Psychrobacter halotolerans sp. nov., a halotolerant plant growth-promoting bacterium that enhances lettuce tolerance to salt stress

Abstract

A polyphasic taxonomic approach was used to characterize strain B38T, isolated from the phyllosphere of Salicornia hispanica. The strain is an aerobic, Gram-negative, halotolerant coccus–rod-shaped bacterium exhibiting optimal growth at 28 °C, pH 6-9, and up to 12 % (w/v) NaCl. The genome of strain B38T is 3.2 Mbp with a DNA G+C content of 43.81 mol%. Phylogenetic analysis based on the 16S rRNA gene sequences placed B38T within the genus Psychrobacter. Although 16S rRNA gene sequencing showed high similarity to P. alimentarius (99.73%), genomic indices (ANI, AAI, and dDDH) remained below species delimitation thresholds. Chemotaxonomic features included C18:1 ω9c as the major fatty acid, Q-8 as the main quinone, and diphosphatidylglycerol as the major polar lipid. Consequently, strain B38T (=CECT 31210; =LMG 33901) is proposed as Psychrobacter halotolerans sp. nov. Additionally, the plant growth-promoting (PGP) potential of the halotolerant strain B38T was evaluated in lettuce under salt stress, alongside the salt-tolerance mechanisms induced by inoculation. Strain B38ᵀ significantly enhanced lettuce biomass, leaf area, and PSII quantum efficiency compared to non-inoculated controls. These benefits were linked to increased soluble sugars and phenolic compounds, modulation polyamine homeostasis, and reduced oxidative damage. Our results demonstrate that P. halotolerans B38ᵀ effectively mitigates salt stress in plants, representing a promising biotechnological tool for enhancing salinity tolerance in agricultural systems.