Determining the Different Mechanisms Used by Pseudomonas Species to Cope With Minimal Inhibitory Concentrations of Zinc via Comparative Transcriptomic Analyses.

Lei Lei,Pulin Liu,Jiahui Chen,Weifang Liao

doi:10.3389/fmicb.2020.573857

Abstract

Pseudomonas is one of the most diverse bacterial genera identified in the environment. Genome sequence analysis has indicated that this genus can be clustered into three lineages and ten groups. Each group can adopt different mechanisms to thrive under zinc-depleted or high-zinc conditions, two environments that are frequently encountered during their environmental propagation. The response of three prominent Pseudomonas strains (Pseudomonas aeruginosa PAO1, Pseudomonas putida KT2440, and Pseudomonas fluorescens ATCC 13525T) to minimal inhibitory concentrations of zinc were compared using RNA-seq and ultra-performance liquid chromatography–tandem mass spectrometry analysis. Results demonstrated that the three strains shared only minimal similarity at the transcriptional level. Only four genes responsible for zinc efflux were commonly upregulated. P. aeruginosa PAO1 specifically downregulated the operons involved in siderophore synthesis and the genes that encode ribosomal protein, while upregulated the genes associated with antibiotic efflux and cell envelope biosynthesis. The membrane transporters in P. putida KT2440 were globally downregulated, indicating changes in cell permeability. Compared with P. aeruginosa PAO1 and P. putida KT2440, the most remarkable transcriptional variation in P. fluorescens ATCC 13525T is the significant downregulation of the type VI secretion system. Metabolite quantitative analysis showed that low concentrations of the metabolites involved in central carbon metabolism and amino acid synthesis were detected in the three strains. In summary, the cellular responses of the three strains under high-zinc condition is quite divergent. Although similar metal efflux systems were upregulated, the three strains employed different pathways to reduce zinc intrusion. In addition, zinc treatment can increase the difficulties of scavenging P. aeruginosa from its colonization area, and reduce the competitiveness of P. fluorescens in microbiota.

Highlights

Zn2+ is the second most abundant essential metal ion after Fe2+/3+ in all three kingdoms of life, which directly interacts with RNA polymerase, zinc-finger proteins and superoxide dismutase to maintain their functionality (Hobman et al, 2007; Watły et al, 2016; Gonzalez et al, 2018)
The results showed that different zinc stress levels strongly influenced (>4 fold change) the transcription of genes from four functional groups, including metal transporting genes, genes associated with membrane homeostasis, antioxidant-encoding genes and genes involved in basic cellular metabolism (Peng et al, 2018)
By combining the transcriptomic and metabolic data obtained in the present study, an overview of the global effects of zinc on three representative Pseudomonas strains was provided

Summary

Introduction

Zn2+ is the second most abundant essential metal ion after Fe2+/3+ in all three kingdoms of life, which directly interacts with RNA polymerase, zinc-finger proteins and superoxide dismutase to maintain their functionality (Hobman et al, 2007; Watły et al, 2016; Gonzalez et al, 2018). Free Zn2+ in the cytoplasm is normally maintained at the femtomolar to picomolar level (Outten and O’Halloran, 2001). Once this threshold is surpassed, excess Zn2+ can replace other metal ions from proteins and alter the stability of biomolecules (Krezel and Maret, 2016; Peng et al, 2018). The results showed that zinc in some sludges is highly bioavailable (the water soluble zinc concentration reached 61.42±7.0 mg Kg−1). Fertilizing use of these sludges may cause severe zinc pollution in soils

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Results

Conclusion