Functional genomics study of Pseudomonas putida to determine traits associated with avoidance of a myxobacterial predator

Predation contributes to the structure and diversity of microbial communities. Predatory myxobacteria are ubiquitous to a variety of microbial habitats and capably consume a broad diversity of microbial prey. Predator–prey experiments utilizing myxobacteria have provided details into predatory mechanisms and features that facilitate consumption of prey. However, prey resistance to myxobacterial predation remains underexplored, and prey resistances have been observed exclusively from predator–prey experiments that included the model myxobacterium Myxococcus xanthus. Utilizing a predator–prey pairing that instead included the myxobacterium, Cystobacter ferrugineus, with Pseudomonas putida as prey, we observed surviving phenotypes capable of eluding predation. Comparative transcriptomics between P. putida unexposed to C. ferrugineus and the survivor phenotype suggested that increased expression of efflux pumps, genes associated with mucoid conversion, and various membrane features contribute to predator avoidance. Unique features observed from the survivor phenotype when compared to the parent P. putida include small colony variation, efflux-mediated antibiotic resistance, phenazine-1-carboxylic acid production, and increased mucoid conversion. These results demonstrate the utility of myxobacterial predator–prey models and provide insight into prey resistances in response to predatory stress that might contribute to the phenotypic diversity and structure of bacterial communities.

Predatory selection of mucoid, antibiotic resistant Pseudomonas putida phenotype by myxobacterium Cystobacter ferrugineus

Predation contributes to the structure and diversity of microbial communities. Predatory myxobacteria are ubiquitous to a variety of microbial habitats and capably consume a broad diversity of microbial prey. Predator-prey experiments utilizing myxobacteria have provided details into predatory mechanisms and features that facilitate consumption of prey. However, prey resistance to myxobacterial predation remains underexplored, and prey resistances have been observed exclusively from predator-prey experiments that included the model myxobacterium Myxococcus xanthus. Utilizing a predator-prey pairing that instead included the myxobacterium, Cystobacter ferrugineus, with Pseudomonas putida as prey, we infrequently observed surviving phenotypes capable of eluding predation. Comparative transcriptomics between P. putida unexposed to C. ferrugineus and the survivor phenotype suggested that increased expression of efflux pumps, genes associated with mucoid conversion, and various membrane features contribute to predator avoidance. The P. putida survivor phenotype was confirmed to be resistant to the antibiotics kanamycin, gentamicin, and tetracycline and to produce more alginate than predator-unexposed P. putida. Unique features observed from the survivor phenotype including small colony variation, efflux-mediated antibiotic resistance, and increased mucoid conversion overlap with traits associated with Pseudomonas aeruginosa predator avoidance and pathogenicity. The survivor phenotype also benefited from increased predator resistance during subsequent predation assays. These results demonstrate the utility of myxobacterial predator-prey models and provide insight into prey resistances in response to predatory stress might contribute to the phenotypic diversity and structure of bacterial communities.

Targeted Chemoenzymatic Synthesis of Sugar Nucleotide Probes Reveal an Inhibitor of the GDP-D-Mannose Dehydrogenase from Pseudomonas Aeruginosa

<p>Sufferers of the autosomal recessive genetic disorder cystic fibrosis are at extremely high risk for contracting chronic lung infections. Over their lifetime one bacterial strain in particular, <i>Pseudomonas aeruginosa</i>, becomes the dominant pathogen. Bacterial strains incur loss-of-function mutations in the mucA gene that lead to a phenomenon known as mucoid conversion, resulting in copious secretion of alginate, a carbohydrate exopolysaccharide. Strategies that can stop the production of alginate in mucoid <i>Pseudomonas aeruginosa </i>infections are therefore of paramount importance. To aid in this we developed a series of sugar nucleotide chemical tools to probe an enzyme critical to alginate biosynthesis, guanosine diphosphate mannose dehydrogenase (GMD). This enzyme catalyses the irreversible formation of the alginate sugar nucleotide building block, guanosine diphosphate mannuronic acid. Using a chemoenzymatic strategy we accessed a series of modified sugar nucleotides, identifying a C6-amide derivative of the native substrate as a micromolar inhibitor of GMD.<b> </b>This discovery will provide a framework for wider inhibition strategies against GMD to be developed.<b></b></p>

Targeted Chemoenzymatic Synthesis of Sugar Nucleotide Probes Reveal an Inhibitor of the GDP-D-Mannose Dehydrogenase from Pseudomonas Aeruginosa

<p>Sufferers of the autosomal recessive genetic disorder cystic fibrosis are at extremely high risk for contracting chronic lung infections. Over their lifetime one bacterial strain in particular, <i>Pseudomonas aeruginosa</i>, becomes the dominant pathogen. Bacterial strains incur loss-of-function mutations in the mucA gene that lead to a phenomenon known as mucoid conversion, resulting in copious secretion of alginate, a carbohydrate exopolysaccharide. Strategies that can stop the production of alginate in mucoid <i>Pseudomonas aeruginosa </i>infections are therefore of paramount importance. To aid in this we developed a series of sugar nucleotide chemical tools to probe an enzyme critical to alginate biosynthesis, guanosine diphosphate mannose dehydrogenase (GMD). This enzyme catalyses the irreversible formation of the alginate sugar nucleotide building block, guanosine diphosphate mannuronic acid. Using a chemoenzymatic strategy we accessed a series of modified sugar nucleotides, identifying a C6-amide derivative of the native substrate as a micromolar inhibitor of GMD.<b> </b>This discovery will provide a framework for wider inhibition strategies against GMD to be developed.<b></b></p>

Polymorphonuclear Leukocytes or Hydrogen Peroxide Enhance Biofilm Development of MucoidPseudomonas aeruginosa

Pseudomonas aeruginosais an opportunistic pathogenic bacterium involved in many human infections, including pneumonia, diabetic foot ulcers, and ventilator-associated pneumonia.P. aeruginosacells usually undergo mucoid conversion during chronic lung infection in patients with cystic fibrosis (CF) and resist destruction by polymorphonuclear leukocytes (PMNs), which release free oxygen radicals (ROS), such as H2O2. PMNs are the main leucocytes in the CF sputum of patients who are infected withP. aeruginosa, which usually forms biofilms. Here, we report that PMNs or H2O2can promote biofilm formation by mucoidP. aeruginosaFRD1 with the use of the hanging-peg method. The mucoid strain infecting CF patients overproduces alginate. In this study, PMNs and H2O2promoted alginate production, and biofilms treated with PMNs or H2O2exhibited higher expression of alginate genes. Additionally, PMNs increased the activity of GDP-mannose dehydrogenase, which is the key enzyme in alginate biosynthesis. Our results demonstrate that PMNs or H2O2can enhance mucoidP. aeruginosabiofilms.

Mixed Communities of Mucoid and NonmucoidPseudomonas aeruginosaExhibit Enhanced Resistance to Host Antimicrobials

ABSTRACTPseudomonas aeruginosacauses chronic pulmonary infections in patients with cystic fibrosis (CF).P. aeruginosamucoid conversion, defined by overproduction of the exopolysaccharide alginate, correlates with accelerated decline in CF patient lung function. Recalcitrance of the mucoid phenotype to clearance by antibiotics and the immune response is well documented. However, despite advantages conferred by mucoidy, mucoid variants often revert to a nonmucoid phenotype bothin vitroandin vivo. Mixed populations of mucoid isolates and nonmucoid revertants are recovered from CF lungs, suggesting a selective benefit for coexistence of these variants. In this study, cocultures of mucoid and nonmucoid variants exhibited enhanced resistance to two host antimicrobials: LL-37, a cationic antimicrobial peptide, and hydrogen peroxide (H2O2). Alginate production by mucoid isolates protected nonmucoid variants in consortia from LL-37, as addition of alginate exogenously to nonmucoid variants abrogated LL-37 killing. Conversely, nonmucoid revertants shielded mucoid variants from H2O2stress via catalase (KatA) production, which was transcriptionally repressed by AlgT and AlgR, central regulators of alginate biosynthesis. Furthermore, extracellular release of KatA by nonmucoid revertants was dependent onlys, encoding an endolysin implicated in autolysis and extracellular DNA (eDNA) release. Overall, these data provide a rationale to study interactions ofP. aeruginosamucoid and nonmucoid variants as contributors to evasion of innate immunity and persistence within the CF lung.IMPORTANCEP. aeruginosamucoid conversion within lungs of cystic fibrosis (CF) patients is a hallmark of chronic infection and predictive of poor prognosis. The selective benefit of mixed populations of mucoid and nonmucoid variants, often isolated from chronically infected CF patients, has not been explored. Here, we show that mixed-variant communities ofP. aeruginosademonstrate advantages in evasion of innate antimicrobials via production of shared goods: alginate and catalase. These data argue for therapeutically targeting multiple constituents (both mucoid and nonmucoid variants) within diversifiedP. aeruginosacommunitiesin vivo, as these variants can differentially shield one another from components of the host response.

The Pseudomonas aeruginosa Sensor Kinase KinB Negatively Controls Alginate Production through AlgW-Dependent MucA Proteolysis

ABSTRACT Mucoidy, or overproduction of the exopolysaccharide known as alginate, in Pseudomonas aeruginosa is a poor prognosticator for lung infections in cystic fibrosis. Mutation of the anti-σ factor MucA is a well-accepted mechanism for mucoid conversion. However, certain clinical mucoid strains of P. aeruginosa have a wild-type (wt) mucA. Here, we describe a loss-of-function mutation in kinB that causes overproduction of alginate in the wt mucA strain PAO1. KinB is the cognate histidine kinase for the transcriptional activator AlgB. Increased alginate production due to inactivation of kinB was correlated with high expression at the alginate-related promoters P algU and P algD . Deletion of alternative σ factor RpoN (σ54) or the response regulator AlgB in kinB mutants decreased alginate production to wt nonmucoid levels. Mucoidy was restored in the kinB algB double mutant by expression of wt AlgB or phosphorylation-defective AlgB.D59N, indicating that phosphorylation of AlgB was not required for alginate overproduction when kinB was inactivated. The inactivation of the DegS-like protease AlgW in the kinB mutant caused loss of alginate production and an accumulation of the hemagglutinin (HA)-tagged MucA. Furthermore, we observed that the kinB mutation increased the rate of HA-MucA degradation. Our results also indicate that AlgW-mediated MucA degradation required algB and rpoN in the kinB mutant. Collectively, these studies indicate that KinB is a negative regulator of alginate production in wt mucA strain PAO1.