Isolation and characterization of drought-tolerant ACC deaminase and exopolysaccharide-producing fluorescent Pseudomonas sp.

Shaik Zulfikar Ali,Vardharajula Sandhya,Linga Venkateswar Rao

doi:10.1007/s13213-013-0680-3

Abstract

The enzyme 1-aminocyclopropane-1-carboxylate deaminase catalyzes the degradation of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of the plant hormone ethylene, into α-ketobutyrate and ammonia. The enzyme has been detected in a limited number of bacteria and plays a significant role in sustaining plant growth and development under biotic and abiotic stress conditions by reducing stress-induced ethylene production in plants. We have screened 32 fluorescent Pseudomonas sp. isolated from rhizosphere and non-rhizosphere soils of different crop production systems for drought tolerance using polyethylene glycol 6000 (PEG 6000). Nine of these isolates were tolerant to a substrate metric potential of −0.30 MPa (15 % PEG 6000) and therefore considered to be drought-tolerant. All of these drought-tolerant isolates were screened for ACC deaminase activity using ACC as the sole nitrogen source, and one (SorgP4) was found to be positive for ACC, producing 3.71 ± 0.025 and 1.42 ± 0.039 μM/mg protein/h of α-ketobutyrate under the non-stress and drought stress condition, respectively. The isolate SorgP4 also showed other plant growth-promoting traits, such as indole acetic acid production, phosphate solubilization, siderophore and hydrogen cyanide production. The ACC deaminase gene (acdS) from the isolate SorgP4 was amplified, and the nucleotide sequence alignment of the acdS gene showed significant homology with acdS genes of NCBI Genbank. The 16S rRNA gene sequencing analysis identified the isolate as Pseudomonas fluorescens. Both sequences have been submitted to the NCBI GenBank under the accession numbers JX885767 and KC192771 respectively.

Highlights

The gaseous hormone ethylene (C2H4) synthesized in plant tissues from the precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is involved in multiple physiological and developmental processes in plants, such as tissue differentiation, lateral bud development, seedling emergence, leaf and flower senescence, root hair development and elongation, anthocyanin synthesis, fruit ripening and degreening, and the production of volatile compounds responsible for aroma in fruits (Abeles et al 1992; Frankenberger and Arshad 1995; Spaink 1997; Bleecker and Kende 2000)
Isolate SorgP4, which tested positive for ACC deaminase, was screened for other PGP (Fig. 3) and found to produce significant amounts of indole acetic acid (IAA) (48.2±3.0 μg/mg protein) and 41.7 ± 5.0 μg/ml solubilized phosphate
A total of 17 fluorescent Pseudomonas strains were isolated on King′s B medium of which nine isolates (SorgP1, SorgP3, SorgP4, GnP9, RdgP10, SunfP12, SunfP13, BriP15 and BriP17) were able to grow at a minimum water potential (−0.30 MPa) (Fig. 1)

Summary

Introduction

The gaseous hormone ethylene (C2H4) synthesized in plant tissues from the precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is involved in multiple physiological and developmental processes in plants, such as tissue differentiation, lateral bud development, seedling emergence, leaf and flower senescence, root hair development and elongation, anthocyanin synthesis, fruit ripening and degreening, and the production of volatile compounds responsible for aroma in fruits (Abeles et al 1992; Frankenberger and Arshad 1995; Spaink 1997; Bleecker and Kende 2000). Ann Microbiol rhizosphere in association with the root system and which enhance the growth and development of the plant either directly or indirectly (Kloepper and Beauchamp 1992; Liu et al 1995) These PGPR strains possess the enzyme ACC deaminase (Jacobson et al 1994; Glick et al 1998; Shah et al 1997) which can cleave the plant ethylene precursor ACC to ammonia and α-ketobutyrate, thereby lowering the level of ethylene under various biotic and abiotic stresses (Glick et al 1998), such as salt stress (Cheng et al 2007, Mayak et al 2004a; Zahir et al 2009), flooding stress (Grichko and Glick 2001), drought stress (Mayak et al 2004b), heavy metal stress (Belimov et al 2005; Stearns et al 2005), and pathogen attack (Wang et al 2000). Soil-borne fluorescent pseudomonads have excellent root colonizing ability and catabolic versatility, and they produce a wide range of enzymes and metabolites which favor plant resistance to various biotic and abiotic stresses (Ramamoorthy et al 2001; Mayak et al 2004; Vivekananthan et al 2004)

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Results

Conclusion