Characterization of the Tellurite-Resistance Properties and Identification of the Core Function Genes for Tellurite Resistance in Pseudomonas citronellolis SJTE-3

Abstract

Tellurite is highly toxic to bacteria and commonly used in the clinical screening for pathogens; it is speculated that there is a potential relationship between tellurite resistance and bacterial pathogenicity. Until now, the core function genes of tellurite resistance and their characteristics are still obscure. Pseudomonas citronellolis SJTE-3 was found able to resist high concentrations of tellurite (250 μg/mL) and formed vacuole-like tellurium nanostructures. The terZABCDE gene cluster located in the large plasmid pRBL16 endowed strain SJTE-3 with the tellurite resistance of high levels. Although the terC and terD genes were identified as the core function genes for tellurite reduction and resistance, the inhibition of cell growth was observed when they were used solely. Interestingly, co-expression of the terA gene or terZ gene could relieve the burden caused by the expression of the terCD genes and recover normal cell growth. TerC and TerD proteins commonly shared the conserved sequences and are widely distributed in many pathogenic bacteria, highly associated with the pathogenicity factors.

Keywords: core function gene; tellurite resistance; terA gene; terC gene; terD gene; terZABCDE gene cluster.

Figure 1

The cell growth curves of P. citronellolis SJTE-3 and SJTE-3ΔpRBL16 cultured with tellurite of different concentrations. Strain SJTE-3 (A) and strain SJTE-3ΔpRBL16 (B) were cultured in liquid media with tellurite (from 0 to 500 μg/mL) and solid plates with tellurite (from 0 to 500 μg/mL). The cell growth was detected every 2 h and showed in CFU/mL. Three independent experiments were performed and the average values were calculated with standard bars.

Figure 2

The TEM images of P. citronellolis SJTE-3 and E. coli DH5α cells cultured with tellurite. Strain SJTE-3 (A–C) and DH5α (D–F) were incubated in liquid medium and cultured to an exponential phase. After being supplied with 10 μg/mL tellurite and cultured for 2 h, the cells were collected, treated, and observed with TEM. The images of the cells were photographed at different magnifications.

Figure 3

Comparison of the tellurite-resistance gene clusters in different bacteria. The terZABCED gene clusters in the plasmids from P. citronellolis SJTE-3, P. aeruginosa PA298, Serratia marcescens CG43, E. coli O157, S. enterica A54560, and Y. pestis FDAARGOS_601 were aligned with Mauve. The terZABCDE genes were labeled in gray, red, green, black, blue, and yellow, respectively. The percentage represented the similarity of tellurite-resistance proteins from other bacteria to those from strain SJTE-3.

Figure 4

The multiple sequences alignment and the phylogenetic analysis of TerC. (A) The sequences of TerC were from P. citronellolis SJTE-3 (WP_010792503.1, bold marked), Serratia marcescens R478 (NP_941152.1), P. syringae DC3000 (NP_790782.1), Y. pestis CO92 (YP_002345379.1), E. coli O157:H7 str. Sakai (NP_309381.1), P. aeruginosa T2436 (QGQ00602.1), P. aeruginosa A298 (QCP73929.1), P. putida SY153 (ASU52179.1), Burkholderia lata A05 (AYQ41720.1), Enterobacter hormaechei E5 (QFH87896.1), Cronobacter sakazakii CFSAN068773 (QGG03267.1), Burkholderia contaminans FL-1-2-30-S1-D0 (AOL07871.1), S. enterica CFSAN002050 (AGQ76204.1), E. coli ST95-32 (QER73290.1). The conserved amino acids were marked black and the secondary motifs were marked. (B) The phylogenetic tree of TerC proteins was constructed in MEGA X using the Neighbor-Joining method, and the bootstrap consensus tree was performed with 1000 replications.

Figure 5

The multiple sequences alignment and the phylogenetic analysis of TerD. (A) The sequences of TerD were from P. citronellolis SJTE-3 (WP_010792502.1, bold marked), Serratia marcescens R478 (NP_941153.1), P. syringae DC3000 (NP_790782.1), Y. pestis CO92 (YP_002345380.1), E. coli O157:H7 str. Sakai (NP_309381.1), P.aeruginosa T2436 (QGQ00603.1), P. aeruginosa A298 (QCP73928.1), P. putida SY153 (ASU52180.1), Burkholderia lata A05 (AYQ41721.1), Enterobacter hormaechei E5 (QFH87897.1), Cronobacter sakazakii CFSAN068773 (QGG03266.1), Burkholderia contaminans FL-1-2-30-S1-D0 (AOL07872.1), S. enterica CFSAN002050 (AGQ76203.1), E. coli ST95-32 (QER73289.1). The conserved amino acids were marked black and the secondary motifs were marked. (B) The phylogenetic tree of these TerD proteins was constructed in MEGA X using the Neighbor-Joining method, and the bootstrap consensus tree was performed with 1000 replications.

Figure 6

The phylogenetic and the co-existence analysis of terZABCDE gene cluster and the pathogen-related genes. The phylogenetic tree of terZABCDE gene cluster in different pathogenic bacteria was constructed in MEGA using the Neighbor-Joining method, and the bootstrap consensus tree was performed with 1000 replications. The existence of genes encoding siderophore, the virulence protein, and the type III secretion system are shown by the red points, green points, and yellow points.