Availability of Zinc Impacts Interactions between Streptococcus sanguinis and Pseudomonas aeruginosa in Coculture

Abstract

Airway infections associated with cystic fibrosis (CF) are polymicrobial. We reported previously that clinical isolates of Pseudomonas aeruginosa promote the growth of a variety of streptococcal species. To explore the mechanistic basis of this interaction, we performed a genetic screen to identify mutants of Streptococcus sanginuis SK36 whose growth was no longer enhanced by P. aeruginosa PAO1. Mutations in the zinc uptake systems of S. sanguinis SK36 reduced growth of these strains by 1 to 3 logs compared to that of wild-type S. sanguinis SK36 when grown in coculture with P. aeruginosa PAO1, and exogenous zinc (0.1 to 10 μM) rescued the coculture defect of zinc uptake mutants of S. sanguinis SK36. Zinc uptake mutants of S. sanguinis SK36 had no obvious growth defect in monoculture. Consistent with competition for zinc driving coculture dynamics, S. sanguinis SK36 grown in coculture with P. aeruginosa showed increased expression of zinc uptake genes compared to that of S. sanguinis grown alone. Strains of P. aeruginosa PAO1 defective in zinc transport also supported ∼2-fold more growth by S. sanguinis compared to that in coculture with wild-type P. aeruginosa PAO1. An analysis of 118 CF sputum samples revealed that total zinc levels varied from ∼5 to 145 μM. At relatively low zinc levels, Pseudomonas and Streptococcus spp. were found in approximately equal abundance; at higher zinc levels, we observed a decline in relative abundance of Streptococcus spp., perhaps as a result of increasing zinc toxicity. Together, our data indicate that the relative abundances of these microbes in the CF airway may be impacted by zinc levels. IMPORTANCE Polymicrobial infections in CF cases likely impact patient health, but the mechanism(s) underlying such interactions is poorly understood. Here, we show using an in vitro model system that interactions between Pseudomonas and Streptococcus are modulated by zinc availability, and clinical data are consistent with this model. Together with previous studies, our work supports a role for metal homeostasis as a key factor driving microbial interactions.

Calprotectin-mediated zinc chelation inhibitsPseudomonas aeruginosaprotease activity in cystic fibrosis sputum

“…Smith et al (1) found that the zinc concentration of 45 CF sputum samples ranged from 678 μg/L (~10 μM) to 1181 μg/L (~18 μM) compared to 103 μg/L (~2 μM) to 597 μg/L (~9 μM) in 8 non-CF sputum samples. Li et al (3) reported that the zinc concentration of 118 CF sputum samples ranged from ~5 μM to ~145 μM. In this study, the zinc concentration of 8 CF sputum samples ranged from 1.002 μg/g (~15 μM) to 7.562 μg/g (~116 μM) ( Fig.…”

“…While the concentration of metals, such as zinc, in CF sputum can vary, the concentration of zinc in expectorated sputum from CF patients is elevated, on average, compared to levels in samples from healthy controls (1)(2)(3). However, studies investigating the transcriptional response of P. aeruginosa in CF sputum show that a common gene expression pattern is the increased expression of zinc uptake and transport genes (4)(5)(6)(7)(8)(9), which are normally expressed when zinc is limited.…”

The zinc transporter ZnuABC is critical for the virulence of Chromobacterium violaceum and contributes to diverse zinc-dependent physiological processes

“…Our data indicated that C. violaceum requires the ZnuABC system to supply zinc to several physiological processes, such as violacein production, swimming motility, biofilm formation, and bacterial competition. It has been described the requirement of zinc for enzymes of the violacein biosynthetic pathway in C. violaceum (45), for flagellar motility in Proteus mirabilis, S. Typhimurium, and P. aeruginosa (46)(47)(48), for biofilm formation via surface adhesion proteins in Staphylococcus epidermidis and Staphylococcus aureus (49), and for bacterial competition in a context of polymicrobial infections (19,50). Although further studies are needed to understand how these processes were impaired under zinc deficiency in C. violaceum, our data suggest an adaptive response to ensure the zinc supply for key metabolic pathways.…”

Metabolic Modeling to Interrogate Microbial Disease: A Tale for Experimentalists

“…While some studies have focused on the metabolic interactions of microbes found in the CF airway, most of them have included two microbial species due to complex experimental methods required to culture multiple microbes in a mixed community in vitro ( Filkins et al, 2015 ; Flynn et al, 2016 ; Scott et al, 2019 ; Camus et al, 2020 ; Li et al, 2020 ). However, metabolic modeling represents a useful tool to interrogate metabolic dependencies of more complex multispecies communities detected in pwCF.…”