Genomic insights into plant growth promoting rhizobia capable of enhancing soybean germination under drought stress

Abstract

Background The role of soil microorganisms in plant growth, nutrient utilization, drought tolerance as well as biocontrol activity cannot be over-emphasized, especially in this era when food crisis is a global challenge. This research was therefore designed to gain genomic insights into plant growth promoting (PGP) Rhizobium species capable of enhancing soybean ( Glycine max L.) seeds germination under drought condition. Results Rhizobium sp. strain R1, Rhizobium tropici strain R2, Rhizobium cellulosilyticum strain R3, Rhizobium taibaishanense strain R4 and Ensifer meliloti strain R5 were found to possess the entire PGP traits tested. Specifically, these rhizobial strains were able to solubilize phosphate, produce exopolysaccharide (EPS), 1-aminocyclopropane-1-carboxylate (ACC), siderophore and indole-acetic-acid (IAA). These strains also survived and grew at a temperature of 45 °C and in an acidic condition with a pH 4. Consequently, all the Rhizobium strains enhanced the germination of soybean seeds (PAN 1532 R) under drought condition imposed by 4% poly-ethylene glycol (PEG); nevertheless, Rhizobium sp. strain R1 and R. cellulosilyticum strain R3 inoculations were able to improve seeds germination more than R2, R4 and R5 strains. Thus, genomic insights into Rhizobium sp. strain R1 and R. cellulosilyticum strain R3 revealed the presence of some genes with their respective proteins involved in symbiotic establishment, nitrogen fixation, drought tolerance and plant growth promotion. In particular, exoX , htrA , Nif , nodA , eptA , IAA and siderophore-producing genes were found in the two rhizobial strains. Conclusions Therefore, the availability of the whole genome sequences of R1 and R3 strains may further be exploited to comprehend the interaction of drought tolerant rhizobia with soybean and other legumes and the PGP ability of these rhizobial strains can also be harnessed for biotechnological application in the field especially in semiarid and arid regions of the globe.

Plant Growth-Promoting Rhizobacteria Isolated from Degraded Habitat Enhance Drought Tolerance of Acacia (Acacia abyssinica Hochst. ex Benth.) Seedlings

“…Higher EPS production has been indicated in culture media supplemented with sucrose and glucose [ 57 ]. These variations are due to the kinds of sugar used and enzymatic metabolism of each strain [ 58 ] and the activity of glucosyltransferases [ 59 , 60 ]. EPS is fundamental for microbial life and provides an ideal environment for chemical reactions, nutrient entrapment, and protection against environmental stresses such as salinity and drought [ 61 ].…”

Plant Growth Promoting Rhizobacterial Mitigation of Drought Stress in Crop Plants: Implications for Sustainable Agriculture

“…Like the PGPR, rhizobia also possess PGP traits such as the ability to synthesize EPS, IAA, ACC deaminase, siderophore, as well as to solubilize phosphate, in addition to fixing nitrogen in soils. Members of the Rhizobiaceae family are attracted to legumes through the release of flavonoids, which induces the transcription of Nod factor (lipochitin oligosaccharides (LCOs) and consequently, the formation of root nodules [160][161][162][163] within which they differentiate into bacteroids and fix atmospheric N in the root nodules of the crops [161,164] in exchange for photosynthetically obtained carbon. LCOs stimulate plant growth promotional activities through the initiation of mutualistic association to varying phytohormone levels, resulting in enhanced photosynthesis and improved resistance to biotic and environmental stresses [130,164,165].…”

Variation of soil microbiome in licorice rhizosphere driven with inoculating dark septate endophytes under drought stress

“…Bacillus, Microbacterium, Nocardioides, Pseudarthrobacter, Sporocytophaga, and Arenimonas comprised 81.3% of the total abundance under the DAV treatment. These bacteria have high drought stress tolerance and most of them promote plant growth [53][54][55]. Bacillus species are also effective biocontrol bacteria [56].…”