Structural and Functional Insights into PpgL, a Metal-Independent β-Propeller Gluconolactonase That Contributes to Pseudomonas aeruginosa Virulence

α-Pyrone mediates quorum sensing through the conservon system in Nocardiopsis sp

Actinobacteria produce a plethora of bioactive secondary metabolites that are often regulated by quorum-sensing signaling molecules via specific binding to their cognate TetR-type receptors. Here, we identified monocyclic α-pyrone as a new class of actinobacterial signaling molecules influencing quorum sensing process in Nocardiopsis sp. LDBS0036, primarily evidenced by a significant reduction in the production of phenazines in the pyrone-null mutant compared to the wild-type strain. Exogenous addition of the α-pyrone can partially restore the expression of some pathways to the wild strain level. Moreover, a unique multicomponent system referred to as a conservon, which is widespread in actinobacteria and generally contains four or five functionally conserved proteins, may play an important role in detecting and transmitting α-pyrone signals in LDBS0036. We found the biosynthetic gene clusters of α-pyrone and their associated conservon genes are highly conserved in Nocardiopsis, indicating the widespread prevalence and significant function of this regulate mechanism within Nocardiopsis genus. Furthermore, homologous α-pyrones from different actinobacterial species were also found to mediate interspecies communication. Our results thus provide insights into a novel quorum-sensing signaling system and imply that various modes of bacterial communication remain undiscovered.

The enzymes of the oxidative phase of the pentose phosphate pathway as targets of reactive species: consequences for NADPH production

The pentose phosphate pathway (PPP) is a key metabolic pathway. The oxidative phase of this process involves three reactions catalyzed by glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconolactonase (6PGL) and 6-phosphogluconate dehydrogenase (6PGDH) enzymes. The first and third steps (catalyzed by G6PDH and 6PGDH, respectively) are responsible for generating reduced nicotinamide adenine dinucleotide phosphate (NAPDH), a key cofactor for maintaining the reducing power of cells and detoxification of both endogenous and exogenous oxidants and electrophiles. Despite the importance of these enzymes, little attention has been paid to the fact that these proteins are targets of oxidants. In response to oxidative stimuli metabolic pathways are modulated, with the PPP often up-regulated in order to enhance or maintain the reductive capacity of cells. Under such circumstances, oxidation and inactivation of the PPP enzymes could be detrimental. Damage to the PPP enzymes may result in a downward spiral, as depending on the extent and sites of modification, these alterations may result in a loss of enzymatic activity and therefore increased oxidative damage due to NADPH depletion. In recent years, it has become evident that the three enzymes of the oxidative phase of the PPP have different susceptibilities to inactivation on exposure to different oxidants. In this review, we discuss existing knowledge on the role that these enzymes play in the metabolism of cells, and their susceptibility to oxidation and inactivation with special emphasis on NADPH production. Perspectives on achieving a better understanding of the molecular basis of the oxidation these enzymes within cellular environments are given.

Peroxyl radicals modify 6-phosphogluconolactonase from Escherichia coli via oxidation of specific amino acids and aggregation which inhibits enzyme activity

6-phosphogluconolactonase (6PGL) catalyzes the second reaction of the pentose phosphate pathway (PPP) converting 6-phosphogluconolactone to 6-phosphogluconate. The PPP is critical to the generation of NADPH and metabolic intermediates, but some of its components are susceptible to oxidative inactivation. Previous studies have characterized damage to the first (glucose-6-phosphate dehydrogenase) and third (6-phosphogluconate dehydrogenase) enzymes of the pathway, but no data are available for 6PGL. This knowledge gap is addressed here. Oxidation of Escherichia coli 6PGL by peroxyl radicals (ROO^•, from AAPH (2,2'-azobis(2-methylpropionamidine) dihydrochloride) was examined using SDS-PAGE, amino acid consumption, liquid chromatography with mass detection (LC-MS), protein carbonyl formation and computational methods. NADPH generation was assessed using mixtures all three enzymes of the oxidative phase of the PPP. Incubation of 6PGL with 10 or 100 mM AAPH resulted in protein aggregation mostly due to reducible (disulfide) bonds. High fluxes of ROO^• induced consumption of Cys, Met and Trp, with the Cys oxidation rationalizing the aggregate formation. Low levels of carbonyls were detected, while LC-MS analyses provided evidence for oxidation of selected Trp and Met residues (Met1, Trp18, Met41, Trp203, Met220 and Met221). ROO^• elicited little loss of enzymatic activity of monomeric 6PGL, but the aggregates showed diminished NADPH generation. This is consistent with in silico analyses that indicate that the modified Trp and Met are far from the 6-phosphogluconolactone binding site and the catalytic dyad (His130 and Arg179). Together these data indicate that monomeric 6PGL is a robust enzyme towards oxidative inactivation by ROO^• and when compared to other PPP enzymes.

Prevalence of algD, pslD, pelF, Ppgl, and PAPI-1 Genes Involved in Biofilm Formation in Clinical Pseudomonas aeruginosa Strains

Introduction

Biofilm formation is one of the main virulence factors in Pseudomonas aeruginosa infections. This study is aimed at investigating the presence of genes involved in biofilm formation in clinical P. aeruginosa isolates. Material and Methods. A cross-sectional study was conducted on 112 P. aeruginosa isolates. The biofilm formation assay was performed on all isolates. Antimicrobial resistance was determined by the disk diffusion method, and the presence of genes was detected by polymerase chain reaction. Isolates were typed with Rep-PCR.

Results

The results of biofilm formation demonstrated that 85 strains (75.9%) were biofilm producers, and 27 strains (24.1%) were nonproducer isolates. Antibiotic susceptibility pattern in biofilm-positive and biofilm-negative isolates obtained from hospitalized patients showed a high rate of antibiotic resistance to amoxicillin with 95.7% and 92.3%, respectively. Based on PCR amplification results, the frequency of genes involved in biofilm formation among all isolates was as follows: algD (78.6%), pelF (70.5%), pslD (36.6%), Ppgl (0%), and PAPI-1 (77.6%). Rep-PCR typing demonstrated that 112 P. aeruginosa isolates were classified into 57 types according to 70% cut-off. The predominant type was A which contained 15 isolates. Moreover, 7 isolates were clustered in genotype B, followed by C type (6), D (4), E (4), F (4), G (4), H (3), I (3), J (3 isolates), and 12 genotypes, each containing two isolates. Also, 35 isolates were distributed in scattered patterns and showed single types.

Conclusion

Study results showed significant association between biofilm formation and resistance to antibiotics such as ceftazidime and meropenem. Analysis of Rep-PCR patterns indicated that the evaluated isolates were heterogeneous, relatively.

Type II Antitoxin HigA Is a Key Virulence Regulator in Pseudomonas aeruginosa

Bacterial type II toxin-antitoxin (TA) systems are abundant genetic elements and are involved in a diverse array of physiological processes. These systems encode an antitoxin protein that directly binds and effectively neutralizes the protein toxin. Recent studies have highlighted the key roles of type II TA modules in bacterial virulence and pathogenesis, but the underlying mechanisms remain unclear. Here, we investigated the antitoxin HigA in Pseudomonas aeruginosa infection. Proteomic analysis of the higA deletion strain revealed an enhanced expression of pathogenic proteins. We further verified that HigA negatively controlled T3SS and T6SS expression by directly interacting with the promoter regions of the regulators amrZ and exsA, respectively. In other words, the reversal of HigA-mediated transcriptional inhibition on stress stimulation could induce virulence genes. These findings confirm the crucial roles of the type II antitoxin in bacterial infection, which highlights the potential of the HigBA TA system as an antibacterial treatment target.