Mn accumulation in a submerged plant Egeria densa (Hydrocharitaceae) is mediated by epiphytic bacteria

Abstract

Many aquatic plants act as biosorbents, removing and recovering metals from the environment. To assess the biosorbent activity of Egeria densa, a submerged freshwater macrophyte, plants were collected monthly from a circular drainage area in Lake Biwa basin and the Mn concentrations of the plants were analysed. Mn concentrations in these plants were generally above those of terrestrial hyperaccumulators, and were markedly higher in spring and summer than in autumn. Mn concentrations were much lower in plants incubated in hydroponic medium at various pH levels with and without Mn supplementation than in field-collected plants. The precipitation of Mn oxides on the leaves was determined by variable pressure scanning electron microscopy-energy dispersive X-ray analysis and Leucoberbelin blue staining. Several strains of epiphytic bacteria were isolated from the field-collected E. densa plants, with many of these strains, including those of the genera Acidovorax, Comamonas, Pseudomonas and Rhizobium, found to have Mn-oxidizing activity. High Mn concentrations in E. densa were mediated by the production of biogenic Mn oxide in biofilms on leaf surfaces. These findings provide new insights into plant epidermal bacterial flora that affect metal accumulation in plants and suggest that these aquatic plants may have use in Mn phytomining.

Two endophytic bacterial strains modulate Mn oxidation and accumulation in the wetland plant Suaeda salsa pall

“…LBB staining and SEM-EDX analysis further indicated that Mn oxides present in the precipitations. A previous study has suggested that the production of biogenic Mn oxides in biofilms on the epidermis of an Mn hyperaccumulator plant, Egeria densa, can elevate Mn levels inside the plants (Tsuji et al 2017). In this study, however, the concentrations of Mn in the leaves, stems, and roots of S. salsa Pall.…”

“…Moreover, the two isolates were clustered together with a short phylogenetic distance and were separated from those above-mentioned marine bacteria. (Tsuji et al 2017). In this work, we observed that when S. salsa Pall.…”

“…So far, most Mn(II)-oxidizing bacteria have been isolated from aquatic environments; only a few works were conducted in terrestrial environments (Zhang et al 2015c). Several Mn-oxidizing strains of epiphytic bacteria have been found on the surface of field-collected E. densa plants, affecting Mn accumulation (Tsuji et al 2017). However, for none of the endophytic bacterial species, Mn oxidization has been observed.…”

“…One factor that can affect the metal uptake of wetland plants is the presence of microbial symbionts (Weis and Weis 2004). A study on the submerged plant species Egeria densa has revealed that epiphytic bacteria, i.e., Acidovorax, Comamonas, Pseudomonas, and Rhizobium, have Mn-oxidizing activities, enabling them to form Mn biofilms on their surfaces (Tsuji et al 2017). This finding provides new insights into the role of bacteria in the mobilization of Mn (II) in plants.…”

Temporary freshwater wetlands floristics in central Mexico highlands

“…Biofilter/ biofuel: Azolla filiculoides and A. microphylla are attractive species for the production of renewable biofuels (Miranda et al 2016). Egeria densa can remove heavy metals from the environment (Tsuji et al 2017), as can Eleocharis aciculares, E. macrostachya, and, E. montana (Ha et al 2011, Olmos-Márquez et al 2012. Lemna gibba, L. obscura, L. minuta are indicated for phytoremediation of contaminated water (Gallardo-Williams et al 2002, Gür et al 2016, Di-Baccio et al 2017.…”