Deciphering the Potential of Rhizobium pusense MB-17a, a Plant Growth-Promoting Root Endophyte, and Functional Annotation of the Genes Involved in the Metabolic Pathway

Abstract

Plant growth-promoting rhizobacteria (PGPR) are root endophytic bacteria used for growth promotion, and they have broader applications in enhancing specific crop yield as a whole. In the present study, we have explored the potential of Rhizobium pusense MB-17a as an endophytic bacterium isolated from the roots of the mung bean (Vigna radiata) plant. Furthermore, this bacterium was sequenced and assembled to reveal its genomic potential associated with plant growth-promoting traits. Interestingly, the root endophyte R. pusense MB-17a showed all essential PGPR traits which were determined by biochemical and PGPR tests. It was noted that this root endophytic bacterium significantly produced siderophores, indole acetic acid (IAA), ammonia, and ACC deaminase and efficiently solubilized phosphate. The maximum IAA and ammonia produced were observed to be 110.5 and 81 μg/ml, respectively. Moreover, the PGPR potential of this endophytic bacterium was also confirmed by a pot experiment for mung bean (V. radiata), whose results show a substantial increase in the plant's fresh weight by 76.1% and dry weight by 76.5% on the 60th day after inoculation of R. pusense MB-17a. Also, there is a significant enhancement in the nodule number by 66.1% and nodule fresh weight by 162% at 45th day after inoculation with 100% field capacity after the inoculation of R. pusense MB-17a. Besides this, the functional genomic annotation of R. pusense MB-17a determined the presence of different proteins and transporters that are responsible for its stress tolerance and its plant growth-promoting properties. It was concluded that the unique presence of genes like rpoH, otsAB, and clpB enhances the symbiosis process during adverse conditions in this endophyte. Through Rapid Annotation using Subsystem Technology (RAST) analysis, the key genes involved in the production of siderophores, volatile compounds, indoles, nitrogenases, and amino acids were also predicted. In conclusion, the strain described in this study gives a novel idea of using such type of endophytes for improving plant growth-promoting traits under different stress conditions for sustainable agriculture.

The Effects of Rhizobium Inoculation On The Growth Of Rice (Oryza Sativa L.) and White Radish (Raphanus Sativus L.)

“…Positive effects of R. pusense GCB108 and GCB117 inoculation on growth of Raphanus sativus L. were comparable to prior investigations that demonstrated beneficial effects of Rhizobium as plant growth promoting bacteria in many plants including the non-legume plant radish [11]. It has been recently reported that the strain R. pusense MB-17a had all essential plant growth promoting traits based on biochemical tests and genomic evidence [7]. In this study, considerable increases in both shoot and root length of Raphanus sativus L. under hydroponic condition by R. pusense GCB108 and GCB117 inoculation suggest the high potential application of these two strains in biofertilizer production to stimulate growth of non-legume plants.…”

“…The results showed that the strains R. pusense GCB108 and GCB117 had the ability to produce catalase. Catalase is an important enzyme that helps bacteria protect their cells from oxidative stress and the ability of producing catalase has been well reported in many Rhizobium bacteria [7]. The ability of tolerance to salinity and different pH conditions is also important for microorganisms to be flexible in the environments.…”

“…In this study, both R. pusense GCB108 and GCB117 strains exhibited moderate growth under high salt concentration (3%), especially the strain GCB117 had a little growth under the salt concentration of 5%. Nitrogenfixing bacteria are quite sensitive to saline environmnents, although according to previous studies, several Rhizobium strains (e.g., Rhizobium meliloti L., Rhizobium pusense MB-17a) have been found to be able to survive and exhibit growth under high saline conditions [7]. High salt concentrations may significantly reduce nitrogen fixation by reducing Rhizobium growth in the soil, inhibiting root colonization and early symbiosis.…”

Sulfur-Oxidizing Bacteria From Coal Mine Enhance Sulfur Nutrition in Pigeonpea (Cajanus cajan L.)

“…They exhibit chemolithotrophic growth in presence of inorganic sulfur. The heterotrophs include species of Achromobacter, Arthrobacter, Brevibacterium, Flavobacterium, Klebsiella, Micrococcus, Mycobacterium, Paracoccus, Streptomyces, Thiosphaera, and Xanthobacter (Wainwight, 1984;Kuenen et al, 1992, Ito et al, 2004Ryan et al, 2009;Sajjad et al, 2016;Chaudhary et al, 2017Chaudhary et al, , 2021. However, mixotrophs including species of Stenotrophomonas, Bacillus, Pseudomonas, Paenibacillus, Micrococcus, Pseudoclavibacter, Diaphorobacter, Aeromonas, Alcaligenes, Citrobacter, Rhizobium, and Bordetella are the key bacterial species playing important roles in nutrient mineralization and promoting plant growth (Sultan and Faisal, 2016;Sanwani et al, 2022).…”

Indole Acetic Acid Producing And Phosphate Solubilizing Bacteria Native To Kenyan Soils Promote Growth of Common Bean (Phaseolus Vulgaris L.)

“…pusense among others synthesizes IAA, thereby playing an important role in legume-rhizobia interaction [12][13][14][15][16][17] . It was reported that IAA acts as a signal molecule which is involved in plant signal processing, motility, or attachment of bacteria in root which help in legume-Rhizobium symbiosis 18 .…”