Temporal Evolution of Bacterial Endophytes Associated to the Roots of Phragmites australis Exploited in Phytodepuration of Wastewater

Abstract

Improvement of industrial productions through more environment-friendly processes is a hot topic. In particular, land and marine environment pollution is a main concern, considering that recalcitrant compounds can be spread and persist for a long time. In this context, an efficient and cost-effective treatment of wastewater derived from industrial applications is crucial. Phytodepuration has been considered as a possible solution and it is based on the use of plants and their associated microorganisms to remove and/or transform pollutants. In this work we investigated the culturable microbiota of Phragmites australis roots, sampled from the constructed wetlands (CWs) pilot plant in the G.I.D.A. SpA wastewater treatment plant (WWTP) of Calice (Prato, Tuscany, Italy) before and after the CW activation in order to check how the influx of wastewater might affect the resident bacterial community. P. australis specimens were sampled and a panel of 294 culturable bacteria were isolated and characterized. This allowed to identify the dynamics of the microbiota composition triggered by the presence of wastewater. 27 out of 37 bacterial genera detected were exclusively associated to wastewater, and Pseudomonas was constantly the most represented genus. Moreover, isolates were assayed for their resistance against eight different antibiotics and synthetic wastewater (SWW). Data obtained revealed the presence of resistant phenotypes, including multi-drug resistant bacteria, and a general trend regarding the temporal evolution of resistance patterns: indeed, a direct correlation linking the appearance of antibiotic-and SWW-resistance with the time of exposure to wastewater was observed. In particular, nine isolates showed an interesting behavior since their growth was positively affected by the highest concentrations of SWW. Noteworthy, this study is among the few investigating the P. australis microbiota prior to the plant activation.

A Review on Microorganisms in Constructed Wetlands for Typical Pollutant Removal: Species, Function, and Diversity

“…The interactions between microorganisms and plants also greatly affects the removal of heavy metals ( González Henao and Ghneim-Herrera, 2021 ). Microorganisms and plants have long been growing together and microorganisms have more or less established associations with plants ( Vassallo et al, 2020 ). In particular, rhizobacteria and endophytic bacteria can support plant growth through uptake of nutrients (e.g., N, P, Mg, Fe, and Ca), biosynthesis of plant growth-promoting phytohormones, and tolerance to pollution and stress ( Syranidou et al, 2018 ; Vassallo et al, 2020 ).…”

“…Microorganisms and plants have long been growing together and microorganisms have more or less established associations with plants ( Vassallo et al, 2020 ). In particular, rhizobacteria and endophytic bacteria can support plant growth through uptake of nutrients (e.g., N, P, Mg, Fe, and Ca), biosynthesis of plant growth-promoting phytohormones, and tolerance to pollution and stress ( Syranidou et al, 2018 ; Vassallo et al, 2020 ). This can alleviate the toxic stress of heavy metals on plants and can also facilitate the accumulation of heavy metals by plants ( Syranidou et al, 2018 ; Vassallo et al, 2020 ).…”

“…In particular, rhizobacteria and endophytic bacteria can support plant growth through uptake of nutrients (e.g., N, P, Mg, Fe, and Ca), biosynthesis of plant growth-promoting phytohormones, and tolerance to pollution and stress ( Syranidou et al, 2018 ; Vassallo et al, 2020 ). This can alleviate the toxic stress of heavy metals on plants and can also facilitate the accumulation of heavy metals by plants ( Syranidou et al, 2018 ; Vassallo et al, 2020 ). In turn, the main function of plants in CWs is to provide additional oxygen and organic matter for microbial growth ( Zhou et al, 2013 ).…”

“… Syranidou et al (2016) found that inoculation of the Juncus acutus with a selected endophytic bacterial consortium removed emergent pollutants and metals faster and more efficiently compared to uninoculated plants. Similarly, Vassallo et al (2020) isolated eight bacterial strains (belonging to the genera Bacillus , Planococcus , and Pseudomonas ) from samples taken from the roots of Phragmites australis . They grew well in wastewater with high concentrations of heavy metals (45 mg/l for Fe and 0.09 mg/l for Se), and the higher the concentration of heavy metals, the faster they grow ( Vassallo et al, 2020 ).…”

“…Regarding heavy metal compounds, which are generally difficult to biodegrade, microorganisms can also remove them from wastewater through biosorption, bioaccumulation and speciation transformation ( Si et al, 2019 ). In addition, microorganisms can improve the tolerance and removal efficiency of CWs to pollutants by enhancing phytoremediation ( Syranidou et al, 2018 ; Vassallo et al, 2020 ). In this context, in order to further optimize CWs, it is necessary to investigate the functional microorganisms associated with pollutant removal.…”