1. DSpace at Nirma University
  2. 05. Institute of Science
  3. Theses, IS
Please use this identifier to cite or link to this item: http://10.1.7.192:80/jspui/handle/123456789/10500
Title: Arabinose and Glucose Dependent Mineral Phosphate Solubilization Phenotype and Its Catabolite Repression in Rhizobial Isolates
Authors: Joshi, Ektaben
Keywords: Science Theses
Theses 2020
14FTPHDS34
Phosphate Solubilization
Rhizobial Isolates
Issue Date: Jun-2020
Publisher: Institute of Science, Nirma University
Series/Report no.: ;ST000076
Abstract: he most efficient mineral phosphate solubilization (MPS) in Gram-negative bacteria occurs through solubilization of insoluble inorganic compounds. Phosphate solubilization by potential nitrogen fixers like rhizobia may prove to be of dual advantage as it can solubilize P as well as fix N2 for the plants. In Gram negative bacteria, gluconic acid produced via PQQ dependent periplasmic glucose dehydrogenase (Gcd) has shown most efficient P solubilization when glucose is the sole carbon source. However, the other rhizospheric sugars have received very little or no attention. After glucose, arabinose and xylose are the most abundant sugars present in the soil that can be utilized by microorganisms. L-arabinose is a superior carbon source and is metabolized by distinct pathways that distinguish rhizobia into slow and fast growers based on its utilization. Role of a pentose such as arabinose, on PGP traits of bacteria especially P solubilization has not been explored that much. The present study was based on the hypothesis that unique rhizobial isolates that solubilize P using more than one rhizospheric sugar (glucose and arabinose) would be more effective as biofertilizers. Rhizobium sp. RM, Rhizobium sp. RS and Rhizobium sp. SE were root nodule isolates of Vigna radiata and Cicer arientinum respectively. Rhizobium sp. RM, RS and SE could solubilize TCP and RP using glucose and arabinose as C sources. RM and RS were unique as they could produce two different organic acids, gluconic acid and oxalic acid using glucose and arabinose respectively. Production of gluconic acid from glucose leading to P solubilization has already been established in several bacterial species but oxalic acid mediated P solubilization using arabinose is not reported. Arabinose utilization leads to production of oxalic acid that aids P solubilization. Thus, the study was aimed to elucidate the pathway of arabinose utilization followed by the rhizobial isolates. In slow growing rhizobia (RM and RS), glycolaldehyde was formed from L-2-keto-3-deoxyarabonate (L-KDA), which gets oxidized oxalate, which was responsible for arabinose dependent P solubilization. On the basis of salt tolerance capacity, expression profile and enzyme activity of arabinose metabolic pathway, RM and RS were characterized as slow growing rhizobia whereas SE was characterized as fast￾growing rhizobia. This is perhaps the first study on mechanism of P solubilization in rhizobia through utilization of two different sugars, glucose and arabinose and its repression by succinate. SMCR of arabinose dependent MPS is the unique aspect of this study. As RM was a better solubilizer and produced higher amounts of organic acids, it was chosen for whole genome sequencing. The genome of RM is 5.6 Mb with 57.1% GC content. Genome of RM comprises the genes which contributing to almost all the PGP traits, nodulation (nod), nitrogen fixation (nif and fix) and arabinose catabolic pathway. Availability of genome sequence of such a versatile plant growth promoting rhizobia will help in elucidating the physiology and regulatory mechanism of catabolite repression and other phyto-beneficial traits for its use as a biofertilizer.
Description: ST000076
URI: http://10.1.7.192:80/jspui/handle/123456789/10500
Appears in Collections:Theses, IS

Files in This Item:
File Description SizeFormat 
ST000076.pdfST0000769.92 MBAdobe PDFThumbnail
View/Open
Show full item record


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.