microbiome.

Antibacterial mechanism of the Asp-Asp-Asp-Tyr peptide

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DDDY affects P. aeruginosa membrane transport and amino acid metabolism.

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DDDY has a stronger effect on POPE than on POPC or POPG membranes.

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DDDY creates a membrane gap by binding the phospholipid head and hydrophobic tail.

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DDDY inhibits the growth of food microorganisms inoculated onto chestnut kernels.

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DDDY is a promising antibacterial for multidrug-resistant gram-negative bacteria.

Previously, we found that ASP-ASP-ASP-TYR (DDDY) from Dendrobium aphyllum has a minimum inhibitory concentration of 36.15 mg/mL against Pseudomonas aeruginosa. Here, we explored the antibacterial mechanism of DDDY and its potential preservation applications. Metabolomic and transcriptomic analyses revealed that DDDY mainly affects genes involved in P. aeruginosa membrane transport and amino acid metabolism pathways. Molecular dynamics simulation revealed that DDDY had a stronger effect on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine phospholipid membranes than on 1-palmitoyl-2-oleoyl-lecithin or 1-palmitoyl-2-oleoyl phosphatidylglycerol membranes, with high DDDY concentrations displaying stronger efficacy on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine. Mechanistically, the N-terminal of DDDY first bound to the phospholipid head group, while its C-terminal amino acid residue bound the hydrophobic tail, thereby creating a gap in the membrane when the phospholipids were clustered by hydrogen bonding. Finally, DDDY inhibited the growth of food microorganisms inoculated onto chestnut kernels, suggesting that DDDY is a promising antibacterial agent against multidrug-resistant gram-negative bacteria.

Phylogenetic Analysis with Prediction of Cofactor or Ligand Binding for Pseudomonas aeruginosa PAS and Cache Domains

PAS domains are omnipresent building blocks of multidomain proteins in all domains of life. Bacteria possess a variety of PAS domains in intracellular proteins and the related Cache domains in periplasmic or extracellular proteins. PAS and Cache domains are predominant in sensory systems, often carry cofactors or bind ligands, and serve as dimerization domains in protein association. To aid our understanding of the wide distribution of these domains, we analyzed the proteome of the opportunistic human pathogen Pseudomonas aeruginosa PAO1 in silico. The ability of this bacterium to survive under different environmental conditions, to switch between planktonic and sessile/biofilm lifestyle, or to evade stresses, notably involves c-di-GMP regulatory proteins or depends on sensory pathways involving multidomain proteins that possess PAS or Cache domains. Maximum likelihood phylogeny was used to group PAS and Cache domains on the basis of amino acid sequence. Conservation of cofactor- or ligand-coordinating amino acids aided by structure-based comparison was used to inform function. The resulting classification presented here includes PAS domains that are candidate binders of carboxylic acids, amino acids, fatty acids, flavin adenine dinucleotide (FAD), 4-hydroxycinnamic acid, and heme. These predictions are put in context to previously described phenotypic data, often generated from deletion mutants. The analysis predicts novel functions for sensory proteins and sheds light on functional diversification in a large set of proteins with similar architecture. IMPORTANCE To adjust to a variety of life conditions, bacteria typically use multidomain proteins, where the modular structure allows functional differentiation. Proteins responding to environmental cues and regulating physiological responses are found in chemotaxis pathways that respond to a wide range of stimuli to affect movement. Environmental cues also regulate intracellular levels of cyclic-di-GMP, a universal bacterial secondary messenger that is a key determinant of bacterial lifestyle and virulence. We study Pseudomonas aeruginosa, an organism known to colonize a broad range of environments that can switch lifestyle between the sessile biofilm and the planktonic swimming form. We have investigated the PAS and Cache domains, of which we identified 101 in 70 Pseudomonas aeruginosa PAO1 proteins, and have grouped these by phylogeny with domains of known structure. The resulting data set integrates sequence analysis and structure prediction to infer ligand or cofactor binding. With this data set, functional predictions for PAS and Cache domain-containing proteins are made.

NtrBC Selectively Regulates Host-Pathogen Interactions, Virulence, and Ciprofloxacin Susceptibility of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a metabolically versatile opportunistic pathogen capable of infecting distinct niches of the human body, including skin wounds and the lungs of cystic fibrosis patients. Eradication of P. aeruginosa infection is becoming increasingly difficult due to the numerous resistance mechanisms it employs. Adaptive resistance is characterized by a transient state of decreased susceptibility to antibiotic therapy that is distinct from acquired or intrinsic resistance, can be triggered by various environmental stimuli and reverted by removal of the stimulus. Further, adaptive resistance is intrinsically linked to lifestyles such as swarming motility and biofilm formation, both of which are important in infections and lead to multi-drug adaptive resistance. Here, we demonstrated that NtrBC, the master of nitrogen control, had a selective role in host colonization and a substantial role in determining intrinsic resistance to ciprofloxacin. P. aeruginosa mutant strains (ΔntrB, ΔntrC and ΔntrBC) colonized the skin but not the respiratory tract of mice as well as WT and, unlike WT, could be reduced or eradicated from the skin by ciprofloxacin. We hypothesized that nutrient availability contributed to these phenomena and found that susceptibility to ciprofloxacin was impacted by nitrogen source in laboratory media. P. aeruginosa ΔntrB, ΔntrC and ΔntrBC also exhibited distinct host interactions, including modestly increased cytotoxicity toward human bronchial epithelial cells, reduced virulence factor production and 10-fold increased uptake by macrophages. These data might explain why NtrBC mutants were less adept at colonizing the upper respiratory tract of mice. Thus, NtrBC represents a link between nitrogen metabolism, adaptation and virulence of the pathogen P. aeruginosa, and could represent a target for eradication of recalcitrant infections in situ.

New markers for sepsis caused by Pseudomonas aeruginosa during burn infection

INTRODUCTION

Sepsis is a leading cause of mortality in burn patients. One of the major causes of sepsis in burn patients is Pseudomonas aeruginosa. We hypothesized that during dissemination from infected burn wounds and subsequent sepsis, P. aeruginosa affects the metabolome of the blood resulting in changes to specific metabolites that would serve as biomarkers for early diagnosis of sepsis caused by P. aeruginosa.

OBJECTIVES

To identify specific biomarkers in the blood after sepsis caused by P. aeruginosa infection of burns.

METHODS

Gas chromatography with time-of-flight mass spectrometry was used to compare the serum metabolome of mice that were thermally injured and infected with P. aeruginosa (B-I) to that of mice that were neither injured nor infected, mice that were injured but not infected, and mice that were infected but not injured.

RESULTS

Serum levels of 19 metabolites were significantly increased in the B-I group compared to controls while levels of eight metabolites were significantly decreased. Thymidine, thymine, uridine, and uracil (related to pyrimidine metabolism), malate and succinate (a possible sign of imbalance in the tricarboxylic acid cycle), 5-oxoproline (related to glutamine and glutathione metabolism), and trans-4-hydroxyproline (a major component of the protein collagen) were increased. Products of amino acid metabolism were significantly decreased in the B-I group, including methionine, tyrosine, indole-3-acetate, and indole-3-propionate.

CONCLUSION

In all, 26 metabolites were identified, including a unique combination of five metabolites (trans-4-hydroxyproline, 5-oxoproline, glycerol-3-galactoside, indole-3-acetate, and indole-3-propionate) that could serve as a set of biomarkers for early diagnosis of sepsis caused by P. aeruginosa in burn patients.

A GntR-Like Transcription Factor HypR Regulates Expression of Genes Associated With L-Hydroxyproline Utilization in Streptomyces coelicolor A3(2)

Bacteria from the genus Streptomyces have been long exploited as the most prolific producers of antibiotics, other secondary metabolites and enzymes. They are important members of soil microbial communities that can adapt to changing conditions thank to the fine regulation of gene expression in response to environmental signals. Streptomyces coelicolor A3(2) is a model organism for molecular studies with the most deeply recognized interactions within the complex metabolic and regulatory network. However, details about molecular signals recognized by specialized regulatory proteins as well as their direct targets are often missing. We describe here a zinc-binding protein HypR (SCO6294) which belongs to FadR subfamily of GntR-like regulators. The DNA sequence 5'-TACAATGTCAC-3' recognized by the HypR protein in its own promoter region was identified by DNase I footprinting. Binding of six DNA fragments containing similar sequences located in other promoter regions were confirmed by the electrophoretic mobility shift assay (EMSA). The sequences of 7 in vitro-determined binding sites were assembled to generate a logo of the HypR binding motif, 5'-CTNTGC(A/C)ATGTCAC-3'. Comparison of luciferase reporter genes expression under the control of cloned promoter regions in S. coelicolor A3(2) wild type and deletion mutant strains revealed, that the HypR protein acts as a repressor of its target genes. Genes belonging to the regulon of HypR code for enzymes putatively involved in collagen degradation and utilization of L-hydroxyproline (L-Hyp) as concluded from predicted structure and conserved domains. Their transcription is induced in the wild type strain by the addition of L-Hyp to the culture medium. Moreover, knockout of one of the genes from the predicted L-Hyp utilization operon abolished the ability of the strain to grow on L-Hyp as a sole source of carbon. To our knowledge, this work is the first indication of the existence of the pathway of L-hydroxyproline catabolism in Streptomycetes.

Transcriptome Analysis of Pseudomonas aeruginosa Cultured in Human Burn Wound Exudates

Pseudomonas aeruginosa is a severe opportunistic pathogen and is one of the major causes of hard to treat burn wound infections. Herein we have used an RNA-seq transcriptomic approach to study the behavior of P. aeruginosa PAO1 growing directly on human burn wound exudate. A chemical analysis of compounds used by this bacterium, coupled with kinetics expression of central genes has allowed us to obtain a global view of P. aeruginosa physiological and metabolic changes occurring while growing on human burn wound exudate. In addition to the numerous virulence factors and their secretion systems, we have found that all iron acquisition mechanisms were overexpressed. Deletion and complementation with pyoverdine demonstrated that iron availability was a major limiting factor in burn wound exudate. The quorum sensing systems, known to be important for the virulence of P. aeruginosa, although moderately induced, were activated even at low cell density. Analysis of bacterial metabolism emphasized importance of lactate, lipid and collagen degradation pathways. Overall, this work allowed to designate, for the first time, a global view of P. aeruginosa characteristics while growing in human burn wound exudate and highlight the possible therapeutic approaches to combat P. aeruginosa burn wound infections.

Molecular characterization and regulation of operons for asparagine and aspartate uptake and utilization in Pseudomonas aeruginosa

Pseudomonas aeruginosa can utilize proteogenic amino acids as the sole source of carbon and nitrogen. In particular, utilization of l-Asp and l-Asn is insensitive to carbon catabolite repression as strong growth remains in the mutants devoid of the essential CbrAB activators of most catabolic genes. Transcriptome analysis was conducted to identify genes for the catabolism, uptake and regulation of these two amino acids. Gene inactivation and growth phenotype analysis established two asparaginases AsnA and AsnB for the degradation of l-Asn to l-Asp, whereas only AnsB is required for the deamidation of d-Asn to d-Asp. While d-Asp is a dead-end product, conversion of l-Asp to fumarate is catalysed by an aspartase AspA as further evidenced by enzyme kinetics. The results of measuring promoter-lacZ expression in vivo and mobility shift assays in vitro demonstrated that asnR and aspR encode two transcriptional regulators in response to l-Asn and l-Asp, respectively, for the induction of the ansPA operon and the aspA gene. Exogenous l-Glu also caused induction of the aspA gene, most likely due to its conversion to l-Asp by the aspartate transaminase AspC. Expression of several transporters were found inducible by l-Asn and/or l-Asp, including AatJQMP for acid amino acids, DctA and DctPQM for C4-dicarboxylates, and PA5530 for C5-dicarboxylates. In summary, a complete pathway and regulation for l-Asn and l-Asp catabolism was established in this study. Cross induction of three transport systems for dicarboxylic acids may provide a physiological explanation for the insensitivity of l-Asn and l-Asp utilization to carbon catabolite repression.

Characterization of a Novel cis-3-Hydroxy-l-Proline Dehydratase and a trans-3-Hydroxy-l-Proline Dehydratase from Bacteria

Hydroxyprolines, such as trans-4-hydroxy-l-proline (T4LHyp), trans-3-hydroxy-l-proline (T3LHyp), and cis-3-hydroxy-l-proline (C3LHyp), are present in some proteins including collagen, plant cell wall, and several peptide antibiotics. In bacteria, genes involved in the degradation of hydroxyproline are often clustered on the genome (l-Hyp gene cluster). We recently reported that an aconitase X (AcnX)-like hypI gene from an l-Hyp gene cluster functions as a monomeric C3LHyp dehydratase (AcnX_{Type I}). However, the physiological role of C3LHyp dehydratase remained unclear. We here demonstrate that Azospirillum brasilense NBRC 102289, an aerobic nitrogen-fixing bacterium, robustly grows using not only T4LHyp and T3LHyp but also C3LHyp as the sole carbon source. The small and large subunits of the hypI gene (hypI_S and hypI_L, respectively) from A. brasilense NBRC 102289 are located separately from the l-Hyp gene cluster and encode a C3LHyp dehydratase with a novel heterodimeric structure (AcnX_{Type IIa}). A strain disrupted in the hypI_S gene did not grow on C3LHyp, suggesting its involvement in C3LHyp metabolism. Furthermore, C3LHyp induced transcription of not only the hypI genes but also the hypK gene encoding Δ¹-pyrroline-2-carboxylate reductase, which is involved in T3LHyp, d-proline, and d-lysine metabolism. On the other hand, the l-Hyp gene cluster of some other bacteria contained not only the AcnX_{Type IIa} gene but also two putative proline racemase-like genes (hypA1 and hypA2). Despite having the same active sites (a pair of Cys/Cys) as hydroxyproline 2-epimerase, which is involved in the metabolism of T4LHyp, the dominant reaction by HypA2 was clearly the dehydration of T3LHyp, a novel type of T3LHyp dehydratase that differed from the known enzyme (Cys/Thr).IMPORTANCE More than 50 years after the discovery of trans-4-hydroxy-l-proline (generally called l-hydroxyproline) degradation in aerobic bacteria, its genetic and molecular information has only recently been elucidated. l-Hydroxyproline metabolic genes are often clustered on bacterial genomes. These loci frequently contain a hypothetical gene(s), whose novel enzyme functions are related to the metabolism of trans-3-hydroxyl-proline and/or cis-3-hydroxyl-proline, a relatively rare l-hydroxyproline in nature. Several l-hydroxyproline metabolic enzymes show no sequential similarities, suggesting their emergence by convergent evolution. Furthermore, transcriptional regulation by trans-4-hydroxy-l-proline, trans-3-hydroxy-l-proline, and/or cis-3-hydroxy-l-proline significantly differs between bacteria. The results of the present study show that several l-hydroxyprolines are available for bacteria as carbon and energy sources and may contribute to the discovery of potential metabolic pathways of another hydroxyproline(s).

Functional characterization of aconitase X as a cis-3-hydroxy-L-proline dehydratase

In the aconitase superfamily, which includes the archetypical aconitase, homoaconitase, and isopropylmalate isomerase, only aconitase X is not functionally annotated. The corresponding gene (LhpI) was often located within the bacterial gene cluster involved in L-hydroxyproline metabolism. Screening of a library of (hydroxy)proline analogues revealed that this protein catalyzes the dehydration of cis-3-hydroxy-L-proline to Δ¹-pyrroline-2-carboxylate. Furthermore, electron paramagnetic resonance and site-directed mutagenic analyses suggests the presence of a mononuclear Fe(III) center, which may be coordinated with one glutamate and two cysteine residues. These properties were significantly different from those of other aconitase members, which catalyze the isomerization of α- to β-hydroxy acids, and have a [4Fe-4S] cluster-binding site composed of three cysteine residues. Bacteria with the LhpI gene could degrade cis-3-hydroxy-L-proline as the sole carbon source, and LhpI transcription was up-regulated not only by cis-3-hydroxy-L-proline, but also by several isomeric 3- and 4-hydroxyprolines.