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. 2018 Jan 11:8:2580.
doi: 10.3389/fmicb.2017.02580. eCollection 2017.

Drought-Tolerant Plant Growth-Promoting Rhizobacteria Associated with Foxtail Millet in a Semi-arid Agroecosystem and Their Potential in Alleviating Drought Stress

Xuguang Niu  1   2 , Lichao Song  1   2 , Yinong Xiao  1   2 , Weide Ge  3
Affiliations

Drought-Tolerant Plant Growth-Promoting Rhizobacteria Associated with Foxtail Millet in a Semi-arid Agroecosystem and Their Potential in Alleviating Drought Stress

Xuguang Niu et al. Front Microbiol. .

Abstract

The application of plant growth promoting rhizobacteria (PGPR) to agro-ecosystems is considered to have the potential for improving plant growth in extreme environments featured by water shortage. Herein, we isolated bacterial strains from foxtail millet (Setaria italica L.), a drought-tolerant crop cultivated in semiarid regions in the northeast of China. Four isolates were initially selected for their ability to produce ACC deaminase as well as drought tolerance. The isolates were identified as Pseudomonas fluorescens, Enterobacter hormaechei, and Pseudomonas migulae on the basis of 16S rRNA sequence analysis. All of these drought-tolerant isolates were able to produce EPS (exopolysaccharide). Inoculation with these strains stimulated seed germination and seedling growth under drought stress. Pseudomonas fluorescens DR7 showed the highest level of ACC deaminase and EPS-producing activity. DR7 could efficiently colonize the root adhering soil, increased soil moisture, and enhance the root adhering soil/root tissue ratio. These results suggest drought tolerant PGPR from foxtail millet could enhance plant growth under drought stress conditions and serve as effective bioinoculants to sustain agricultural production in arid regions.

Keywords: 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase; drought stress; foxtail millet (Setaria italica L.); plant growth-promoting rhizobacteria (PGPR); semi-arid region.

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Figures

FIGURE 1
FIGURE 1
Growth patterns of the four rhizobacteria under non-stressed (NS) and drought-stressed conditions of differing matric potential. (A) DR7, (B) DR11, (C) DR16, (D) DR35. Error bars show standard deviations of mean values.
FIGURE 2
FIGURE 2
ACC deaminase activity in isolated bacteria under non-stressed (NS) and drought-stressed (–0.30 MPa) conditions. Values with different letters are significantly different according to Duncan’s multiple range test (P = 0.05). Error bars show standard deviations of mean values.
FIGURE 3
FIGURE 3
Phylogenetic analysis of the four ACC deaminase-producing bacteria based on acdS gene sequences available from the NCBI GenBank database. Distance and clustering analyses were performed using the neighbor-joining method using MEGA ver. 4.0. Bootstrap values (n = 1,000) are listed as percentages at the branching points.
FIGURE 4
FIGURE 4
Population density of different bacteria inoculated to foxtail millet at different time intervals under axenic conditions. 10 DI, 10 days after inoculation; 21 DI, 21 days after inoculation; 30 DI, 30 days after inoculation (9 days after water stress). Values with different letters are significantly different according to Duncan’s multiple range test (P = 0.05). Error bars show standard deviations of mean values.
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