Pseudomonas aeruginosa Mobbing-Like Behavior against Acanthamoeba castellanii Bacterivore and Its Rapid Control by Quorum Sensing and Environmental Cues

A. castellanii and P. aeruginosa mutually exacerbate damage to corneal cells during coinfection

IMPORTANCE

At the National Cheng Kung University Hospital, numerous cases of amoebic keratitis had been identified with concurrent bacterial infections. Among these bacterial coinfections, Pseudomonas aeruginosa accounted for 50% of the reported cases. However, the impact of pathogenic bacteria on amoeba-induced corneal damage remains unclear. In our study, we successfully demonstrated that P. aeruginosa accumulated on the Acanthamoeba castellanii surface and caused more severe corneal damage. We also indicated that the exposure of P. aeruginosa to amoeba-soluble antigens enhanced its adhesion ability, promoted biofilm formation, and led to more severe corneal cell damage. These findings significantly contributed to our understanding of the risk associated with P. aeruginosa coinfection in the progression of amoeba keratitis.

Quantification of bacterial adhesion to tissue in high-throughput kinetics

Bacterial adhesion to tissue is the starting point for many pathogenic processes and beneficial interactions. The dynamics and speed of adhesion (minutes) make high-resolution temporal kinetic data important, but this capability is absent from the current toolset. We present a high-throughput method with a second-to-minute kinetic resolution, testing the adhesion of Pseudomonas aeruginosa PAO1 wild-type, flagella-, pili-, and quorum-sensing mutants to human embryonic kidney (HEK293) cells. Adhesion rates were in good correlation with HEK293 confluence, and the ways in which various bacterial mutations modified adhesion patterns are in agreement with the published literature. This simple assay can facilitate drug screening and treatment development as well as provide a better understanding of the interactions of pathogenic and probiotic bacteria with tissues, allowing the design of interventions and prevention treatments.

Shifts from cooperative to individual-based predation defense determine microbial predator-prey dynamics

Predation defense is an important feature of predator-prey interactions adding complexity to ecosystem dynamics. Prey organisms have developed various strategies to escape predation which differ in mode (elude vs. attack), reversibility (inducible vs. permanent), and scope (individual vs. cooperative defenses). While the mechanisms and controls of many singular defenses are well understood, important ecological and evolutionary facets impacting long-term predator-prey dynamics remain underexplored. This pertains especially to trade-offs and interactions between alternative defenses occurring in prey populations evolving under predation pressure. Here, we explored the dynamics of a microbial predator-prey system consisting of bacterivorous flagellates (Poteriospumella lacustris) feeding on Pseudomonas putida. Within five weeks of co-cultivation corresponding to about 35 predator generations, we observed a consistent succession of bacterial defenses in all replicates (n = 16). Initially, bacteria expressed a highly effective cooperative defense based on toxic metabolites, which brought predators close to extinction. This initial strategy, however, was consistently superseded by a second mechanism of predation defense emerging via de novo mutations. Combining experiments with mathematical modeling, we demonstrate how this succession of defenses is driven by the maximization of individual rather than population benefits, highlighting the role of rapid evolution in the breakdown of social cooperation.

Acanthamoeba, an environmental phagocyte enhancing survival and transmission of human pathogens

The opportunistic protist Acanthamoeba, which interacts with other microbes such as bacteria, fungi, and viruses, shows significant similarity in cellular and functional aspects to human macrophages. Intracellular survival of microbes in this microbivorous amoebal host may be a crucial step for initiation of infection in higher eukaryotic cells. Therefore, Acanthamoeba-microbe adaptations are considered an evolutionary model of macrophage-pathogen interactions. This paper reviews Acanthamoeba as an emerging human pathogen and different ecological interactions between Acanthamoeba and microbes that may serve as environmental training grounds and a genetic melting pot for the evolution, persistence, and transmission of potential human pathogens.