Legionella pneumophila exploits the endo-lysosomal network for phagosome biogenesis by co-opting SUMOylated Rab7.

Legionella pneumophila strains harboring wild-type rpsL such as Lp02rpsLWT cannot replicate in mouse bone marrow-derived macrophages (BMDMs) due to induction of extensive lysosome damage and apoptosis. The bacterial factor directly responsible for inducing such cell death and the host factor involved in initiating the signaling cascade that leads to lysosome damage remain unknown. Similarly, host factors that may alleviate cell death induced by these bacterial strains have not yet been investigated. Using a genome-wide CRISPR/Cas9 screening, we identified Hmg20a and Nol9 as host factors important for restricting strain Lp02rpsLWT in BMDMs. Depletion of Hmg20a protects macrophages from infection-induced lysosomal damage and apoptosis, allowing productive bacterial replication. The restriction imposed by Hmg20a was mediated by repressing the expression of several endo-lysosomal proteins, including the small GTPase Rab7. We found that SUMOylated Rab7 is recruited to the bacterial phagosome via SulF, a Dot/Icm effector that harbors a SUMO-interacting motif (SIM). Moreover, overexpression of Rab7 rescues intracellular growth of strain Lp02rpsLWT in BMDMs. Our results establish that L. pneumophila exploits the lysosomal network for the biogenesis of its phagosome in BMDMs.

Optimizing Energy Levels and Improving Film Compactness in PbS Quantum Dot Solar Cells by Silver Doping.

PbS quantum dot (QD) solar cells harvest near-infrared solar radiation. Their conventional hole transport layer has limited hole collection efficiency due to energy level mismatch and poor film quality. Here, how to resolve these two issues by using Ag-doped PbS QDs are demonstrated. On the one hand, Ag doping relieves the compressive stress during layer deposition and thus improves film compactness and homogeneity to suppress leakage currents. On the other hand, Ag doping increases hole concentration, which aligns energy levels and increases hole mobility to boost hole collection. Increased hole concentration also broadens the depletion region of the active layer, decreasing interface charge accumulation and promoting carrier extraction efficiency. A champion power conversion efficiency of 12.42% is achieved by optimizing the hole transport layer in PbS QD solar cells, compared to 9.38% for control devices. Doping can be combined with compressive strain relief to optimize carrier concentration and energy levels in QDs, and even introduce other novel phenomena such as improved film quality.

The Relationship between physical activity, nutritional status, and sarcopenia in community- dwelling older adults with type 2 diabetes: a cross-sectional study.

AIM: This study was conducted in Urumqi, Xinjiang, to assess the prevalence of sarcopenia and to determine the relationship between physical activity, nutritional status, and sarcopenia among community-dwelling patients with type 2 diabetes mellitus. METHODS: Four hundred eight cases of older people patients with type 2 diabetes mellitus in the community in Urumqi, Xinjiang, from May to August 2022 were selected for a cross-sectional on-site survey, and general information questionnaires, clinical information surveys, physical function measurements, and criteria developed by the Asian sarcopenia working group in 2019 were selected for diagnosis of sarcopenia, and unifactorial and multifactorial binary Logistic regression were applied to analyze the influencing factors of T2DM combined with sarcopenia in patients with sarcopenia. RESULTS: Among the 408 patients, 84 (20.6%) had sarcopenia, with a prevalence of 12.6%, 32.1%, and 51.9% in those aged 60-70, 71- 80, and 81 or older respectively. The prevalence increased significantly with age. Adjusting for variables, the study found that FFM of the Left Leg (OR: 0.710, 95% CI: 0.612-0.804, P = 0.024), FFM of the Right Arm (OR: 0.710, 95% CI: 0.612-0.804, P < 0.001), Age (OR: 1.246, 95% CI: 1.031-1.505, P = 0.023), Fasting Blood Glucose (OR: 1.649, 95% CI: 1.066-2.550, P = 0.025), and Post-Prandial Blood Glucose (OR: 1.455, 95% CI: 0.999-2.118, P = 0.025) were independent associated factors. An increase in MNA score (OR: 0.398, 95% CI: 0.244-0.6500, P < 0.001), ASMI (OR: 0.000, 95% CI: 0.00-0.01, P < 0.001) walking energy expenditure (MET-min) (OR: 0.998, 95% CI: 0.996-0.999, P = 0.001) reduced the prevalence of sarcopenia. CONCLUSION: This study shows that increased age, increased skeletal muscle mass index, decreased right arm FFM, increased postprandial glucose, increased MNA scores, and increased walking energy expenditure (MET-min) were associated with type 2 diabetes with sarcopenia.

Size-selective sampler combined with an immunochromatographic assay for the rapid detection of airborne Legionella pneumophila.

Airborne biological aerosols (also called bioaerosols) are found in various environmental and occupational settings. Among these, pathogenic bioaerosols can cause diseases such as legionellosis, influenza, measles, and tuberculosis. To prevent or minimize people's exposure to these pathogenic bioaerosols in the field, a rapid detection method is required. In this study, a size-selective bioaerosol (SSB) sampler was combined with the immunochromatographic assay (ICA). The SSB sampler can collect bioaerosols on the sampling swab and the lateral flow test kit used in ICA can rapidly detect the pathogens in bioaerosols collected on the swab. Before testing the combined method, the lower limit of detection (LOD) of the lateral flow test kit was determined. Legionella pneumophila (L. pneumophila) was used as a target pathogen. The results show that at least 1.3 × 103L. pneumophila cells are required to be detected by the lateral flow test kit. To test the developed method, L. pneumophila suspension was aerosolized in the sampling chamber and collected using two SSB samplers with different sampling times (10 and 20 min). The developed method could detect aerosolized L. pneumophila and also estimate the concentrations from the lower LOD, sampling time, and formation of a positive line on a test strip. When positive results were obtained from sampling for 10 min and 20 min, concentrations of respirable L. pneumophila were estimated ≥5.2 × 104 CFUresp/m3 and ≥2.6 × 104 CFUresp/m3, respectively. The conventional sampler Andersen impactor with colony counting was also used for comparison. In all cases, the estimated concentrations obtained by the developed method were higher than those obtained by the conventional method. These findings confirm that the developed method can overcome the limitations of conventional methods and eventually benefit environmental and occupational health by providing a better method for risk assessment.

Bacterial ubiquitin ligases hijack the host deubiquitinase OTUB1 to inhibit MTORC1 signaling and promote autophagy.

Many bacterial pathogens have evolved effective strategies to interfere with the ubiquitination network to evade clearance by the innate immune system. Here, we report that OTUB1, one of the most abundant deubiquitinases (DUBs) in mammalian cells, is subjected to both canonical and noncanonical ubiquitination during Legionella pneumophila infection. The effectors SidC and SdcA catalyze OTUB1 ubiquitination at multiple lysine residues, resulting in its association with a Legionella-containing vacuole. Lysine ubiquitination by SidC and SdcA promotes interactions between OTUB1 and DEPTOR, an inhibitor of the MTORC1 pathway, thus suppressing MTORC1 signaling. The inhibition of MTORC1 leads to suppression of host protein synthesis and promotion of host macroautophagy/autophagy during L. pneumophila infection. In addition, members of the SidE family effectors (SidEs) induce phosphoribosyl (PR)-linked ubiquitination of OTUB1 at Ser16 and Ser18 and block its DUB activity. The levels of the lysine and serine ubiquitination of OTUB1 are further regulated by effectors that function to antagonize the activities of SidC, SdcA and SidEs, including Lem27, DupA, DupB, SidJ and SdjA. Our study reveals an effectors-mediated complicated mechanism in regulating the activity of a host DUB.Abbreviations: BafA1: bafilomycin A1; BMDMs: bone marrow-derived macrophages; DUB: deubiquitinase; Dot/Icm: defective for organelle trafficking/intracellular multiplication; DEPTOR: DEP domain containing MTOR interacting protein; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; L. pneumophila: Legionella pneumophila; LCV: Legionella-containing vacuole; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOI: multiplicity of infection; MTORC1: mechanistic target of rapamycin kinase complex 1; OTUB1: OTU deubiquitinase, ubiquitin aldehyde binding 1; PR-Ub: phosphoribosyl (PR)-linked ubiquitin; PTM: posttranslational modification; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SidEs: SidE family effectors; Ub: ubiquitin.

Legionella metaeffector MavL reverses ubiquitin ADP-ribosylation via a conserved arginine-specific macrodomain.

ADP-ribosylation is a reversible post-translational modification involved in various cellular activities. Removal of ADP-ribosylation requires (ADP-ribosyl)hydrolases, with macrodomain enzymes being a major family in this category. The pathogen Legionella pneumophila mediates atypical ubiquitination of host targets using the SidE effector family in a process that involves ubiquitin ADP-ribosylation on arginine 42 as an obligatory step. Here, we show that the Legionella macrodomain effector MavL regulates this pathway by reversing the arginine ADP-ribosylation, likely to minimize potential detrimental effects caused by the modified ubiquitin. We determine the crystal structure of ADP-ribose-bound MavL, providing structural insights into recognition of the ADP-ribosyl group and catalytic mechanism of its removal. Further analyses reveal DUF4804 as a class of MavL-like macrodomain enzymes whose representative members show unique selectivity for mono-ADP-ribosylated arginine residue in synthetic substrates. We find such enzymes are also present in eukaryotes, as exemplified by two previously uncharacterized (ADP-ribosyl)hydrolases in Drosophila melanogaster. Crystal structures of several proteins in this class provide insights into arginine specificity and a shared mode of ADP-ribose interaction distinct from previously characterized macrodomains. Collectively, our study reveals a new regulatory layer of SidE-catalyzed ubiquitination and expands the current understanding of macrodomain enzymes.

Ginsenoside F2-Mediated Intestinal Microbiota and Its Metabolite Propionic Acid Positively Impact the Gut-Skin Axis in Atopic Dermatitis Mice.

Atopic dermatitis (AD) is a complex inflammatory skin disease induced by multiple factors. AD can also cause intestinal inflammation and disorders of the gut microbiota. Ginseng is a kind of edible and medicinal plant; its main active components are ginsenosides. Ginsenosides have a variety of anti-inflammatory effects and regulate the gut microbiota; however, their role in AD and the underlying mechanisms are unclear. In this study, we found that intragastric administration of ginsenoside F2 improved AD-like skin symptoms and reduced inflammatory cell infiltration, serum immunoglobulin E levels, and mRNA expression of inflammatory cytokines in AD mice. 16s rRNA sequencing analysis showed that ginsenoside F2 altered the intestinal microbiota structure and enriched the short-chain fatty acid-producing microbiota in AD mice. Metabolomic analysis revealed that ginsenoside F2 significantly increased the propionic acid (Pa) content of feces and serum in AD mice, which was positively correlated with significant enrichment of Parabacteroides goldsteinii and Lactobacillus plantarum in the intestines. Pa inhibits inflammatory responses in the gut and skin of AD mice through the G-protein-coupled receptor43/NF-κB pathway, thereby improving skin AD symptoms. These results revealed, for the first time, the mechanism by which ginsenoside F2 improves AD through the Pa (a metabolite of intestinal microbiota)-gut-skin axis.

Acinetobacter nosocomialis utilizes a unique type VI secretion system to promote its survival in niches with prey bacteria.

Pathogenic bacteria of the Acinetobacter genus pose a severe threat to human health worldwide due to their strong adaptability, tolerance, and antibiotic resistance. Most isolates of these bacteria harbor a type VI secretion system (T6SS) that allows them to outcompete co-residing microorganisms, but whether this system is involved in acquiring nutrients from preys remains less studied. In this study, we found that Ab25, a clinical isolate of Acinetobacter nosocomialis, utilizes a T6SS to kill taxonomically diverse microorganisms, including bacteria and fungi. The T6SS of Ab25 is constitutively expressed, and among the three predicted effectors, T6e1, a member of the RHS effector family, contributes the most for its antimicrobial activity. T6e1 undergoes self-cleavage, and a short carboxyl fragment with nuclease activity is sufficient to kill target cells via T6SS injection. Interestingly, strain Ab25 encodes an orphan VgrG protein, which when overexpressed blocks the firing of its T6SS. In niches such as dry plastic surfaces, the T6SS promotes prey microorganism-dependent survival of Ab25. These results reveal that A. nosocomialis employs T6SSs that are highly diverse in their regulation and effector composition to gain a competitive advantage in environments with scarce nutrient supply and competing microbes.IMPORTANCEThe type VI secretion system (T6SS) plays an important role in bacterial adaptation to environmental challenges. Members of the Acinetobacter genus, particularly A. baumannii and A. nosocomialis, are notorious for their multidrug resistance and their ability to survive in harsh environments. In contrast to A. baumannii, whose T6SS has been well-studied, few research works have focused on A. nosocomialis. In this study, we found that an A. nosocomialis strain utilizes a contitutively active T6SS to kill diverse microorganisms, including bacteria and fungi. Although T6SS structural proteins of A. nosocomialis are similar to those of A. baumannii, the effector repertoire differs greatly. Interestingly, the T6SS of the A. nosocomialis strain codes for an ophan VgrG protein, which blocks the firing of the system when overexpressed, suggesting the existence of a new regulatory mechanism for the T6SS. Importantly, although the T6SS does not provide an advantage when the bacterium is grown in nutrient-rich medium, it allows A. nosocomialis to survive better in dry surfaces that contain co-existing bacteria. Our results suggest that killing of co-residing microorganisms may increase the effectiveness of strategies designed to reduce the fitness of Acinetobacter bacteria by targeting their T6SS.

The Shigella kinase effector OspG modulates host ubiquitin signaling to escape septin-cage entrapment.

Shigella flexneri is a Gram-negative bacterium causing severe bloody dysentery. Its pathogenesis is largely dictated by a plasmid-encoded type III secretion system (T3SS) and its associated effectors. Among these, the effector OspG has been shown to bind to the ubiquitin conjugation machinery (E2~Ub) to activate its kinase activity. However, the cellular targets of OspG remain elusive despite years of extensive efforts. Here we show by unbiased phosphoproteomics that a major target of OspG is CAND1, a regulatory protein controlling the assembly of cullin-RING ubiquitin ligases (CRLs). CAND1 phosphorylation weakens its interaction with cullins, which is expected to impact a large panel of CRL E3s. Indeed, global ubiquitome profiling reveals marked changes in the ubiquitination landscape when OspG is introduced. Notably, OspG promotes ubiquitination of a class of cytoskeletal proteins called septins, thereby inhibiting formation of cage-like structures encircling cytosolic bacteria. Overall, we demonstrate that pathogens have evolved an elaborate strategy to modulate host ubiquitin signaling to evade septin-cage entrapment.

Legionella maintains host cell ubiquitin homeostasis by effectors with unique catalytic mechanisms.

The intracellular bacterial pathogen Legionella pneumophila modulates host cell functions by secreting multiple effectors with diverse biochemical activities. In particular, effectors of the SidE family interfere with host protein ubiquitination in a process that involves production of phosphoribosyl ubiquitin (PR-Ub). Here, we show that effector LnaB converts PR-Ub into ADP-ribosylated ubiquitin, which is further processed to ADP-ribose and functional ubiquitin by the (ADP-ribosyl)hydrolase MavL, thus maintaining ubiquitin homeostasis in infected cells. Upon being activated by actin, LnaB also undergoes self-AMPylation on tyrosine residues. The activity of LnaB requires a motif consisting of Ser, His and Glu (SHxxxE) present in a large family of toxins from diverse bacterial pathogens. Thus, our study sheds light on the mechanisms by which a pathogen maintains ubiquitin homeostasis and identifies a family of enzymes capable of protein AMPylation.

Legionella maintains host cell ubiquitin homeostasis by effectors with unique catalytic mechanisms.

The reversal of ubiquitination induced by members of the SidE effector family of Legionella pneumophila produces phosphoribosyl ubiquitin (PR-Ub) that is potentially detrimental to host cells. Here we show that the effector LnaB functions to transfer the AMP moiety from ATP to the phosphoryl moiety of PR-Ub to convert it into ADP-ribosylated ubiquitin (ADPR-Ub), which is further processed to ADP-ribose and functional ubiquitin by the (ADP-ribosyl)hydrolase MavL, thus maintaining ubiquitin homeostasis in infected cells. Upon being activated by Actin, LnaB also undergoes self-AMPylation on tyrosine residues. The activity of LnaB requires a motif consisting of Ser, His and Glu (S-HxxxE) present in a large family of toxins from diverse bacterial pathogens. Our study not only reveals intricate mechanisms for a pathogen to maintain ubiquitin homeostasis but also identifies a new family of enzymes capable of protein AMPylation, suggesting that this posttranslational modification is widely used in signaling during host-pathogen interactions.

Ciprofloxacin enhances the biofilm formation of Staphylococcus aureus via an agrC-dependent mechanism.

Staphylococcus aureus readily forms biofilms on host tissues and medical devices, enabling its persistence in chronic infections and resistance to antibiotic therapy. The accessory gene regulator (Agr) quorum sensing system plays a key role in regulating S. aureus biofilm formation. This study reveals the widely used fluoroquinolone antibiotic, ciprofloxacin, strongly stimulates biofilm formation in methicillin-resistant S. aureus, methicillin-sensitive S. aureus, and clinical isolates with diverse genetic backgrounds. Crystal violet staining indicated that ciprofloxacin induced a remarkable 12.46- to 15.19-fold increase in biofilm biomass. Confocal laser scanning microscopy revealed that ciprofloxacin induced denser biofilms. Phenotypic assays suggest that ciprofloxacin may enhance polysaccharide intercellular adhesin production, inhibit autolysis, and reduce proteolysis during the biofilm development, thus promoting initial adhesion and enhancing biofilm stability. Mechanistically, ciprofloxacin significantly alters the expression of various biofilm-related genes (icaA, icaD, fnbA, fnbB, eap, emp) and regulators (agrA, saeR). Gene knockout experiments revealed that deletion of agrC, rather than saeRS, abolishes the ciprofloxacin-induced enhancement of biofilm formation, underscoring the key role of agrC. Thermal shift assays showed ciprofloxacin binds purified AgrC protein, thereby inhibiting the Agr system. Molecular docking results further support the potential interaction between ciprofloxacin and AgrC. In summary, subinhibitory concentrations of ciprofloxacin stimulate S. aureus biofilm formation via an agrC-dependent pathway. This inductive effect may facilitate local infection establishment and bacterial persistence, ultimately leading to therapeutic failure.

Legionella pneumophila temporally regulates the activity of ADP/ATP translocases by reversible ADP-ribosylation.

The mitochondrion is an important signaling hub that governs diverse cellular functions, including metabolism, energy production, and immunity. Among the hundreds of effectors translocated into host cells by the Dot/Icm system of Legionella pneumophila, several are targeted to mitochondria but the function of most of them remains elusive. Our recent study found that the effector Ceg3 inhibits the activity of ADP/ATP translocases (ANTs) by ADP-ribosylation (ADPR). Here, we show that the effect of Ceg3 is antagonized by Larg1, an effector encoded by lpg0081, a gene that is situated next to ceg3. Larg1 functions to reverse Ceg3-mediated ADPR of ANTs by cleaving the N-glycosidic bond between the ADPR moiety and the modified arginine residues in ANTs, leading to restoration of their activity in ADP/ATP exchange. Structural analysis of Larg1 and its complex with ADPR reveals that this ADPR glycohydrolase harbors a unique macrodomain that catalyzes the removal of ADPR modification on ANTs. Our results also demonstrate that together with Ceg3, Larg1 imposes temporal regulation of the activity of ANTs by reversible ADPR during L. pneumophila infection.