Estuaries of the Tinto, Odiel and Piedras rivers as source of new species of Pseudomonas with biofertilizer potential under stress conditions

Abstract

Abstract The estuaries of the Tinto, Odiel, and Piedras rivers have been extensively studied by several groups due to ecological aspects such as heavy metal contamination, nutrient deficiency and degradation influenced by climate change. Aimed to recover these ecosystems, a large collection of plant growth-promoting bacteria (PGPB), several of them previously identified as new species, was isolated from the rhizosphere and tissues of native plants. In this study, we analyse the strains N4, N8 T , L1 T , and SDT3 T as potential new species. A phylogenomic analysis revealed that four strains belong to the genus Pseudomonas , forming distinct clades with full support. Digital DNA-DNA hybridization and average nucleotide identity values were below the species delineation thresholds (70% and 95–96%), confirming the novelty of strains N8 T , L1 T , and SDT3 T , while N4 and N8 T were identified as the same species. As a result, we propose the names Pseudomonas medicaginis sp. nov., Pseudomonas onubensis sp. nov., and Pseudomonas spartinae sp. nov., with P. medicaginis comprising two strains. These strains, previously identified as PGPB, harboured genes related to PGP traits and were further characterized phenotypically and biochemically. To evaluate the agroecological potential of N8 T strain, it was tested in co-inoculation with the corresponding rhizobia on lentil, pea, alfalfa, and bean under greenhouse conditions. In all legumes, N8 T enhanced shoot and root biomass, increased nodule numbers, and improved nitrogen content compared with single rhizobia inoculation. In summary, these estuarine ecosystems are not only ecologically significant for their microbial diversity but also serve as reservoirs of beneficial bacteria with promising agroecological applications.