Abstract
The bacterial genus Pantoea has been widely evaluated as promising bacteria to increase phosphorus (P) availability in soil. The aim of this study was to characterize the phosphate solubilizing (PS) activity of a Pantoea agglomerans strain and to evaluate the impact of its application in a semi-arid soil on phosphate availability and structure of the bacterial communities as a whole. An incubation experiment under close-to-natural soil environmental conditions was conducted for 15 days at 30 °C. High-throughput sequencing of the bacterial 16S rRNA gene was used to characterize and to compare the bacterial community structure of P. agglomerans-inoculated soil with non-inoculated control. Furthermore, a qPCR-based method was developed for detection and quantification of the functional genes related to the expression of mineral phosphate solubilization (MPS) phenotype in P. agglomerans. The results showed that in vitro solubilization of Ca3(PO4)2 by P. agglomerans strain was very efficient (980 mg/L), and it was associated with a drop in pH due to the secretion of gluconic acid; these changes were concomitant with the detection of gdh and pqqC genes. Moreover, P. agglomerans inoculum application significantly increased the content of available P in semi-arid soil by 69%. Metagenomic analyses showed that P. agglomerans treatment modified the overall edaphic bacterial community, significantly impacting its structure and composition. In particular, during P. agglomerans inoculation the relative abundance of bacteria belonging to Firmicutes (mainly Bacilli class) significantly increased, whereas the abundance of Actinobacteria together with Acidobacteria and Chloroflexi phyla decreased. Furthermore, genera known for their phosphate solubilizing activity, such as Aneurinibacillus, Lysinibacillus, Enterococcus, and Pontibacter, were exclusively detected in P. agglomerans-treated soil. Pearson’s correlation analysis revealed that changes in soil bacterial community composition were closely affected by soil characteristics, such as pH and available P. This study explores the effect of the inoculation of P. agglomerans on the bacterial community structure of a semi-arid soil. The effectiveness in improving the phosphate availability and modification in soil bacterial community suggested that P. agglomerans represent a promising environmental-friendly biofertilizer in arid and semi-arid ecosystems.
Highlights
Phosphorus (P) makes up 0.7% of the Earth’s lithosphere and represents the eleventh most abundant element [1]
Cells of P. agglomerans V8R67 inoculated in National Botanical Research Institute’s Phosphate (NBRIP) medium containing Ca3 (PO4 )2 as the sole P source started to grow exponentially after an initial log phase of about 3 days and reached the stationary phase after 4 days of growth (Figure 1a)
Cells of P. agglomerans V8R67 inoculated in NBRIP medium containing Ca3(PO4)2 as the sole P source started to grow exponentially after an initial lo phase of about 3 days and reached the stationary phase after 4 days of growth7 of(Figure
Summary
Phosphorus (P) makes up 0.7% of the Earth’s lithosphere and represents the eleventh most abundant element [1]. P is the most important key element next to nitrogen that often limits plant productivity [2]. Chemical phosphate fertilizer has been used as a source of replenishing soil P. The main source of manufacturing phosphate fertilizers is mined rock phosphate, which in turn is non-renewable and may only last for 100–400 years [4,5]. In addition to resource issues, chemical phosphate fertilizers represent the main cost of agricultural production and can cause environmental complications, including reduction of crop yield, water quality, and waterway eutrophication [4], along with changes in the edaphic microbial communities [6]
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