Derepression of Mineral Phosphate Solubilization Phenotype by Insertional Inactivation of iclR in Klebsiella pneumoniae

Abstract

The mode of succinate mediated repression of mineral phosphate solubilization and the role of repressor in suppressing phosphate solubilization phenotype of two free-living nitrogen fixing Klebsiella pneumoniae strains was studied. Organic acid mediated mineral phosphate solubilization phenotype of oxalic acid producing Klebsiella pneumoniae SM6 and SM11 were transcriptionally repressed by IclR in presence of succinate as carbon source. Oxalic acid production and expression of genes of the glyoxylate shunt (aceBAK) was found only in glucose but not in succinate- and glucose+succinate-grown cells. IclR, repressor of aceBAK operon, was inactivated using an allelic exchange system resulting in derepressed mineral phosphate solubilization phenotype through constitutive expression of the glyoxylate shunt. Insertional inactivation of iclR resulted in increased activity of the glyoxylate shunt enzymes even in succinate-grown cells. An augmented phosphate solubilization up to 54 and 59% soluble phosphate release was attained in glucose+succinate-grown SM6Δ and SM11Δ strains respectively, compared to glucose-grown cells, whereas phosphate solubilization was absent or negligible in wildtype cells grown in glucose+succinate. Both wildtype and iclR deletion strains showed similar indole-3-acetic acid production. Wheat seeds inoculated with wildtype SM6 and SM11 improved both root and shoot length by 1.2 fold. However, iclR deletion SM6Δ and SM11Δ strains increased root and shoot length by 1.5 and 1.4 folds, respectively, compared to uninoculated controls. The repressor inactivated phosphate solubilizers better served the purpose of constitutive phosphate solubilization in pot experiments, where presence of other carbon sources (e.g., succinate) might repress mineral phosphate solubilization phenotype of wildtype strains.

Inorganic Phosphate Solubilization by Rhizosphere Bacterium Paenibacillus sonchi: Gene Expression and Physiological Functions

“…Divya et al (2011) showed that succinate and malate individually and as mixtures repressed gluconate production and PS in Pseudomonas aeruginosa. It is also a component that represses PS phenotype in Klebsiella pneumoniae (Rajput et al, 2013(Rajput et al, , 2015. Based on that and our findings, the reduction of the metabolic flux toward the TCA cycle might be one strategy utilized by SBR5 to perform PS.…”

Enterobacter cloacae, an Endophyte That Establishes a Nutrient-Transfer Symbiosis With Banana Plants and Protects Against the Black Sigatoka Pathogen

“…E. cloacae was found to release an appreciable amount of IAA (74.2 μg/mL) after 120 h of incubation, which was induced by L -tryptophan (50 mM). Otherwise, the K. pneumoniae strain was a low auxin producer (0.328 μg/mL); this concentration is much lower compared to those reported in rhizospheric and free-living strains of K. pneumoniae (Sachdev et al, 2009; Rajput et al, 2015; Kuan et al, 2016).…”

“…As shown in Table 1, E. cloacae and K. pneumoniae have phosphate solubilization indices of 148.59 ± 5.38 and 131.11 ± 7.84, respectively. Congruently, both genera have been previously reported to be phosphate solubilizers (Rajput et al, 2015; Dhole et al, 2016; Shabanamol et al, 2018; Zheng et al, 2018). The production of phytohormones such IAA is another factor influencing plant growth.…”

Isolation and characterization of two phosphate-solubilizing fungi from rhizosphere soil of moso bamboo and their functional capacities when exposed to different phosphorus sources and pH environments

“…was higher in the media of AlPO 4 than other P sources [ 35 ]. The PSF secretes various organic acids, such as malic, gluconic, tartaric, oxalic, citric and butyric et al [ 36 , 37 ]. Li et al found oxalic acid was the main product during FePO 4 and AlPO 4 solubilization by Aspergillus spp., whereas gluconic acid was mainly produced by Penicillium spp.…”