Abstract
A novel Pseudomonas, designated strain BBB001T, an aerobic, rod-shaped bacterium, was isolated from the rhizosphere of Nicotiana glauca in Las Palmas Gran Canaria, Spain. Genomic analysis revealed that it could not be assigned to any known species of Pseudomonas, so the name Pseudomonas palmensis sp. nov. was proposed. A 16S rRNA gene phylogenetic analysis suggested affiliation to the Pseudomonas brassicae group, being P. brassicae MAFF212427 T the closest related type strain. Upon genomic comparisons of both strains, all values were below thresholds established for differentiation: average nucleotide identity (ANI, 88.29%), average amino acid identity (AAI, 84.53%), digital DNA-DNA hybridization (dDDH, 35.4%), and TETRA values (0.98). When comparing complete genomes, a total of 96 genes present exclusively in BBB001T were identified, 80 of which appear associated with specific subsystems. Phenotypic analysis has shown its ability to assimilate glucose, potassium gluconate, capric acid malate, trisodium citrate, and phenylacetic acid; it was oxidase positive. It is able to produce auxins and siderophores in vitro; its metabolic profile based on BIOLOG Eco has shown a high catabolic capacity. The major fatty acids accounting for 81.17% of the total fatty acids were as follows: C16:0 (33.29%), summed feature 3 (22.80%) comprising C16:1 ω7c and C16:1 ω6c, summed feature 8 (13.66%) comprising C18:1 ω7c, and C18:1ω6c and C17:0 cyclo (11.42%). The ability of this strain to improve plant fitness was tested on tomato and olive trees, demonstrating a great potential for agriculture as it is able to trigger herbaceous and woody species. First, it was able to improve iron nutrition and growth on iron-starved tomatoes, demonstrating its nutrient mobilization capacity; this effect is related to its unique genes related to iron metabolism. Second, it increased olive and oil yield up to 30% on intensive olive orchards under water-limiting conditions, demonstrating its capacity to improve adaptation to adverse conditions. Results from genomic analysis together with differences in phenotypic features and chemotaxonomic analysis support the proposal of strain BBB001T (=LMG 31775T = NCTC 14418T) as the type strain of a novel species for which the name P. palmensis sp. nov is proposed.
Highlights
Plant growth–promoting bacteria (PGPBs) are bacteria that colonize plant roots and promote plant growth
Strain BBB001T grows on plate count agar (PCA) at 28◦C forming circular colonies < 1 mm ∅, with smooth borders, opaque, yellowish, and creamy texture
The analysis based on 16S rRNA gene indicated that the strain BBB001T shared the highest similarity with P. qingdaonensis JJ3T (100%, non-validated taxon), P. brassicae MAFF212427T (99.85%), and Pseudomonas
Summary
Plant growth–promoting bacteria (PGPBs) are bacteria that colonize plant roots and promote plant growth. These bacteria live in the rhizosphere and play a very important role in plant fitness; in some species, they live in symbiosis with the plant, whereas in most of them, they establish a loose relationship colonizing the root surface. Many different bacterial genera have been reported to be PGPBs, and among them, Pseudomonas strains are very abundant. They are Gram-negative flagellated bacteria, often known because of the pigment production; they play crucial roles in soil health and plant development (Kloepper, 1992) and affect plant growth (Van Loon, 2007). Among the mechanisms frequently used by Pseudomonas species to benefit plant growth are siderophore production (Mavrodi et al, 2001; RasouliSadaghiani et al, 2014), phosphate solubilization (Anzuay et al, 2013), or stimulation of plant protection triggering induced systemic resistance (Bakker et al, 2007; Fatima and Anjum, 2017)
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