Assessing the Toxic Effects of Nickel, Cadmium and EDTA on Growth of the Plant Growth-Promoting Rhizobacterium Pseudomonas brassicacearum

Abstract

Plant growth-promoting rhizobacteria (PGPR) play an important role in the biodegradation of natural and xenobiotic organic compounds in soil. They can also alter heavy metal bioavailability and contribute to phytoremediation in the presence or absence of synthetic metal chelating agents. In this study, the inhibitory effect of Cd 2+ and Ni 2+ at different concentrations of Ca 2+ and Mg 2+ , and the influence of the widely used chelator EDTA on growth of the PGPR Pseudomonas brassicacearum in a mineral salt medium with a mixture of four main plant exudates (glucose, fructose, citrate, succinate) was investigated. Therefore, the bacteriostatic effect of Cd 2+ , Ni 2+ and EDTA on the maximum specific growth rate and the determination of EC50 values was used to quantify inhibitory impact. At high concentrations of Ca 2+ (800 μmol L -1 ) and Mg 2+ (1,250 μmol L -1 ), only a small inhibitory effect of Cd 2+ and Ni 2+ on growth of P. brassicacearum was observed (EC50 Cd 2+ , 18,849 ± 80 μmol L − 1 ; EC50 Ni 2 + , 3,578 ± 1,002 μmol L −1 ). The inhibition was much greater at low concentrations of Ca 2+ (25 μmol L −1 ) and Mg 2+ (100 μmol L −1 ) (EC50 Cd 2+ , 85±0.5 μmol L −1 and EC Ni 2+ , 62±1.8 μmol L −1 ). For the chosen model system, a competitive effect of the ions Cd 2+ and Ca 2+ on the one hand and Ni 2+ and Mg 2+ on the other hand can be deduced. However, the toxicity of both, Cd 2+ and Ni 2+ , could be significantly reduced by addition of EDTA, but if this chelating agent was added in stoichiometric excess to the cations, it also exhibited an inhibitory effect on growth of P. brassicacearum.

Characterization and comparison of the bacterial communities of rhizosphere and bulk soils from cadmium-polluted wheat fields

“…Recently, the effects of Cd on microbial communities, such as the decrease of microbial taxonomic species and the change of microbial compositions in soil have received research attention ( Vig et al, 2003 ; Krujatz et al, 2012 ; Feng et al, 2018b ). Luo et al (2018) reported that high Cd level of agricultural paddy soil displayed lower bacterial community diversity than low Cd level sites.…”

Bioaccumulation of Potentially Toxic Elements in Cereal and Legume Crops: A Review

“…When the content of PTEs increases in soil, especially in the rhizosphere zone, it causes changes in microbial activities and their composition. This could lead to poor nodulation in the legumes and inefficient root growth in cereals resulting in reduced nutrient translocation and absorption . As a result of poor nodulation in the legumes and imbalance of nutrients in the rhizosphere, the health of leguminous plants like green gram, pea, lentil, chickpea, and cereals such as rice, wheat, and maize, is adversely affected while grown on PTEs contaminated soils .…”

Cadmium Phytotoxicity, Tolerance, and Advanced Remediation Approaches in Agricultural Soils; A Comprehensive Review

“…Contrarily, where chemical amendments using chelating agents are conducted to phytoextract Cd from soil ( Lambrechts et al, 2011 ), at the same time, these chemical amendments have a limitation of stunted plant growth, e.g., Pseudomonas brassicacearum ( Krujatz, 2012 ), Lolium perenne , Brassica juncea , and Typha angustifolia ( Muhammad et al, 2009 ; Goel and Gautam, 2010 ; Xu et al, 2010 ). Under such circumstances where the application of a single chelating agent resulted in stunted growth, application of a quick biodegradable chelate complex is a potential option for enhancing Cd phytoextraction ( Wang et al, 2019 ).…”