Pseudomonas algeriensis sp. nov.: A Promising Phosphate-Solubilizing Endophytic Bacterium Isolated from Legume Root Nodules in the Coastal Dunes of Northwest Algeria.

Strain NR3^T, an endophytic bacterium, was isolated from the root nodules of Retama monosperma collected in the coastal dunes of Cap-Falcon beach, northwestern Algeria. Its taxonomic position was determined using a polyphasic approach. Analysis of the 16S rRNA gene sequence revealed that strain NR3^T shared the highest pairwise sequence similarity with Pseudomonas canavaninivorans HB002^T (99.6%), Pseudomonas alvandae SWRI17^T (99.5%), Pseudomonas bijieensis L22-9^T (99.5%), and Pseudomonas tehranensis SWRI196^T (99.4%). Further 16S rRNA phylogenetic analysis confirmed these species as its closest relatives. Multi-locus sequence analysis (MLSA) based on four housekeeping genes (16S rRNA, gyrB, rpoB and rpoD) positioned strain NR3^T in a distinct, well-separated clade, differentiating it from all other Pseudomonas species. A comprehensive phylogenomic analysis, conducted using the Type (Strain) Genome Server and genome-scale phylogenetic reconstruction, based on a concatenated alignment of 72 housekeeping genes reinforced the unique phylogenetic placement of strain NR3^T, highlighting its divergence from its closest relatives, including P. canavaninivorans HB002^T, P. alvandae SWRI17^T, while identifying "Pseudomonas agronomica" SAICEU22^T as its nearest phylogenetic neighbor. Whole-genome sequence comparisons using digital DNA-DNA hybridization (dDDH) and pairwise orthologous average nucleotide identity (OrthoANIu) yielded values well below the species delineation thresholds (39.0 and 38.6% for dDDH, 89.5 and 89.2% for OrthoANIu), further confirming that strain NR3^T represents a distinct Pseudomonas species. The genome of strain NR3^T consists of 5,694,417 bp with a G + C content of 60.7% and is predicted to encode 5102 coding sequences (CDSs). Notably, several genes associated with plant growth-promoting traits, particularly those involved in phosphate solubilization, were identified, suggesting its potential for enhancing sustainable agricultural practices. The phenotypic characterization revealed that strain NR3^T is a Gram-negative, rod-shaped, motile bacterium. It grows at temperatures ranging from 4 to 47 °C, with an optimum at 28 °C, within a pH range of 5.0 to 10.0 (optimum at pH 7), and tolerates NaCl concentrations up to 4% (w/v), with optimal growth at 0.5%. The predominant cellular fatty acids of strain NR3^T are C_16:0, summed feature 2 (C_14:0 3-OH/C_16:1 iso I), and summed feature 8 (C_18:1 ω7c/C_18:1 ω6c). Based on phylogenetic, genomic, and phenotypic analyses, strain NR3^T (= DSM 117380^T = CIP 112483^T = LMG 33617^T) is designated as the type strain of a novel Pseudomonas species, for which the name Pseudomonas algeriensis sp. nov. is proposed.