Succinate irrepressible periplasmic glucose dehydrogenase of Rhizobium sp. Td3 and SN1 contributes to its phosphate solu
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ORIGINAL PAPER
Succinate irrepressible periplasmic glucose dehydrogenase of Rhizobium sp. Td3 and SN1 contributes to its phosphate solubilization ability Bhagya Iyer1 · Shalini Rajkumar1 Received: 19 November 2018 / Revised: 24 January 2019 / Accepted: 12 February 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract Td3 and SN1 are phosphate-solubilizing nodule rhizobia of Cajanus cajan and Sesbania rostrata, respectively. They solubilized 423 µg/mL and 428 µg/mL phosphate from tricalcium phosphate through the secretion of 19.2 mM and 29.6 mM gluconic acid, respectively, when grown in 100 mM glucose. However, 90% and 80% reduction in phosphate solubilization coupled to the production of 40 mM (Td3) and 28.2 mM (SN1) gluconic acid was observed when the two isolates were grown in 50 mM succinate + 50 mM glucose. Our results illustrate the role of succinate irrepressible glucose dehydrogenase (gcd) in phosphate solubilization and the role of succinate: proton symport in succinate-mediated repression of phosphate solubilization in these rhizobia. Calcium ion supplementation reduced the 88% and 72% repression in P solubilization to 18% and 9% in Td3 and SN1, respectively, coupled to a reduction in media pH from 6.8 to 4.9 in Td3 and 6.3 to 4.8 in SN1. Hence, repression had no genetic basis and is purely due to the biochemical interplay of protons and other cations. Keywords Rhizobia · Phosphate solubilization · Periplasmic glucose dehydrogenase · Gluconic acid · Succinate · Catabolite repression.
Introduction The excessive application of chemical fertilizers in an attempt to improve the crop productivity not only poses harm to the soil but also to the air and water bodies (Savci 2012). Mining microorganisms for augmenting soil fertility and improving plant growth and productivity has gained interest due to the escalating cost of fertilizers and their negative environmental impacts (Nakhro and Dkhar 2010). Rhizosphere, a soil region influenced by root secretion supports a multitude of active microbial population with beneficial, neutral as well as detrimental effects on plant Communicated by Jorge Membrillo-Hernández. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00203-019-01630-2) contains supplementary material, which is available to authorized users. * Shalini Rajkumar [email protected] 1
Institute of Science, Nirma University, Sarkhej‑Gandhinagar Highway, Ahmedabad, Gujarat 382 481, India
growth. Rhizospheric and root-colonizing bacteria induce plant growth promotion (PGP) by direct and indirect mechanisms (Glick 1995) where mineral phosphate solubilization (MPS) is one of the chief direct mechanism to improve plant nutrient uptake. Phosphorous (P) the second major macronutrient next to nitrogen (N) (Ezawa et al. 2002) is exceedingly vital for plant growth and development. However, soil P bioavailability is very limited because of its adsorption to charged metal ions; making it unavailable for plant uptake. In fertile soil, a
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