Hfe Permease and Haemophilus influenzae Manganese Homeostasis

Haemophilus influenzae is a commensal of the human upper respiratory tract that can infect diverse host niches due, at least in part, to its ability to withstand both endogenous and host-mediated oxidative stresses. Here, we show that hfeA, a gene previously linked to iron import, is essential for H. influenzae manganese recruitment via the HfeBCD transporter. Structural analyses show that metal binding in HfeA uses a unique mechanism that involves substantial rotation of the C-terminal lobe of the protein. Disruption of hfeA reduced H. influenzae manganese acquisition and was associated with decreased growth under aerobic conditions, impaired manganese-superoxide dismutase activity, reduced survival in macrophages, and changes in biofilm production in the presence of superoxide. Collectively, this work shows that HfeA contributes to H. influenzae manganese acquisition and virulence attributes. High conservation of the hfeABCD permease in Haemophilus species suggests that it may serve similar roles in other pathogenic Pasteurellaceae.

Zinc acquisition and its contribution to Klebsiella pneumoniae virulence

Klebsiella pneumoniae is a World Health Organization priority pathogen and a significant clinical concern for infections of the respiratory and urinary tracts due to widespread and increasing resistance to antimicrobials. In the absence of a vaccine, there is an urgent need to identify novel targets for therapeutic development. Bacterial pathogens, including K. pneumoniae, require the d-block metal ion zinc as an essential micronutrient, which serves as a cofactor for ~6% of the proteome. During infection, zinc acquisition necessitates the use of high affinity uptake systems to overcome niche-specific zinc limitation and host-mediated nutritional immunity. Here, we report the identification of ZnuCBA and ZniCBA, two ATP-binding cassette permeases that are highly conserved in Klebsiella species and contribute to K. pneumoniae AJ218 zinc homeostasis, and the high-resolution structure of the zinc-recruiting solute-binding protein ZniA. The Znu and Zni permeases appear functionally redundant with abrogation of both systems required to reduce K. pneumoniae zinc accumulation. Disruption of both systems also exerted pleiotropic effects on the homeostasis of other d-block elements. Zinc limitation perturbed K. pneumoniae cell morphology and compromised resistance to stressors, such as salt and oxidative stress. The mutant strain lacking both systems showed significantly impaired virulence in acute lung infection models, highlighting the necessity of zinc acquisition in the virulence and pathogenicity of K. pneumoniae.

The Impact of Chromate on Pseudomonas aeruginosa Molybdenum Homeostasis

Acquisition of the trace-element molybdenum via the high-affinity ATP-binding cassette permease ModABC is essential for Pseudomonas aeruginosa respiration in anaerobic and microaerophilic environments. This study determined the X-ray crystal structures of the molybdenum-recruiting solute-binding protein ModA from P. aeruginosa PAO1 in the metal-free state and bound to the group 6 metal oxyanions molybdate, tungstate, and chromate. Pseudomonas aeruginosa PAO1 ModA has a non-contiguous dual-hinged bilobal structure with a single metal-binding site positioned between the two domains. Metal binding results in a 22° relative rotation of the two lobes with the oxyanions coordinated by four residues, that contribute six hydrogen bonds, distinct from ModA orthologues that feature an additional oxyanion-binding residue. Analysis of 485 Pseudomonas ModA sequences revealed conservation of the metal-binding residues and β-sheet structural elements, highlighting their contribution to protein structure and function. Despite the capacity of ModA to bind chromate, deletion of modA did not affect P. aeruginosa PAO1 sensitivity to chromate toxicity nor impact cellular accumulation of chromate. Exposure to sub-inhibitory concentrations of chromate broadly perturbed P. aeruginosa metal homeostasis and, unexpectedly, was associated with an increase in ModA-mediated molybdenum uptake. Elemental analyses of the proteome from anaerobically grown P. aeruginosa revealed that, despite the increase in cellular molybdenum upon chromate exposure, distribution of the metal within the proteome was substantially perturbed. This suggested that molybdoprotein cofactor acquisition may be disrupted, consistent with the potent toxicity of chromate under anaerobic conditions. Collectively, these data reveal a complex relationship between chromate toxicity, molybdenum homeostasis and anaerobic respiration.

Global reprogramming of virulence and antibiotic resistance in Pseudomonas aeruginosa by a single nucleotide polymorphism in elongation factor, fusA1

Clinical isolates of the opportunistic pathogen Pseudomonas aeruginosa from patients with cystic fibrosis (CF) frequently contain mutations in the gene encoding an elongation factor, FusA1. Recent work has shown that fusA1 mutants often display elevated aminoglycoside resistance due to increased expression of the efflux pump, MexXY. However, we wondered whether these mutants might also be affected in other virulence-associated phenotypes. Here, we isolated a spontaneous gentamicin-resistant fusA1 mutant (FusA1^P443L) in which mexXY expression was increased. Proteomic and transcriptomic analyses revealed that the fusA1 mutant also exhibited discrete changes in the expression of key pathogenicity-associated genes. Most notably, the fusA1 mutant displayed greatly increased expression of the Type III secretion system (T3SS), widely considered to be the most potent virulence factor in the P. aeruginosa arsenal, and also elevated expression of the Type VI (T6) secretion machinery. This was unexpected because expression of the T3SS is usually reciprocally coordinated with T6 secretion system expression. The fusA1 mutant also displayed elevated exopolysaccharide production, dysregulated siderophore production, elevated ribosome synthesis, and transcriptomic signatures indicative of translational stress. Each of these phenotypes (and almost all of the transcriptomic and proteomic changes associated with the fusA1 mutation) were restored to levels comparable with that in the progenitor strain by expression of the WT fusA1 gene in trans, indicating that the mutant gene is recessive. Our data show that in addition to elevating antibiotic resistance through mexXY expression (and also additional contributory resistance mechanisms), mutations in fusA1 can lead to highly selective dysregulation of virulence gene expression.

Laser mode selection by internal reflection prisms

Internal reflection prisms were used to produce a narrow angular range of high reflectivity within a laser cavity. The selectivity was obtained from the sharp angular variation of internal reflectivity near the critical angle. Angular mode selection of a Nd: glass normal laser was achieved by this critical internal reflection (CIR) technique. Two-dimensional angular mode selection was observed with two orthogonal Lummer-Gehrcke plates within the laser cavity.