Plant growth-promoting traits of Rhizophora mangle-associated bacteria and their effects on tomato (Solanum lycopersicum)

• Bioinoculants enhanced S. lycopersicum yield, which was reflected in its growth. • All bacterial isolates exhibited nitrogen-fixing capacity, confirmed by nif H gene amplification. • First report of IAA production in N. resinovorum, A. insuavis and Curtobacterium sp. • Potassium solubilization was observed in 72 % of strains; 90.9 % solubilized phosphate. Mangrove ecosystems harbor a remarkable microbial diversity that plays essential roles in nutrient recycling and transformation, contributing to soil fertility and quality. However, the exploration of this microbiota as a source of plant growth-promoting bacteria (PGPB) remains at an early stage. In this study, bacterial strains associated with the rhizosphere of Rhizophora mangle from Colombian Pacific mangroves were characterized and their effects on Solanum lycopersicum var. cerasiforme were evaluated. Strains were isolated using nitrogen-free media and identified through 16S rRNA gene sequencing. Key plant growth-promoting (PGP) functions were assessed, including biological nitrogen fixation (confirmed by the presence of the nifH gene), indole-3-acetic acid (IAA) production, siderophore synthesis, and phosphate and potassium solubilization. All isolates fixed nitrogen and produced IAA; 50 % synthesized siderophores, 72 % solubilized potassium, and 90.9 % solubilized phosphate. A factorial analysis of mixed data (FAMD) was used to select four functionally promising strains: Raoultella terrigena RFN53, Klebsiella variicola RFN55, Cellulosimicrobium sp. RFN73, and Klebsiella sp. RFN75, which were evaluated in independent paired greenhouse trials. Inoculation with Cellulosimicrobium sp. RFN73, as well as the combinations RFN53+RFN55 and RFN73+RFN75, significantly enhanced plant growth, increasing plant height, leaf area, and biomass accumulation ( p < 0.05) compared to the control. These findings highlight the potential of R. mangle -associated bacteria as biofertilizers and underscore the importance of including safety assessments and detailed functional characterization to ensure their responsible use in sustainable agricultural systems.