Taxonomic description of Pseudomonas rhizovicinus sp. nov., isolated from the rhizosphere of a desert shrub Haloxylon ammodendron.

A Gram-negative aerobic bacterium, strain M30-35 T, was isolated from the rhizosphere of Haloxylon ammodendron in Tengger desert, Gansu province, northwest China. Our previous research indicated that strain M30-35 T can promote the growth of ryegrass (Lolium perenne L.). In this study, strain M30-35 T was subjected to a polyphasic taxonomic study. Phylogenetic analysis of the 16S rRNA gene and two other housekeeping genes (gyrB, rpoD) showed that strain M30-35 T is a member of Pseudomonas anguilliseptica group. The average nucleotide identity (ANI) scores for strains KMM 3042 T and FR1439T were 76.5% and 83.7%, respectively, and DNA-DNA hybridization (DDH) were 21.6% and 26.6%, respectively, and the rates were less than the threshold range for species determination. The dominant cellular fatty acids of strain M30-35 T were C16:0 (22.7%), summed feature 3 (C16:1ω7c and/or C16:1ω6c; 18.5%), summed feature 8 (C18:1ω7c and/or C18:1ω6c; 23.1%). The major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phospholipid and aminophospholipid and the predominant respiratory quinone was ubiquinone (Q9). On the basis of above data, it can be concluded that strain M30-35 T represents a novel species in the genus Pseudomonas, for which the name Pseudomonas rhizovicinus sp. nov. is proposed. The type strain is M30-35 T (= MCCC 1K03247T = KCTC 52664 T).

Altererythrobacter rhizovicinus sp. nov., isolated from rhizosphere soil of Haloxylon ammodendron.

A salt-tolerant, Gram-negative, rod-shaped and yellow-pigmented bacterium, designated strain AY-3RT, was isolated from rhizosphere soil of a desert xerophyte, Haloxylon ammodendron, sampled at Badain Jaran Desert, Alxa region, Inner Mongolia, PR China. Growth of this strain was observed at 20-42 °C (optimum, 28-30 °C), at pH 6.0-9.0 (optimum, pH 6.0-7.0) and at 0-8 % (w/v) NaCl (optimum, 3 %). Results of phylogenetic analysis based on 16S rRNA gene sequences showed that strain AY-3RT was a member of the genus Altererythrobacter, with the highest similarity to Altererythrobacter aerophilus Ery1T (97.6 %), followed by Altererythrobacter xinjiangensis S3-63T (96.9 %). The predominant fatty acids (>10.0 %) were C18 : 1ω7c, C17 : 1ω6c and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). The major polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, sphingoglycolipid and one unknown polar lipid. The predominant respiratory quinone was ubiquinone-10. The G+C content of the genomic DNA of strain AY-3RT was 66.3 mol%. On the basis of the data from this polyphasic taxonomic study, strain AY-3RT represents a novel species of the genus Altererythrobacter, named Altererythrobacter rhizovicinus sp. nov. (=MCCC 1K03572T=KCTC 72280T).

Biofertilizers with beneficial rhizobacteria improved plant growth and yield in chili (Capsicum annuum L.).

Chemical fertilizers can supply essential nutrients to crops increasing their yield, however, they can also cause serious environmental problems. Biofertilizer has received more and more attention because of its environmentally friendly and pollution-free characteristics. Haloxylon ammodendron, a desert succulent shrub, has become an important plant species for vegetation restoration in several deserts in China because of its strong drought tolerance. Its extensive root systems and unique rhizosphere bacterial community aid H. ammodendron adapt to this extreme environment. In this study, Bacillus sp. WM13-24 and Pseudomonas sp. M30-35 isolated from the rhizosphere of H. ammodendron in our previous study and Bacillus amyloliquefaciens GB03 and Sinorhizobium meliloti ACCC17578 as well-studied beneficial strains were used to prepare two types of biofertilizer, WM13-24 biofertilizer containing Bacillus sp. WM13-24 and integrated biofertilizer containing all the four strains. Results presented here showed that WM13-24 biofertilizer and the integrated biofertilizer improved chili plant growth, fruit yield and quality and the rhizosphere soil nitrogen content, enzyme activities, and the quantity and biodiversity of viable bacteria. Compared to the control, WM13-24 biofertilizer and a commercial biofertilizer, the integrated biofertilizer performed best in significantly increasing plant height, stem diameter, leaf length and width, chlorophyll content, fruit yield, soluble sugar content, ascorbic acid content, organic acid content, soil urease activity, catalase activity and the quantity and biodiversity of viable bacteria. This study provided a theoretical and practical basis for large scale development of integrated biofertilizers using beneficial rhizobacterial strains from the desert plant rhizosphere.

Induced Salt Tolerance of Perennial Ryegrass by a Novel Bacterium Strain from the Rhizosphere of a Desert Shrub Haloxylon ammodendron.

Drought and soil salinity reduce agricultural output worldwide. Plant-growth-promoting rhizobacteria (PGPR) can enhance plant growth and augment plant tolerance to biotic and abiotic stresses. Haloxylon ammodendron, a C4 perennial succulent xerohalophyte shrub with excellent drought and salt tolerance, is naturally distributed in the desert area of northwest China. In our previous work, a bacterium strain numbered as M30-35 was isolated from the rhizosphere of H. ammodendron in Tengger desert, Gansu province, northwest China. In current work, the effects of M30-35 inoculation on salt tolerance of perennial ryegrass were evaluated and its genome was sequenced to identify genes associated with plant growth promotion. Results showed that M30-35 significantly enhanced growth and salt tolerance of perennial ryegrass by increasing shoot fresh and dry weights, chlorophyll content, root volume, root activity, leaf catalase activity, soluble sugar and proline contents that contributed to reduced osmotic potential, tissue K⁺ content and K⁺/Na⁺ ratio, while decreasing malondialdehyde (MDA) content and relative electric conductivity (REC), especially under higher salinity. The genome of M30-35 contains 4421 protein encoding genes, 12 rRNA, 63 tRNA-encoding genes and four rRNA operons. M30-35 was initially classified as a new species in Pseudomonas and named as Pseudomonas sp. M30-35. Thirty-four genes showing homology to genes associated with PGPR traits and abiotic stress tolerance were identified in Pseudomonas sp. M30-35 genome, including 12 related to insoluble phosphorus solubilization, four to auxin biosynthesis, four to other process of growth promotion, seven to oxidative stress alleviation, four to salt and drought tolerance and three to cold and heat tolerance. Further study is needed to clarify the correlation between these genes from M30-35 and the salt stress alleviation of inoculated plants under salt stress. Overall, our research indicated that desert shrubs appear rich in PGPRs that can help important crops tolerate abiotic stress.