Genome Sequence and Mutational Analysis of Plant-Growth-Promoting Bacterium Agrobacterium tumefaciens CCNWGS0286 Isolated from a Zinc-Lead Mine Tailing

Abstract

The plant-growth-promoting bacterium Agrobacterium tumefaciens CCNWGS0286, isolated from the nodules of Robinia pseudoacacia growing in zinc-lead mine tailings, both displayed high metal resistance and enhanced the growth of Robinia plants in a metal-contaminated environment. Our goal was to determine whether bacterial metal resistance or the capacity to produce phytohormones had a larger impact on the growth of host plants under zinc stress. Eight zinc-sensitive mutants and one zinc-sensitive mutant with reduced indole-3-acetic acid (IAA) production were obtained by transposon mutagenesis. Analysis of the genome sequence and of transcription via reverse transcriptase PCR (RT-PCR) combined with transposon gene disruptions revealed that ZntA-4200 and the transcriptional regulator ZntR1 played important roles in the zinc homeostasis of A. tumefaciens CCNWGS0286. In addition, interruption of a putative oligoketide cyclase/lipid transport protein reduced IAA synthesis and also showed reduced zinc and cadmium resistance but had no influence on copper resistance. In greenhouse studies, R. pseudoacacia inoculated with A. tumefaciens CCNWGS0286 displayed a significant increase in biomass production over that without inoculation, even in a zinc-contaminated environment. Interestingly, the differences in plant biomass improvement among A. tumefaciens CCNWGS0286, A. tumefaciens C58, and zinc-sensitive mutants 12-2 (zntA::Tn5) and 15-6 (low IAA production) revealed that phytohormones, rather than genes encoding zinc resistance determinants, were the dominant factor in enhancing plant growth in contaminated soil. P lant-growth-promoting bacteria (PGPB) play a key role in host plant adaptation to metal-contaminated environments through triggering physiological changes in plant cell metabolism so that growing plants can tolerate high concentrations of transition or heavy metals (7,26). PGPB have been isolated from various plants in heavy-metal-contaminated environments (3, 47-49). They were able to enhance plant growth, make plants more tolerant to heavy and transition metals, and thus accelerate phytoremediation by mechanisms including nitrogen fixation, nitrogen and phosphorus metabolism, and the production of siderophores, organic acids, 1-aminocyclopropane-1-carboxylate deaminase (ACC), and phytohormones such as indole-3-acetic acid (IAA), cytokinins, acetoin, and 2,3-butanediol (21, 41, 54). It was reported previously that the existence of high concentrations of metals selected for more metal resistant PGPB to resist these adverse environmental conditions (20,26). However, it is often not known which trait of the PGPB, e.g., tolerance to heavy and transition metals, phytohormones, or a combination of the two, plays the dominant role in the survival of a given plant in a metal-contaminated environment.Agrobacterium tumefaciens is a soilborne alphaproteobacterium belonging to the family Rhizobiaceae whose ability to induce crown gall tumors on dicotyledonous plants makes it of great concern worldwide. Recently, many nonpath...

Ancestral genome estimation reveals the history of ecological diversification inAgrobacterium

“…Genome sequences were then annotated with the MicroScope platform (Vallenet et al 2013) (Goodner et al 2001;Wood et al 2001;Li et al 2011;Ruffing et al 2011;Wibberg et al 2011;Hao, Lin, et al 2012;Hao, Xie, et al 2012). These 22 genomes covered 10 closely related but genomically differentiated species (G1 to G9 and G13), with up to five isolates per species.…”

Plant–phytopathogen interactions: bacterial responses to environmental and plant stimuli

“…Even the most susceptible plants exposed to large pathogen populations will not develop diseases unless environmental conditions are favourable. As a consequence, bacteria have evolved to monitor environmental cues, such as temperature, light, water deficit, soil and rhizosphere pH, heavy metals and pesticides (Silver and Phung le, 2005;Efetova et al, 2007;Jing et al, 2007;Oberpichler et al, 2008;Hao et al, 2012;Haldar and Sengupta, 2015;Wei et al, 2015). In addition, soil texture and moisture content also affect root exudation and, therefore, modulate plantmicrobe interactions (Haldar and Sengupta, 2015).…”

Transcriptome Response to Heavy Metals in Sinorhizobium meliloti CCNWSX0020 Reveals New Metal Resistance Determinants That Also Promote Bioremediation by Medicago lupulina in Metal-Contaminated Soil

“…Our previous studies showed that several metal resistance determinants in rhizobia were required for effective symbiosis formation or could enhance phytohormone indole-3-acetic acid (IAA) production (20,21,23). However, the exact molecular mechanisms explaining how the rhizobial metal resistance determinants interact with the synthesis of growth-promoting substances, nodulation and nitrogen fixation, and, ultimately, phytoremediation processes still remain largely elusive.…”

“…In our previous greenhouse studies, the metal resistance determinants in rhizobia were shown to affect the functional symbiosis formation under heavy metal stress (20,21,23). Therefore, the Cu-sensitive mutant (ΔcueO) and three mutants that were both Cu and Zn sensitive (ΔyedYZ, ΔcusA-like, and ΔfixH-like) were selected for further study of the effects of the metal resistance determinants on root nodule symbiosis.…”