Impact of Soil Salinity on the Structure of the Bacterial Endophytic Community Identified from the Roots of Caliph Medic (Medicago truncatula)

Abstract

In addition to being a forage crop, Caliph medic (Medicago truncatula) is also a model legume plant and is used for research focusing on the molecular characterization of the interaction between rhizobia and plants. However, the endophytic microbiome in this plant is poorly defined. Endophytic bacteria play a role in supplying plants with the basic requirements necessary for growth and development. Moreover, these bacteria also play a role in the mechanism of salinity stress adaptation in plants. As a prelude to the isolation and utilization of these bacteria in Caliph medic farming, 41 bacterial OTUs were identified in this project from within the interior of the roots of this plant by pyrosequencing of the small ribosomal subunit gene (16S rDNA) using a cultivation-independent approach. In addition, the differential abundance of these bacteria was studied following exposure of the plants to salinity stress. About 29,064 high-quality reads were obtained from the sequencing of six libraries prepared from control and salinity-treated tissues. Statistical analysis revealed that the abundance of ~70% of the OTUs was significantly (p ≤ 0.05) altered in roots that were exposed to salinity stress. Sequence analysis showed a similarity between some of the identified species and other, known, growth-promoting bacteria, marine and salt-stressed soil-borne bacteria, and nitrogen-fixing bacterial isolates. Determination of the amendments to the bacterial community due to salinity stress in Caliph medic provides a crucial step toward developing an understanding of the association of these endophytes, under salt stress conditions, in this model plant. To provide direct evidence regarding their growth promoting activity, a group of endophytic bacteria were isolated from inside of plant roots using a cultivation-dependent approach. Several of these isolates were able to produce ACC-deaminase, ammonia and IAA; and to solubilize Zn+2 and PO4-3. This data is consistent with the predicted occurrence (based on cultivation-independent techniques) of these bacteria and provides some insight into the importance of the endophytic bacteria in Caliph medic when grown under normal and saline conditions.

Agricultural and Other Biotechnological Applications Resulting from Trophic Plant-Endophyte Interactions

“…It was demonstrated that plant growth promoting (PGP) abilities and biological nitrogen fixation, followed by the production of secondary metabolites and bioactive compounds, synthesis of fungicides and bactericides, and protection against environmental stresses are the most important benefits that are provided to plants by endophytes (Table 1). [39] Grasses (roots) Actinobacteria PGP abilities Agilent 2100 [40] Recently, Akinsanya et al [11] used NGS (mainly the Illumina method) for a metagenomic study of endophytes in Aloe vera and an assessment of their microbial diversity, whilst Yaish et al [8] conducted metagenomic studies of endophytes inhabiting Medicago truncatula roots. They found that Proteobacteria, Actinobacteria, Bacteroidetes were the dominant phyla of bacteria, and Firmicutes dominated in Aloe vera.…”

“…Salt stress usually induces osmotic and ionic imbalance inside plant cells [8,92,93]. In unfavorable conditions, endophytes reduce stress in plants by synthesizing osmoprotectants, e.g., proline and/or trehalose, volatile organic molecules, and exopolysaccharides [8].…”

“…These organisms are isolated from stems, roots, leaves, fruits, bulbs, and seeds [7]. Some of them stimulate the growth of plants [8], provide protection against biotic and abiotic stress [7,9], facilitate nutrient absorption from soil [10], and contribute to nitrogen assimilation [11]. All of these features are extremely important from the agricultural and biotechnological points of view.…”

Antioxidant Response to Salinity in Salt-Tolerant and Salt-Susceptible Cultivars of Date Palm

“…All these mechanisms involve gene expression alterations [14,15], epigenetic changes [16][17][18], and community changes in the microbes associated with the plants [19][20][21][22][23][24].…”

Isolation and Studies on Bacterial Endophytes from Two Venezuelan Rice Cultivars

“…Medicago truncatula when subjected to salinity stress [42], and also has been found in the endosphere of cannabis, potato and banana [43]- [45]. Other species enriched in both endospheres were P.…”