Protective Role of Native Rhizospheric Soil Microbiota Against the Exposure to Microcystins Introduced into Soil-Plant System via Contaminated Irrigation Water and Health Risk Assessment

Abstract

Microcystins (MCs) produced in eutrophic waters may decrease crop yield, enter food chains and threaten human and animal health. The main objective of this research was to highlight the role of rhizospheric soil microbiota to protect faba bean plants from MCs toxicity after chronic exposure. Faba bean seedlings were grown in pots containing agricultural soil, during 1 month under natural environmental conditions of Marrakech city in Morocco (March–April 2018) and exposed to cyanobacterial extracts containing up to 2.5 mg·L−1 of total MCs. Three independent exposure experiments were performed (a) agricultural soil was maintained intact “exposure experiment 1”; (b) agricultural soil was sterilized “exposure experiment 2”; (c) agricultural soil was sterilized and inoculated with the rhizobia strain Rhizobium leguminosarum RhOF34 “exposure experiment 3”. Overall, data showed evidence of an increased sensitivity of faba bean plants, grown in sterilized soil, to MCs in comparison to those grown in intact and inoculated soils. The study revealed the growth inhibition of plant shoots in both exposure experiments 2 and 3 when treated with 2.5 mg·L−1 of MCs. The results also showed that the estimated daily intake (EDI) of MCs, in sterilized soil, exceeded 2.18 and 1.16 times the reference concentrations (0.04 and 0.45 µg of microcysin-leucine arginine (MC-LR). Kg−1 DW) established for humans and cattle respectively, which raises concerns about human food chain contamination.

Algal Toxic Compounds and Their Aeroterrestrial, Airborne and other Extremophilic Producers with Attention to Soil and Plant Contamination: A Review

“…According to the accumulated knowledge, such infested water may impair the photosynthesis, inflict severe oxidative stress, affect mineral accumulation by plants, provoke adverse histological modifications in primary plant tissues, reduce the germination rate of seeds, inhibit the growth and development of seedlings, cause alteration of the quality and the productivity of crop plants with a potential to move these toxins into farm animals and thus have detrimental impact in the whole food chain [ 115 , 217 , 223 , 226 , 227 , 228 , 236 , 244 , 245 , 246 ]. The reported effects on metabolic processes and related germination and growth rates depend both on the toxin variant used and on the detoxication enzymatic activity of tested plants, such as Azolla filiculoides , Anethum graveolens , Brassica napus , Brassica cretica (Syn.…”

“…MCs, due to their ring structure, are stable under sunlight, and their long persistence in soils, with half-life between 6 and 17.8 days, was proved [ 220 , 236 , 256 , 257 ]. Similarly, MCs introduced through irrigation water are bioavailable to crop systems during long period but can be affected also by soil structure, chemical composition and local or modified microbiota [ 218 , 221 , 227 , 235 , 246 , 258 , 259 , 260 , 261 , 262 , 263 , 264 , 265 , 266 ]. To exemplify, sandy soil was incapable to remove cyanotoxins [ 259 ] but modified clays and soils can accelerate the improvement of the quality in eco-friendly manner [ 265 , 267 , 268 ].…”

“…To exemplify, sandy soil was incapable to remove cyanotoxins [ 259 ] but modified clays and soils can accelerate the improvement of the quality in eco-friendly manner [ 265 , 267 , 268 ]. The degradation and removal of MCs from the soils in agroecosystems or decrease of plant stress seems to be possible due to microbial activity in the rhizosphere [ 246 ]. The plants cultivated in hydroponic systems accumulated more MCs in their organs in comparison with soil-grown plants [ 269 , 270 ], and this is explainable in cases when the roots were in direct contact with toxin solutions [ 217 ].…”

“…In regard with the movement of MCs through the food chains, the research was oriented towards their absorption, translocation and accumulation in plants, and in edible plants in particular (e.g., [ 34 , 217 , 226 , 232 , 235 , 239 , 241 , 246 , 248 , 255 , 270 ]). Additional problem comes from the fact that plants can absorb MC-LR in low external concentrations (0.5 µg L −1 ); this was firstly shown on aquatic macrophytes [ 229 , 231 ].…”

Role of Rhizospheric Microbiota as a Bioremediation Tool for the Protection of Soil-Plant Systems from Microcystins Phytotoxicity and Mitigating Toxin-Related Health Risk

“…Indeed, researchers have started to investigate the role of native soil microbiota in the removal of MCs to mitigate their load in the plant-soil system; and thus, attenuate their toxicity and accumulation in plant tissues, including the edible parts [ 39 , 40 ]. In this light, our previous works have highlighted the role of rhizobia in Leguminosae protection against chronic exposure to MCs [ 41 , 42 , 43 , 44 ]. We also found evidence that the native microbiota of faba bean rhizosphere was capable of mitigating MCs adverse effects on plant growth and physiology, besides reducing their uptake and accumulation in plant biomass [ 44 ].…”