Exopolysaccharide-producing bacteria enhanced Pb immobilization and influenced the microbiome composition in rhizosphere soil of pakchoi (Brassica chinensis L.)

Abstract

Lead (Pb) contamination of planting soils is increasingly serious, leading to harmful effects on soil microflora and food safety. Exopolysaccharides (EPSs) are carbohydrate polymers produced and secreted by microorganisms, which are efficient biosorbent materials and has been widely used in wastewater treatment to remove heavy metals. However, the effects and underlying mechanism of EPS-producing marine bacteria on soil metal immobilization, plant growth and health remain unclear. The potential of Pseudoalteromonas agarivorans Hao 2018, a high EPS-producing marine bacterium, to produce EPS in soil filtrate, immobilize Pb, and inhibit its uptake by pakchoi (Brassica chinensis L.) was studied in this work. The effects of strain Hao 2018 on the biomass, quality, and rhizospheric soil bacterial community of pakchoi in Pb-contaminated soil were further investigated. The results showed that Hao 2018 reduced the Pb concentration in soil filtrate (16%–75%), and its EPS production increased in the presence of Pb2+. When compared to the control, Hao 2018 remarkably enhanced pakchoi biomass (10.3%–14.3%), decreased Pb content in edible tissues (14.5%–39.2%) and roots (41.3%–41.9%), and reduced the available Pb content (34.8%–38.1%) in the Pb-contaminated soil. Inoculation with Hao 2018 raised the pH of the soil, the activity of several enzymes (alkaline phosphatase, urease, and dehydrogenase), the nitrogen content (NH4+-N and NO3−-N), and the pakchoi quality (Vc and soluble protein content), while also raising the relative abundance of bacteria that promote plant growth and immobilize metals, such as Streptomyces and Sphingomonas. In conclusion, Hao 2018 reduced the available Pb in soil and pakchoi Pb absorption by increasing the pH and activity of multiple enzymes and regulating microbiome composition in rhizospheric soil.

Biochar and organic fertilizer drive the bacterial community to improve the productivity and quality of Sophora tonkinensis in cadmium-contaminated soil

“…Even at minimal levels of exposure, Cd can induce kidney and skeletal diseases, cardiac metabolic dysfunction, cancer, and mortality in humans ( Menahem et al, 2018 ; Hui et al, 2019 ; Rachael et al, 2019 ). Additionally, excessive Cd accumulation in the soil can disrupt the metabolic processes of plants ( Meghan et al, 2017 ; Zhu et al, 2020 ), such as protein synthesis ( Lian et al, 2015 ; Sha et al, 2019 ), nitrogen and carbohydrate metabolism ( Huang et al, 2020 ; Zhu et al, 2022 ; Cao et al, 2023 ), enzyme activation ( Chmielowska and Deckert, 2012 ; Lian et al, 2018 ; AlHuqail et al, 2023 ), photosynthesis, and chlorophyll synthesis ( Abeer et al, 2016 ; Raletsena et al, 2022 ; Tunçtürk et al, 2023 ), leading to abnormal plant growth and metabolism and ultimately mortality ( Mohammadhossein et al, 2019 ; Li et al, 2023 ). Therefore, reducing Cd concentrations in agricultural soils is crucial for sustainable agriculture and human health.…”

Heavy Metal Tolerance of Microorganisms Isolated from Coastal Marine Sediments and Their Lead Removal Potential

“…Microorganisms employ several mechanisms for bioremediation of soil and water polluted with heavy metals including the secretion of extracellular barriers, extracellular and intracellular sequestration, active transport of metal ions, production of metal chelators, and enzymatic detoxification [15,16]. The permeability barrier involves the production of exopolysaccharides and biofilm formation to physically sequester and chemically modify metal ions into less toxic molecules [17]. On the other hand, the extracellular sequestration process is a passive uptake mechanism that involves the accumulation of metal ions in the cellular periplasm or the complexation of metal ions into insoluble compounds, causing metal precipitation.…”

“…For example, cadmium pollution is often linked with the use of agrochemicals, of battery manufacturing, pigments, anticorrosive agents, and contaminated irrigation water [23][24][25]; zinc contamination may result from discharge of dyes and detergents, while lead is mainly derived from the textile industry, battery production, paint manufacturing, insecticide use, fossil fuel consumption, waste incineration, and metallurgical processes [26,27]. In particular, lead represents one of the most significant heavy metal contaminants on a global scale, raising alarming concerns on both human health and biodiversity [17]. Distribution reports in Colombia indicate the presence of this metal across different environmental matrices, posing a public health risk [5,28].…”