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Acinetobacter baumannii is a multidrug-resistant pathogen that has become one of the most challenging pathogens in global healthcare. Several antibiotic-resistant genes, including catB8, have been identified in the A. baumannii genome. CatB8 protein, one of the chloramphenicol acetyltransferases (Cats), is encoded by the catB8 gene. Cats can convert chloramphenicol (chl) to 3-acetyl-chl, leading to bacterial resistance to chl. Here, we present the high-resolution cocrystal structure of CatB8 with chl. The structure that we resolved showed that each monomer of CatB8 binds to four chl molecules, while its homologous protein only binds to one chl molecule. One of the newly discovered chl binding site overlaps with the site of another substrate, acetyl-CoA. Through structure-based biochemical analyses, we identified key residues for chl recruiting and acetylation of chl in CatB8. Our work is of significant importance for understanding the drug resistance of A. baumannii and the effectiveness of antibiotic treatment.

Acinetobacter baumannii (A. baumannii) has become a notorious pathogen causing nosocomial and community-acquired infections, especially ventilator-associated pneumonia. This opportunistic pathogen is found to possess powerful genomic plasticity and numerous virulence factors that facilitate its success in the infectious process. Although the interactions between A. baumannii and the pulmonary epitheliums have been extensively studied, a complete and specific description of its overall pathogenic process is lacking. In this review, we summarize the current knowledge of the antibiotic resistance and virulence factors of A. baumannii, specifically focusing on the pathogenic mechanisms of this detrimental pathogen in respiratory infectious diseases. An expansion of the knowledge regarding A. baumannii pathogenesis will contribute to the development of effective therapies based on immunopathology or intracellular signaling pathways to eliminate this harmful pathogen during infections.

Toll-like and interleukin-1/18 receptor/resistance (TIR) domain-containing proteins function as important signaling and immune regulatory molecules. TIR domain-containing proteins identified in eukaryotic and prokaryotic species also exhibit NAD+ hydrolase activity in select bacteria, plants, and mammalian cells. We report the crystal structure of the Acinetobacter baumannii TIR domain protein (AbTir-TIR) with confirmed NAD+ hydrolysis and map the conformational effects of its interaction with NAD+ using hydrogen-deuterium exchange-mass spectrometry. NAD+ results in mild decreases in deuterium uptake at the dimeric interface. In addition, AbTir-TIR exhibits EX1 kinetics indicative of large cooperative conformational changes, which are slowed down upon substrate binding. Additionally, we have developed label-free imaging using the minimally invasive spectroscopic method 2-photon excitation with fluorescence lifetime imaging, which shows differences in bacteria expressing native and mutant NAD+ hydrolase-inactivated AbTir-TIRE208A protein. Our observations are consistent with substrate-induced conformational changes reported in other TIR model systems with NAD+ hydrolase activity. These studies provide further insight into bacterial TIR protein mechanisms and their varying roles in biology.

Salmonella enterica is a diverse species of bacterial pathogens comprised of >2,500 serovars with variable host ranges and virulence properties. Accumulating evidence indicates that two AB5-type toxins, typhoid toxin and ArtAB toxin, contribute to the more severe virulence properties of the Salmonella strains that encode them. It was recently discovered that there are two distinct types of artAB-like genetic elements in Salmonella: those that encode ArtAB toxins (artAB elements) and those in which the artA gene is degraded and the ArtB homolog, dubbed PltC, serves as an alternative delivery subunit for typhoid toxin (pltC elements). Here, we take a multifaceted approach to explore the evolutionary diversification of artAB-like genetic elements in Salmonella. We identify 7 subtypes of ArtAB toxins and 4 different PltC sequence groups that are distributed throughout the Salmonella genus. Both artAB and pltC are encoded within numerous diverse prophages, indicating a central role for phages in their evolutionary diversification. Genetic and structural analyses revealed features that distinguish pltC elements from artAB and identified evolutionary adaptations that enable PltC to efficiently engage typhoid toxin A subunits. For both pltC and artAB, we find that the sequences of the B subunits are especially variable, particularly amongst amino acid residues that fine tune the chemical environment of their glycan binding pockets. This study provides a framework to delineate the remarkably complex collection of Salmonella artAB/pltC-like genetic elements and provides a window into the mechanisms of evolution for AB5-type toxins.

Antimicrobial resistance (AMR) seriously threatens public health by reducing antibiotic effectiveness in curing bacterial infections. Atmospheric particulate matter (APM) is a common environmental hazard that affects human health by causing various diseases and disseminating bacterial pathogenesis, of which pathogenic bacteria and AMR are essential parts. The properties of APM microbiomes and resistomes, along with their shaping factors and mutual relationships, need further examination. To address this, we analyzed APMs collected from 13 cities within four clusters (North and South China, Inner Mongolia, and Tibet). Significant regionalization was found for both the microbiomes (P < 0.001) and core resistomes (P < 0.001) for APMs, with statistical analyses showing significant differences in different regions. Principal coordinate analysis (PCoA) and accompanying ANOSIM analyses showed that microbiomes and core resistomes followed the same regional subclustering hierarchy patterns. This finding, together with response analysis of APM microbiomes and core resistomes to environmental parameters that showed similar response patterns, as well as Procrustes analysis (M2 = 0.963, P < 0.05) between APM microbiomes and core resistomes, strongly suggested that APM microbiomes and core resistomes are correlated. Co-occurrence network analysis further revealed key taxa and antimicrobial resistance determinants in the interactions between APM microbiomes and core resistomes. Thus, it was concluded that APM microbiome and resistome compositions were highly regional, that environmental pollutants and APM levels impacted APM microbiomes and resistomes, and that microbiomes and resistomes in APMs are significantly correlated (P < 0.05). IMPORTANCE Bacteria associated with atmospheric particulate matter (APMs) can transmit over long distances. A large portion of these bacteria can potentially threaten human health. The antimicrobial resistance (AMR) of pathogenic bacteria carried by APMs prevents curing from infections. Therefore, both the pathogenic bacteria in APMs and their AMR are receiving more attention. The literature suggests a knowledge gap that exists for bacterial AMR and bacterial pathogenesis in APMs, including their distribution patterns, mutual relationships, and factors influencing their compositions. This work aimed to bridge this knowledge gap by studying APM samples collected from 13 cities. The results demonstrated that both bacteria and antibiotic resistance determinants were highly regional and that their composition patterns were significantly correlated, and influenced by the same group of environmental factors. This study thus determined the relationship between the two important aspects of bacterial pathogenesis in APMs and represents significant progress in understanding bacterial pathogenesis in APMs.

Cigarette smoking is a major risk factor for colorectal cancer (CRC). We aimed to investigate whether cigarette smoke promotes CRC by altering the gut microbiota and related metabolites.
Azoxymethane-treated C57BL/6 mice were exposed to cigarette smoke or clean air 2 hours per day for 28 weeks. Shotgun metagenomic sequencing and liquid chromatography mass spectrometry were parallelly performed on mice stools to investigate alterations in microbiota and metabolites. Germ-free mice were transplanted with stools from smoke-exposed and smoke-free control mice.
Mice exposed to cigarette smoke had significantly increased tumour incidence and cellular proliferation compared with smoke-free control mice. Gut microbial dysbiosis was observed in smoke-exposed mice with significant differential abundance of bacterial species including the enrichment of Eggerthella lenta and depletion of Parabacteroides distasonis and Lactobacillus spp. Metabolomic analysis showed increased bile acid metabolites, especially taurodeoxycholic acid (TDCA) in the colon of smoke-exposed mice. We found that E. lenta had the most positive correlation with TDCA in smoke-exposed mice. Moreover, smoke-exposed mice manifested enhanced oncogenic MAPK/ERK (mitogen-activated protein kinase/extracellular signal‑regulated protein kinase 1/2) signalling (a downstream target of TDCA) and impaired gut barrier function. Furthermore, germ-free mice transplanted with stools from smoke-exposed mice (GF-AOMS) had increased colonocyte proliferation. Similarly, GF-AOMS showed increased abundances of gut E. lenta and TDCA, activated MAPK/ERK pathway and impaired gut barrier in colonic epithelium.
The gut microbiota dysbiosis induced by cigarette smoke plays a protumourigenic role in CRC. The smoke-induced gut microbiota dysbiosis altered gut metabolites and impaired gut barrier function, which could activate oncogenic MAPK/ERK signalling in colonic epithelium.

In Xanthomonas spp., the biosynthesis of the yellow pigment xanthomonadin and fatty acids originates in the type II polyketide synthase (PKS II) and fatty acid synthase (FAS) pathways, respectively. The acyl carrier protein (ACP) is the central component of PKS II and FAS and requires posttranslational phosphopantetheinylation to initiate these pathways. In this study, for the first time, we demonstrate that the posttranslational modification of ACPs in X. campestris pv. campestris is performed by an essential 4\'-phosphopantetheinyl transferase (PPTase), XcHetI (encoded by Xc_4132). X. campestris pv. campestris strain XchetI could not be deleted from the X. campestris pv. campestris genome unless another PPTase-encoding gene such as Escherichia coli acpS or Pseudomonas aeruginosa pcpS was present. Compared with wild-type strain X. campestris pv. campestris 8004 and mutant XchetI::PapcpS, strain XchetI::EcacpS failed to generate xanthomonadin pigments and displayed reduced pathogenicity for the host plant, Brassica oleracea. Further experiments showed that the expression of XchetI restored the growth of E. coli acpS mutant HT253 and, when a plasmid bearing XchetI was introduced into P. aeruginosa, pcpS, which encodes the sole PPTase in P. aeruginosa, could be deleted. In in vitro enzymatic assays, XcHetI catalyzed the transformation of 4\'-phosphopantetheine from coenzyme A to two X. campestris pv. campestris apo-acyl carrier proteins, XcAcpP and XcAcpC. All of these findings indicate that XcHetI is a surfactin PPTase-like PPTase with a broad substrate preference. Moreover, the HetI-like PPTase is ubiquitously conserved in Xanthomonas spp., making it a potential new drug target for the prevention of plant diseases caused by Xanthomonas.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Phytopathogens like Pseudomonas syringae induce \"water soaking\" in the apoplastic space of plant leaf tissue as a key virulence mechanism. Water soaking is commonly observed in diverse pathosystems, yet the underlying physiological basis remains largely elusive. Here, we show that one of the strong P. syringae water-soaking inducers, AvrE, alters the regulation of abscisic acid (ABA) to induce ABA signaling, stomatal closure, and, thus, water soaking. AvrE binds and inhibits the function of Arabidopsis type one protein phosphatases (TOPPs), which negatively regulate ABA by suppressing SnRK2s, a key node of the ABA signaling pathway. The topp12537 quintuple mutants display significantly enhanced water soaking after P. syringae inoculation, whereas the loss of the ABA pathway dampens P. syringae-induced water soaking and disease. Our study uncovers the hijacking of ABA signaling and stomatal closure by P. syringae effectors as key mechanisms of disease susceptibility.

The East Asian region, including China, Japan and Korea, accounts for half of gastric cancer deaths. However, different areas have contrasting gastric cancer incidences and the population structure of Helicobacter pylori in this ethnically diverse region is yet unknown. We aimed to investigate genomic differences in H. pylori between these areas to identify sequence polymorphisms associated with increased cancer risk. We analysed 381 H. pylori genomes collected from different areas of the three countries using phylogenetic and population genetic tools to characterize population differentiation. The functional consequences of SNPs with a highest fixation index (Fst) between subpopulations were examined by mapping amino acid changes on 3D protein structure, solved or modelled. Overall, 329/381 genomes belonged to the previously identified hspEAsia population indicating that import of bacteria from other regions of the world has been uncommon. Seven subregional clusters were found within hspEAsia, related to subpopulations with various ethnicities, geographies and gastric cancer risks. Subpopulation-specific amino acid changes were found in multidrug exporters (hefC), transporters (frpB-4), outer membrane proteins (hopI) and several genes involved in host interaction, such as a catalase site, involved in H2O2 entrance, and a flagellin site mimicking host glycosylation. Several of the top hits, including frpB-4, hefC, alpB/hopB and hofC, have been found to be differentiated within the Americas in previous studies, indicating that a handful of genes may be key to local geographic adaptation. H. pylori within East Asia are not homogeneous but have become differentiated geographically at multiple loci that might have facilitated adaptation to local conditions and hosts. This has important implications for further evaluation of these changes in relation to the varying gastric cancer incidence between geographical areas in this region.