Characterization of a Selenium-Tolerant Rhizosphere Strain from a Novel Se-Hyperaccumulating PlantCardamine hupingshanesis

Abstract

A novel selenium- (Se-) hyperaccumulating plant, Cardamine hupingshanesis, accumulating Se as a form of SeCys2, was discovered in Enshi, Hubei, China, which could not be explained by present selenocysteine methyltransferase (SMT) theory. However, it is interesting to investigate if rhizosphere bacteria play some roles during SeCys2 accumulation. Here, one Se-tolerant rhizosphere strain, Microbacterium oxydans, was isolated from C. hupingshanesis. Phylogenetic analysis and 16S rRNA gene sequences determined the strain as a kind of Gram positive bacillus and belonged to the family Brevibacterium frigoritolerans. Furthermore, Se tolerance test indicated the strain could grow in extreme high Se level of 15.0 mg Se L−1. When exposed to 1.5 mg Se L−1, SeCys2 was the predominant Se species in the bacteria, consistent with the Se species in C. hupingshanesis. This coincidence might reveal that this strain played some positive effect in SeCys2 accumulation of C. hupingshanesis. Moreover, when exposed to 1.5 mg Se L−1 or 15.0 mg Se L−1, As absorption diminished in the logarithmic phase. In contrast, As absorption increased when exposed to 7.5 mg Se L−1, indicating As metabolism processes could be affected by Se on this strain. The present study provided a sight on the role of rhizosphere bacteria during Se accumulation for Se-hyperaccumulating plant.

Bacterial Microbiota Isolated from Cysts of Globodera rostochiensis (Nematoda: Heteroderidae)

“…Similar observations were reported by other authors. Brevibacterium frigoritolerans was in the same group with other Bacillus spp., i.e., B. simplex , B. muralis , B. psychrosaccharolyticus [ 20 , 21 , 22 ]. This bacterium can biosynthesize silver nanoparticles and tolerate silver as some Bacillus species can tolerate salt [ 23 ].…”

Hyperaccumulator Plants from China: A Synthesis of the Current State of Knowledge

“…149,150 The rhizosphere of C. hupingshanensis harbors a Se-tolerant bacterium that can transfer Se (IV) into SeCys, indicating an important role of rhizosphere bacteria in Se hyperaccumulation by this plant species. 151 In contrast, an endophytic fungus that produces elemental Se was shown to be potentially involved in Se hyperaccumulation in A. bisulcatus. 150…”

“…This is remarkable, given that the two other well-studied Se hyperaccumulators (i.e., Astragalus bisulcatus and Stanleya pinnata) outside China were found to accumulate Se in their tissues mainly in the form of methylselenocysteine (approximately 70%). , The rhizosphere of C. hupingshanensis harbors a Se-tolerant bacterium that can transfer Se (IV) into SeCys, indicating an important role of rhizosphere bacteria in Se hyperaccumulation by this plant species . In contrast, an endophytic fungus that produces elemental Se was shown to be potentially involved in Se hyperaccumulation in A.…”

Biological Inoculant of Salt-Tolerant Bacteria for Plant Growth Stimulation under Different Saline Soil Conditions

“…Brevibacterium frigoritolerans as a novel organism can effectively degrade 89.81% of the residual phorate in soil [ 7 ]. It has also been reported that B. frigoritolerans can tolerate 5% NaCl stress, and greatly reduce the accumulation of Se in plants [ 8 ]. Nevertheless, there have been fewer studies of B. frigoritolerans as a salt-tolerant species capable of alleviating salt stress and promoting plant growth.…”

“…In addition, B. frigoritolerans strain SMA23 is endowed with plant growth-promoting activities such as siderophore capacity, phosphate solubilization, and IAA production under abiotic stress at different temperatures [ 14 ]. B. frigoritolerans as a salt-tolerant microorganism has favorable salt tolerance [ 8 , 15 ], but there have been few studies on its application to promote plant growth under salt stress. Therefore, the plant growth-promoting activities of B. frigoritolerans under salt stress needed further study.…”