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Availability of Zinc Impacts Interactions between Streptococcus sanguinis and Pseudomonas aeruginosa in Coculture
Kewei Li1,2, Alex H Gifford3, Thomas H Hampton1
1Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
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.
Insights
Zinc availability impacts polymicrobial infections in cystic fibrosis (CF). Our study shows zinc competition between Pseudomonas aeruginosa and Streptococcus species influences their growth, with implications for CF airway environments.
Area of Science:
- Microbiology
- Medical Science
- Bioinorganic Chemistry
Background:
- Cystic Fibrosis (CF) airway infections are polymicrobial, involving complex interactions between bacterial species.
- Previous work demonstrated that Pseudomonas aeruginosa promotes the growth of various streptococcal species in CF airways.
- The mechanistic basis for these polymicrobial interactions remains poorly understood.
Purpose of the Study:
- To identify genetic factors in Streptococcus sanguinis that mediate growth enhancement by Pseudomonas aeruginosa.
- To elucidate the role of zinc homeostasis in the interaction between P. aeruginosa and S. sanguinis.
- To investigate the impact of zinc levels on the relative abundance of these bacteria in CF sputum.
Main Methods:
- Conducted a genetic screen of Streptococcus sanguinis SK36 to identify mutants with impaired growth in co-culture with Pseudomonas aeruginosa PAO1.
- Assessed the growth of wild-type and mutant S. sanguinis strains in monoculture and co-culture with P. aeruginosa under varying zinc concentrations.
- Analyzed gene expression of zinc uptake systems in S. sanguinis during co-culture.
- Quantified zinc levels and bacterial abundance in clinical CF sputum samples.
Main Results:
- Mutations in Streptococcus sanguinis' zinc uptake systems significantly reduced its growth in co-culture with Pseudomonas aeruginosa, a defect rescued by exogenous zinc.
- Zinc uptake mutants showed no growth defect in monoculture, indicating zinc competition drives the co-culture interaction.
- P. aeruginosa strains with impaired zinc transport supported greater S. sanguinis growth, further supporting zinc competition.
- CF sputum analysis revealed that low zinc levels correlated with equal abundance of Pseudomonas and Streptococcus, while high zinc levels showed a decline in Streptococcus abundance.
Conclusions:
- Zinc availability is a critical factor modulating the interaction and relative abundance of Pseudomonas and Streptococcus species in CF airways.
- Competition for zinc plays a significant role in the dynamics of polymicrobial infections in cystic fibrosis.
- Metal homeostasis, specifically zinc, is a key driver of microbial interactions in polymicrobial infections.
