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Aspergillus fumigatus and Pseudomonas aeruginosa are the most prevalent fungal and bacterial pathogens associated with cystic-fibrosis-related infections, respectively. P. aeruginosa eventually predominates as the primary pathogen, though it is unknown why this is the case. Label-free quantitative proteomics was employed to investigate the cellular response of the alveolar epithelial cell line, A549, to coexposure of A. fumigatus and P. aeruginosa . These studies revealed a significant increase in the rate of P. aeruginosa proliferation where A. fumigatus was present. Shotgun proteomics performed on A549 cells exposed to either A. fumigatus or P. aeruginosa or to A. fumigatus and P. aeruginosa sequentially revealed distinct changes to the host cell proteome in response to either or both pathogens. While key signatures of infection were retained among all pathogen-exposed groups, including changes in mitochondrial activity and energy output, the relative abundance of proteins associated with endocytosis, phagosomes, and lysosomes was decreased in sequentially exposed cells compared to cells exposed to either pathogen. Our findings indicate that A. fumigatus renders A549 cells unable to internalize bacteria, thus providing an environment in which P. aeruginosa can proliferate. This research provides novel insights into the whole-cell proteomic response of A549 cells to A. fumigatus and P. aeruginosa and highlights distinct differences in the proteome following sequential exposure to both pathogens, which may explain why P. aeruginosa can predominate.

The relationship between aphids and their host plants is thought to be functionally analogous to plant-pathogen interactions. Although virulence effector proteins that mediate plant defenses are well-characterized for pathogens such as bacteria, oomycetes, and nematodes, equivalent molecules in aphids and other phloem-feeders are poorly understood. A dual transcriptomic-proteomic approach was adopted to generate a catalog of candidate effector proteins from the salivary glands of the pea aphid, Acyrthosiphon pisum. Of the 1557 transcript supported and 925 mass spectrometry identified proteins, over 300 proteins were identified with secretion signals, including proteins that had previously been identified directly from the secreted saliva. Almost half of the identified proteins have no homologue outside aphids and are of unknown function. Many of the genes encoding the putative effector proteins appear to be evolving at a faster rate than homologues in other insects, and there is strong evidence that genes with multiple copies in the genome are under positive selection. Many of the candidate aphid effector proteins were previously characterized in typical phytopathogenic organisms (e.g., nematodes and fungi) and our results highlight remarkable similarities in the saliva from plant-feeding nematodes and aphids that may indicate the evolution of common solutions to the plant-parasitic lifestyle.

The health of animals, including humans, is dependent on their resident microbiota, but the complexity of the microbial communities makes these associations difficult to study in most animals. Exceptionally, the microbiology of the pea aphid Acyrthosiphon pisum is dominated by a single bacterium Buchnera aphidicola (B. aphidicola). A (1)H NMR-based metabonomic strategy was applied to investigate metabolic profiles of aphids fed on a low essential amino acid diet and treated by antibiotic to eliminate B. aphidicola. In addition, differential gel electrophoresis (DIGE) with mass spectrometry was utilized to determine the alterations of proteins induced by these treatments. We found that these perturbations resulted in significant changes to the abundance of 15 metabolites and 238 proteins. Ten (67%) of the metabolites with altered abundance were amino acids, with nonessential amino acids increased and essential amino acids decreased by both perturbations. Over-represented proteins in the perturbed treatments included catabolic enzymes with roles in amino acid degradation and glycolysis, various cuticular proteins, and a C-type lectin and regucalcin with candidate defensive roles. This analysis demonstrates the central role of essential amino acid production in the relationship and identifies candidate proteins and processes underpinning the function and persistence of the association.